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

Bernard S. Marasa, Lan Xiao, Jaladanki N. Rao, Tongtong Zou, Lan Liu, Jian Wang, Emily Bellavance, Douglas J. Turner, Jian Ying Wang

Research output: Contribution to journalArticlepeer-review

Abstract

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-κB activation. However, the exact mechanism by which increased TRPC1 results in NF-κB 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-κB activation by increasing PP2A activity through Ca 2+ 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-κB proteins and a reduction in NF-κB-dependent transcriptional activity, although there were no changes in total NF-κB protein levels. Inhibition of PP2A activity by treatment with okadaic acid or PP2A silencing with small interfering RNA not only enhanced NF-κB transactivation but also prevented the increased susceptibility of IEC-TRPC1 cells to apoptosis induced by treatment with tumor necrosis factor-α (TNF-α)/cycloheximide (CHX). Decreasing Ca2+ influx by exposure to the Ca2+-free medium reduced PP2A mRNA levels, destabilized PP2A proteins, and induced NF-κB activation, thus blocking the increased sensitivity of IEC-TRPC1 cells to TNF-α/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-κB inactivation.

Original languageEnglish (US)
Pages (from-to)C1277-C1287
JournalAmerican Journal of Physiology - Cell Physiology
Volume294
Issue number5
DOIs
StatePublished - May 2008
Externally publishedYes

Keywords

  • Capacitative Ca entry mechanism
  • Intestinal epithelium
  • IκB
  • Mucosal homeostasis
  • Programmed cell death
  • Small interfering ribonucleic acid
  • Store-operated Ca channels
  • Transient receptor potential canonical-1

ASJC Scopus subject areas

  • Physiology
  • Cell Biology

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