Contact alters cAMP metabolism in aggregation-competent Dictyostelium amoebae

cAMP and cell-cell contact are involved in the coordination of differentiation and morphogenesis in Dictyostelium discoideum. The experiments described in this paper establish a relationship between cAMP and cell-cell contact. Contact between Enterobacter aerogenes and aggregation-competent Dictyostelium amoebae and contact between Dictyostelium amoebae themselves results in the transient secretion of cAMP and an alteration in the amount of cAMP secreted in response to subsequent stimulation by cAMP, i.e., an alteration in magnitude of a cAMP relay response. The subsequent cAMP relay response can be enhanced or diminished depending upon the number of contacts formed and the concentration of cAMP present at the time of contact. Latex beads are capable of evoking cAMP secretion. However, the bead/amoebal contact is unable to alter the magnitude of a subsequent response to cAMP. This suggests that a nonspecific interaction via cell-cell contact elicits transient cAMP secretion in aggregation-competent Dictyostelium amoebae. The two responses to cell-cell contact are distinct from each other and distinct from the cAMP relay response. 1) The dose-response curves for the responses to Enterobacter contact are clearly different. 2) Contact with latex beads can elicit cAMP secretion but not alter the magnitude of a subsequent cAMP relay response. 3) The temperature dependences of the contact-induced responses and the cAMP relay response show that only the contact-induced cAMP secretion is inhibited at 12 and 15 degrees C, while only the cAMP relay response is inhibited at 28 degrees C. A 4-second application of cAMP at the time that contact is initiated enhances both contact-induced responses. Whether the relationship between these two developmental regulators is important for the regulation of Dictyostelium development has yet to be established.