Cell type-specific regulation of the TGF-beta-responsive alpha2(I) collagen gene by CpG methylation

TGF-β mediated DNA methylation in prostate cancer

Almost all tumors harbor a defective negative feedback loop of signaling by transforming growth factor-β (TGF-β). Epigenetic mechanisms of gene regulation, including DNA methylation, are fundamental to normal cellular function and also play a major role in carcinogenesis. Recent evidence demonstrated that TGF-β signaling mediates cancer development and progression. Many key events in TGF-β signaling in cancer included auto-induction of TGF-β1 and increased expression of DNA methyltransferases (DNMTs), suggesting that DNA methylation plays a significant role in cancer development and progression. In this review, we performed an extensive survey of the literature linking TGF-β signaling to DNA methylation in prostate cancer. It appeared that almost all DNA methylated genes detected in prostate cancer are directly or indirectly related to TGF-β signaling. This knowledge has provided a basis for our future directions of prostate cancer research and strategies for prevention and therapy for prostate cancer.

Lysyl oxidase binds transforming growth factor-beta and regulates its signaling via amine oxidase activity

Lysyl oxidase (LOX), an amine oxidase critical for the initiation of collagen and elastin cross-linking, has recently been shown to regulate cellular activities possibly by modulating the functions of growth factors. In this study, we investigated the interaction between LOX and transforming growth factor-beta1 (TGF-beta1), a potent growth factor abundant in bone, the effect of LOX on TGF-beta1 signaling, and its potential mechanism. The specific binding between mature LOX and mature TGF-beta1 was demonstrated by immunoprecipitation and glutathione S-transferase pulldown assay in vitro. Both proteins were colocalized in the extracellular matrix in an osteoblastic cell culture system, and the binding complex was identified in the mineral-associated fraction of bone matrix. Furthermore, LOX suppressed TGF-beta1-induced Smad3 phosphorylation likely through its amine oxidase activity. The data indicate that LOX binds to mature TGF-beta1 and enzymatically regulates its signaling in bone and thus may play an important role in bone maintenance and remodeling.

Epigenetic regulation of the human mucin gene MUC4 in epithelial cancer cell lines involves both DNA methylation and histone modifications mediated by DNA methyltransferases and histone deacetylases

The human gene MUC4 encodes a transmembrane mucin, ligand of ErbB2, that is associated with pancreatic tumor progression. In the normal pancreas, MUC4 is not expressed, whereas activation of its expression is observed in the early steps of pancreatic carcinogenesis. The molecular mechanisms responsible for MUC4 gene activation are however still unknown. The MUC4 5'-flanking region being GC-rich and including two CpG islands, we hypothesized that epigenetic regulation may be involved and undertook to decipher the molecular phenomenons implied. By treating cancer cell lines with 5-aza-2'-deoxycytidine (5-aza) and trichostatin A (TSA), we were able to restore MUC4 expression in a cell-specific manner. We showed by bisulfite-treated genomic DNA sequencing and chromatin immunoprecipitation that methylation of five CpG sites and establishment of a repressive histone code at the 5'-untranslated region were associated with MUC4 silencing and impaired its activation by Sp1. Direct involvement of DNMT3A, DNMT3B, HDAC1, and HDAC3 was demonstrated by RNA interference and chromatin immunoprecipitation. Moreover, inhibition of histone deacetylation by TSA was associated with strong MUC4 repression in high-expressing cells. In conclusion, this work shows for the first time the importance of epigenetics in regulating MUC4 expression and may represent a new strategy to inhibit its expression in epithelial tumors.

Collagen alpha1(I) gene (COL1A1) is repressed by RFX family

Collagen type I is composed of three polypeptide chains transcribed from two separate genes (COL1A1 and COL1A2) with different promoters requiring coordinate regulation. Our recent publications, centering on COL1A2 regulation, demonstrate that methylation in the first exon of COL1A2 at a regulatory factor for X box (RFX) site (at -1 to +20) occurs in human cancer cells and correlates with increased RFX1 binding and decreased collagen transcription (Sengupta, P. K., Erhlich, M., and Smith, B. D. (1999) J. Biol. Chem. 274, 36649-36655; Sengupta, S., Smith, E. M., Kim, K., Murnane, M. J., and Smith, B. D. (2003) Cancer Res. 63, 1789-1797). In normal cells, RFX5 complex along with major histocompatibility class II transactivator (CIITA) is induced by interferon-gamma to occupy this site and repress collagen transcription (Xu, Y., Wang, L., Buttice, G., Sengupta, P. K., and Smith, B. D. (2004) J. Biol. Chem. 279, 41319-41332). In this paper, we demonstrate that COL1A1 has an RFX consensus binding site surrounding the transcription start site (-11 to +10) that contains three methylation sites rather than one in the COL1A2 gene RFX binding site. RFX1 interacts weakly with the unmethylated COL1A1 site, and binds with higher affinity to the methylated site. RFX1 represses the unmethylated COL1A1 less efficiently than COL1A2. COL1A1 promoter activity is sensitive to DNA methylation and the COL1A1 gene is methylated in human cancer cells with coordinately decreased collagen expression. The DNA methylation inhibitor, 5-aza-2'-deoxycytidine (aza-dC) increases collagen gene expression with time in human cancer cells. On the other hand, RFX5 interacts with both collagen type I genes with a similar binding affinity and represses both promoters equally in transient transfections. Two dominant negative forms of RFX5 activate both collagen genes coordinately. Finally, CIITA RNA interference experiments indicate that CIITA induction is required for interferon gamma-mediated repression of both collagen type I genes.