Bifunctional activity of epidermal growth factor on alpha- and kappa-casein gene expression in rodent mammary glands in vitro.

Explants from mammary glands of virgin rats and pregnant rats and mice were cultured under serum-free conditions in the presence of various combinations of the hormones insulin (I), aldosterone (A), corticosterone (C), PRL, and epidermal growth factor (EGF). Bifunctional activity of EGF was found on expression of the alpha- and kappa-casein genes. In the presence of I, A, and C, EGF increased the level of alpha-casein mRNA in pregnant mouse mammary gland explants, but not in rats. kappa-Casein mRNA sequences in mouse mammary gland explants were also significantly increased by EGF in the presence of I, A, and C, but in rat mammary gland explants, the increase was less. In contrast, in the presence of I, A, C, and PRL, EGF inhibited the induction of both alpha- and kappa-casein mRNA sequences in tissue from rats and mice. This bifunctionality of EGF in terminal differentiation of the rodent mammary gland was also reflected in the levels of synthesis of total casein and alpha-lactalbumin.