The v-mos and H-ras oncogene expression represses glucocorticoid hormone-dependent transcription from the mouse mammary tumor virus LTR.

We have subjected the viral mos oncogene (v-mos), the activated human H-ras oncogene [H-ras (A)] and the normal human H-ras protooncogene [H-ras (N)] to the transcriptional regulation of glucocorticoid hormones by in vitro recombination with the promoter region of the mouse mammary tumor virus long terminal repeat (MMTV LTR) and transfection into NIH 3T3 cells. Cell clones were selected which exhibit a transformed phenotype strictly dependent on the presence of hormone in the growth medium. The expression of the chimeric genes as a function of time after hormone stimulation was studied at the level of transcriptional rate, mRNA and protein accumulation. Oncogene expression was stimulated rapidly to high levels, after hormone addition, but declined in the continuous presence of hormone. Measurements of the transcriptional rates in nuclei from LTR v-mos and LTR H-ras (A) transfected cells showed a repression of LTR v-mos and LTR H-ras (A) transcription after the initial stimulation by hormone. LTR H-ras (N) transcription was not affected. An independently transfected LTR H-2Ld construct in LTR v-mos or LTR H-ras (A) containing cells is also transcriptionally repressed. These experiments demonstrated a transcriptional repression effect of the oncogene products on the glucocorticoid hormone-dependent MMTV LTR transcription.