| Abstrakt: |
The signaling routes connecting G protein-coupled receptors to the mitogen-activated protein kinase (MAPK) pathway reveal a high degree of complexity and cell specificity. In the human colon carcinoma cell line SW-480, we detected a mitogenic effect of bradykinin (BK) that is mediated via a pertussis toxin-insensitive G protein of the Gq/11family and that involves activation of MAPK. Both BK-induced stimulation of DNA synthesis and activation of MAPK in response to BK were abolished by two different inhibitors of phosphatidylinositol 3-kinase (PI3K), wortmannin and LY 294002, as well as by two different inhibitors of protein kinase C (PKC), bisindolylmaleimide and Ro 31-8220. Stimulation of SW-480 cells by BK led to increased formation of PI3K lipid products (phosphatidylinositol 3,4,5-trisphosphate and phosphatidylinositol 3,4-bisphosphate) and to enhanced translocation of the PKCε isoform from the cytosol to the membrane. Both effects of BK were inhibited by wortmannin, too. Using subtype-specific antibodies, only the PI3K subunits p110β and p85, but not p110α and p110γ, were detected in SW-480 cells. Finally, p110β was found to be co-immunoprecipitated with PKCε. Our data suggest that in SW-480 cells, (i) dimeric PI3Kβ is activated via a Gq/11protein; (ii) PKCε is a downstream target of PI3Kβ mediating the mitogenic signal to the MAPK pathway; and (iii) PKCε associates with the p110 subunit of PI3Kβ. Thus, these results add a novel possibility to the emerging picture of multiple pathways linking G protein-coupled receptors to MAPK. |
