Regulation of intracellular calcium by a signalling complex of IRAG, IP3 receptor and cGMP kinase Iβ

Top Cited Papers
Publisher Website
Google Scholar
Abstract
Calcium release from the endoplasmic reticulum controls a number of cellular processes, including proliferation and contraction of smooth muscle and other cells1,2. Calcium release from inositol 1,4,5-trisphosphate (IP3)-sensitive stores is negatively regulated by binding of calmodulin to the IP3 receptor (IP3R)3,4 and the NO/cGMP/cGMP kinase I (cGKI) signalling pathway5,6. Activation of cGKI decreases IP3-stimulated elevations in intracellular calcium7, induces smooth muscle relaxation8 and contributes to the antiproliferative9 and pro-apoptotic effects of NO/cGMP10. Here we show that, in microsomal smooth muscle membranes, cGKIβ phosphorylated the IP3R and cGKIβ, and a protein of relative molecular mass 125,000 which we now identify as the IP3R-associated cGMP kinase substrate (IRAG). These proteins were co-immunoprecipitated by antibodies directed against cGKI, IP3R or IRAG. IRAG was found in many tissues including aorta, trachea and uterus, and was localized perinuclearly after heterologous expression in COS-7 cells. Bradykinin-stimulated calcium release was not affected by the expression of either IRAG or cGKIβ, which we tested in the absence and presence of cGMP. However, calcium release was inhibited after co-expression of IRAG and cGKIβ in the presence of cGMP. These results identify IRAG as an essential NO/cGKI-dependent regulator of IP3-induced calcium release.

This publication has 29 references indexed in Scilit: