Obligatory role for PKCδ in PIP2 -mediated activation of store-operated TRPC1 channels in vascular smooth muscle cells

In vascular smooth muscle cells (VMSCs), stimulation of Ca2+ -permeable canonical transient receptor potential channel 1 (TRPC1)-based store-operated channels (SOCs) mediate Ca2+ entry pathways which regulate cell contraction, proliferation and migration that 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 (PIP2 ). Experimental protocols used to activate TRPC1-based SOCs suggest that the PKC isoform involved requires diacylglycerol (DAG) but is Ca2+ -insensitive, which are characteristics of the novel group of PKC isoforms (δ, ε, η, θ). Hence the present study examines if 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 PIP2 and TRPC1 interactions were blocked by PKCδ inhibition, and PKCδ was required for PIP2 -mediated activation of TRPC1 currents. These results identify involvement of PKCδ in stimulation of TRPC1-based SOCs and highlights that store-operated PKCδ activity is obligatory for channel opening by PIP2 , the likely activating ligand.