Alteration in Gs-mediated signal transduction in S49 lymphoma cells treated with inhibitors of microtubules.

We have assessed the possible interaction between the microtubular component of the cytoskeleton and signal transducing GTP-binding (G) proteins by examining the ability of colchicine and vinblastine (two microtubule disrupters) to alter Gs and Gi protein activity in S49 lymphoma cells. Treatment of wild type S49 cells with cholchicine and vinblastine increased beta-adrenergic agonist- and prostaglandin (PG) E1-stimulated formation of cAMP. The microtubular inhibitor nocodazole also enhanced isoproterenol-stimulated cAMP accumulation, whereas the inactive analog of colchicine, beta-lumicolchicine, did not have this action. Based on data obtained with wild type, cyc-, and UNC S49 cells, we determined that enhancement in cyclic AMP accumulation is proximal to the catalytic (C) unit of adenylylcyclase, distal to hormone receptors, and seems to be located on Gs. Treatment with colchicine increased guanosine 5'-(gamma-thio)triphosphate-stimulated accumulation of cAMP in permeabilized wild type cells. The increase in activity of Gs appeared not to result from a change in the intracellular concentration of GTP. Treatment of cells with colchicine or vinblastine also increased the amount of the alpha s-C complex, as assessed by the binding of [3H]forskolin to intact cells at 37 degrees C. In contrast to the observed effect on Gs, treatment of wild type S49 cells with colchicine failed to modify the degree of inhibition of cAMP formation produced by somatostatin, which acts via the activation of Gi. These data suggest that microtubules regulate the ability of Gs to interact with and activate the catalyst of adenylylcyclase.