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Am J Physiol Cell Physiol 293: C95-C105, 2007. First published March 7, 2007; doi:10.1152/ajpcell.00611.2006
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CELLULAR METABOLISM

Autoactivation of matriptase in vitro: requirement for biomembrane and LDL receptor domain

Ming-Shyue Lee,1 I-Chu Tseng,3 Youhong Wang,3 Ken-ichi Kiyomiya,2 Michael D. Johnson,3 Robert B. Dickson,3 and Chen-Yong Lin3

1Graduate Institute of Biochemistry and Molecular Biology, College of Medicine, National Taiwan University, Taipei, Taiwan; 2Osaka Prefecture University, Graduate School of Veterinary Medicine, Department of Toxicology, Sakai, Osaka, Japan; and 3Department of Oncology, Lombardi Cancer Center, Georgetown University Medical Center, Washington, District of Columbia

Submitted 7 December 2006 ; accepted in final form 28 February 2007


    ABSTRACT
 TOP
 ABSTRACT
 EXPERIMENTAL PROCEDURES
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
In live cells, autoactivation of matriptase, a membrane-bound serine protease, can be induced by lysophospholipids, androgens, and the polyanionic compound suramin. These structurally distinct chemicals induce different signaling pathways and cellular events that somehow, in a cell type-specific manner, lead to activation of matriptase immediately followed by inhibition of matriptase by hepatocyte growth factor activator inhibitor 1 (HAI-1). In the current study, we established an analogous matriptase autoactivation system in an in vitro cell-free setting and showed that a burst of matriptase activation and HAI-1-mediated inhibition spontaneously occurred in the insoluble fractions of cell homogenates and that this in vitro activation could be attenuated by a soluble suppressive factor(s) in cytosolic fractions. Immunofluorescence staining and subcellular fractionation studies revealed that matriptase activation occurred in the perinuclear regions. Solubilization of matriptase from cell homogenates by Triton X-100 or sonication of cell homogenates completely inhibited the effect, suggesting that matriptase activation requires proper lipid bilayer microenvironments, potentially allowing appropriate interactions of matriptase zymogens with HAI-1 and other components. Matriptase activation occurred in a narrow pH range (from pH 5.2 to 7.2), with a sharp increase in activation at the transition from pH 5.2 to 5.4, and could be completely suppressed by moderately increased ionic strength. Protease inhibitors only modestly affected activation, whereas 30 nM (5 µg/ml) of anti-matriptase LDL receptor domain 3 monoclonal antibodies completely blocked activation. These atypical biochemical features are consistent with a mechanism for autoactivation of matriptase that requires protein-protein interactions but not active proteases.

hepatocyte growth factor activator inhibitor 1; protease activation; low-density lipoprotein


MATRIPTASE AND HEPATOCYTE growth factor activator inhibitor 1 (HAI-1) are a pair of epithelium-derived, membrane-associated proteins: a proteolytic enzyme and its cognate inhibitor, respectively (22, 49). Matriptase, a member of the type II transmembrane serine protease (8, 35, 50), contains a transmembrane domain at the amino terminus, followed by a sperm protein, enterokinase, and agrin (SEA) domain, two tandem C1r/s, Uegf, and bone morphogenic protein-1 (CUB) domains, four tandem LDL receptor class A domains, and a trypsin-like serine protease domain (15, 22, 23, 52, 54). HAI-1, a type 1 transmembrane protein, contains two Kunitz-type serine protease inhibitor domains and an LDL receptor class A domain (46). Matriptase and HAI-1 are broadly expressed and may have diverging functions in the epithelial cells of most epithelium-containing tissues (15, 22, 26, 36, 39, 52, 54). For example, matriptase was shown to be required for postnatal survival, epidermal barrier function, hair follicle development, and thymic homeostasis in matriptase knockout mice (25). The roles of matriptase in epidermal differentiation apparently result from its activation of prostasin, a glycosylphosphatidylinositol-anchored membrane serine protease (34), targeted deletion of which in mice shows exactly the same phenotype as matriptase-deficient mice (21). Aberrant maturation of profilaggrin, a large (>300 kDa), insoluble phosphoprotein involved in terminal differentiation of keratinocytes, was observed in epidermal tissues of matriptase knockout mice (28). In addition, matriptase was detected in a variety of human tumors of epithelial origins or phenotype and has been implicated in the initiation and progression of human carcinomas (7, 13, 18, 36, 38, 4143, 47, 53). Elevated expression of matriptase and HAI-1 has been associated with poor disease outcome in node-negative human breast cancer (13), and an imbalance between matriptase and HAI-1, favoring matriptase proteolysis, was reported in advanced human ovarian and prostate cancers (38, 41). In a transgenic mouse model, List et al. (27) showed that modestly increased expression of matriptase in the epidermis was sufficient to induce spontaneous squamous cell carcinomas and to strongly potentiate skin chemical carcinogenesis. Overexpression of matriptase significantly enhanced lymph node metastasis of gastric cancer cells in nude mice (10). Consistent with these results, matriptase-selective inhibitory drugs, matriptase antisense, and small interfering RNA have been shown to suppress malignant phenotypes of cancers in culture cells and xenograft models (5, 6, 10, 48). Therefore, the pathological deregulation of matriptase in human cancers could result from its increased expressions and from an imbalance relative to its cognate inhibitor, HAI-1. The role of matriptase in cancer is thought to result, at least to some extent, from its ability to process extracellular matrix components (44) and adhesion molecules (1) and to activate urokinase plasminogen activator, stromelysin, hepatocyte growth factor, and protease-activated receptor-2 on the surfaces of cancer cells (12, 16, 20, 48, 51). Thus matriptase may regulate cell adhesion, ECM degradation, and cell motility and contribute to cancer growth, invasion, metastasis, and angiogenesis.

Deregulation of the control of matriptase activation can result from overexpression of the enzyme and alteration of the ratio of the protein relative to HAI-1 and may also be due to altered glycosylation mediated by beta1-6-N-acetylglucosaminyltransferase V (10, 11), which causes beta1-6 N-acetylglucosamine branching. This oligosaccharide modification results in enhanced matriptase stability. Altered subcellular localization of matriptase from cell-cell junctions in mammary epithelial cells to the membrane ruffles in breast cancer cells also results in uncontrolled activation (2, 4, 9). Matriptase is activated by a cleavage at its canonical activation motif, converting a single-chain zymogen into a two-chain active protease (2). Because the functional active site triad of matriptase is required for the activation of matriptase (mutation of these amino acids blocks activation), the activational cleavage of matriptase is not carried out by other active proteases, as is the case for most other serine proteases. In addition, the normal posttranslational modifications of the protein, such as NH2-terminal processing via cleavage at Gly-149 within the SEA domain and N-linked glycosylations and the intact LDL receptor class A domains of matriptase, are also required for its activation. Paradoxically, HAI-1 via its LDL receptor class A domain is also involved in matriptase activation (40). Therefore, we have proposed that autoactivation, via the interactions of matriptase zymogens, HAI-1, and other components not yet identified, is the mechanism for activation of this membrane-bound serine protease (40). In mammary epithelial cells, matriptase activation can be induced by sphingosine 1-phosphate (S1P), a blood-borne lysophospholipid, and occurs at cell-cell junctions (2, 3, 9). In contrast, breast cancer cells constitutively activate matriptase on the cell surfaces in the absence of contact with other cells and concentrate activated matriptase at membrane ruffles in response to EGF treatment (4). Furthermore, translocation and accumulation of both matriptase and HAI-1 at "activation foci" has been observed in 184 A1N4 immortal mammary epithelial cells during induced activation of matriptase (19). In these cells, matriptase is initially located primarily in perinuclear regions, where its activation does not occur. Upon the stimulation of cells with serum or S1P, matriptase translocates and accumulates at the cell-cell junctions (2, 3). The onset of activation of matriptase occurs at the activation foci at cell-cell junctions as tiny spots, after which the activation expands and elongates along the cell-cell junctions (9). The activation foci have also been observed inside the cells, different from cell-cell junctions, when the cells are exposed to suramin, a chemical inducer for matriptase activation (9, 19). The accumulation of matriptase at activation foci is consistent with the hypothesis that autoactivation occurs where dimerizations or oligomerizations of matriptase and other proteins are concentrated at particular cellular locations for interactions with each other and the occurrence of an activational cleavage. Despite the understanding of the processes described above, the detailed mechanisms of how matriptase activation occurs, how it is regulated, and what other proteins, besides HAI-1, are involved in matriptase activation, remain unknown. One of the major obstacles is the lack of a reliable and controllable cell-free system for biochemical characterization of matriptase activation. In the current study, we set out to establish and characterize such an in vitro system for further biochemical study of matriptase activation.


