Opposite effects of cyclic AMP on the expression of the genes encoding ribonucleotide reductase in Swiss 3T3 and RAT 1 cells.

RAT-1 and Swiss mouse 3T3 cells are fibroblast cell lines that differ in their response to agents that elevate cyclic AMP levels. We examined the effect of agents that increase cyclic AMP on the expression of the genes that encode the two subunits of ribonucleotide reductase in these two cell lines. While serum stimulation leads to comparable expression in both cell lines, agents that increase cyclic AMP result in increased gene expression in Swiss 3T3 cells but diminished expression in RAT-1 cells. In addition, forskolin could inhibit serum or insulin augmented entry into S phase in RAT-1 cells, while promoting entry in Swiss 3T3 cells. Thus, in fibroblasts differential response to cyclic AMP is evident at the level of ribonucleotide reductase gene expression.