RESUMO
We investigated the aberrant promoter methylation status of 12 genes in skin lesions, both malignant (basal cell carcinomas (BCCs), n=68 and squamous cell carcinomas (SCCs), n=35) and non-malignant (tags, n=58) skin lesions and compared the results of lesions from sun exposed (SE) and sun protected (SP) regions. Methylation was studied using a methylation specific PCR (MSP) and methylation of CDH1 was also measured using a semi-quantitative fluorescence based real-time MSP method. The methylation index (MI) was calculated as the methylated fraction of the genes examined. In this report, we found high frequencies of methylation of several known or suspected tumor suppressor genes in tags and skin cancers. Among the 12 genes, for the cadherin genes CDH1 and CDH3 and for two of the laminin 5 encoding genes LAMA3 and LAMC2 methylation frequencies greater than 30% were noted in one or more specimen types. We investigated whether methylation was tumor related. Surprisingly, the differences in the methylation profile of genes among the three specimen types were modest, and the MI, indicators of overall methylation frequencies, was nearly identical. However, significant differences were noted in the frequencies of methylation among the three specimen types for the genes RASSF1A (P=0.002), CDH1 (P=0.007) and one or more of three CAD genes (P=0.02). Methylation was highly significantly related to sun exposure, and sun protected specimens had little or no methylation. As methylation of CDH1 was completely SE specific we analyzed all the skin samples using a semi-quantitative real-time PCR assay for the CDH1 gene. The concordance between standard MSP and real-time MSP for all the samples (n=161) was 75% (P<0.0001). While weak signals were detected in the SP samples by real time PCR, the differences between SE and SP specimens were 148 fold for tags and 390 fold for BCCs. These differences were highly significant (P<0.0001). These findings suggest that methylation commences in UV exposed skin at a relatively early age and occurs in skin prior to the onset of recognizable preneoplastic changes.
Assuntos
Metilação de DNA/efeitos da radiação , Neoplasias Cutâneas/genética , Pele/efeitos da radiação , Luz Solar , Idoso , Caderinas/genética , Carcinoma Basocelular/genética , Carcinoma Basocelular/patologia , Carcinoma de Células Escamosas/genética , Carcinoma de Células Escamosas/patologia , Claudinas , Ciclina D2 , Inibidor p16 de Quinase Dependente de Ciclina/genética , Ciclinas/genética , Exposição Ambiental , Proteínas da Matriz Extracelular/genética , Feminino , Humanos , Laminina/genética , Masculino , Proteínas de Membrana/genética , Pessoa de Meia-Idade , Reação em Cadeia da Polimerase/métodos , Pele/metabolismo , Pele/patologia , Neoplasias Cutâneas/patologia , Fator de Crescimento Transformador beta/genética , Proteínas Supressoras de Tumor/genética , Proteína da Zônula de Oclusão-2RESUMO
PURPOSE: Ovarian carcinomas are believed to arise de novo from surface epithelium, but the actual molecular pathogenesis is unknown. The aim of this study was to compare the promoter hypermethylation profiles of ovarian epithelial neoplasms to better understand the role of epigenetic silencing in carcinogenesis. EXPERIMENTAL DESIGN: We analyzed the DNA promoter methylation status of eight tumor suppressor and cancer-related genes (p16, RARbeta, E-cadherin,H-cadherin, APC, GSTP1, MGMT, RASSF1A) in 23 benign cystadenomas, 23 low malignant potential (LMP) tumors, and 23 invasive carcinomas by methylation-specific PCR. RESULTS: Benign cystadenomas exhibited promoter hypermethylation in only two genes, p16 (13%) and E-cadherin (13%). LMP tumors also showed p16 (22%) and E-cadherin (17%) methylation, in addition to RARbeta (9%) and H-cadherin (4%). All eight genes were hypermethylated in invasive cancers at a frequency of 9% to 30%. The mean methylation index was highest in invasive tumors [0.20 versus 0.065 (LMP) and 0.033 (cystadenomas); P = 0.001]. Promoter methylation of at least one gene was most commonly observed among invasive cancers [78% versus 44% (LMP; P = 0.03) and 26% (cystadenomas; P = 0.0009)]. Three genes exhibited higher methylation frequencies in invasive tumors: RASSF1A (30% versus 0%; P = 0.0002), H-cadherin (22% versus 2%; P = 0.013), and APC (22% versus 0%; P = 0.003). CONCLUSIONS: Promoter hypermethylation is a frequent epigenetic event that occurs most commonly in invasive epithelial ovarian carcinomas. The profile of aberrant methylation suggests that an accumulation of events at specific genes may trigger malignant transformation of some benign cystadenomas and LMP tumors.
Assuntos
Metilação de DNA , Neoplasias Epiteliais e Glandulares/genética , Neoplasias Ovarianas/genética , Regiões Promotoras Genéticas , Proteína da Polipose Adenomatosa do Colo/genética , Adulto , Idoso , Idoso de 80 Anos ou mais , Caderinas/genética , Carcinoma/genética , Carcinoma/patologia , Transformação Celular Neoplásica , Inibidor p16 de Quinase Dependente de Ciclina/genética , Cistadenoma/genética , DNA/metabolismo , Epigênese Genética , Feminino , Inativação Gênica , Glutationa S-Transferase pi/genética , Humanos , Pessoa de Meia-Idade , Invasividade Neoplásica , Metástase Neoplásica , O(6)-Metilguanina-DNA Metiltransferase/genética , Reação em Cadeia da Polimerase , Receptores do Ácido Retinoico/genética , Proteínas Supressoras de Tumor/genéticaRESUMO
Expression of the cadherin family member CDH13 (H-cadherin) is reduced in several human tumors, and it has been hypothesized that this gene functions as a tumor suppressor gene. Previously, we reported that the 5' region of CDH13 is frequently methylated in breast and lung cancers. Here we confirmed the promoter activity of 5' region of CDH13 by luciferase assay and examined its aberrant methylation in colorectal cancers, cell lines, and adenomas. Methylation status was investigated by methylation-specific PCR (MSP) and by bisulfite DNA sequencing of cloned DNA of PCR amplicons. In cell lines, we examined the correlation between methylation status and mRNA expression by reverse transcription-PCR. Aberrant methylation of CDH13 was present in 7 of 13 (54%) cell lines, and expression was absent in 6 of 13 (46%) cell lines. CDH13 expression was present in six cell lines that showed only the unmethylated form by MSP and in one cell line that showed both the methylated and unmethylated forms. Treatment with 5-aza-2'-deoxycytidine restored CDH13 expression in methylated cell lines. In surgically resected samples, 17 of 35 (49%) cases of primary colorectal cancer, 2 of 33 (6%) cases of corresponding nonmalignant colorectal mucosa, and 8 of 19 (42%) adenomas were methylated. Sequence data after bisulfite treatment indicated that primary cancers and two cell lines with loss of expression were highly methylated compared with nonmalignant colorectal epithelial cells, especially at the attachment sites of primers for MSP, although there was heterogeneity in methylation status. Our results suggest that CDH13 expression is frequently silenced by aberrant methylation in colorectal cancers and adenomas and that methylation of CDH13 commences at an early stage of multistep colorectal tumorigenesis.