A NOVEL MITOGENIC SIGNALING PATHWAY OF BRADYKININ IN THE HUMAN COLON-CARCINOMA CELL-LINE SW-480 INVOLVES SEQUENTIAL ACTIVATION OF A G(Q 11)PROTEIN, PHOSPHATIDYLINOSITOL-3-KINASE-BETA, AND PROTEIN-KINASE-C-IS-AN-ELEMENT-OF/

The signaling routes connecting G protein-coupled receptors to the mit ogen-activated protein kinase (MAPK) pathway reveal a high degree of c omplexity and cell specificity. In the human colon carcinoma cell line SW-480, we detected a mitogenic effect of bradykinin (BK) that is med iated via a pertussis toxin-insensitive G protein of the G(q/11) famil y and that involves activation of MAPK. Both BK-induced stimulation of DNA synthesis and activation of MAPK: in response to BK were abolishe d by two different inhibitors of phosphatidylinositol 3-kinase (PI3K), wortmannin and LY 294002, as well as by two different inhibitors of p rotein kinase C (PBC), bisindolylmaleimide and Ro 31-8220. Stimulation of SW-480 cells by BK led to increased formation of PI3K lipid produc ts (phosphatidylinositol 3,4,5-trisphosphate and phosphatidylinositol 3,4-bisphosphate) and to enhanced translocation of the PKC epsilon iso form hom the cytosol to the membrane. Both effects of BK were inhibite d by wortmannin, too. Using subtype-specific antibodies, only the PIER subunits p110 beta and p85, but not p110 alpha and p110 gamma, were d etected in SW-480 cells. Finally, p110 beta was found to be co-immunop reaipitated with PKC epsilon. Our data suggest that in SW-480 cells, ( i) dimeric PI3K beta is activated via a G(q/11) protein; (ii) PKC epsi lon is a downstream target of PI3K beta mediating the mitogenic signal to the MAPK pathway; and (iii) PKC epsilon associates with the p110 s ubunit of PI3K beta. Thus, these results add a novel possibility to th e emerging picture of multiple pathways linking G protein-coupled rece ptors to MAPK.