Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.1.1.37 (DNA methyltransferase)
 4,983 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The claudin (CLDN) genes encode a family of proteins involved in the formation and function of tight junctions. CLDN gene expression is frequently altered in several human cancers, and in particular, CLDN3 and CLDN4 are commonly overexpressed in ovarian cancer. However, the mechanisms leading to the deregulation of these genes in cancer remain unclear. In the present study, we have examined the CLDN3 promoter and have identified a minimal region containing an Sp1 site crucial for its activity. In addition, we find that the CLDN3 promoter is regulated through epigenetic processes. Cells that express high levels of CLDN3 exhibit low DNA methylation and high histone H3 acetylation of the critical CLDN3 promoter region, and the reverse is observed in cells that do not express this gene. CLDN3-negative cells can be induced to express CLDN3 through treatment with DNA methyltransferase or histone deacetylase inhibitors. Interestingly, in vitro binding experiments, as well as chip assays show that Sp1 binds the unmethylated promoter much more efficiently, providing a mechanism for CLDN3 silencing in non-expressing cells. Finally, siRNA-mediated knockdown of Sp1 led to a significant decrease of CLDN3 expression at both the mRNA and protein levels, demonstrating a crucial role for this transcription factor in the regulation of CLDN3. Our data provide a basis for CLDN3 expression in ovarian cancer cells, as well as a mechanism for the silencing of this promoter in tumors lacking expression of claudin-3.
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PMID:Regulation of the CLDN3 gene in ovarian cancer cells. 1798 52

Breast cancer progression is associated with aberrant DNA methylation and expression of genes that control the epithelial-mesenchymal transition (EMT), a critical step in malignant conversion. Although the genes affected have been studied, there is little understanding of how aberrant activation of the DNA methylation machinery itself occurs. Using a breast cancer cell-based model system, we found that cells that underwent EMT exhibited overactive transforming growth factor beta (TGFbeta) signaling and loss of expression of the CDH1, CGN, CLDN4, and KLK10 genes as a result of hypermethylation of their corresponding promoter regions. Based on these observations, we hypothesized that activated TGFbeta-Smad signaling provides an "epigenetic memory" to maintain silencing of critical genes. In support of this hypothesis, disrupting Smad signaling in mesenchymal breast cancer cells resulted in DNA demethylation and reexpression of the genes identified. This epigenetic reversal was accompanied by an acquisition of epithelial morphology and a suppression of invasive properties. Notably, disrupting TGFbeta signaling decreased the DNA binding activity of DNA methyltransferase DNMT1, suggesting that failure to maintain methylation of newly synthesized DNA was the likely cause of DNA demethylation. Together, our findings reveal a hyperactive TGFbeta-TGFbetaR-Smad2 signaling axis needed to maintain epigenetic silencing of critical EMT genes and breast cancer progression.
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PMID:Smad signaling is required to maintain epigenetic silencing during breast cancer progression. 2008 75