Caffeine and heat shock induce adenylate cyclase in Dictyostelium discoideum

When vegetative cells of Dictyostelium discoideum were incubated in nutrient medium containing 5 mM caffeine, adenylate cyclase was induced and exceeded control values 30-fold after 6 h of incubation. The effect was dose-dependent and blocked by cycloheximide. Contact site A, a developmentally regulated membrane glycoprotein characteristic of aggregation-competent cells, was not induced by the treatment. The expression of a developmentally regulated gene coding for an unknown protein and hybridizing with the cDNA clone P26E8 was also stimulated, indicating that the regulation of expression occurs at the transcript level. Cells pretreated with caffeine in growth medium, washed and developed in starvation buffer showed an acceleration of development by 2 h as judged by stream formation and the appearance of contact sites A. The same effects were observed when cells were incubated under heat shock conditions (30 degrees C). The results indicate that caffeine stimulates the expression of devevelopmentally regulated early genes, and that their products, together with exogeneous factor(s), initiate subsequent steps of development.