STIM1 regulates TRPC6 heteromultimerization and subcellular location.

STIM1 (stromal interaction molecule 1) regulates store-operated channels in the plasma membrane, but the regulation of TRPC (transient receptor potential canonical) heteromultimerization and location by STIM1 is poorly understood. STIM1 is a single transmembrane protein that communicates the filling state of the endoplasmic reticulum to store-operated channels. STIM1 has been reported to regulate the activity of all of the TRPC family members, except TRPC7. TRPC6 has been predominantly associated to second messenger-activated Ca2+ entry pathways. In the present paper we report that STIM1 regulates the expression of TRPC6 in the plasma membrane and evokes translocation of this channel to the endoplasmic reticulum. Attenuation of TRPC6 expression in the plasma membrane resulted in a reduction in the association of this channel with TRPC1 and TRPC3. We have found that expression of TRPC6 in the endoplasmic reticulum results in an increase in the passive Ca2+ efflux and basal cytosolic Ca2+ concentration, but not in the ability of cells to accumulate Ca2+ into the endoplasmic reticulum. We propose a novel mechanism for the regulation of TRPC6 channel location and function by STIM1, probably as a mechanism to modulate second messenger-operated Ca2+ entry while potentiating store-operated Ca2+ influx. Abbreviations: [Ca2+]c, cytosolic free calcium concentration; DAG, diacylglycerol; ER, endoplasmic reticulum; fura 2/AM, fura 2 acetoxymethyl ester; HBS, Hepes-buffered saline; sulfo-NHS-LC-biotin, sulfosuccinimidyl-6′-(biotinamido)hexanoate; PMCA, plasma-membrane Ca2+-ATPase; SERCA, sarcoplasmic/endoplasmic reticulum Ca2+-ATPase; SOCE, store-operated Ca2+ entry; STIM1, stromal interaction molecule 1; TBST, TBS with Tween 20; TG, thapsigargin; TRP, transient receptor potential; TRPC, transient receptor potential canonical; TRPM, transient receptor potential melastatin; TRPV, transient receptor potential vanilloid