cAMP stimulation of Dictyostelium discoideum destabilizes the mRNA for 117 antigen

Transcription of the 117 gene and changes in its mRNA levels in Dictyostelium discoideum were studied by mRNA hybridization with a cDNA probe. In wild type cells (Ax-2), the expression is developmentally regulated during cell aggregation, while in the aggregateless mutant, Agip 45, 117 mRNA is not detectable during cell starvation. Low concentrations of cAMP, given in the form of extracellular pulses to induce the development of starved Agip 45 cells to aggregation competence, are able to induce the appearance of 117 mRNA. The induction seems to be via the cell surface cAMP receptor and by a mechanism which does not involve changes in intracellular cAMP. Interestingly, high concentrations of cAMP, which down-regulate the cell surface cAMP receptor, elicit a rapid decrease in the level of 117 mRNA in aggregation-competent cells. Nuclear run-off and pulse-chase experiments show that the high concentrations of cAMP selectively destabilize the mRNA for 117 antigen. This destabilization requires both de novo mRNA synthesis and protein synthesis since the addition of inhibitors of these processes eliminates the effects of cAMP on 117 mRNA. The data suggest that a cAMP-induced protein(s) may be involved in the destabilization of selective mRNAs.