Sensitivity to promotion of transformation by tumor promoters in mouse epidermal JB6 cells appears to have a genetic basis since the phenotypes of both promotable and nonpromotable JB6 cells derived from a common parent line are stable. Hybridization of promotable (P+) and nonpromotable (P−) cells previously indicated that promotability appears to behave as a dominant trait. These results suggest that it should be possible to find DNA sequences which specify sensitivity to promotion of anchorage independence by 12-o-tetradecanoyl-phorbol-13-acetate (TPA). Cellular DNA isolated from one of two P+lines, JB6 Cl 41 or JB6 Cl 22, was CaPO4precipitated and used to transfect the P−cell line JB6 Cl 30. At 7 days posttransfection, the cells were suspended in agar with or without TPA at 1.6 × 10−8M and assayed 10 days later for TPA-dependent colony formation. Untreated or Cl 30 DNA-treated P−JB6 Cl 30 cells yielded 40 to 50 colonies per 105cells. In contrast, transfection of Cl 30 cells with “P+DNA” derived from either Cl 41 or Cl 22 yielded 200 to 500 TPA-induced colonies per 105cells, or a five- to eightfold enhancement of promotability. The enhanced promotability obtained after transfection with P+DNA was stable, as judged by the retention of promotability for at least eight passages in cell lines derived from TPA-induced agar colonies. Other transfectants showed irreversible transformation by TPA, as observed in the parental P+lines. When NIH 3T3 cells instead of the putative preneoplastic JB6 Cl 30 cells were used as recipients for transfection of P+DNA, no evidence for acquisition of promotability was obtained. P−JB6 Cl 25, like Cl 30, also permitted expression of transfected P+DNA. These results suggest that sensitivity to phorbol ester promotion of transformation in JB6 cells is determined by DNA sequence(s) present in the P+DNA and requires recipient cells of the appropriate phenotype for expression.
Transfected human beta-polymerase promoter contains a ras-responsive element.
