RESUMO
Malignant pleural mesothelioma (MPM) remains a cancer of poor prognosis. It is hoped that implementation of effective screening biomarkers will lead to earlier diagnoses and improved outcomes. Serum-measured soluble mesothelin-related peptide (SMRP) has been demonstrated to have excellent specificity for MPM, but poor sensitivity precludes its use as a screening biomarker. Using a case series of MPM patients from the International Mesothelioma Program at the Brigham and Women's hospital, we sought to determine whether epigenetic change at the MSLN gene in patient tumors is responsible for the poor sensitivity of SMRP. We identified three potential target regions for CpG methylation silencing in the MSLN promoter, one of which was amenable to bisulfite pyrosequencing and located 214 bp upstream of the transcription start site. MSLN promoter methylation was significantly higher in normal pleura than tumor tissue (P < 6.0x10-9). Next, we compared cases according to serum SMRP status and observed that MSLN methylation was significantly higher among tumors from patients testing negative for SMRP (< 1.5nM) versus those that were SMRP positive (P < 0.03). These results demonstrate that MSLN is normally methylated in the pleura, and that methylation is lost in most tumors. However, in a subset of tumors methylation is retained, and this mechanism explains the poor sensitivity of the SMRP assay. These results may lead to additional biomarker targets that will resolve the poor sensitivity of the SMRP assay and allow implementation of screening among exposed populations.
Assuntos
Biomarcadores Tumorais/sangue , Biomarcadores Tumorais/genética , Metilação de DNA , Proteínas Ligadas por GPI/sangue , Proteínas Ligadas por GPI/genética , Mesotelioma/sangue , Mesotelioma/genética , Neoplasias Pleurais/sangue , Neoplasias Pleurais/genética , Idoso , Asbestose/sangue , Ilhas de CpG/genética , Epigênese Genética , Feminino , Regulação Neoplásica da Expressão Gênica , Humanos , Masculino , Mesotelina , Mesotelioma/patologia , Pessoa de Meia-Idade , Neoplasias Pleurais/patologia , Prognóstico , Regiões Promotoras Genéticas/genéticaRESUMO
P53 is a key regulatory molecule in the cellular response to ultraviolet radiation, and TP53 mutation is the most common alteration in non-melanoma skin cancer. The MDM2 oncogene negatively regulates p53 protein levels, and both genes have functional polymorphisms that may modify skin cancer risk. Furthermore, prior research suggests that TP53 mutations preferentially occur on the arginine allele to selectively inactivate the p63 pathway. We tested these hypotheses of susceptibility and preferential mutation in non-melanoma skin cancer. The TP53 Arg72Pro and MDM2 309 polymorphisms were genotyped in a population-based case-control study of non-melanoma skin cancer, and TP53 alteration (mutation and immunohistochemistry staining) was evaluated in case tumors. In 902 cases of basal cell carcinoma (BCC), 676 cases of squamous cell carcinoma (SCC) and 812 controls, no association was found between the TP53 polymorphism and risk of non-melanoma skin cancer [odds ratio (OR)(BCC) 0.98, 95% confidence interval (CI) 0.80-1.20; OR(SCC) 0.93, 95% CI 0.75-1.16]. However, carriers of the MDM2 SNP309 G allele did have an elevated risk of non-melanoma skin cancer (OR(BCC) 1.15, 95% CI 0.93-1.42; OR(SCC) 1.29, 95% CI 1.02-1.63). We observed an association between TP53 alterations in the tumors and constitutive TP53 genotype (P < 0.01), with alterations preferentially occurring on the proline allele. Collectively, these data highlight the significant effects of genotype on gene-specific mutation events in carcinogenesis.
