RE: P16 INK41 promoter hypermethylation is associated with invasiveness and prognosis of oral squamous cell carcinoma in an age dependent manner. Su et al. Oral Oncology 46 (2010) 734-739

Histopathological analysis of oral squamous cell carcinoma in nonsmokers and nondrinkers

A distinct clinical subgroup of nonsmoking (NS) and nondrinking (ND) patients with oral squamous cell carcinoma (OSCC) has been identified. The objective of the study was to assess this cohort for molecular variations in the disease process and if these could be attributed to clinical or epidemiological characteristics. One hundred and twenty-nine consecutive patients (71 males, 58 females) treated for OSCC were assessed at the Royal Melbourne Hospital between January 2007 and July 2010. Formalin-fixed paraffin embedded (FFPE) sections were stained for p53, p16, cyclin D1, and epidermal growth factor receptor (EGFR). Biomarker overexpression was observed in 72 (56%) cases for p53, 23 (18%) for p16, 45 (35%) for cyclin D1, and 72 (56%) for EGFR. Multiple logistic regression analysis revealed that tongue tumors ( p = 0.012) and late stage cancers ( p = 0.031) were more likely to have cyclin D1 overexpression. Further, older patients significantly more often had cyclin D1 overexpression ( p = 0.008) and NSND patients had more p16 expression ( p = 0.043). In contrast, smokers were more likely to have EGFR overexpression ( p = 0.033). Concurrent overexpression of p53 and cyclin D1 were observed ( p = 0.030). Smoking, site, and stage of OSCC can influence biomarker expression, with p16 overexpression specifically observed in NSND, indicating fundamental differences in the mechanisms of oral carcinogenesis among different patient cohorts.

Promoter region hypermethylation and mRNA expression of MGMT and p16 genes in tissue and blood samples of human premalignant oral lesions and oral squamous cell carcinoma

Promoter methylation and relative gene expression of O(6)-methyguanine-DNA-methyltransferase (MGMT) and p16 genes were examined in tissue and blood samples of patients with premalignant oral lesions (PMOLs) and oral squamous cell carcinoma (OSCC). Methylation-specific PCR and reverse transcriptase PCR were performed in 146 tissue and blood samples from controls and patients with PMOLs and OSCC. In PMOL group, significant promoter methylation of MGMT and p16 genes was observed in 59% (P = 0.0010) and 57% (P = 0.0016) of tissue samples, respectively, and 39% (P = 0.0135) and 33% (P = 0.0074) of blood samples, respectively. Promoter methylation of both genes was more frequent in patients with OSCC, that is, 76% (P = 0.0001) and 82% (P = 0.0001) in tissue and 57% (P = 0.0002) and 70% (P = 0.0001) in blood, respectively. Significant downregulation of MGMT and p16 mRNA expression was observed in both tissue and blood samples from patients with PMOLs and OSCC. Hypermethylation-induced transcriptional silencing of MGMT and p16 genes in both precancer and cancer suggests important role of these changes in progression of premalignant state to malignancy. Results support use of blood as potential surrogate to tissue samples for screening or diagnosing PMOLs and early OSCC.

Environmental chemical exposures and human epigenetics

Every year more than 13 million deaths worldwide are due to environmental pollutants, and approximately 24% of diseases are caused by environmental exposures that might be averted through preventive measures. Rapidly growing evidence has linked environmental pollutants with epigenetic variations, including changes in DNA methylation, histone modifications and microRNAs. Environ mental chemicals and epigenetic changes All of these mechanisms are likely to play important roles in disease aetiology, and their modifications due to environmental pollutants might provide further understanding of disease aetiology, as well as biomarkers reflecting exposures to environmental pollutants and/or predicting the risk of future disease. We summarize the findings on epigenetic alterations related to environmental chemical exposures, and propose mechanisms of action by means of which the exposures may cause such epigenetic changes. We discuss opportunities, challenges and future directions for future epidemiology research in environmental epigenomics. Future investigations are needed to solve methodological and practical challenges, including uncertainties about stability over time of epigenomic changes induced by the environment, tissue specificity of epigenetic alterations, validation of laboratory methods, and adaptation of bioinformatic and biostatistical methods to high-throughput epigenomics. In addition, there are numerous reports of epigenetic modifications arising following exposure to environmental toxicants, but most have not been directly linked to disease endpoints. To complete our discussion, we also briefly summarize the diseases that have been linked to environmental chemicals-related epigenetic changes.