TRPC channels function independently of STIM1 and Orai1

J Physiol. 2009 May 15;587(Pt 10):2275-98. doi: 10.1113/jphysiol.2009.170431. Epub 2009 Mar 30.

Abstract

Recent studies have defined roles for STIM1 and Orai1 as calcium sensor and calcium channel, respectively, for Ca(2+)-release activated Ca(2+) (CRAC) channels, channels underlying store-operated Ca(2+) entry (SOCE). In addition, these proteins have been suggested to function in signalling and constructing other channels with biophysical properties distinct from the CRAC channels. Using the human kidney cell line, HEK293, we examined the hypothesis that STIM1 can interact with and regulate members of a family of non-selective cation channels (TRPC) which have been suggested to also function in SOCE pathways under certain conditions. Our data reveal no role for either STIM1 or Orai1 in signalling of TRPC channels. Specifically, Ca(2+) entry seen after carbachol treatment in cells transiently expressing TRPC1, TRPC3, TRPC5 or TRPC6 was not enhanced by the co-expression of STIM1. Further, knockdown of STIM1 in cells expressing TRPC5 did not reduce TRPC5 activity, in contrast to one published report. We previously reported in stable TRPC7 cells a Ca(2+) entry which was dependent on TRPC7 and appeared store-operated. However, we show here that this TRPC7-mediated entry was also not dependent on either STIM1 or Orai1, as determined by RNA interference (RNAi) and expression of a constitutively active mutant of STIM1. Further, we determined that this entry was not actually store-operated, but instead TRPC7 activity which appears to be regulated by SERCA. Importantly, endogenous TRPC activity was also not regulated by STIM1. In vascular smooth muscle cells, arginine-vasopressin (AVP) activated non-selective cation currents associated with TRPC6 activity were not affected by RNAi knockdown of STIM1, while SOCE was largely inhibited. Finally, disruption of lipid rafts significantly attenuated TRPC3 activity, while having no effect on STIM1 localization or the development of I(CRAC). Also, STIM1 punctae were found to localize in regions distinct from lipid rafts. This suggests that TRPC signalling and STIM1/Orai1 signalling occur in distinct plasma membrane domains. Thus, TRPC channels appear to be activated by mechanisms dependent on phospholipase C which do not involve the Ca(2+) sensor, STIM1.

Publication types

  • Research Support, N.I.H., Intramural

MeSH terms

  • Arginine Vasopressin / pharmacology
  • Barium / pharmacology
  • Calcium Channels / physiology*
  • Calcium Signaling / drug effects
  • Carbachol / pharmacology
  • Cell Adhesion Molecules / genetics
  • Cell Line
  • Cell Membrane / drug effects
  • Cell Membrane / metabolism
  • Chelating Agents / pharmacology
  • Diglycerides / pharmacology
  • Electrophysiological Phenomena / drug effects
  • Electrophysiological Phenomena / physiology
  • Gadolinium / pharmacology
  • Humans
  • Inositol 1,4,5-Trisphosphate / pharmacology
  • Membrane Microdomains / drug effects
  • Membrane Microdomains / metabolism
  • Membrane Proteins / physiology*
  • Myocytes, Smooth Muscle / drug effects
  • Myocytes, Smooth Muscle / physiology
  • Neoplasm Proteins / physiology*
  • ORAI1 Protein
  • RNA, Small Interfering / genetics
  • Stromal Interaction Molecule 1
  • Stromal Interaction Molecule 2
  • TRPC Cation Channels / physiology*
  • TRPC6 Cation Channel
  • Thapsigargin / pharmacology
  • Transfection
  • beta-Cyclodextrins / pharmacology

Substances

  • 1-oleoyl-2-acetoyl-sn-glycerol
  • Calcium Channels
  • Cell Adhesion Molecules
  • Chelating Agents
  • Diglycerides
  • Membrane Proteins
  • Neoplasm Proteins
  • ORAI1 Protein
  • ORAI1 protein, human
  • RNA, Small Interfering
  • STIM1 protein, human
  • STIM2 protein, human
  • Stromal Interaction Molecule 1
  • Stromal Interaction Molecule 2
  • TRPC Cation Channels
  • TRPC3 cation channel
  • TRPC5 protein, human
  • TRPC6 Cation Channel
  • TRPC6 protein, human
  • TRPC7 protein, human
  • beta-Cyclodextrins
  • methyl-beta-cyclodextrin
  • transient receptor potential cation channel, subfamily C, member 1
  • Arginine Vasopressin
  • Barium
  • Thapsigargin
  • Inositol 1,4,5-Trisphosphate
  • Carbachol
  • Gadolinium