Grolli S, Accornero P, Ramoni R, Donofrio G, Whitelaw CB. Expression of c-myc is down-regulated as mouse mammary epithelial cells become confluent.
Biochem Biophys Res Commun 1997;
239:566-9. [PMID:
9344871 DOI:
10.1006/bbrc.1997.7498]
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Abstract
We have investigated the expression profile of c-myc in the mammary gland. During pregnancy when the gland is actively growing c-myc mRNA was present, while in the differentiated lactating gland no c-myc mRNA was detected. This correspondence between the differentiation state and c-myc mRNA levels in the mouse mammary gland in vivo was paralleled by HC11 mouse mammary epithelial cells in vitro. Firstly, the endogenous c-myc gene was suppressed in confluent compared to growing HC11 cells. In addition, treating the cells with lactogenic hormones did not induce c-myc expression. Secondly, a stably transfected c-myc-CAT reporter construct was similarly down-regulated. Furthermore, using this transfection model, we demonstrate that the mechanism(s) involved in regulating c-myc expression must act through the P1 and P2 core promoter and exon 1. Finally, we demonstrate that suppression of c-myc expression occurs when HC11 cells growth-arrest as they become confluent.
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