RGS2 Regulates Urotensin II-Induced Intracellular Ca2+ Elevation and Contraction in Glomerular Mesangial Cells

Urotensin II (UII), a vasoactive peptide modulates renal hemodynamics. However, the physiological functions of UII in glomerular cells are unclear. In particular, whether UII alters mesangial tone remains largely unknown. The present study investigates the physiological effects of UII on glomerular mesangial cells (GMCs). This study also tested the hypothesis that the regulator of G-protein signaling (RGS) controls UII receptor (UTR) activity in GMCs. RT-PCR, Western immunoblotting, and immunofluorescence revealed UTR expression in cultured murine GMCs. Mouse UII (mUII) stimulated Ca2+ release from intracellular stores and activated store-operated Ca2+ entry (SOCE) in the cells. mUII also caused a reduction in planar GMC surface area. mUII-induced [Ca2+](i) elevation and contraction were attenuated by SB 657510, a UTR antagonist, araguspongin B, an inositol 1,4,5-trisphosphate receptor antagonist, thapsigargin, a sarco/endoplasmic reticulum Ca2+-ATPase inhibitor, and La3+, a store-operated Ca2+ channel blocker, but not nimodipine, an L-type Ca2+ channel blocker. In situ proximity ligation assay indicated molecular proximity between endogenous RGS2 and UTR in the cells. Treatment of GMCs with mUII elevated plasma membrane expression of RGS2 by approximate to 2-fold. mUII also increased the interaction between RGS2 and UTR in the cells. siRNA-mediated knockdown of RGS2 in murine GMCs increased mUII-induced [Ca2+](i) elevation and contraction by approximate to 35 and 31%, respectively. These findings indicate that mUII-induced SOCE results in murine GMC contraction. These data also suggest that UTR activation stimulates RGS2 recruitment to GMC plasma membrane as a negative feedback mechanism to regulate UTR signaling. J. Cell. Physiol. 229: 502-511, 2014. (c) 2013 Wiley Periodicals, Inc.