Aberrant CpG island hypermethylation of multiple genes in colorectal neoplasia

Abstract

CpG island hypermethylation is a potential means of inactivating tumor suppressor genes, and many genes have been demonstrated to be hypermethylated and silenced in colorectal cancer. However, limited data is available upon the concurrent methylation of multiple genes in colorectal cancer and in its precursor lesion. To address changes in the methylation profiles of multiple genes during colorectal carcinogenesis, we investigated the methylation of 12 genes (APC, COX-2, DAP-kinase, E-cadherin, GSTP1, hMLH1, MGMT, p14, p16, RASSF1A, THBS1, and TIMP3) in normal colon (n ¼ 24), colon adenoma (n ¼ 95), and colorectal cancer (n ¼ 149), using methylation-specific PCR. The average number of these genes methylated per sample was 0.12, 1.8, and 3.0 in normal colon mucosa, adenoma, and carcinoma, respectively, showing a stepwise increase (Po0.001). All the genes were methylated in colorectal cancer at frequencies varying from 51 to 9.4% and colon adenoma displayed methylation for the 11 genes, except for GSTP1, at frequencies varying from 40 to 1.1%. In contrast, normal colon mucosa demonstrated methylation for APC only, at a frequency of 12.5%. The total number of methylated genes per tumor showed a continuous, nonbimodal distribution in colon adenoma or cancer. CpG island hypermethylation exhibited a proclivity toward proximal colon cancer or adenoma, and the average number of genes methylated was higher in proximal colon cancer or adenoma than in distal colon cancer or adenoma, respectively (3.5 vs 2.6, P ¼ 0.018 for cancer, and 2.5 vs 1.4, P ¼ 0.003 for adenoma).In conclusion, concurrent CpG island methylation is an early and frequent event during colorectal carcinogenesis. It appears that CpG island methylation plays a more important role in proximal colon cancer development than in distal colon cancer development. Keywords: CpG island; colon adenoma; colorectal cancer; DNA methylation; tumor suppressor genes There are two well-known pathways of colorectal carcinogenesis, that is, chromosomal instability (CIN) and microsatellite instability (MSI). The CIN pathway is characterized by alterations of chromosomal number and structure affecting protooncogenes and tumor suppressor genes. 1 The CIN phenotype shows a high frequency of allelic losses and abnormal DNA content by flow cytometry. 2 Whereas, the MSI pathway features alterations in repeated nucleotides within the coding sequences, which result in the inactivation of tumor suppressor genes. 3,4 In contrast to the CIN phenotype, the MSI phenotype shows near-diploidy and very low allelic loss frequencies. 2 Recently the CpG island methylation phenotype has been added to these two phenotypes, and is characterized by the concordant methylation of the promoter regions of multiple genes that play a role in carcinogenesis. 5 Moreover, accumulating evidence has now linked promoter CpG island methylation with transcriptional silencing in human cells. Although the mechanism whereby CpG island methylation suppresses gene transcription has not been fully elucidated, it has bee...

CpG island methylation in aberrant crypt foci and cancers from the same patients

“…The smaller numbers of epigenetic alterations detected in ACF compared to colorectal cancers from the same patients support the role of ACF as early precursors of some colorectal cancers; this follows the same trend reported for adenomas and colon cancers in a larger study. 22 Concordant methylation or lack of methylation of the same loci in both benign and malignant lesions from the same patients or methylation of cancers but not precursor lesions (Table II) was reported previously for small numbers of polyps and cancers. 9,15 Of particular interest were our findings of methylation in 11 ACF from 10 patients whose cancers lacked methylation of the same loci (Table II) and the lack of concordance of the same methylated loci among ACF from the same patients (Fig.…”

“…The smaller numbers of epigenetic alterations detected in ACF compared to colorectal cancers from the same patients support the role of ACF as early precursors of some colorectal cancers; this follows the same trend reported for adenomas and colon cancers in a larger study. 22 Concordant methylation or lack of methylation of the same loci in both benign and malignant lesions from the same patients or FIGURE 1 -ACF after staining intact human colonic mucosa with methylene blue (a, original magnification Â160; b, original magnification Â25). The methylation patterns of these ACF are illustrated in Figure 3.…”

Aberrant promoter methylation of multiple genes during multistep pathogenesis of colorectal cancers

“…Other more limited studies on the methylation patterns of CAs are consistent with our observations and conclusions. [55][56][57][58] Five of the Group 1 genes (3OST2, HPP1, CDH13, CRBP1 and APC) were frequently methylated (>30%) in both CRCs and CAs. These genes may represent markers for risk assessment.…”

SPARC promoter hypermethylation in colorectal cancers can be reversed by 5-Aza-2′deoxycytidine to increase SPARC expression and improve therapy response

“…In this study, we proceeded to examine the methylation status of the SPARC promoter, as aberrant methylation is commonly observed in colorectal cancers (Toyota et al, 1999;Lee et al, 2004), and recent studies in other cancers have revealed aberrant hypermethylation of the SPARC promoter to be responsible for low levels of SPARC expression (Sato et al, 2003;Suzuki et al, 2005;DiMartino et al, 2006). We were able to identify specific CpG sites that were consistently methylated in colorectal cancers by DNA bisulfite sequencing.…”