Compartmentalization of TRPC1‐STIM1 interactions into lipid raft domains

Abstract

Lipid rafts are cholesterol enriched plasma membrane microdomains that serve as cellular signaling platforms. Numerous physiological signals are relayed to the cells interior via these distinctly compartmentalized plasma membrane microdomains. Here we demonstrate the association of Transient Receptor Potential Cannonical-1 (TRPC1, a store operated calcium entry (SOCE) channel) with lipid raft/caveolar compartments of the plasma membrane. Depletion of endoplasmic reticulum(ER) calcium stores by thapsigargin (Tg, a inhibitor for sarco/endoplasmic calcium ATPase) enhanced the recruitment of TRPC1 protein to the plasma membrane rafts. This was associated with the calcium influx property of TRPC1 that was sensitive to specific SOCE blockers. We also identify Stromal Interacting Molecule-1(STIM1 an ER calcium sensor) as a candidate SOCE element involved in ER store dependant activation of TRPC1. STIM1 communicates the ER calcium store depletion status by translocating to the plasma membrane and interacting with TRPC1. Down-regulation of STIM1 by siRNA reduced SOCE which was similar in cells expressing TRPC1-siRNA. Alternatively, sequestration of membrane cholesterol by MβCD or Fillipin-III altered raft-associated TRPC1 localization and its calcium influx property. Altogether, our findings demonstrate activation of TRPC1 relies on its association with STIM1 and lipid raft integrity.