INVOLVEMENT OF CYCLIC-AMP CELL-SURFACE RECEPTORS AND G-PROTEINS IN SIGNAL TRANSDUCTION DURING SLUG MIGRATION OF DICTYOSTELIUM-DISCOIDEUM

The presence of G-proteins, interacting with cAMP surface receptors, was investigated in vegetative cells, aggregation-competent cells, and migrating slugs of Dictyostelium discoideum. Our results indicate that G-proteins are present in all stages. In vegetative cells there is a limited number of cAMP receptors but no effect of GTPτS on cAMP binding could be detected; in addition, no effect of cAMP on GTPτS binding or GTPase activity was observed. In both aggregation-competent cells and slugs GTPτS inhibits cAMP binding, while cAMP stimulates GTPτS binding and high-affinity GTPase. Since the presence of G-proteins coupled to cAMP receptors could be demonstrated in slugs, the involvement of the effector enzymes adenylate cyclase and phospholipase C was investigated. The results show that adenylate cyclase activity is stimulated by GTPτS in both stages and that in cells from migrating slugs the Ins(1,4,5)P3 production is increased upon stimulation with cAMP. The possible involvement of G-proteins in signal transduction during the slug stage of D. discoideum is discussed. © 1991.