Mediation of angiotensin II-induced Ca²⁺ signaling by polycystin 2 in glomerular mesangial cells

Ca⁺ influx across the plasma membrane is a major component of mesangial cell (MC) response to vasoconstrictors. Polycystin 2 (PC2), the protein product of the gene mutated in type 2 autosomal dominant polycystic kidney disease, has been shown to function as a nonselective cation channel in a variety of cell types. The present study was performed to test the hypothesis that PC2 and its binding partners constitute a Ca²⁺-permeable channel and contribute to ANG II-induced Ca²⁺ signaling in MCs. Western blot and immunocytochemistry showed PC2 expression in cultured human MCs. The existence of PC2 in MCs was further confirmed by immunohistochemsitry in rat kidney sections. Coimmunoprecipitation displayed a selective interaction of PC2 with canonical transient receptor potential (TRPC) proteins TRPC1 and TRPC4. Cell-attached patch-clamp experiments revealed that ANG II-induced membrane currents were enhanced by overexpression of pkd2 but significantly inhibited by knock down of pkd2, 30 μM Gd³⁺ (a PC2 channel blocker), and dominant-negative pkd2 mutant (pkd2-D511V). Corresponding to the increase in channel currents, ANG II stimulation increased expression of PC2 on the cell surface of MCs and interaction with TRPC1 and TRPC4. Furthermore, ANG II-induced MC contraction was significantly reduced in pkd2-knocked down MCs. These data suggest that PC2 selectively assembles with TRPC1 and TRPC4 to form channel complexes mediating ANG II-induced Ca²⁺ responses in MCs.