EXPRESSION OF THE GENES ENCODING CCAAT-ENHANCER BINDING-PROTEIN ISOFORMS IN THE MOUSE MAMMARY-GLAND DURING LACTATION AND INVOLUTION

Transcription factors belonging to the CCAAT-enhancer binding protein (C/EBP) family have been implicated in the activation of gene expressi on in the mammary gland during lactation. We have therefore investigat ed the detailed expression profile of the C/EBP family during lactatio n and involution of the mouse mammary gland. The expression of C/EBP b eta and C/EBP delta mRNA was low during lactation, increased dramatica lly at the beginning of involution and remained constant thereafter. I n contrast, C/EBP alpha mRNA expression was relatively high during the early stages of lactation, declined to low levels during the late sta ges of lactation and at the start of involution, and increased again d uring involution. Electrophoretic mobility-shift assays showed a close correlation between the expression of the C/EBP genes and the functio nal C/EBP DNA-binding activity and, additionally, demonstrated the par ticipation of heterodimers, formed from among the three proteins, in D NA-protein interactions. The DNA-binding activity of the activator pro tein 1 (API) family of transcription factors was also induced during i nvolution. These results therefore point to potentially important regu latory roles for both the C/EBP and the API family during lactation an d involution of the mammary gland.