Hormone-regulated expression of cellular rasH oncogene in mammary carcinomas in rats.

Differential gene expression has been observed in hormone-dependent rat mammary carcinomas during their growth and regression. A 22K MW protein, a prominent in vitro translation product of the growing as compared to the regressing tumor, was identified as the c-rasH-21,000-dalton transforming protein (p21) using a monoclonal antibody that reacts specifically with Harvey-related p21 species. The amount of p21-translated protein sharply decreased in the translation products of the regressing tumors within 6 hours post ovariectomy or dibutyryl cyclic AMP treatment. The results show that an enhanced expression of the c-rasH oncogene is associated with hormone-dependent growth of mammary carcinomas in vivo and that suppression of this oncogene precedes the tumor regression induced by either hormone withdrawal or dibutyryl cyclic AMP treatment.