Extracellular Matrix-regulated Gene Expression Requires Cooperation of SWI/SNF and Transcription Factors

Abstract

Extracellular cues play crucial roles in the transcriptional regulation of tissue-specific genes, but whether and how these signals lead to chromatin remodeling is not understood and subject to debate. Using chromatin immunoprecipitation assays and mammary-specific genes as models, we show here that extracellular matrix molecules and prolactin cooperate to induce histone acetylation and binding of transcription factors and the SWI/SNF complex to the ␤-and ␥-casein promoters. Introduction of a dominant negative Brg1, an ATPase subunit of SWI/ SNF complex, significantly reduced both ␤-and ␥-casein expression, suggesting that SWI/SNF-dependent chromatin remodeling is required for transcription of mammary-specific genes. Chromatin immunoprecipitation analyses demonstrated that the ATPase activity of SWI/SNF is necessary for recruitment of RNA transcriptional machinery, but not for binding of transcription factors or for histone acetylation. Co-immunoprecipitation analyses showed that the SWI/SNF complex is associated with STAT5, CCAAT/enhancer-binding protein ␤, and glucocorticoid receptor. Thus, extracellular matrix-and prolactin-regulated transcription of the mammary-specific casein genes requires the concerted action of chromatin remodeling enzymes and transcription factors.Differentiated function of mammary epithelial cells is regulated by signals from both ECM 2 and lactogenic hormones (1-3). The gene encoding the milk protein, ␤-casein, has been used widely as a marker for functional differentiation of MECs. We and others have shown that in both primary mouse mammary epithelial cells and immortalized mammary epithelial cell lines (4 -6), transcription of ␤-casein requires signals from both laminin-111 (previously referred to as laminin-1) and prolactin (1, 2, 7-10). A number of transcription factors, including STAT5, C/EBP␤, and GR, have been shown to be involved in this process (reviewed in Ref. 7).Modulation of chromatin structure by histone modifications and ATP-dependent remodeling has been implicated in cell differentiation and transcriptional control of tissue-specific and inducible genes (11-13). Histone-modifying enzymes are believed to be recruited to promoter regions through their association with transcription factors and are critical for tissue-specific gene expression and functional differentiation of specific cell types (14, 15). Histone acetylation is a dynamic process and is regulated by histone acetyltransferases and histone deacetylases (16). The mapping of global histone acetylation patterns has demonstrated that chromatin accessibility and gene expression are correlated with histone hyperacetylation of promoters and other cis-elements (17, 18). The p300 histone acetyltransferase cooperates with STAT5 to enhance exogenous ␤-casein promoter activity in COS cells, indicating that histone acetylation may play a role in ␤-casein transcription (19). Trichostatin A (TSA), an inhibitor of histone deacetylase, was shown to activate the bovine casein ECM response element (BCE-1) in an ECM-independent...

The contribution of adhesion signaling to lactogenesis

“…There is evidence suggesting that the ECM maintains a high level of histone H4 acetylation upstream of the αs1-casein gene, especially at the level of a distal prolactin and ECM-sensitive enhancer region (Jolivet et al 2005). Recently, Xu et al determined that extracellular matrix molecules cooperate with prolactin to induce histone acetylation and the binding of transcription factors as well as the ATP-dependent SWI chromatin remodeling complex to the β-casein promoter (Xu et al 2007).…”

“…The diagram includes the pathways known to be affected by CTGF/ CCN2 during lactogenic differentiation of mammary epithelial cells in primary cells or established cell lines process. Lactogenic differentiation may also depend on expression and stabilization of CTGF/CCN2 -integrin complexes that promote prolactin-induced Stat5 activity (Xu et al 2007(Xu et al , 2009.…”

Novel Mechanism of Negative Regulation of 1,25-Dihydroxyvitamin D3-induced 25-Hydroxyvitamin D3 24-Hydroxylase (Cyp24a1) Transcription

“…BRG1 has been shown to direct different cellular processes by recruitment to cis elements through divergent transcription factors including hormone receptors, the erythroid factors erythroid Krüppel-like factor and GATA-1 (which activate the ␤-globin gene) and C/EBP␤ (16,17,42,43). Similar to our findings related to the regulation of Cyp24a1 transcription, C/EBP␤ has been reported to recruit and cooperate with BRG1 to regulate the expression of myeloid genes (15), the osteocalcin gene in osteoblastic cells (16), and the mammary tissue-specific ␤-and ␥-casein genes (17).…”

“…In additional studies in COS-7 cells, suboptimal 1,25(OH) 2 Previous studies from our laboratory showed that C/EBP␤ is induced by 1,25(OH) 2 D 3 in kidney and osteoblastic cells and is a potent enhancer of VDR-mediated Cyp24a1 transcription (26). C/EBP␤ has also been reported to recruit the SWI/SNF complex to regulate cell type-specific genes (15)(16)(17). Hence, we next investigated the role of BRG1 in the C/EBP␤ enhancement of 1,25(OH) 2 D 3 -induced Cyp24a1 transcription.…”

“…BRG1-null mice are embryonic lethal, whereas Brm-null mice are viable (exhibiting a mild phenotype of increased body weight) (13,14). C/EBP␤ has been reported to recruit the SWI/SNF complex to specific gene promoters to promote tissue-specific transcription (15)(16)(17). In addition, it has been shown that ATP-dependent chromatin remodeling complexes can act together with histone-modifying enzymes to modulate transcription (18 -20).…”