    EXPERIMENTAL PROCEDURES
 TOP
 ABSTRACT
 EXPERIMENTAL PROCEDURES
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
Chemicals and reagents. Formaldehyde solution was purchased from EM Science (EM Industries, Bibbstown, NJ). All other chemical reagents were obtained from Sigma (St. Louis, MO), unless otherwise specified.

Cell lines and culture conditions. Immortalized 184 A1N4 human mammary epithelial cells were a gift from Dr. Martha Stampfer (Lawrence Berkeley National Laboratory, Berkeley, CA) and routinely maintained, as previously described (2).

Monoclonal antibodies. Human matriptase protein was detected using the M32 monoclonal antibody (MAb), which recognizes both the latent (one chain) and activated (two chain) forms of the protease; the activated matriptase was detected using the M69 MAb, which recognizes an epitope present only in the activated (two chain) form of the enzyme (2, 3). Human HAI-1 was detected using the HAI-1-specific MAb M19 (22). We have summarized the forms of matriptase and HAI-1 and the interactions of these MAbs with matriptase and HAI-1 in Fig. 1.


Figure 1
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Fig. 1. Schematic representation of matriptase activation, hepatocyte growth factor activator inhibitor 1 (HAI-1)-mediated inhibition, and MAb recognition. Matriptase is biosynthesized as a 95-kDa polypeptide that contains a serine protease domain (SPD) at the COOH terminus, followed by 4 LDL receptor class A (LDLR) domains, 2 C1r/s, Uegf, and bone morphogenic protein-1 (CUB) domains, a sperm protein, enterokinase, and agrin (SEA) domain, and a transmembrane domain. Matriptase undergoes NH2-terminal processing by a cleavage within the SEA domain to generate 2 fragments that are still associated together. HAI-1 is a type 1 transmembrane protein, which contains 2 Kunitz domains (I and II) and an LDLR domain. MAb M32 recognizes the third LDLR domain of matriptase (9, 40). Matriptase undergoes autoactivation to become a 2-chain active enzyme that is immediately bound and inhibited by HAI-1 to form a 120-kDa complex, which can be recognized by both the anti-matriptase MAb M32 and the anti-HAI-1 MAb M19 (19, 22). MAb M69 recognizes an epitope specifically associated with the autoactivation of matriptase (2, 3), and therefore, this MAb interacts only with the 120-kDa matriptase-HAI-1 complex and not with the 70-kDa latent matriptase or the 55-kDa HAI-1.

 
Western blotting. Protein for Western blotting was prepared after lysis of cell homogenates of 184 A1N4 cells in 1% Triton X-100. Insoluble debris was removed by centrifugation. The lysates were diluted immediately in 5x sample buffer. The sample buffer did not contain a reducing agent, and samples were not boiled before SDS-PAGE was performed, since reducing agents destroy the epitopes recognized by the MAbs and boiling disrupts matriptase-HAI-1 complexes. Proteins were resolved by 7.5% SDS-PAGE and then transferred from SDS gels by diffusion overnight to two Protran nitrocellulose membranes (Schleicher & Schuell, Keene, NH). Individual nitrocellulose membranes were probed with the MAbs M32 for total matriptase, M69 for activated matriptase, or M19 for HAI-1. The binding of the primary antibody was followed by recognition with a goat anti-mouse horseradish peroxidase (HRP)-conjugated secondary antibody (Jackson ImmunoResearch Laboratories, West Grove, PA) and detected using the Western Lightening Chemiluminescence Reagent Plus (PerkinElmer, Boston, MA). The almost identical patterns of 120-kDa matriptase-HAI-1 complex probed by M32 or M69 MAbs in GoGoGoFigs. 59 were obtained by using two almost identical nitrocellulose membranes prepared by diffusion transfer methodology but not by reprobing the same nitrocellulose membrane. The HRP-conjugated M32 or M69 MAbs were used for immunoblot analysis (see Fig. 10).


Figure 2
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Fig. 2. Spontaneous matriptase activation in cell homogenates. Cell homogenates were prepared in sodium phosphate-citric acid buffer, pH 6.0, containing 0.25 M sucrose, from 184 A1N4 immortal human mammary epithelial cells. Equal volumes of cell homogenates were then either untreated (RT), supplemented with 1% Triton X-100 (Tx), or sonicated (Sn) on ice. These cell homogenates were incubated at room temperature (RT, Tx, Sn) for 10 min or left on ice (4°C). After incubation, the cell homogenates were lysed by adding Triton X-100 up to 1%. The total and activated forms of matriptase were analyzed by immunoblot using the anti-matriptase MAb M32 (total matriptase) and the anti-2-chain matriptase MAb M69 (activated matriptase), respectively.

 

Figure 3
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Fig. 3. Matriptase activation in vitro occurred in the insoluble fractions and was suppressed by cytosolic fractions. A: cell homogenates were subjected to subcellular fractionation by sequential centrifugation at 1,000 g for 10 min, followed by 15,000 g for 10 min. The first centrifugation yielded an insoluble pellet, the "insoluble fraction" (lanes 1), and the second yielded a pellet, the "post-nuclear (mitochondria/lysosomal) fraction" (lanes 2) and a cytosolic supernatant fraction. Both the insoluble and post-nuclear fractions were resuspended in sodium phosphate-citric acid buffer, pH 6.0, and incubated at room temperature for 10 min. Both fractions were then lysed in 1% Triton X-100 and subjected to immunoblot analysis using the anti-matriptase MAb M32 (total) and the anti-2-chain matriptase MAb M69 (activated). Roughly equal amounts of total matriptase from both fractions were examined for the activation of matriptase. B: the insoluble fractions alone (lanes 1 and 2) or in the presence of the cytosolic fractions (lanes 3 and 4) were incubated on ice (lanes 1 and 3) or at room temperature (lanes 3 and 4) for 10 min. The samples were then lysed in 1% Triton X-100 and subjected to immunoblot analysis using the anti-matriptase MAb M32 (total) and the anti-2-chain matriptase MAb M69 (activated).

 

Figure 4
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Fig. 4. Matriptase activation in vitro occurred at the cytoplasmic filament areas surrounding cell nuclei. The insoluble fractions of 184 A1N4 cells were resuspended in sodium phosphate-citric acid buffer and incubated on ice (A) and at room temperature (B) for 10 min to allow matriptase activation. The insoluble fractions were fixed with 3.7% formaldehyde-PBS and then stained for matriptase with Alexa Fluor 488-conjugated MAb M32 (green), for activated matriptase with Alex Fluor 647-conjugated MAb M69 (red), and for nuclei with 4',6-diamidino-2-phenylindole (blue).

