The expression of DNA methyltransferases and methyl-CpG-binding proteins is not associated with the methylation status of p14ARF, p16INK4a and RASSF1A in human lung cancer cell lines

Abstract

Promoter hypermethylation is an important means for the transcriptional repression of a number of cancerassociated genes. However, the underlying mechanism of this aberration in cancer remains unclear. Here, we examined 5' CpG island methylation status and expression of the p14 ARF , p16 INK4a and RASSF1A tumor suppressor genes, and investigated the relationship of these factors with the mRNA expression of DNA methyltransferases (DNMTs) and/or methyl-CpG-binding proteins (MBPs) in 30 lung cancer cell lines including 12 small cell lung cancers (SCLCs) and 18 non-small cell lung cancers (NSCLCs). When b-actin was used as an internal control, the mRNA expression of three DNMTs (DNMT1, DNMT3A, and DNMT3B) and five MBPs (MBD1, MBD2, MBD3, MBD4, and MeCP2) was upregulated in SCLC, while only that of DNMT1, DNMT3B and MBD3 was upregulated in NSCLC, compared with normal lung tissues. However, when normalized using proliferating cell nuclear antigen (PCNA) as an internal control, these differences disappeared or diminished; there was even a significant reduction in the expression ratios of DNMT1, MBD2 and MeCP2 in SCLC and DNMT1, MBD2 and MBD4 in NSCLC. Furthermore, although significant correlations between PCNA expression and mRNA expression levels of the three DNMTs and four of the MBPs (excluding MeCP2) were observed, there was no obvious correlation between promoter hypermethylation of these tumor suppressor genes and the expression level of any of the DNMTs or MBPs. Our results suggest that upregulation of DNMTs and MBPs probably reflects an increased cell proliferation in human lung cancers and that there are likely to exist gene-specific mechanisms for epigenetic gene silencing.

Expression of methylation-related genes is associated with overall survival in patients with non-small cell lung cancer

“…These findings suggest that DNMT1 hypermethylates survival-associated tumour suppressor genes, leading to their functional inactivation. However, a recent report (Sato et al, 2002) found no significant association between DNMT1 expression and DNA methylation of some tumour-associated genes, suggesting that DNMT1 also contributes to cancer development and progression through alternative pathways. For example, Number of patients may not add up to the total number due to assay failure.…”

“…Thus, new prognostic markers are needed to help identify patients with poor prognoses, who may benefit from more aggressive treatment approaches. Previous studies have consistently reported that DNMT isoforms are significantly upregulated in human lung cancer cell lines and NSCLC tissue specimens (Sato et al, 2002;Vallbohmer et al, 2006). However, studies of the association between DNMT expression and clinical outcome in NSCLC patients have produced inconsistent results (Kim et al, 2006;Vallbohmer et al, 2006;Lin et al, 2007), and few have evaluated the prognostic value of MBD2.…”

Epigenetic silencing contributes to the loss of BRMS1 expression in breast cancer

“…Deregulation of DNA methyltransferases have been implicated as a potential link to hypermethylation [54]. Some studies suggest that the activity of DNA methyltransferases does not correlate with the hypermethylation of CpGs within a gene [55] yet, others have shown elevated DNA methyltransferases in a subset of patients which exhibit gene hypermethylation [53,56,57].…”

UHRF1‐mediated tumor suppressor gene inactivation in nonsmall cell lung cancer

“…[20][21][22] However, other reports suggest that DNMT overexpression does not by itself seem to sufficiently account for the hypermethylation of TSG promoters. 19,21,23,24 UHRF1 (also known as ICBP90) has recently been shown to play an important role in methylation maintenance. 25 It has the ability to bind hemimethylated DNA through its SET-and RING-associated domain, 26,27 triggering the recruitment of DNMT1 25,28 and histone deacetylace-1.…”