Translocation of PKG1α acts on TRPV4-C1 heteromeric channels to inhibit endothelial Ca2+ entry

Aim: TRPV4-C1 heteromeric channels contribute to store-operated Ca2+ entry in vascular endothelial cells. However, the negative regulation of these channels is not fully understood. This study was conducted to investigate the inhibitory effect of PKG1 alpha on TRPV4-C1 heteromeric channels. Methods: Immuno-fluorescence resonance energy transfer (FRET) was used to explore the spatial proximity of PKG1 alpha and TRPC1. Phosphorylation of endogenous TRPC1 was tested by phosphorylation assay. [Ca2+](i) transients and cation current in MAECs were assessed with Fura-2 fluorescence and whole-cell recording, respectively. In addition, rat mesenteric arteries segments were prepared, and vascular relaxation was examined with wire myography. Results: In immuno-FRET experiments, after exposure of these cells to 8-Br-cGMP, more PKG1 alpha was observed in the plasma membrane, and PKG1 alpha and TRPC1 were observed to be in closer proximity. TAT-TRPC1S172 and TAT-TRPC1T313 peptide fragments, which contain the PKG targeted residues Ser172 and Thr313, respectively, were introduced into isolated endothelial cells to abrogate the translocation of PKG1 alpha. Furthermore, a phosphorylation assay demonstrated that PKG directly phosphorylates TRPC1 at Ser172 and Thr313 in endothelial cells. In addition, PKG activator 8-Br-cGMP markedly reduced the magnitude of the 4 alpha PDD-induced and 11,12-EET-induced [Ca2+](i) transients, the cation current and vascular relaxation. Conclusion: This study uncovers a novel mechanism by which PKG negatively regulates endothelial heteromeric TRPV4-C1 channels through increasing the spatial proximity of TRPV4-C1 to PKG1 alpha via translocation and through phosphorylating Ser172 and Thr313 of TRPC1.