 

Figure 5
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Fig. 5. Time course of matriptase activation in vitro. The insoluble fractions of cell homogenates were resuspended in sodium phosphate-citric acid buffer, pH 6.0, and aliquots of insoluble fractions were incubated at room temperature for different times as indicated. Matriptase activation was terminated by the addition of Triton X-100 up to 1%. Total matriptase, activated matriptase, and HAI-1 were probed using anti-matriptase MAb M32, anti-2-chain matriptase MAb M69, and anti-HAI-1 MAb M19, respectively.

 

Figure 9
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Fig. 9. Effect of protease inhibitors on matriptase activation in vitro. Aliquots of the insoluble fractions of cell homogenates were resuspended in sodium phosphate-citric acid buffer, pH 6.0, containing no protease inhibitors (lanes 1 and 2), 5 µM sunflower trypsin inhibitor (lane 3), 5 µM matriptase-selective inhibitor CVS 3983 (lane 4), protease inhibitor cocktail (Complete, mini, EDTA free, 1 tablet/10 ml; Roche) (lane 5), or 5 µM EDTA (lane 6). Matriptase activation was allowed to occur in these samples (lanes 2–6) at room temperature for 10 min, compared with the control sample on ice (lane 1). Matriptase activation was terminated by adding Triton X-100 up to 1%. Total matriptase and activated matriptase were probed using anti-matriptase MAb M32 and anti-2-chain matriptase MAb M69, respectively.

 

Figure 10
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Fig. 10. Inhibition of matriptase activation in vitro by anti-matriptase MAbs. Aliquots of the insoluble fractions of cell homogenates were resuspended in PBS containing mouse IgG at 5 µg/ml, mouse-derived anti-matriptase MAb M32 at 5, 1, or 0.2 µg/ml, or rat-derived anti-matriptase MAb 21-9 at 5, 1, or 0.2 µg/ml. The samples were then incubated at 4°C for 2 h, followed by centrifugation. The antibody-treated insoluble fractions were then resuspended in sodium phosphate-citric acid buffers, pH 6.0, and incubated at room temperatures for 10 min. Matriptase activation was terminated by adding Triton X-100 up to 1%. Matriptase and activated matriptase were probed using horseradish peroxidase (HRP)-conjugated MAb M32 and HRP-conjugated MAb M69, respectively.

 
Immunofluorescence microscopy. The insoluble fractions of 184 A1N4 cells, prepared as described in RESULTS, were fixed in 3.7% formaldehyde in PBS for 20 min at room temperature and then washed with PBS three times. Both total and activated matriptase were detected with Alexa Fluor dye-conjugated M32 and M69 MAb, respectively. Nuclei were stained with 4',6-diamidino-2-phenyindole dilactate. After fluorescent staining, the homogenates of the cells were loaded on glass slides mounted with cover glasses. The fluorescent images were captured using the MetaVue software package on a Nikon Eclipse E600 digital fluorescence microscope.


    RESULTS
 TOP
 ABSTRACT
 EXPERIMENTAL PROCEDURES
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
Dissection of matriptase regulatory mechanisms in cell-free conditions. In previous studies, our group has shown that matriptase activation can be induced by lysophospholipids (3), steroid sex hormones (17), and suramin (19). These three chemicals are structurally different and elicit different cellular responses, some of which are cell type specific. Despite the differences among these inducers, in all cases, matriptase activation is immediately followed by HAI-1-mediated inhibition, resulting in all of the activated matriptase being complexed with HAI-1. Furthermore, whereas breast cancer cells constitutively activate matriptase, activated matriptase was also detected in its HAI-1 complexes (4). These observations suggest that inhibition of active matriptase by HAI-1 immediately follows its activation, regardless of whether the cells are normal or cancerous. This tight control of matriptase activity by HAI-1 might result from the requirement that HAI-1 plays a role in matriptase activation (40) and the coexistence of HAI-1 along with matriptase at activation foci during matriptase activation (19, 37). Although these inducers of activation may work through different upstream pathways, they apparently lead to the same common matriptase activation machinery, resulting in not only increased matriptase activity but also the likely activation of downstream matriptase substrates and the rapid inhibition of matriptase activity by HAI-1 binding. Therefore, we hypothesized that matriptase function could be regulated at two independent levels: a downstream mechanism in which activation, substrate processing, and inhibition occur in a well-integrated and rapid fashion, and an upstream regulatory mechanism that can serve as the convergence point for different exogenous signals. To validate this hypothesis and characterize the activation machinery, we set out to establish an in vitro assay for matriptase activation. Several attempts using detergent-lysed cell extracts or purified latent matriptase failed. Since induced matriptase activation in living human mammary epithelial cells occurs in activation foci, either in intracellular vesicle-like structures or at cell-cell contacts, both of which appear to involve cell membranes (2, 3, 9, 19), we turned our attempt to the use of cell homogenates, avoiding lysis of cell membrane.

By systematic evaluation of various assay conditions, such as pH and the salt concentrations in buffer systems, we discovered that matriptase activation can occur spontaneously in cell homogenates (Fig. 2). We used 184 A1N4 immortal human mammary epithelial cells for our model system; however, we have demonstrated that in vitro matriptase activation assays can be conducted in various other cell lines that endogenously express matriptase and HAI-1 (data not shown). 184 A1N4 cells express high levels of matriptase, but when grown in culture media supplemented with 0.5% FBS for 2 days, they become devoid of matriptase activation (2). Following cellular homogenization by Dounce homogenizer in phosphate-citric acid buffer (pH 6.0), the resultant homogenates were incubated at room temperature for 10 min. Under these conditions, matriptase activation occurred spontaneously (Fig. 2, lanes 1). However, matriptase activation did not occur when the homogenates were additionally lysed by the addition of a nonionic detergent such as Triton X-100 (Fig. 2, lanes 2), subjected to sonication for few seconds on ice using a Tekmar Sonic Disruptor at setting 80 for microtip (Fig. 2, lanes 3), or incubated on ice at 4°C (Fig. 2, lanes 4). Activation of matriptase was evaluated by determining the levels of activated matriptase detected using the MAb M69, which is specifically directed against the two-chain activated matriptase but not the single-chain zymogen (2). We also determined the levels of total matriptase by using the MAb M32, which is directed against the third LDL receptor class A domain of the protease (9) [and is thus able to interact with both two-chain and single-chain matriptases containing this noncatalytic domain (19)].

In live cells, activation of matriptase induced by S1P or suramin is immediately followed by the inhibition of the protease by its cognate inhibitor HAI-1, resulting in a 120-kDa matriptase-HAI-1 complex, due to the requirement for HAI-1 in matriptase activation (40) and its presence with matriptase in activation foci (19, 37). Interestingly, the simultaneous HAI-1-mediated inhibition of active matriptase also occurred in this in vitro setting, since the majority of activated matriptase was detected in a 120-kDa complex (Fig. 2, lanes 1). As expected, the anti-total matriptase M32 MAb also recognized this 120-kDa matriptase-HAI-1 complex, in addition to the 70-kDa latent form of matriptase (Fig. 2). Concomitant with the appearance of the 120-kDa matriptase-HAI-1 complex, the levels of 70-kDa latent matriptase decreased. The 120-kDa matriptase-HAI-1 complex was also detected by anti-HAI-1 M19 monoclonal antibody (see Fig. 5). These results suggest that the in vitro matriptase activation model shares some characteristics with the induced matriptase activation in live cells, such as simultaneous HAI-1-mediated inhibition, formation of HAI-1 complex, and the involvement of membrane structures. Because active matriptase is inhibited by HAI-1 following its activation, it is not feasible to express the level of matriptase activation in terms of matriptase proteolytic activity by using synthetic substrates or gelatin zymography (2).

