Transcriptional repression of the transforming growth factor-β type I receptor gene by DNA methylation results in the development of TGF-β resistance in human gastric cancer

Abstract

The transforming growth factor-b (TGF-b) signaling pathway subserves an essential tumor suppressor function in various cell types. A heteromeric complex composed of TGF-b type I (RI) and type II (RII) receptors is required for TGF-b signaling. We have identi®ed a subset of human gastric cancer cell lines which are insensitive to TGF-b and which express a low level of TGF-b type I receptor mRNA relative to a gastric cancer cell line which is highly responsive to TGF-b. Using these cells, we show that hypermethylation of a CpG island in the 5' region of the TGF-b RI gene provides another potentially important mechanism of escape from negative growth control by TGF-b. This hypermethylation was found in four of ®ve human gastric cancer cell lines and ®ve out of 40 (12.5%) primary tumors examined. In human gastric cancer cell lines, treatment with the demethylating agent, 5-aza-2'-deoxycytidine, resulted in increased expression of the TGF-b RI gene, but not the RII gene. Transient transfection of an RI expression vector into the TGF-b resistant SNU-601 cell line restores TGF-b responsiveness. These ®ndings suggest that one of the mechanisms of escape from autocrine or paracrine growth control by TGF-b during carcinogenesis could involve aberrant methylation of CpG islands in the 5' region of the TGF-b RI gene.

Aberrant methylation of integrin α4 gene in human gastric cancer cells

“…In addition, DNA methylation and the chromatin condensation of integrin aL were detected in fibroblasts, and were suggested to contribute to the tissue-specific expression of integrin aL (Akama et al, 1997;Lu et al, 2002). Previously, we reported that DNA methylation is one of the predominant mechanisms for inactivating various genes, like, TGF-b type I receptor, TIMP-3, p16, COX-2 and DLC-1, during gastric carcinogenesis (Kang et al, 1999;Kang et al, 2000;Song et al, 2000Song et al, , 2001Kim et al, 2003). These findings led us to investigate whether integrin a4 expression could be regulated by DNA methylation, because integrin a4 expression is very low in our gastric carcinoma cells (Figure 1a).…”

“…Recently, several studies have found that the methylation of the CpG island is associated with gene silencing in tumors; these include pRb, p15 Ink4b , p16 Ink4a , hMLH1 and TGF-type I receptor (Herman et al, 1996a(Herman et al, , b, 1998Stirzaker et al, 1997;Kang et al, 1999;Song et al, 2000). Moreover, genes silenced by DNA methylation can be reactivated by treatment with 5-aza-2 0 -deoxycytidine (5-Aza-dC), a well-established inhibitor of DNA methyltransferase (Jones and Taylor, 1980).…”

FR901228, an inhibitor of histone deacetylases, increases the cellular responsiveness to IL-6 type cytokines by enhancing the expression of receptor proteins

“…Armenante et al, 1999;Birger et al, 1999;Kang et al, 1999;Melki et al, 1999;Antequera et al, 1990;Baylin and Herman, 2000). Moreover, direct associations between DNA methylation and chromatin structure have been established after the identification of several repressor complexes containing methyl-CpG binding proteins, chromatin remodeling factors, and histone deacetylases (Ng and Bird, 1999;Nan et al, 1998;Magdinier and Wolffe, 2001).…”

E-cadherin gene (CDH1) promoter methylation as the second hit in sporadic diffuse gastric carcinoma

“…These results o er an example of promoter methylation providing a key event in gastric carcinogenesis and add to the growing list of tumor suppressor genes silenced by promoter methylation in gastric carcinoma, e.g. P16(INK4A) (Lee et al, 1997), hMLH1 (Leung et al, 1999), P57 (Shin et al, 2000) and TGFBRI (Kang et al, 1999). As pointed out by Grady et al (2000) promoter methylation might provide, due to its reversible nature, an attractive target for the development of new anti-cancer therapies.…”