COLCHICINE AND CYTOCHALASIN-B ENHANCE CYCLIC-AMP ACCUMULATION VIA POSTRECEPTOR ACTIONS

The role of cytoskeletal microtubules and microfilaments in modulating cAMP generation in S49 lymphoma cells was investigated using the agen ts colchicine and cytochalasin B, respectively, which are known to dis rupt these structures. A 1-hr pretreatment of S49 cells with 10 mu M c olchicine typically enhanced maximal isoproterenol-(beta-adrenergic re ceptor) stimulated cAMP accumulation by 100%, whereas cytochalasin B i ncreased isoproterenol-stimulated cAMP by 30%. The combination of colc hicine and cytochalasin B synergistically enhanced agonist-stimulated cAMP to 225% over control values. A synergistic increase in cAMP accum ulation was also observed in cells treated with the agonist prostaglan din E(1) or cholera toxin (which activates the stimulatory guanine nuc leotide regulatory (G(s)) protein). Colchicine and cytochalasin B did not ablate the inhibitory effects of somatostatin or the stimulatory e ffect of pertussis toxin treatment on beta-receptor-stimulated cAMP ac cumulation, indicating that these cytoskeletal disrupting agents do no t enhance responsiveness in S49 cells via alterations in the inhibitor y guanine nucleotide regulatory protein pathway. Moreover, colchicine, but not cytochalasin B treatment, enhances expression of isoprotereno l-promoted H-3-forskolin binding in intact cells (a measure of G(s)/ad enylyl cyclase coupling). Thus, colchicine and cytochalasin B appear t o enhance signaling in the G(s)/adenylyl cyclase pathway by alteration s of components distal to hormone receptors, most likely at the G(s) p rotein and/or via cAMP generation. These results imply that microtubul es and microfilaments can interact in the regulation of this pathway a nd that increases in cellular cAMP may contribute to the action of dru gs that alter function of these cytoskeletal elements.