We further fractionated the cell homogenates by sequential centrifugations at 1,000 g for 10 min, which yielded insoluble pellets that contained mainly nuclei encompassed with cytoplasmic filaments and endoplasmic reticulum, and at 15,000 g for 10 min, yielding insoluble membrane pellets, which contained mainly membrane vesicles, mitochondria, and lysosomes (post-nuclear fraction), as well as the supernatant, which contained soluble cytosolic factors and proteins. The bulk of matriptase was detected in the insoluble pellets with a very small portion of the protease in the post-nuclear fraction, based on the yield of matriptase in both fractions (data not shown). When the insoluble pellets and the post-nuclear fraction were resuspended in phosphate-citric acid buffer and incubated at room temperature for in vitro matriptase activation, the levels of matriptase activation were examined by normalization of roughly equal amounts of total matriptase from both fractions (Fig. 3A). Activation of matriptase occurred in the insoluble pellets but not in the post-nuclear fraction (Fig. 3A). These data suggest the soluble cytosolic molecules in cell homogenates are not necessary for matriptase activation and that the insoluble pellets contain all the required elements for matriptase activation in vitro. Furthermore, although cell membranes are required for matriptase to undergo activation (Fig. 2), the simple presence of matriptase in membrane vesicles is not sufficient for its in vitro activation.

Although the soluble cytosolic molecules were not required for matriptase activation, it was interesting to note that their removal by separation of the soluble cytosolic fractions from the insoluble pellets significantly increased the rate of matriptase activation in the insoluble pellets (Fig. 3B, compare lanes 2 and 4). These data suggest that matriptase activation may be regulated by two independent mechanisms: a soluble cytosolic suppressor and insoluble autonomous activation machinery. Homogenization of cells in the absence of detergent apparently preserves the function of the activation machinery and may also sufficiently dilute the cytosolic suppressor to allow matriptase activation to proceed spontaneously. Removal of the cytosolic suppressor from the insoluble activation machinery by centrifugation allowed matriptase activation to proceed to a much greater extent, as illustrated by comparing the ratios between activated matriptase (in the 120-kDa HAI-1 complex) relative to the latent matriptase (the 70-kDa band). In the absence of the cytosolic suppressor(s), about one-third to one-half of the matriptase underwent activation within 10 min at room temperature (see Figs. 3 and 510). In contrast, in the presence of the cytosolic suppressor(s), <10% of the matriptase underwent activation under the same conditions (Figs. 2 and 3B). In addition to 184 A1N4 mammary epithelial cells, in vitro activation of matriptase and a soluble suppressor of matriptase activation were observed in a variety of breast cancer cells, including T-47D and MCF-7 cells, and in prostate cancer cells, including LNCaP cells (data not shown), suggesting the ubiquity of these mechanisms governing matriptase activation.

Biochemical characterization of matriptase activation in vitro. In this study, we have focused on the biochemical characterization of the activation machinery. Characterization of the nature and identity of the cytosolic suppressor of matriptase activation must be the subject of a future study.

We began our characterization by examining the location of the protease and where its activation occurred in the insoluble pellets by immunofluorescent staining (Fig. 4). By phase-contrast microscopy, the insoluble pellets were observed mainly as the broken cells that contained nuclei surrounded by cytoplasmic filaments (perinuclei) (Fig. 4, blue color for nuclei in merged image). Total matriptase (Fig. 4, M32, green) was detected at the cytoplasmic filament area surrounding the nuclei. Activated matriptase, detected by MAb M69 (Fig. 4, M69, red) also was observed in the perinuclear area only for those insoluble fractions incubated at room temperature (Fig. 4B, M69, red), not for the controls, which were kept on ice (Fig. 4A, M69, red). In live cells, the majority of the matriptase was detected in the perinuclear, presumably Golgi-endoplasmic reticulum (ER), area (Fig. 4B, inset bottom right, green) (9, 19, 24, 37). This specific perinuclear distribution of matriptase in cellular homogenates simply reflected its perinuclei localization in live cells. The spontaneous activation of matriptase in the insoluble pellets suggests that matriptase and its activation machinery were still well preserved after cell fractionations (cellular homogenization).

Time course of matriptase activation in vitro. Activation of matriptase began to occur as soon as 5 min after incubation at room temperature (Fig. 5). This in vitro activation of matriptase apparently occurred in a robust fashion, with more than one-third of latent matriptase becoming activated after 10 min of incubation at room temperature and more than one-half after 30 min, comparing the ratio of the level of the 120-kDa matriptase complex to the 70-kDa latent matriptase form (Fig. 5, total matriptase). The appearance of activated matriptase, mainly in the 120-kDa matriptase-HAI-1 complex, was at the cost of the 70-kDa latent matriptase form; increased levels of the 120-kDa matriptase-HAI-1 complex were accompanied with a decrease in the 70-kDa latent form. As described above, the activated matriptase was detected mainly in its 120-kDa complex with its cognate inhibitor HAI-1 by using MAb M69, which can specifically recognize the two-chain form of matriptase. We further confirmed that this 120-kDa band contains HAI-1 by using anti-HAI-1 MAb M19, which recognizes both the 120-kDa complex and the 55-kDa full-length HAI-1 (Fig. 5, HAI-1). Although more than one-half of the total matriptase was activated after 30 min of incubation, only a small portion of HAI-1 was detected in the matriptase-HAI-1 complex. Since the stoichiometry of the interaction between active matriptase and HAI-1 is likely to be 1:1, based on the size of their complex (120 kDa) and the fact that only the Kunitz domain 1 of HAI-1 can inhibit matriptase (16), the relatively small proportion of the available HAI-1 in the 120-kDa complex suggests that HAI-1 is present in considerable excess relative to matriptase levels in the intracellular pools. Together, these results suggest that matriptase activation in vitro shares many features with its counterpart in live cells, such as rapidity of activation (occurrence within 10 min) (3, 19) and the maintenance of a significant molar excess of HAI-1 relative to matriptase (19).

Matriptase activation in vitro occurs in narrow pH range. To determine the optimal pH range for matriptase activation, we first tested a broad range of pH. Matriptase activation only occurred over a narrow range from pH 5 to 8. Thus a buffer system spanning pH 4.8 to 7.4, with intervals of 0.2 pH unit, was established by mixing 0.1 M citric acid with 0.2 M disodium phosphate (32). Although matriptase activation did not occur at pH 5 and occurred only slightly at pH 5.2, a sharp increase in activation was observed at pH 5.4 (Fig. 6). The optimal pH for matriptase activation was found to be between 5.8 and 6.0. A gradual decrease in activation was observed with increased pH between 6.4 and 7.2.


Figure 6
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Fig. 6. Effect of pH on matriptase activation in vitro. Aliquots of insoluble fractions of cell homogenates were resuspended in sodium phosphate-citric acid buffers with pH values ranging from 4.8 to 7.4 and incubated at room temperature for 10 min. Matriptase activation was terminated by adding Triton X-100 up to 1%. Matriptase and activated matriptase were detected using anti-matriptase MAb M32 and anti-2-chain matriptase MAb M69, respectively.

 
Effect of temperature on matriptase activation in vitro. As described above, matriptase activation did not occur at 4°C (Fig. 2). Thus we further tested the effect of temperature on matriptase activation. The insoluble fractions were prepared in phosphate-citric acid buffer (pH 6.0) and incubated at different temperatures at an interval of 1°C, ranging from 12 to 16°C. The negative control was incubated on ice, and the positive control was at 20°C. Low levels of activation were detected at 12°C, and activation of matriptase gradually increased along with the increase in temperatures of incubation (Fig. 7).


Figure 7
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Fig. 7. Effect of temperature on matriptase activation in vitro. The insoluble fractions of cell homogenates were resuspended in sodium phosphate-citric acid buffer, pH 6.0, and aliquots of the insoluble fractions were incubated at different temperatures as indicated. Matriptase activation was terminated by adding Triton X-100 up to 1%. Total matriptase and activated matriptase were probed using anti-matriptase MAb M32 and anti-2-chain matriptase MAb M69, respectively.

