Expression of c-myc is down-regulated as mouse mammary epithelial cells become confluent.
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.
Grolli
S
S
Facolta di Medicina Veterinaria, Universita de Parma, Parma, 43100, Italy. vetbioc@ipruniv.cce.unipr.it
Accornero
P
P
Ramoni
R
R
Donofrio
G
G
Whitelaw
C B
CB
D000818:Animals; D002454:Cell Differentiation / Q000235:genetics; D002455:Cell Division / Q000235:genetics; D015536:Down-Regulation / Q000235:genetics*; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism*; D005091:Exons; D005786:Gene Expression Regulation; D016259:Genes, myc; D008321:Mammary Glands, Animal / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D008894:Milk Proteins / Q000096:biosynthesis / Q000235:genetics; D011401:Promoter Regions, Genetic; D014162:Transfection
D008894:Milk Proteins