ADP activates protooncogene expression in renal epithelial cells

Purine nucleotides, particularly adenosine diphosphate (ADP), are the most potent mitogens known for monkey kidney epithelial cells of the BSC-1 line. To explore the molecular mechanisms by which ADP exerts its mitogenic effect, we tested the hypothesis that stimulation of DNA synthesis in these renal cells is mediated by activation of protooncogenes. Transcripts of the c-Ha-ras protooncogene were identified in quiescent, high density cells. Addition of ADP to the culture medium stimulated protooncogene expression fourfold. Maximal expression of c-ras was observed by 12 h after exposure to ADP, and preceded the initiation of DNA synthesis. Expression of the c-myc protooncogene was not detected in unstimulated cells, but accumulated maximally after 1 h of exposure to ADP. As with ADP-stimulated expression of the c-ras protooncogene, transcripts of the transferrin receptor gene reached a maximal value at 12 h, whereas the abundance of gamma-actin mRNA was not altered for up to 24 h. The results indicate that exogenous ADP stimulates protooncogene expression before initiation of DNA synthesis in renal epithelial cells in culture. These findings suggest that some physiological effects of this adenine nucleotide could be mediated by proteins specified by protooncogenes.