Obligatory role for PKCδ in PIP(2)‐mediated activation of store‐operated TRPC1 channels in vascular smooth muscle cells

KEY POINTS: In vascular smooth muscle cells (VSMCs), activation of Ca(2+)‐permeable store‐operated channels (SOCs) composed of canonical transient receptor potential channel 1 (TRPC1) subunits mediates Ca(2+) entry pathways that regulate contraction, proliferation and migration, which are processes associated with vascular disease. Activation of TRPC1‐based SOCs requires protein kinase C (PKC) activity, which is proposed to phosphorylate TRPC1 proteins to promote channel opening by phosphatidylinositol 4,5‐bisphosphate (PIP(2)). We investigated the identity of the PKC isoform involved in activating TRPC1‐based SOCs in rat mesenteric artery VSMCs. TRPC1‐based SOCs were reduced by PKCδ inhibitors and knockdown of PKCδ expression. Store depletion induced interactions between TRPC1 and PKCδ and PKCδ‐dependent phosphorylation of TRPC1. Furthermore, generation of store‐operated interactions between PIP(2) and TRPC1 and activation of TRPC1‐based SOCs by PIP(2) required PKCδ. These findings reveal that PKCδ activity has an obligatory role in activating TRPC1‐based SOCs, through regulating PIP(2)‐mediated channel opening. ABSTRACT: In vascular smooth muscle cells (VMSCs), stimulation of Ca(2+)‐permeable canonical transient receptor potential channel 1 (TRPC1)‐based store‐operated channels (SOCs) mediates Ca(2+) entry pathways that regulate cell contraction, proliferation and migration, which are processes associated with vascular disease. It is therefore important to understand how TRPC1‐based SOCs are activated. Stimulation of TRPC1‐based SOCs requires protein kinase C (PKC) activity, with store‐operated PKC‐dependent phosphorylation of TRPC1 essential for channel opening by phosphatidylinositol 4,5‐bisphosphate (PIP(2)). Experimental protocols used to activate TRPC1‐based SOCs suggest that the PKC isoform involved requires diacylglycerol (DAG) but is Ca(2+)‐insensitive, which are characteristics of the novel group of PKC isoforms (δ, ε, η, θ). Hence, the present study examined whether a novel PKC isoform(s) is involved in activating TRPC1‐based SOCs in contractile rat mesenteric artery VSMCs. Store‐operated whole‐cell cation currents were blocked by Pico145, a highly selective and potent TRPC1/4/5 channel blocker and T1E3, a TRPC1 blocking antibody. PKCδ was expressed in VSMCs, and selective PKCδ inhibitory peptides and knockdown of PKCδ expression with morpholinos oligomers inhibited TRPC1‐based SOCs. TRPC1 and PKCδ interactions and phosphorylation of TRPC1 induced by store depletion were both reduced by pharmacological inhibition and PKCδ knockdown. In addition, store‐operated PIP(2) and TRPC1 interactions were blocked by PKCδ inhibition, and PKCδ was required for PIP(2)‐mediated activation of TRPC1 currents. These results identify the involvement of PKCδ in stimulation of TRPC1‐based SOCs and highlight that store‐operated PKCδ activity is obligatory for channel opening by PIP(2), the probable activating ligand.