Role of intercellular communication in the promotion of C3H/10T1/2 cell transformation

The effects of 12-O-tetradecanoylphorbol-13-acetate (TPA) upon intercellular communication and promotion were studied in cultures of C3H/10T1/2 mouse embryo fibroblasts. Cell-to-cell communication was quantitated by autoradiographic analysis of [3H]uridine transfer from prelabelled donor cells to an excess of unlabelled recipient cells during a 4 h co-cultivation. Extensive transfer of label was observed from donor to recipient cells in contact. Treatment of non-transformed C3H/10T1/2 cultures with 250 ng/ml TPA at co-cultivation of donor and recipient cells markedly inhibited intercellular communication during the 4 h incubation, producing an 80% reduction in uridine exchange relative to solvent-treated control cultures. Concentrations of TPA ranging from 0.25 to 25 ng/ml were also effective in inhibiting [3H]uridine exchange in a dose dependent fashion from 13% to 74%. This inhibition of intercellular communication was transient; cells exposed to 250 ng/ml TPA for 1.5 h prior to co-cultivation with TPA exhibited a 60% inhibition and the exchange of uridine had increased to control values in cultures pretreated for 12-72 h. An examination of label transfer between non-transformed and transformed C3H/10T1/2 cells indicated that both the extent of inhibition by TPA and the kinetics of communication inhibition were similar to that observed for non-transformed cells. Initiation and promotion experiments demonstrated that exposure to 250 ng/ml TPA for 5 weeks, but not to reduced concentrations of 0.25, 2.5 or 25 ng/ml, was capable of promoting morphological transformation. The lack of correlation between the dose responses of TPA for promotion and for reduction of cell-to-cell communication, and the transient nature of intercellular communication inhibition by TPA, suggests that an inhibition of cell-to-cell communication is not a sufficient event for promotion of oncogenic transformation in these cells.