 
Effect of ionic strength on matriptase activation in vitro. A pilot experiment showed that addition of 0.2 M sodium chloride to phosphate-citric acid buffer completely suppressed matriptase activation. Therefore, we studied the effects of ionic strength on in vitro matriptase activation by increasing of NaCl concentrations from 20 to 140 mM in the phosphate-citric acid buffer system. Matriptase activation was either unchanged or slightly enhanced when the concentration of NaCl was between 20 and 40 mM. The adverse effect of ionic strength on matriptase activation began to be evident at 60 mM NaCl, and inhibition was nearly complete at 100 mM NaCl (Fig. 8).


Figure 8
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Fig. 8. Effect of ionic strength on matriptase activation in vitro. Aliquots of insoluble fractions of cell homogenates were resuspended in sodium phosphate-citric acid buffers, pH 6.0, containing NaCl at the indicated concentrations and then incubated at room temperature for 10 min. Matriptase activation was terminated by adding Triton X-100 up to 1%. Total matriptase and activated matriptase were probed using anti-matriptase MAb M32 and anti-2-chain matriptase MAb M69, respectively.

 
Effects of protease inhibitors on in vitro activation of matriptase. Like most other serine proteases, activation of matriptase requires cleavage at its canonical activation motif to convert a single-chain zymogen to a two-chain active protease (2). We tested to see whether protease inhibitors could inhibit matriptase activation in vitro (Fig. 9). These protease inhibitors included the sunflower trypsin inhibitor 1 (SFTI-1), a small molecule inhibitor, CVS 3983, a protease inhibitor cocktail, and EDTA. SFTI-1, which is a 14-amino acid residue cyclic peptide, inhibits trypsin (Ki = 100 pM), cathepsin G (Ki < 0.15 nM), and matriptase (Ki = 92 pM) (30, 31). Despite its potent inhibition of the catalytic activity of various serine proteases, including matriptase, a high concentration of SFTI-1 (5 µM) had no inhibitory effect on matriptase activation in vitro (Fig. 9, lanes 3). CVS 3983, a selective small-molecule matriptase inhibitor, has been shown to inhibit the growth of androgen-independent cancer cells as tumors in a xenograft model (6). CVS 3983 (5 µM) was also unable to inhibit the activation of matriptase in vitro (Fig. 9, lanes 4). These negative results with matriptase-selective inhibitors suggest that the active matriptase does not play a role in the activation of latent enzyme and that the autoactivation of matriptase mainly lies in the interactions of matriptase zymogens. A commercial protease inhibitor cocktail (Complete, mini, EDTA free, 1 tablet/10 ml; Roche) is designed to inhibit serine proteases, cysteine proteases, and metalloproteases. The protease inhibitor cocktail (Fig. 9, lanes 5) and EDTA (Fig. 9, lanes 6) showed similarly modest inhibitory activity on matriptase activation in vitro. These results suggest that the proteolytic activities of proteases that can be inhibited by these enzyme-oriented inhibitors are not important for matriptase activation, consistent with our previous conclusion that matriptase activation is carried out by autoactivation via the interactions of matriptase zymogens that cannot be inhibited by enzymatic-oriented protease inhibitors (40). Those unusual biochemical features of matriptase activation, including the burst of matriptase activation (Fig. 5), the narrow pH optimum (Fig. 6), and the sensitivities to temperatures (Fig. 7) and ionic strength (Fig. 8), could result from its unconventional mechanism of activation.

Anti-matriptase MAbs M32 and 21-9 inhibit matriptase activation in vitro. In previous studies (9, 37), our group demonstrated that the mouse-derived, anti-matriptase MAb M32, which recognizes an epitope at the third LDL receptor class A domain of matriptase, was able to inhibit S1P-induced in vivo matriptase activation in mammary epithelial cells. A similar effect on in vivo S1P-induced matriptase activation was also demonstrated with another rat-derived, anti-matriptase MAb, 21-9 (data not shown). Although the epitope recognized by this rat-derived anti-matriptase MAb has not been determined, MAb 21-9 likely recognizes the LDL receptor class A domains of the protease, based on its interaction with a 40-kDa matriptase fragment, which presumably contains the serine protease domain and LDL receptor class A domains (24), but lack of interaction with the serine protease domain of matriptase (data not shown). Pretreatment of insoluble pellets with either of these anti-matriptase MAbs for 2 h at 4°C inhibited subsequent in vitro matriptase activation in a dose-response manner (Fig. 10). Monoclonal antibody 21-9 at 5 µg/ml (30 nM) completely inhibited matriptase activation in vitro, with M32 being slightly less potent. This minor difference in the inhibitory potency between both MAbs could result from their binding affinities or localizations of the epitopes recognized by these two MAbs in LDL receptor class A domains. Control mouse IgG at 5 µg/ml produced no inhibition. Directly HRP-labeled M69 MAb was used to detect activated matriptase in this study to avoid the use of an anti-mouse IgG secondary antibody, which would have interacted with the antibodies added to the insoluble pellets, generating problems with background bands. The blockage of matriptase activation by anti-matriptase MAbs further supports the idea that protein-protein interactions between matriptase zymogens are involved in matriptase activation.


    DISCUSSION
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 ABSTRACT
 EXPERIMENTAL PROCEDURES
 RESULTS
 DISCUSSION
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In the current study, we have described an in vitro, cell-free model system for matriptase activation. In contrast to previous studies by our group in which matriptase activation was induced and characterized in live cells, this in vitro matriptase activation system was characterized by utilizing the insoluble intracellular pools of matriptase in conjunction with the removal of a soluble cytosolic suppressor(s). The demonstration of an insoluble, autonomous matriptase activation mechanism may facilitate multiple insights and future directions for research. Specifically, this new model could provide information about mechanisms regulating matriptase activation, raising intriguing questions regarding how cells prevent premature matriptase activation before S1P-induced trafficking to its physiological subcellular locations for its activation. Matriptase is a type II transmembrane serine protease, and its localization on surfaces of cells is expected. Indeed, matriptase has been specifically detected on cell surfaces at cell-cell junctions in normal epithelial cells, where its activation occurs (9, 19, 37). However, matriptase was also detected intracellularly in the perinuclear area, presumably in the Golgi-ER regions (Fig. 4) (9, 19, 24, 37). In 184 A1N4 immortal human mammary epithelial cells, stimulation with the physiological activation inducer S1P results in some of the intracellular matriptase translocating and accumulating at cell-cell junctions for its activation (9). Therefore, we have hypothesized that matriptase and the other components required for activation (collectively termed activation machinery or activation complex) are cotranslocated to cell-cell junctions to facilitate autoactivation of matriptase. Since the intracellular matriptase can spontaneously undergo activation, as shown in the current study, the factors, both known and unidentified, required for matriptase autoactivation may also be in close proximity to matriptase inside the cells. Since the organelles of the secretory pathway exhibit a gradient of decreasing pH from near neutrality in ER (pH 7.1) to mildly acidic in Golgi (pH 6.2–7.0) to quite acidic within the secretory granules (~pH 5) (14, 29, 33, 45), activation of matriptase may occur during its intracellular trafficking to cell surfaces, particularly during its transit through the Golgi, since the optimal pH for matriptase activation is around 6 (Fig. 6). Therefore, interference with pH may represent one of the mechanisms for suppressing matriptase activation in ER during intracellular trafficking. However, the presence of other activation suppressor seems likely to be required during its trafficking. In contrast to preventing premature matriptase activation during trafficking, the neutral pH at cell-cell contacts or the cell surfaces may present a barrier to matriptase activation that must be overcome by S1P-induced activation of matriptase in the context of whole cells.

