To date, several reports have been published about CpG island methylation of various genes in prostate cancer. However, most of these studies have focused on cancer tissue only or a single gene and data about concurrent methylation of multiple genes in prostate cancer or prostatic intraepithelial neoplasia (PIN) are limited. The aim of the present study was to determine the methylation profile of 11 tumour-related genes in prostate cancer and PIN. Seventy-one samples, including 37 prostate cancers, 14 PINs, and 20 normal prostates, were examined for the methylation status of 11 tumour-related genes using methylation-specific PCR. The mean number of genes methylated was significantly higher in prostate cancer and PIN than in non-neoplastic prostate (4.4, 3, and 0.2, respectively; p < 0.001). In prostate cancer, APC, GSTP1, MGMT, and RASSF1A were frequently methylated at a frequency of 56.8%, 86.5%, 75.7%, and 83.8%, respectively. These genes were methylated in more than 30% of PINs. Prostate cancers with high serum prostate-specific antigen (PSA) (more than 8 ng/ml) or a high Gleason score (GS) (3 + 4 or more) showed higher numbers of methylated genes than those with low serum PSA (8 or less) or low GS (3 + 3 or less) (5.4 versus 2.5 and 5.4 versus 3.1, respectively; p < 0.05). The methylation frequency of APC, RASSF1A, and RUNX3 was higher in prostate cancers with high serum PSA or with high GS than in those with low PSA or with low GS, respectively, the differences reaching statistical significance (p < 0.05). A strong association between MGMT methylation and loss of MGMT expression was demonstrated by immunohistochemistry. CpG island methylation is a frequent event, occurs early, and accumulates during multi-step prostatic carcinogenesis. High levels of CpG island hypermethylation might serve as a potential biological marker for aggressive prostate cancer.

Aberrant hypermethylation of promoter CpG islands is an important mechanism for the inactivation of tumor suppressor genes. CpG island hypermethylation occurs in relation to tumorigenesis or aging.Gastric cancer is one of the tumors with a high level of aberrant CpG island methylation. However, the data on the methylation status of normal gastric mucosa has been very limited. The present study attempted to compare the methylation status of nonneoplastic gastric mucosa, using clinicopathological parameters, including age, gender, Helicobacter pylori (H. pylori), acute and chronic inflammation, and intestinal metaplasia. Two hundred sixty-eight nonneoplastic gastric mucosa samples were studied for the methylation status of 11 genes (COX-2, DAP-kinase, E-cadherin, GSTP1, MGMT, hMLH1, p14, p16, THBS1, TIMP3, and RASSF1A), using methylationspecific PCR. CpG island hypermethylation was found in 53.7, 41, 37.7, 23.1, 18.7, 10.9, 10, 4.1, 3.4, 1.7, 0.4% for DAP-kinase, E-cadherin, THBS1, TIMP3, p14, MGMT, p16, COX-2, GSTP1, hMLH1 and RASSF1A, respectively. Five genes (DAP-kinase, E-cadherin, p14, THBS1, and TIMP-3) showed a general progressive increase in the methylation frequency as a function of aging, whereas the other genes (COX-2, GSTP1, MGMT, hMLH1, p16, and RASSF1A) were rarely methylated. Male patients showed higher numbers of methylated genes than females (3.2 vs. 2.1, respectively, P ‫؍‬ 0.002). Gastritis samples with marked intestinal metaplasia, showed higher numbers of genes methylated than those without (3.7 vs. 2.6, respectively, P ‫؍‬ 0.021). Aberrant DNA methylation is a feature of human cancers, characterized by generalized hypomethylation and regional hypermethylation. 1-4 The regional hypermethylation involves CpG islands located in the promoter and upstream exons. Hypermethylation of CpG islands recruits methyl DNA binding proteins, and subsequently histone deacetylases. 5,6 Deacetylation of the histone backbones makes the DNA structure of the promoter into a closed chromatin structure, inaccessible to transcription factors, resulting in gene inactivation. 7,8 Aberrant hypermethylation of CpG islands located in the promoter, and/or upstream exons, acts as an alternative to genetic changes for the inactivation of tumor suppressor genes. 3,4 CpG islands are normally protected from DNA methylation, 9 but in relation to cancer or aging, they are aberrantly methylated. 3,10 The stomach is one of the organs that shows frequent methylation of CpG islands of genes in nonneoplastic epithelial cells. [11][12][13] Many genes have been demonstrated to be methylated in nonneoplastic gastric mucosae, whether in association with gastric cancer or not. [11][12][13] Our previous study has demonstrated that these genes are not methylated in pediatric gastric mucosae, or at a frequency significantly lower than that in gastric mucosae from adults. 11 If these methylations are an age-related event, they would be expected to be progressively prominent with age. However, no study has ever displayed plots correlating the m...

Accumulating evidence has identified a mechanism potentially responsible for the inactivation of tumor suppressor genes, namely transcriptional silencing by aberrant methylation of CpG islands. A previous study has shown the loss of RUNX3 expression, due to aberrant methylation of its CpG island, in gastric cancer cell lines, suggesting that RUNX3 is a target for epigenetic gene silencing in gastric carcinogenesis. However, there are limited data on the methylation status of RUNX3 in the neoplastic and non-neoplastic tissues in various types of human cancers, including gastric cancer. Here, we report that 60% of gastric cancer cell lines and 64% of primary gastric carcinomas (n ¼ 75) were methylated at the RUNX3 CpG island. RUNX3 methylation was also detected in hepatocellular carcinomas (73%, n ¼ 48), larynx cancers (62%, n ¼ 37), lung cancers (46%, n ¼ 24), breast cancers (25%, n ¼ 25), prostate cancers (23%, n ¼ 44), endometrial cancers (12.5%, n ¼ 24), colon cancers (4.9%, n ¼ 61) and uterine cervical cancers (2.5%, n ¼ 40), showing that RUNX3 methylation is not restricted to gastric cancer. Interestingly, the RUNX3 methylation was especially frequent in tumors from tissues of a foregut derivative, that is, the stomach, liver, larynx and lung. Next, the methylation status of RUNX3 in various nonneoplastic tissues was examined, including the premalignant lesions of gastric carcinomas. The RUNX3 methylation was found in 8.1% of chronic gastritis (n ¼ 99), 28.1% of intestinal metaplasia (n ¼ 32), 27.3% of gastric adenomas (n ¼ 77) and 64% of gastric carcinomas (n ¼ 75), but not in chronic hepatitis B, normal prostate and colon mucosa, even though in cases of chronic hepatitis, the methylation frequency of its neoplastic tissues was very high. In conclusion, RUNX3 methylation is frequently found in human cancers, including gastric cancer, and is mostly cancer specific, with the exception of the stomach, and thus, might be useful as a potential diagnostic biomarker of cancer.

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...

No abstract