Enhanced expression and state of the c-myc oncogene in chemically and X-ray-transformed C3H/10T1/2 Cl 8 mouse embryo fibroblasts.

ABSTRACT

We examined expression of the c-myc oncogene in nontransformed, in three chemically transformed, and in two X-ray-transformed C3H/10T1/2 Cl 8 cell lines. In nontransformed C3H/10T1/2 cells, c-myc was expressed when cells were logarithmically growing, and expression decreased as cells reached confluence. In a methylcholanthrene-transformed cell line, MCA Si 24, c-myc expression was similar to that observed in nontransformed cells, while in two chemically transformed cell lines, Bleo Cl 2 and DMBA Cl 2, and in two radiation-transformed cell lines, F17 and F29, steady-state levels of the c-myc transcript were 5-7-fold greater than observed in nontransformed C3H/10T1/2 cells. All cell lines, both transformed and nontransformed, produced a 2.3-kilobase c-myc transcript. There was no detectable amplification or rearrangement of c-myc DNA sequences in any of the cell lines examined as determined by DNA dot blot and restriction endonuclease-Southern blotting analyses. In addition, the c-myc gene in nontransformed and transformed cell lines showed similar methylation patterns as determined by HpaII/MpsI digestion analysis, except that F19 and F29 cells lost a 0.95-kilobase HpaII band, suggesting extra region-specific methylation in these two cell lines compared to C3H/10T1/2 cells. Therefore, increased c-myc expression in the four transformed lines did not generally correlate with changes in DNA methylation in the vicinity of the c-myc gene. Our results suggest that expression of the c-myc gene is growth related and that elevated steady-state levels of c-myc RNA in certain chemically and X-ray transformed C3H/10T1/2 cell lines, such as Bleo Cl 2, DMBA Cl 2, F17, and F29, are correlated with and may participate in conversion to or maintenance of cells in the transformed state.