title: cAMP-stimulated adenylate cyclase activation in Dictyostelium discoideum is inhibited by agents acting at the cell surface.
abstract: The ability of Dictyostelium discoideum amoebae to synthesize and secrete cAMP in response to exogenous cAMP is called cAMP signaling. Concanavalin A is a potent, rapid, noncompetitive inhibitor of this response, with the rate of inhibition consistent with its rate of binding. The concanavalin A does not deplete cellular ATP, alter cAMP binding to its surface receptors, or affect basal adenylate cyclase activity, but blocks the cAMP-stimulated activation of adenylate cyclase. Therefore, concanavalin A appears to inhibit a step between the receptor and the adenylate cyclase which is necessary for the transduction of the cAMP signal. Wheat germ agglutinin, a polyclonal antibody against an 80-kDa glycoprotein, four monoclonal antibodies against the amoebal surface, and a chemical cross-linking agent which reacts with cell surface primary amines also inhibit signaling. To determine the importance of cross-linking in the inhibition, succinylated concanavalin A and the unlinked, reactive portion of the chemical cross-linker were tested and found to be relatively ineffective inhibitors. Thus it appears that ligands capable of cross-linking molecules on the external surface of D. discoideum amoebae inhibit cAMP signaling. It is proposed that these cross-linking agents prevent membrane or cytoskeletal rearrangement and that this rearrangement must occur before the adenylate cyclase is activated.
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism*; D003208:Concanavalin A / Q000494:pharmacology*; D003432:Cross-Linking Reagents / Q000494:pharmacology; D000242:Cyclic AMP / Q000037:antagonists & inhibitors / Q000378:metabolism*; D004023:Dictyostelium / Q000201:enzymology*; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects; D037102:Lectins / Q000494:pharmacology; D013388:Succinimides / Q000494:pharmacology; D013499:Surface Properties; D013997:Time Factors; D014909:Wheat Germ Agglutinins
chemical_list: D003432:Cross-Linking Reagents; D037102:Lectins; D013388:Succinimides; D014909:Wheat Germ Agglutinins; D003208:Concanavalin A; D000242:Cyclic AMP; D000262:Adenylyl Cyclases; C011240:dithiobis(succinimidylpropionate)