Effect of GRK4 on renal gastrin receptor regulation in hypertension.

Objective: To investigate whether GRK4 regulates the phosphorylation and function of renal CCKBR.

Methods: GRK4 A142V transgenic mice were used as an animal model of enhanced GRK4 activity, and siRNA was used to silence the GRK4 gene to investigate the regulatory effect of GRK4 on CCKBR phosphorylation and function. Finally, the co-localization and co-connection of GRK4 and CCKBR in RPT cells were observed by laser confocal microscopy and immunoprecipitation to explore the mechanism of GRK4 regulating CCKBR.

Results: Gastrin infusion significantly increased urinary flow and sodium excretion rates in GRK4 WT mice ( < .05). GRK4 siRNA did not affect CCKBR protein expression in WKY RPT cells and SHR RPT cells, but remarkably reduced CCKBR phosphorylation in WKY and SHR RPT cells ( < .05). The inhibitory effect of gastrin on Na-K -ATPase activity in WKY RPT cells was further enhanced by the reduction of GRK4 expression ( < .05), while GRK4 siRNA restored the inhibitory effect of gastrin on Na-K -ATPase activity in SHR RPT cells. Laser confocal and Co-immunoprecipitation results showed that GRK4 and CCKBR co-localized in cultured RPT cells' cytoplasm.

Conclusion: GRK4 participates in the development of hypertension by regulating the phosphorylation of renal CCKBR leading to impaired CCKBR function and water and sodium retention. Knockdown of GRK4 restored the function of CCKBR. The enhanced co-connection between GRK4 and CCKBR may be an important reason for the hyperphosphorylation of GRK4 and CCKBR involved in the pathogenesis of hypertension.