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 agents colchicine and cytochalasin B, respectively, which are known to disrupt these structures. A 1-hr pretreatment of S49 cells with 10 microM colchicine typically enhanced maximal isoproterenol-(beta-adrenergic receptor) stimulated cAMP accumulation by 100%, whereas cytochalasin B increased isoproterenol-stimulated cAMP by 30%. The combination of colchicine and cytochalasin B synergistically enhanced agonist-stimulated cAMP to 225% over control values. A synergistic increase in cAMP accumulation was also observed in cells treated with the agonist prostaglandin E1 or cholera toxin (which activates the stimulatory guanine nucleotide regulatory (Gs) protein). Colchicine and cytochalasin B did not ablate the inhibitory effects of somatostatin or the stimulatory effect of pertussis toxin treatment on beta-receptor-stimulated cAMP accumulation, indicating that these cytoskeletal disrupting agents do not enhance responsiveness in S49 cells via alterations in the inhibitory guanine nucleotide regulatory protein pathway. Moreover, colchicine, but not cytochalasin B treatment, enhances expression of isoproterenol-promoted 3H-forskolin binding in intact cells (a measure of Gs/adenylyl cyclase coupling). Thus, colchicine and cytochalasin B appear to enhance signaling in the Gs/adenylyl cyclase pathway by alterations of components distal to hormone receptors, most likely at the Gs protein and/or via cAMP generation. These results imply that microtubules and microfilaments can interact in the regulation of this pathway and that increases in cellular cAMP may contribute to the action of drugs that alter function of these cytoskeletal elements.