Beta-casein gene promoter activity is regulated by the hormone-mediated relief of transcriptional repression and a mammary-gland-specific nuclear factor.

Abstract

Transcription from the beta-casein milk protein gene promoter is induced by the synergistic action of glucocorticoid and prolactin hormones in the murine mammary epithelial cell line, HC11. We analyzed the binding of nuclear proteins to the promoter and determined their binding sites. Site-directed mutagenesis was used to determine the function of nuclear factor binding. During lactogenic hormone induction of HC11 cells, the binding of two nuclear factors increased. The binding of two other nuclear factors, present in uninduced cells, decreased. The basal activity of the promoter could be increased to and above the level of the induced wild-type promoter when the recognition sequences of the negatively regulated factors were mutated. This suggests that the beta-casein promoter is regulated by the relief of the repression of transcription. An essential tissue-specific factor was also found in nuclear extracts from the mammary glands of mice. Mutation of its recognition sequence in the beta-casein promoter led to the abolition of the induction of transcription by lactogenic hormones. The DNA sequences recognized by all five of these nuclear factors are conserved in the promoters of different casein genes from several species, confirming their importance in the regulation of milk protein gene transcription.