Extracellular matrix regulates alpha s1-casein gene expression in rabbit primary mammary cells and CCAAT enhancer binding protein (C/EBP) binding activity

✍ Scribed by Geneviève Jolivet; Chantal Meusnier; Gilles Chaumaz; Louis-Marie Houdebine

• Publisher: John Wiley and Sons
• Year: 2001
• Tongue: English
• Weight: 327 KB
• Volume: 82
• Category: Article
• ISSN: 0730-2312
• DOI: 10.1002/jcb.1166

✦ Synopsis

Abstract

Previous studies have shown that both the signal transducer and activator of transcription 5 (STAT5) and the CCAAT enhancer binding proteins (C/EBPs) are involved in the regulation of casein gene expression by mammary epithelial cells. Prolactin (Prl) activation of STAT5 is necessary for casein gene expression. The extracellular matrix (ECM) regulates also casein gene expression. Here, we have investigated whether ECM regulates C/EBPs activity in primary rabbit mammary epithelial cells. Isolated primary mammary cells were cultured on plastic or on floating collagen I gel. Prolactin induced αs 1‐casein gene expression when cells were cultured on collagen but not on plastic. It is noteworthy that activated STAT5 was detected in both culture conditions. Several STAT5 isoforms (STAT5a, STAT5b, and other STAT5 related isoforms, some with lower molecular weight than the full‐length STAT5a and STAT5b) were detected under the different culture conditions. However, their presence was not related to the expression of αs 1‐casein gene. The binding of nuclear factors to a C/EBP specific binding site and the protein level of C/EBPβ differed in cells cultured on plastic or on collagen but these parameters were not modified by Prl. This suggests that C/EBP binding activity was regulated by ECM and not by Prl. Interestingly, these modifications were correlated to the expression of the αs 1‐casein gene. Hence, the activation of the αs 1‐casein gene expression depends on two independent signals, one delivered by Prl via the activation of STAT5, the other delivered by ECM via C/EBP. J. Cell. Biochem. 82:371–386, 2001. © 2001 Wiley‐Liss, Inc.