CYCLIC GMP-DEPENDENT PROTEIN-KINASE BLOCKS PERTUSSIS-TOXIN-SENSITIVE HORMONE-RECEPTOR SIGNALING PATHWAYS IN CHINESE-HAMSTER OVARY CELLS

cGMP-dependent protein kinase (cGMP kinase) has been implicated in the regulation of the cytosolic calcium level ([Ca2+](i)). In Chinese ham ster ovary (CHO) cells stably transfected with the cGMP kinase I alpha (CHO-cGK cells), cGMP kinase suppressed the thrombin-induced increase in inositol 1,4,5-trisphosphate and [Ca2+](i) (Ruth, P,, Wang, G.-X., Boekhoff, I., May, B,, Pfeifer, A., Penner, R., Korth, M,, Breer, H,, and Hofmann, F, (1993) Proc. Natl. Acad. Sci. U.S.A. 90, 2623-2627), Cholecystokinin activated intracellular calcium release via a pertussi s toxin (PTX)-insensitive pathway in CHO-cGK cells. cGMP kinase did no t attenuate the CCK stimulated [Ca2+](i). In contrast, cGMP kinase sup pressed calcium influx stimulated by insulinlike growth factors 1 and 2 (IGF-1 and IGF-2) via PTX-sensitive pathways. The effects of PTX and cGMP kinase on [Ca2+](i) were not additive. 8-Bromo-cGMP had no effec t on [Ca2+](i) stimulated by IGF-1 or IGF-2 in wild type CHO cells, Th ese results suggested that cGMP kinase inhibited the different signali ng pathways by the phosphorylation of a PTX-sensitive G protein. cGMP kinase phosphorylated the alpha subunits of G(i1), G(i2), and G(i3) in vitro. Phosphorylation stoichiometry was 0.4 mol of phosphate/mol of G(alpha i1) after reconstitution of heterotrimeric G(i1) in phospholip id vesicles. The alpha subunit of G(i) was also phosphorylated in vivo , These results show that cGMP kinase blocks transduction of distinct hormone pathways that signal via PTX-sensitive G(i) proteins.