Integration of Phosphoinositide- and Calmodulin-Mediated Regulation of TRPC6

Multiple TRP channels are regulated by phosphoinositides (PIs). However, it is not known whether PIs bind directly to TRP channels. Furthermore, the mechanisms through which PIs regulate TRP channels are obscure. To analyze the role of PI/TRP interactions, we used a biochemical approach, focusing on TRPC6. TRPC6 bound directly to PIs, and with highest potency to phosphatidylinositol 3,4,5-trisphosphate (PIP₃). We found that PIP₃ binding disrupted the association of calmodulin (CaM) with TRPC6. We identified the PIP₃-binding site and found that mutations that increased or decreased the affinity of the PIP₃/TRPC6 interaction enhanced or reduced the TRPC6-dependent current, respectively. PI-mediated disruption of CaM binding appears to be a theme that applies to other TRP channels, such as TRPV1, as well as to the voltage-gated channels KCNQ1 and Ca_v1.2. We propose that regulation of CaM binding by PIs provides a mode for integration of channel regulation by Ca²⁺ and PIs.