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VASCULAR BIOLOGY
1Department of Cell Biology, Lerner Research Institute and Cleveland Clinic Lerner College of Medicine, and 2Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, Ohio
Submitted 9 May 2007 ; accepted in final form 6 November 2007
We have previously reported that MAPK phosphatase-1 (MKP-1/CL100) is a thrombin-responsive gene in endothelial cells (ECs). We now show that VEGF is another efficacious activator of MKP-1 expression in human umbilical vein ECs. VEGF-A and VEGF-E maximally induced MKP-1 expression in ECs; however, the other VEGF subtypes had no effect. Using specific neutralizing antibodies, we determined that VEGF induced MKP-1 specifically through VEGF receptor 2 (VEGFR-2), leading to the downstream activation of JNK. The VEGF-A165 isoform stimulated MKP-1 expression, whereas the VEGF-A162 isoform induced the gene to a lesser extent, and the VEGF-A121 isoform had no effect. Furthermore, specific blocking antibodies against neuropilins, VEGFR-2 coreceptors, blocked MKP-1 induction. A Src kinase inhibitor (PP1) completely blocked both VEGF- and thrombin-induced MKP-1 expression. A dominant negative approach revealed that Src kinase was required for VEGF-induced MKP-1 expression, whereas Fyn kinase was critical for thrombin-induced MKP-1 expression. Moreover, VEGF-induced MKP-1 expression required JNK, whereas ERK was critical for thrombin-induced MKP-1 expression. In ECs treated with short interfering (si)RNA targeting MKP-1, JNK, ERK, and p38 phosphorylation were prolonged following VEGF stimulation. An ex vivo aortic angiogenesis assay revealed a reduction in VEGF- and thrombin-induced sprout outgrowth in segments from MKP-1-null mice versus wild-type controls. MKP-1 siRNA also significantly reduced VEGF-induced EC migration using a transwell assay system. Overall, these results demonstrate distinct MAPK signaling pathways for thrombin versus VEGF induction of MKP-1 in ECs and point to the importance of MKP-1 induction in VEGF-stimulated EC migration.
angiogenesis; neuropilin; Src kinase; mitogen-activated protein kinase phosphatase-1
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