C/EBPß LIP and c-Jun synergize to regulate expression of the murine progesterone receptor.

CCAAT/enhancer binding protein ß (C/EBPß) is required for murine mammary ductal morphogenesis and alveologenesis. Progesterone is critical for proliferation and alveologenesis in adult mammary glands, and there is a similar requirement for progesterone receptor isoform B (PRB) in alveologenesis. We examined C/EBPß regulation of PR expression. All three C/EBPß isoforms, including typically inhibitory LIP, transactivated the PR promoter. LIP, particularly, strongly synergized with c-Jun to drive PR transcription. Endogenous C/EBPß and c-Jun stimulated a PR promoter-reporter and these two factors showed promoter occupancy on the endogenous PR gene. Additionally, LIP overexpression elevated endogenous PR protein expression. In pregnancy, both PRB and the relative abundance of LIP among C/EBPß isoforms increase. Consistent with a role in PRB expression, in vivo C/EBPß and PR isoform A expression showed mutually exclusive localization in mammary epithelium, while C/EBPß and PRB largely co-localized. We suggest a critical role for C/EBPß, particularly LIP, in PRB expression.

Identification of an octamer-binding site controlling the activity of the small breast epithelial mucin gene promoter.

e human small breast epithelial mucin (SBEM) gene has been identified as being preferentially expressed in mammary epithelial cells and over-expressed in breast tumors. In this report, we have characterized the promoter of SBEM gene in order to identify sequences responsible for this strong mammary expression. A series of SBEM promoter/luciferase constructs were transiently transfected into both breast (MCF-7, BT-20) and non-breast (HeLa and HepG2) cell lines. In addition to the minimal promoter and to a repressor region, we have identified an 87-bp sequence (-357/-270) driving a strong breast-specific expression. Site-directed mutagenesis of a putative octamer-binding transcription factor binding site located within this latter region led to a strong decrease of the transcriptional activity of the SBEM promoter. Furthermore, transient over-expression of Oct1 and Oct2 not only increased SBEM promoter reporter activity, but also enhanced endogenous SBEM mRNA level. Overall, the data suggest that octamer-binding transcription factors participate in the strong expression of SBEM gene in breast tissues. Clarifying the SBEM gene regulation will help to dissect mechanisms underlying transcription of normal breast and breast cancer-associated genes.

Identification of a novel breast- and salivary gland-specific, mucin-like gene strongly expressed in normal and tumor human mammary epithelium.

Expression profiling using the public expressed sequence tag (EST) and serial analysis of gene expression (SAGE) databases resulted in the identification of a putative breast-specific mRNA that we have termed small breast epithelial mucin (SBEM). Hybridization analysis performed on 43 normal human tissues revealed that the SBEM gene was only expressed in mammary and salivary glands. Further reverse-transcription PCR analyses confirmed SBEM expression in most of established human breast epithelial cell lines analyzed (7 of 8) but not in cell lines of non-breast origin (0 of 6). SBEM mRNA expression was detected in >90% of invasive ductal carcinomas and correlated with the expression of a previously characterized breast-specific gene, mammaglobin-1 (n = 54; Spearman r = 0.34, P = 0.011). Interestingly, a higher SBEM:mammaglobin-1 ratio was observed in primary tumors with axillary lymph node metastasis than in node-negative tumors (n = 46; Mann-Whitney, P = 0.04). In a subset of 20 primary breast tumors and their matched axillary lymph nodes, a high concordance (Fisher's exact test, P < 0.001) was seen between PCR detection of SBEM mRNA in lymph node tissue and their histopathological status, indicating that SBEM mRNA expression is conserved in nodal metastasis. The SBEM gene is predicted to code for a putative low molecular weight, secreted sialoglycoprotein, potentially useful for the diagnosis of metastatic breast cancer.