Lack of induction of murine mammary tumor virus expression in cultured mammary glands treated with chemical carcinogens

Abstract

AbstractChemical carcinogens have previously been found to bring about an epithelial transformation of mouse mammary glands in whole‐organ culture, as evidenced by the escape of lobuloalveoli from the normal hormonal controls of mammary development, and by glandular hyperplasia, dysplasia and metaplasia. In order to assess whether a general induction of endogenous murine mammary tumor virus (MuMTV) genes is associated with the chemical transformation process, we assayed steady‐state levels of MuMTV RNA and protein after treatment of the cultured mammary glands with the carcinogens, 7,12‐dimethylbenz[a]anthracene and N‐2‐fluorenylacetamide. Viral RNA was measured by hybridization with a representative MuMTV‐complementary DNA probe, and viral protein was analyzed by a group‐specific radioimmunoassay for the major MuMTV envelope glycoprotein, gp52. In control glands not treated with carcinogen, there were extremely low levels of MuMTV‐specific RNA in the cultured mammary glands originating from BALB/c mice, and between 10‐ and 50‐fold higher levels in glands from C57BL/6 and C3H mice. Among the untreated glands, only those from C3H mice contained a detectable level of gp52. This order of MuMTV gene expression in the cultured glands of the three strains of mice is consistent with that observed in vivo. Treatment of the cultured mammary glands of these three strains of mice with either of the two chemical carcinogens resulted in all cases in no elevation in the level of either MuMTV RNA or protein. Thus, our studies indicate that the transformation of the cultured mammary glands by the two chemical carcinogens occurs by a process that apparently does not involve a general induction of endogenous MuMTV gene expression.