Matriptase activation in vitro occurs only in the insoluble fractions. Solubilization of matriptase from the insoluble fractions by the nonionic detergent Triton X-100 completely inhibited matriptase activation. This result suggests that matriptase and its activation machinery must be anchored on lipid bilayers in order for activation to proceed. However, the anchoring of matriptase in lipid bilayers is not sufficient for its activation, since matriptase, when anchored in membrane vesicles in the post-nuclear fractions, failed to undergo in vitro activation (Fig. 3). Furthermore, physical disruption of the insoluble fractions by sonication also completely abolished matriptase activation (Fig. 2). Therefore, simple lipid bilayers may provide necessary platforms for the anchoring of matriptase and its activation machinery, whereas more complicated, higher order structures of lipid bilayers may be required for efficient matriptase activation. Because of the likely involvement of lipid bilayers in matriptase activation, the fluidity of the lipid bilayer may also affect activation. Since temperature is a major factor affecting the fluidity of lipid bilayers, the effect of temperature on matriptase activation in vitro, which occurred at very low rate at 12°C but at a much higher rate at 13°C and above (Fig. 7), may be the result of a phase transition of membranes from a gel (frozen) state to a liquid state. In the gel state, it would be predicted that the movement of the matriptase enzyme and other proteins would be much slower, interfering with the protein-protein interactions required for activation.

The involvement of lipid bilayers and higher order membrane structures in matriptase activation may explain the atypical biochemical characteristics of in vitro matriptase activation. If matriptase activation depended on the activity of other proteases, the protease inhibitors (including the protease inhibitor cocktail), would have been expected to inhibit matriptase activation more effectively (Fig. 9), and matriptase activation would likely have occurred in the presence of Triton X-100 or following the sonication of cell homogenates (Fig. 2). Moreover, for a classic protease-catalyzed reaction, a symmetrical, bell-shaped profile would be expected for the plots of activity vs. pH, because the enzymatic activity would drop on either side of the optimal pH due to ionization or protonation of the amino acids participating in catalysis with the increase or decrease of pH, respectively. In vitro activation of matriptase occurs within a relatively narrow pH range with an asymmetrical profile of activation rate vs. pH. This unique pH effect may result from interference with the protein-protein interactions or the higher order structure of the lipid bilayers, rather than from interference with the amino acid residues actually participating in the subsequent proteolytic cleavage. This hypothesis is also supported by the effects of ionic strength on matriptase activation, where a sharp decrease in matriptase activation was observed with an increase in NaCl concentration from 80 to 100 mM. This modest increase in ionic strength again may disrupt protein-protein interactions or the higher order structure of the lipid bilayers. The marginal inhibition of matriptase activation by protease inhibitor cocktail further supports the suggestion that activation of matriptase is not via the activity of other proteases (Fig. 9). Taken together, these unique biochemical features of in vitro matriptase activation are consistent with autoactivation of matriptase in which the cleavage of the activation motif of matriptase is proposed to be carried out by the intrinsic, weak proteolytic activity of matriptase zymogens. It is conceivable that dimerization or oligomerization of matriptase zymogens is required for the activational cleavage. The anchor of matriptase on lipid bilayers could facilitate the interactions between matriptase zymogen molecules. The unidentified proteins could play roles in facilitating the contacts between two matriptase zymogen molecules. The noncatalytic domains and posttranslational modification of matriptase could provide structural basis for the protein-protein interactions required for matriptase activation. For example, the CUB domain possesses self-assembly potential, and the LDL receptor class A domain could interact with other proteins.

The essential roles of protein-protein interactions and the maintenance of proper lipid bilayer structures in matriptase activation provide attractive targets for novel strategies for the development of anti-matriptase inhibitors. Classic protease inhibitors, which inhibit the activity of the catalytic domain, often present serious problems in terms of selectivity for the protease that they are designed to inhibit due to the overlapping specificity of serine protease catalytic domains. The unconventional activation mechanism for matriptase may provide a unique opportunity to inhibit the protease function before its activation. Indeed, we have shown that interference with these protein-protein interactions by using the anti-matriptase MAbs was indeed able to inhibit matriptase activation. In future studies, high-throughput screening of small molecules could yield inhibitors of matriptase activation.

In conclusion, based on these biochemical characterizations, matriptase activation can be considered to be a complex process, probably involving multiple steps of protein-protein interactions. Anchoring matriptase, HAI-1, and other components not yet identified in cell membranes, as well as the organization of theses membrane-anchored proteins into subcellular, higher order lipid-bilayer membrane structures, may be critical to ensure appropriate protein-protein interactions. The in vitro matriptase activation system seems to faithfully replicate many features of the inducible matriptase activation found in whole cells, including a rapid reaction profile, involvement of cell membranes, HAI-1-mediated inhibition, and the formation of 120-kDa matriptase-HAI-1 complex as an end product. This new activation system may not only shed light on how cells regulate matriptase activity but may also provide a new strategy for development of matriptase activation inhibitors.


    GRANTS
 TOP
 ABSTRACT
 EXPERIMENTAL PROCEDURES
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
This study was supported by National Cancer Institute (NCI) Grants R01 CA096851 and R01 CA104944 (to C.-Y. Lin) and Taiwan National Science Council Grant NSC 95-2320-B-002-117 (to M.-S. Lee). Salary support for M.-S. Lee was provided by Department of Defense Grant DAMD 17-00-1-0271. This work was supported in part by the Lombardi Cancer Center Microscopy and Imaging Shared Resource NCI Grant 4P30 CA-51008.


    FOOTNOTES
 

Address for reprint requests and other correspondence: C.-Y. Lin, Greenebaum Cancer Center and Dept. of Biochemistry and Molecular Biology, University of Maryland, 10-027 Bressler Research Bld., 655 W. Baltimore St., Baltimore, MD 21201 (e-mail: cylin{at}som.umaryland.edu)

The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.


    REFERENCES
 TOP
 ABSTRACT
 EXPERIMENTAL PROCEDURES
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
1. Ahmed S, Jin X, Yagi M, Yasuda C, Sato Y, Higashi S, Lin CY, Dickson RB, Miyazaki K. Identification of membrane-bound serine proteinase matriptase as processing enzyme of insulin-like growth factor binding protein-related protein-1 (IGFBP-rP1/angiomodulin/mac25). FEBS J 273: 615–627, 2006.[CrossRef][Medline]

2. Benaud C, Dickson RB, Lin CY. Regulation of the activity of matriptase on epithelial cell surfaces by a blood-derived factor. Eur J Biochem 268: 1439–1447, 2001.[Web of Science][Medline]

3. Benaud C, Oberst M, Hobson JP, Spiegel S, Dickson RB, Lin CY. Sphingosine 1-phosphate, present in serum-derived lipoproteins, activates matriptase. J Biol Chem 277: 10539–10546, 2002.[Abstract/Free Full Text]

4. Benaud CM, Oberst M, Dickson RB, Lin CY. Deregulated activation of matriptase in breast cancer cells. Clin Exp Metastasis 19: 639–649, 2002.[CrossRef][Web of Science][Medline]

5. Forbs D, Thiel S, Stella MC, Sturzebecher A, Schweinitz A, Steinmetzer T, Sturzebecher J, Uhland K. In vitro inhibition of matriptase prevents invasive growth of cell lines of prostate and colon carcinoma. Int J Oncol 27: 1061–1070, 2005.[Web of Science][Medline]

6. Galkin AV, Mullen L, Fox WD, Brown J, Duncan D, Moreno O, Madison EL, Agus DB. CVS-3983, a selective matriptase inhibitor, suppresses the growth of androgen independent prostate tumor xenografts. Prostate 61: 228–235, 2004.[CrossRef][Web of Science][Medline]

7. Hoang CD, D'Cunha J, Kratzke MG, Casmey CE, Frizelle SP, Maddaus MA, Kratzke RA. Gene expression profiling identifies matriptase overexpression in malignant mesothelioma. Chest 125: 1843–1852, 2004.[CrossRef][Web of Science][Medline]

