Store‐operated STIM1 translocation and interaction with TRPC1 at the plasma membrane stimulates PLC activity to induce channel gating in vascular smooth muscle cells

In vascular smooth muscle cells (VSMCs), stimulation of TRPC1-based SOCs mediate Ca2+ entry pathways which regulate contractility, proliferation and migration. It is therefore important to understand how these channels are activated. Studies have shown that stimulation of TRPC1-based SOCs requires Gαq/PLCβ1 activities and PKC phosphorylation, but it is unclear how store depletion stimulates this gating pathway. The present work examines this issue by focusing on the role of STIM1, an endo/sarcoplasmic reticulum Ca2+ sensor. Store-operated TRPC1 channel activity was inhibited by TRPC1 and STIM1 antibodies and STIM1 shRNA in wild-type VSMCs, and was absent in TRPC1−/− VSMCs. Store-operated PKC phosphorylation of TRPC1 was reduced by knockdown of STIM1. Moreover, store-operated PLCβ1 activity measured with the fluorescent PIP2/InsP3 biosensor GFP-PLCδ1-PH was reduced by STIM1 shRNA and absent in TRPC1−/− cells. Immunocytochemistry, co-immunoprecipitation, and proximity ligation assays revealed that store depletion activated STIM1 translocation from within the cell to the plasma membrane (PM) where it formed STIM1-TRPC1 complexes, which then associated with Gαq and PLCβ1. Noradrenaline also evoked TRPC1 channel activity and associations between TRPC1, STIM1, Gαq and PLCβ1, which were inhibited by STIM1 knockdown. Effects of N-terminal and C-terminal STIM1 antibodies on TRPC1-based SOCs and STIM1 staining suggest that channel activation may involve insertion of STIM1 into the PM. Our findings identify a new activation mechanism of TRPC1-based SOCs in VSMCs, and a novel role for STIM1, in which store-operated STIM1-TRPC1 interactions stimulate PLCβ1 activity to induce PKC phosphorylation of TRPC1 and channel gating. This article is protected by copyright. All rights reserved