The Phosphatidylinositol(4,5)Bisphosphate–Binding Sequence of Transient Receptor Potential Channel Canonical 4a Is Critical for Its Contribution to Cardiomyocyte Hypertrophy

Cardiomyocyte hypertrophy requires a source of Ca21 distinct from the Ca21 that regulates contraction. The canonical tran-sient receptor potential channel (TrpC) family, a family of cation channels regulated by activation of phospholipase C (PLC), has been implicated in this response. Cardiomyocyte hypertrophy downstream of Gq-coupled receptors is mediated specifically by PLCb1b that is scaffolded onto a SH3 and ankyrin repeat protein 3 (Shank3) complex at the sarcolemma. TrpC4 exists as two splice variants (TrpC4a and TrpC4b) that differ only in an 84-residue sequence that binds to phosphatidylinositol(4,5) bisphosphate (PIP2), the substrate of PLCb1b. In neonatal rat cardiomyocytes, TrpC4a, but not TrpC4b, coimmunoprecipi-tated with both PLCb1b and Shank3. Heightened PLCb1b expression caused TrpC4a, but not TrpC4b, translocation to the sarcolemma, where it colocalized with PLCb1b. When overex-pressed in cardiomyocytes, TrpC4a, but not TrpC4b, increased cell area (893 6 18 to 1497 6 29 mm2, P, 0.01) and marker gene expression (atrial natriuretic peptide increased by 409 6 32%, and modulatory calcineurin inhibitory protein 1 by 315 6 28%, P, 0.01). Dominant-negative TrpC4 reduced hypertrophy initiated by PLCb1b, or PLCb1b-coupled receptor activation, by 726 8 % and 396 5 %, respectively. We conclude that TrpC4a is selectively involved in mechanisms downstream of PLCb1b culminating in cardiomyocyte hypertrophy, and that the hyper-trophic response is dependent on the TrpC4a splice variant-specific sequence that binds to PIP2