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This Article Full Text Full Text (PDF) All Versions of this Article: 294/5/C1277    most recent ajpcell.90635.2007v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Marasa, B. S. Articles by Wang, J.-Y. Search for Related Content PubMed PubMed Citation Articles by Marasa, B. S. Articles by Wang, J.-Y.

GROWTH, DIFFERENTIATION, AND APOPTOSIS

Induced TRPC1 expression increases protein phosphatase 2A sensitizing intestinal epithelial cells to apoptosis through inhibition of NF-B activation

¹Cell Biology Group, Department of Surgery and ²Department of Pathology, University of Maryland School of Medicine, Baltimore, Maryland; ³Baltimore Veterans Affairs Medical Center, Baltimore, Maryland; and ⁴Division of Pulmonary and Critical Care Medicine, Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland

Submitted 18 December 2007 ; accepted in final form 4 March 2008

Transient receptor potential canonical-1 (TRPC1) functions as a store-operated Ca²⁺ channel in intestinal epithelial cells (IECs), and induced TRPC1 expression sensitizes IECs to apoptosis by inhibiting NF-B activation. However, the exact mechanism by which increased TRPC1 results in NF-B inactivation remains elusive. Protein phosphatase 2A (PP2A) is a widely conserved protein serine/threonine phosphatase that is implicated in the regulation of a wide array of cellular functions including apoptosis. The present study tests the hypothesis that induced TRPC1 expression inhibits NF-B activation by increasing PP2A activity through Ca²⁺ influx in IECs. The expression of TRPC1 induced by stable transfection with the wild-type TRPC1 gene increased PP2A activity as indicated by increases in levels of PP2A proteins and their phosphatase activity. Increased levels of PP2A activity in stable TRPC1-transfected IEC-6 cells (IEC-TRPC1) were associated with decreased nuclear levels of NF-B proteins and a reduction in NF-B-dependent transcriptional activity, although there were no changes in total NF-B protein levels. Inhibition of PP2A activity by treatment with okadaic acid or PP2A silencing with small interfering RNA not only enhanced NF-B transactivation but also prevented the increased susceptibility of IEC-TRPC1 cells to apoptosis induced by treatment with tumor necrosis factor- (TNF-)/cycloheximide (CHX). Decreasing Ca²⁺ influx by exposure to the Ca²⁺-free medium reduced PP2A mRNA levels, destabilized PP2A proteins, and induced NF-B activation, thus blocking the increased sensitivity of IEC-TRPC1 cells to TNF-/CHX-induced apoptosis. These results indicate that induced TRPC1 expression increases PP2A activity through Ca²⁺ influx and that increased PP2A sensitizes IECs to apoptosis as a result of NF-B inactivation.

store-operated Ca²⁺ channels; capacitative Ca²⁺ entry mechanism; programmed cell death; IB; small interfering ribonucleic acid; intestinal epithelium; mucosal homeostasis; transient receptor potential canonical-1