Complex mitogenic requirements of Na(+)-K(+)-Cl(-)-cotransport-deficient BALB/c-3T3 cells

The ability of 12-O-tetradecanoylphorbol-13-acetate (TPA) to stimulate mitogenesis in BALB/c-3T3 cells and in a Na+K+Cl(-)-cotransport-defective variant subclone was investigated. This transport variant had previously been reported to be TPA mitogenically nonresponsive (O'Brien and Prettyman: Journal of Cellular Physiology 130:377-381, 1987) since the addition of TPA to the spent medium of density-arrested cultures stimulated DNA synthesis in the parent but not the variant cell line. We now report that the addition of TPA plus insulin, either directly to the spent medium or together with fresh medium, stimulated DNA synthesis in both the parent and variant cells to approximately the same extent. The parent and transport-deficient cells differed, however, in their sensitivity to the co-mitogenic effects of insulin or insulin-like growth factors.