TY - JOUR
T1 - Induced TRPC1 expression increases protein phosphatase 2A sensitizing intestinal epithelial cells to apoptosis through inhibition of NF-κB activation
AU - Marasa, Bernard S.
AU - Xiao, Lan
AU - Rao, Jaladanki N.
AU - Zou, Tongtong
AU - Liu, Lan
AU - Wang, Jian
AU - Bellavance, Emily
AU - Turner, Douglas J.
AU - Wang, Jian Ying
PY - 2008/5
Y1 - 2008/5
N2 - 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.
AB - 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.
KW - Capacitative Ca entry mechanism
KW - Intestinal epithelium
KW - IκB
KW - Mucosal homeostasis
KW - Programmed cell death
KW - Small interfering ribonucleic acid
KW - Store-operated Ca channels
KW - Transient receptor potential canonical-1
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UR - http://www.scopus.com/inward/citedby.url?scp=48249148378&partnerID=8YFLogxK
U2 - 10.1152/ajpcell.90635.2007
DO - 10.1152/ajpcell.90635.2007
M3 - Article
C2 - 18322138
AN - SCOPUS:48249148378
SN - 0363-6143
VL - 294
SP - C1277-C1287
JO - American Journal of Physiology - Cell Physiology
JF - American Journal of Physiology - Cell Physiology
IS - 5
ER -