Lactation status influences expression of CCAAT/enhancer binding protein isoform mRNA in the mouse mammary gland

Abstract

The CCAAT/enhancer binding proteins (C/EBPs) are a highly conserved family of DNA binding proteins implicated in the transcriptional control of genes involved in cell growth and differentiation in a variety of tissues. The expression of C/EBP-α, β, and δ mRNA in the normal mouse mammary gland was investigated during pregnancy, lactation, and involution via Northern blotting and in situ hybridization. Mammary gland C/EBP-α mRNA is detectable at low levels during pregnancy and postlactational involution. C/EBP-β mRNA levels are elevated during pregnancy, decline slightly in midlactation, and are induced within 48 hours of the onset of involution. C/EBP-δ mRNA content is low throughout pregnancy and lactation, but increases dramatically ( > 100-fold) within 12 hours after the onset of postlactational involution. In situ hybridization demonstrates that mammary epithelial cells are responsible for the expression of C/EBP-δ mRNA during involution. In contrast to mammary gland, C/EBP-α is the predominate isoform expressed in liver with relatively low expression of C/EBP-β and C/EBP-δ mRNA. Liver C/EBP isoform mRNA levels are unaffected by lactation status. These results demonstrate the tissue-specific regulation of C/EBPs. The pronounced sequential induction of C/EBP-δ and C/EBP-β during postlactational involution is consistent with a role for C/EBPs in the regulation of mammary epithelial cell apoptosis. J. Cell. Physiol. 174:232–239, 1998.