Homer binds to Orai1 and TRPC channels in the neointima and regulates vascular smooth muscle cell migration and proliferation.

The molecular components of store-operated Ca influx channels (SOCs) in proliferative and migratory vascular smooth muscle cells (VSMCs) are quite intricate with many channels contributing to SOCs. They include the Ca-selective Orai1 and members of the transient receptor potential canonical (TRPC) channels, which are activated by the endoplasmic reticulum Ca sensor STIM1. The scaffolding protein Homer assembles SOC complexes, but its role in VSMCs is not well understood. Here, we asked whether these SOC components and Homer1 are present in the same complex in VSMCs and how Homer1 contributes to VSMC SOCs, proliferation, and migration leading to neointima formation. Homer1 expression levels are upregulated in balloon-injured vs. uninjured VSMCs. Coimmunoprecipitation assays revealed the presence and interaction of all SOC components in the injured VSMCs, where Homer1 interacts with Orai1 and various TRPC channels. Accordingly, knockdown of Homer1 in cultured VSMCs partially inhibited SOCs, VSMC migration, and VSMC proliferation. Neointimal area was reduced after treatment with an adeno-associated viral vector expressing a short hairpin RNA against Homer1 mRNA (AAV-shHomer1). These findings stress the role of multiple Ca influx channels in VSMCs and are the first to show the role of Homer proteins in VSMCs and its importance in neointima formation.