Casein and alpha-lactalbumin messenger RNA in experimental breast cancer.

A transplantable rat mammary carcinoma (R3230AC) was previously shown to contain prolactin receptors. Our objective was to determine whether these receptors were functional by measuring specific markers of prolactin action: casein and alpha-lactalbumin (alphaLA) messenger RNA's (mRNA's). Total RNA exacts were translated in a wheat germ cell-free system. Newly synthesized 3H-casein and 3H-alphaLA were separately precipitated with specific antibodies and identified by their mobilities on sodium dodecyl sulfate-acrylamide gels and by competition with nonradioactive casein and alphaLA. Casein and alphaLA mRNA's were both present in unstimulated tumors grown in virgin rats. Casein mRNA but not alphaLA mRNA was markedly stimulated by injections of exogenous ovine prolactin or perphenazine, an agent that stimulates endogenous prolactin. This response was selective in that total mRNA was not significantly altered by prolactin.