8. Hooper JD, Clements JA, Quigley JP, Antalis TM. Type II transmembrane serine proteases. Insights into an emerging class of cell surface proteolytic enzymes. J Biol Chem 276: 857–860, 2001.[Free Full Text]

9. Hung RJ, Hsu I, Dreiling JL, Lee MJ, Williams CA, Oberst MD, Dickson RB, Lin CY. Assembly of adherens junctions is required for sphingosine 1-phosphate-induced matriptase accumulation and activation at mammary epithelial cell-cell contacts. Am J Physiol Cell Physiol 286: C1159–C1169, 2004.[Abstract/Free Full Text]

10. Ihara S, Miyoshi E, Ko JH, Murata K, Nakahara S, Honke K, Dickson RB, Lin CY, Taniguchi N. Prometastatic effect of N-acetylglucosaminyltransferase V is due to modification and stabilization of active matriptase by adding beta1-6 GlcNAc branching. J Biol Chem 277: 16960–16967, 2002.[Abstract/Free Full Text]

11. Ihara S, Miyoshi E, Nakahara S, Sakiyama H, Ihara H, Akinaga A, Honke K, Dickson RB, Lin CY, Taniguchi N. Addition of beta1-6 GlcNAc branching to the oligosaccharide attached to Asn 772 in the serine protease domain of matriptase plays a pivotal role in its stability and resistance against trypsin. Glycobiology 14: 139–146, 2004.[Abstract/Free Full Text]

12. Jin X, Yagi M, Akiyama N, Hirosaki T, Higashi S, Lin CY, Dickson RB, Kitamura H, Miyazaki K. Matriptase activates stromelysin (MMP-3) and promotes tumor growth and angiogenesis. Cancer Sci 97: 1327–1334, 2006.[CrossRef][Medline]

13. Kang JY, Dolled-Filhart M, Ocal IT, Singh B, Lin CY, Dickson RB, Rimm DL, Camp RL. Tissue microarray analysis of hepatocyte growth factor/Met pathway components reveals a role for Met, matriptase, and hepatocyte growth factor activator inhibitor 1 in the progression of node-negative breast cancer. Cancer Res 63: 1101–1105, 2003.[Abstract/Free Full Text]

14. Kim JH, Johannes L, Goud B, Antony C, Lingwood CA, Daneman R, Grinstein S. Noninvasive measurement of the pH of the endoplasmic reticulum at rest and during calcium release. Proc Natl Acad Sci USA 95: 2997–3002, 1998.[Abstract/Free Full Text]

15. Kim MG, Chen C, Lyu MS, Cho EG, Park D, Kozak C, Schwartz RH. Cloning and chromosomal mapping of a gene isolated from thymic stromal cells encoding a new mouse type II membrane serine protease, epithin, containing four LDL receptor modules and two CUB domains. Immunogenetics 49: 420–428, 1999.[CrossRef][Web of Science][Medline]

16. Kirchhofer D, Peek M, Li W, Stamos J, Eigenbrot C, Kadkhodayan S, Elliott JM, Corpuz RT, Lazarus RA, Moran P. Tissue expression, protease specificity, and Kunitz domain functions of hepatocyte growth factor activator inhibitor-1B (HAI-1B), a new splice variant of HAI-1. J Biol Chem 278: 36341–36349, 2003.[Abstract/Free Full Text]

17. Kiyomiya KI, Lee MS, Tseng IC, Zuo H, Barndt RJ, Johnson MD, Dickson RB, Lin CY. Matriptase activation and subsequent shedding with HAI-1 is induced by steroid sex hormones in human prostate cancer cells, but not in breast cancer cells. Am J Physiol Cell Physiol 291: C40–C49, 2006.[Abstract/Free Full Text]

18. Lee JW, Yong SS, Choi JJ, Lee SJ, Kim BG, Park CS, Lee JH, Lin CY, Dickson RB, Bae DS. Increased expression of matriptase is associated with histopathologic grades of cervical neoplasia. Hum Pathol 36: 626–633, 2005.[CrossRef][Web of Science][Medline]

19. Lee MS, Kiyomiya K, Benaud C, Dickson RB, Lin CY. Simultaneous activation and HAI-1-mediated inhibition of matriptase induced at activation foci in immortal human mammary epithelial cells. Am J Physiol Cell Physiol 288: C932–C941, 2005.[Abstract/Free Full Text]

20. Lee SL, Dickson RB, Lin CY. Activation of hepatocyte growth factor and urokinase/plasminogen activator by matriptase, an epithelial membrane serine protease. J Biol Chem 275: 36720–36725, 2000.[Abstract/Free Full Text]

21. Leyvraz C, Charles RP, Rubera I, Guitard M, Rotman S, Breiden B, Sandhoff K, Hummler E. The epidermal barrier function is dependent on the serine protease CAP1/Prss8. J Cell Biol 170: 487–496, 2005.[Abstract/Free Full Text]

22. Lin CY, Anders J, Johnson M, Dickson RB. Purification and characterization of a complex containing matriptase and a Kunitz-type serine protease inhibitor from human milk. J Biol Chem 274: 18237–18242, 1999.[Abstract/Free Full Text]

23. Lin CY, Anders J, Johnson M, Sang QA, Dickson RB. Molecular cloning of cDNA for matriptase, a matrix-degrading serine protease with trypsin-like activity. J Biol Chem 274: 18231–18236, 1999.[Abstract/Free Full Text]

24. Lin CY, Wang JK, Torri J, Dou L, Sang QA, Dickson RB. Characterization of a novel, membrane-bound, 80-kDa matrix-degrading protease from human breast cancer cells. Monoclonal antibody production, isolation, and localization. J Biol Chem 272: 9147–9152, 1997.[Abstract/Free Full Text]

25. List K, Haudenschild CC, Szabo R, Chen W, Wahl SM, Swaim W, Engelholm LH, Behrendt N, Bugge TH. Matriptase/MT-SP1 is required for postnatal survival, epidermal barrier function, hair follicle development, and thymic homeostasis. Oncogene 21: 3765–3779, 2002.[CrossRef][Web of Science][Medline]

26. List K, Szabo R, Molinolo A, Nielsen BS, Bugge TH. Delineation of matriptase protein expression by enzymatic gene trapping suggests diverging roles in barrier function, hair formation, and squamous cell carcinogenesis. Am J Pathol 168: 1513–1525, 2006.[Abstract/Free Full Text]

27. List K, Szabo R, Molinolo A, Sriuranpong V, Redeye V, Murdock T, Burke B, Nielsen BS, Gutkind JS, Bugge TH. Deregulated matriptase causes ras-independent multistage carcinogenesis and promotes ras-mediated malignant transformation. Genes Dev 19: 1934–1950, 2005.[Abstract/Free Full Text]

28. List K, Szabo R, Wertz PW, Segre J, Haudenschild CC, Kim SY, Bugge TH. Loss of proteolytically processed filaggrin caused by epidermal deletion of matriptase/MT-SP1. J Cell Biol 163: 901–910, 2003.[Abstract/Free Full Text]

29. Llopis J, McCaffery JM, Miyawaki A, Farquhar MG, Tsien RY. Measurement of cytosolic, mitochondrial, and Golgi pH in single living cells with green fluorescent proteins. Proc Natl Acad Sci USA 95: 6803–6808, 1998.[Abstract/Free Full Text]

30. Long YQ, Lee SL, Lin CY, Enyedy IJ, Wang S, Li P, Dickson RB, Roller PP. Synthesis and evaluation of the sunflower derived trypsin inhibitor as a potent inhibitor of the type II transmembrane serine protease, matriptase. Bioorg Med Chem Lett 11: 2515–2519, 2001.[CrossRef][Medline]

