Regulation of milk protein gene expression in normal mammary epithelial cells by tumor necrosis factor

Tumor necrosis factor-alpha (TNF) is a physiologically significant regulato r of mammary gland development, stimulating growth and branching morphogene sis of mammary epithelial cells (MEC) and modulating functional differentia tion. The present studies were performed to determine the mechanism by whic h TNF modulated functional differentiation. In rat MEC in primary culture, TNF inhibited accumulation of whey acidic protein and beta -casein messenge r RNAs in a time- and concentration-dependent manner. In contrast, levels o f transferrin messenger RNA, the product of another milk protein gene, were not inhibited by TNF, suggesting selectivity. Using a nuclear run-on assay in the immortalized HC11 mammary epithelial cell line and the transcriptio nal inhibitor actinomycin D in MEC in primary culture, the effects of TNF w ere shown to be mediated by both a decrease in transcription and a decrease in the stability of the whey acidic protein and beta -casein transcripts. Additionally, TNF stimulated the binding of nuclear factor-kappaB to a cons ensus kappaB-oligonucleotide, increased the stability of matrix metalloprot einase-9 (MMP-9) transcripts, and increased MMP-9 activity. Together, these data suggest that TNF may exert its effects on milk protein gene expressio n either directly via nuclear factor-kappaB modulation of transcription, or indirectly via MMP-9-induced remodeling of the architectural or hormonal e nvironment surrounding the MEG.