STIM1 and STIM2 Proteins Regulation of Endogenous Store-Operated Calcium Channels in HEK293 Cells

Abstract

The endoplasmic reticulum calcium sensors STIM1 and STIM2 are key modulators of store-operated calcium entry. They play a major role in physiological functions in the norm and pathology, however, available data on native STIM2-regulated plasma membrane channels are scarce: it is in only a few studies that STIM2-induced CRAC currents have been recorded. The STIM1 protein has been shown to regulate not only CRAC but also TRPC channels, but it has remained unclear whether STIM2 is capable of regulating store-operated non-CRAC channels. Here we present experimental evidence for the existence of endogenous non-CRAC STIM2-regulated channels. In single-channel patch-clamp experiments on HEK293 cells, store-operated Imin channels were induced by selective activation of native STIM2 proteins or STIM2 overexpression. It was found that STIM1 activation blocked store-operated mode of Imin activation. Changes in the ratio between active STIM2 and STIM1 proteins could switch Imin channels regulation between store-operated and store-independent modes.We have previously characterized electrophysiological properties of different Ca2+ influx channels coexisting in HEK293 cells. The results of this study show that STIM1 and STIM2 differ in the ability to activate these store-operated channels: Imin channels are regulated by STIM2, TRPC3-containing INS channels are induced by STIM1, and TRPC1-composed Imax channels are activated by both STIM1 and STIM2. These new data about cross-talk between STIM1 and STIM2 and their different roles in store-operated channel activation are indicative of an additional level in the regulation of store-operated calcium entry pathways.This study was supported by the Russian Scientific Foundation 14-14-00720 (to E.K. and A.S.); the program “Molecular and Cellular Biology” of the RAS (to G.N.M and L.G.); the Scientific School Support Program SS-1721.2014.4 (to G.N.M.); the Dynasty Foundation; and the Russian Foundation for Basic Research.