31. Luckett S, Garcia RS, Barker JJ, Konarev AV, Shewry PR, Clarke AR, Brady RL. High-resolution structure of a potent, cyclic proteinase inhibitor from sunflower seeds. J Mol Biol 290: 525–533, 1999.[CrossRef][Web of Science][Medline]

32. McIlvaine TC. A buffer solution for colorimetric comparison. J Biol Chem 49: 183–186, 1921.[Free Full Text]

33. Miesenbock G, De Angelis DA, Rothman JE. Visualizing secretion and synaptic transmission with pH-sensitive green fluorescent proteins. Nature 394: 192–195, 1998.[CrossRef][Medline]

34. Netzel-Arnett S, Currie BM, Szabo R, Lin CY, Chen LM, Chai KX, Antalis TM, Bugge TH, List K. Evidence for a matriptase-prostasin proteolytic cascade regulating terminal epidermal differentiation. J Biol Chem 281: 32941–32945, 2006.[Abstract/Free Full Text]

35. Netzel-Arnett S, Hooper JD, Szabo R, Madison EL, Quigley JP, Bugge TH, Antalis TM. Membrane anchored serine proteases: a rapidly expanding group of cell surface proteolytic enzymes with potential roles in cancer. Cancer Metastasis Rev 22: 237–258, 2003.[CrossRef][Web of Science][Medline]

36. Oberst M, Anders J, Xie B, Singh B, Ossandon M, Johnson M, Dickson RB, Lin CY. Matriptase and HAI-1 are expressed by normal and malignant epithelial cells in vitro and in vivo. Am J Pathol 158: 1301–1311, 2001.[Abstract/Free Full Text]

37. Oberst MD, Chen LY, Kiyomiya KI, Williams CA, Lee MS, Johnson MD, Dickson RB, Lin CY. Hepatocyte growth factor activator inhibitor 1 (HAI-1) regulates activation and expression of matriptase, a membrane-bound serine protease. Am J Physiol Cell Physiol 289: C462–C470, 2005.[Abstract/Free Full Text]

38. Oberst MD, Johnson MD, Dickson RB, Lin CY, Singh B, Stewart M, Williams A, al Nafussi A, Smyth JF, Gabra H, Sellar GC. Expression of the serine protease matriptase and its inhibitor HAI-1 in epithelial ovarian cancer: correlation with clinical outcome and tumor clinicopathological parameters. Clin Cancer Res 8: 1101–1107, 2002.[Abstract/Free Full Text]

39. Oberst MD, Singh B, Ossandon M, Dickson RB, Johnson MD, Lin CY. Characterization of matriptase expression in normal human tissues. J Histochem Cytochem 51: 1017–1025, 2003.[Abstract/Free Full Text]

40. Oberst MD, Williams CA, Dickson RB, Johnson MD, Lin CY. The activation of matriptase requires its noncatalytic domains, serine protease domain, and its cognate inhibitor. J Biol Chem 278: 26773–26779, 2003.[Abstract/Free Full Text]

41. Saleem M, Adhami VM, Zhong W, Longley BJ, Lin CY, Dickson RB, Reagan-Shaw S, Jarrard DF, Mukhtar H. A novel biomarker for staging human prostate adenocarcinoma: overexpression of matriptase with concomitant loss of its inhibitor, hepatocyte growth factor activator inhibitor-1. Cancer Epidemiol Biomarkers Prev 15: 217–227, 2006.[Abstract/Free Full Text]

42. Santin AD, Cane' S, Bellone S, Bignotti E, Palmieri M, Las Casas LE, Anfossi S, Roman JJ, O'Brien T, Pecorelli S. The novel serine protease tumor-associated differentially expressed gene-15 (matriptase/MT-SP1) is highly overexpressed in cervical carcinoma. Cancer 98: 1898–1904, 2003.[CrossRef][Web of Science][Medline]

43. Santin AD, Zhan F, Bellone S, Palmieri M, Cane S, Bignotti E, Anfossi S, Gokden M, Dunn D, Roman JJ, O'Brien TJ, Tian E, Cannon MJ, Shaughnessy J Jr, Pecorelli S. Gene expression profiles in primary ovarian serous papillary tumors and normal ovarian epithelium: identification of candidate molecular markers for ovarian cancer diagnosis and therapy. Int J Cancer 112: 14–25, 2004.[CrossRef][Web of Science][Medline]

44. Satomi S, Yamasaki Y, Tsuzuki S, Hitomi Y, Iwanaga T, Fushiki T. A role for membrane-type serine protease (MT-SP1) in intestinal epithelial turnover. Biochem Biophys Res Commun 287: 995–1002, 2001.[CrossRef][Web of Science][Medline]

45. Seksek O, Biwersi J, Verkman AS. Direct measurement of trans-Golgi pH in living cells and regulation by second messengers. J Biol Chem 270: 4967–4970, 1995.[Abstract/Free Full Text]

46. Shimomura T, Denda K, Kitamura A, Kawaguchi T, Kito M, Kondo J, Kagaya S, Qin L, Takata H, Miyazawa K, Kitamura N. Hepatocyte growth factor activator inhibitor, a novel Kunitz-type serine protease inhibitor. J Biol Chem 272: 6370–6376, 1997.[Abstract/Free Full Text]

47. Siddiqui SF, Pawelek J, Handerson T, Lin CY, Dickson RB, Rimm DL, Camp RL. Coexpression of beta1,6-N-acetylglucosaminyltransferase V glycoprotein substrates defines aggressive breast cancers with poor outcome. Cancer Epidemiol Biomarkers Prev 14: 2517–2523, 2005.[Abstract/Free Full Text]

48. Suzuki M, Kobayashi H, Kanayama N, Saga Y, Suzuki M, Lin CY, Dickson RB, Terao T. Inhibition of tumor invasion by genomic down-regulation of matriptase through suppression of activation of receptor-bound pro-urokinase. J Biol Chem 279: 14899–14908, 2004.[Abstract/Free Full Text]

49. Szabo R, Molinolo A, List K, Bugge TH. Matriptase inhibition by hepatocyte growth factor activator inhibitor-1 is essential for placental development. Oncogene 26: 1546–1556, 2007.[CrossRef][Web of Science][Medline]

50. Szabo R, Wu Q, Dickson RB, Netzel-Arnett S, Antalis TM, Bugge TH. Type II transmembrane serine proteases. Thromb Haemost 90: 185–193, 2003.[Web of Science][Medline]

51. Takeuchi T, Harris JL, Huang W, Yan KW, Coughlin SR, Craik CS. Cellular localization of membrane-type serine protease 1 and identification of protease-activated receptor-2 and single-chain urokinase-type plasminogen activator as substrates. J Biol Chem 275: 26333–26342, 2000.[Abstract/Free Full Text]

52. Takeuchi T, Shuman MA, Craik CS. Reverse biochemistry: use of macromolecular protease inhibitors to dissect complex biological processes and identify a membrane-type serine protease in epithelial cancer and normal tissue. Proc Natl Acad Sci USA 96: 11054–11061, 1999.[Abstract/Free Full Text]

53. Tanimoto H, Shigemasa K, Tian X, Gu L, Beard JB, Sawasaki T, O'Brien TJ. Transmembrane serine protease TADG-15 (ST14/matriptase/MT-SP1): expression and prognostic value in ovarian cancer. Br J Cancer 92: 278–283, 2005.[Web of Science][Medline]

54. Tanimoto H, Underwood LJ, Wang Y, Shigemasa K, Parmley TH, O'Brien TJ. Ovarian tumor cells express a transmembrane serine protease: a potential candidate for early diagnosis and therapeutic intervention. Tumour Biol 22: 104–114, 2001.[CrossRef][Medline]




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