Role of RACK1 in the differential proliferative effects of neuropeptide Y1–36 and peptide YY1–36 in SHR vs. WKY preglomerular vascular smooth muscle cells
Previous studies show that neuropeptide Y1–36 (NPY1–36) and peptide YY1–36 (PYY1–36), by engaging Y1 receptors, stimulate proliferation of spontaneous hypertensive rat (SHR) preglomerular vascular smooth muscle cells (PGVSMCs). In contrast, these peptides have little effect on proliferation of Wistar-Kyoto (WKY) PGVSMCs. Why SHR and WKY PGVSMCs differ in this regard is unknown. Because receptor for activated C kinase 1 (RACK1) can modulate cell proliferation, we tested the hypothesis that differences in RACK1 levels/localization may explain the differential response of SHR vs. WKY PGVSMCs to NPY1–36 and PYY1–36. Western blotting for RACK1 in subcellular fractions of cultured SHR and WKY PGVSMCs demonstrated increased levels of RACK1 in the membrane and cytoskeletal subcellular fractions of SHR vs. WKY PGVSMCs. NPY1–36 and PYY1–36 stimulated proliferation of SHR PGVSMCs, and siRNA knockdown of RACK1 abrogated this effect. Neither NPY1–36 nor PYY1–36 stimulated the proliferation of WKY PGVSMCs. However, in WKY PGVSMCs treated with a RACK1 plasmid, both NPY1–36 and PYY1–36 stimulated proliferation. In SHR PGVSMCs, inhibitors of the Gi/phospholipase C/PKC pathway (a pathway known to be organized by RACK1) attenuated the ability of NPY1–36 to stimulate the proliferation of SHR PGVSMCs. Our results suggest that RACK1 modulates the ability of PGVSMCs to respond to the proliferative actions of NPY1–36 and PYY1–36 and differences in RACK1 levels/localization account for, in part, differential proliferative responses to NPY1–36 and PYY1–36 in SHR vs. WKY PGVSMCs. Because dipeptidyl peptidase IV inhibitors increase NPY1–36 and PYY1–36 levels, our findings have implications for the use of such drugs in diabetic patients.