Abstract 4807: P16 and MGMT hypermethylation status evaluation in squamous cell penile carcinomas by pyrosequencing
Authors: Luciane T. Kagohara, Gustavo C. Guimaraes, Ademar Lopes, Isabela W. Cunha, Renata A. Coudry, Fernando A. Soares
Journal: Cancer Research (2011)

Abstract Penile carcinoma is an uncommon disease and the most frequent subtype is squamous cell carcinoma. This cancer represents less than 1% of all cases in developed countries. However, in some regions of developing countries it represents 20% of all male cancers. The main risk factors associated to this tumor are poor hygienic habits, low quality of life, HPV infections and high number of sexual partners. Very little is known about penile carcinoma, including its pathogenesis, etiology and molecular biology features. In this study, we evaluated the hypermethylation status of two genes that present high frequencies of methylation in various tumor types. P16 plays an important role in cell cycle control. It encodes the protein p16 that binds to CDK proteins and inhibits pRB phosphorilation, blocking cell cycle progression. MGMT encodes a DNA repair protein that removes alkyl groups from guanines. The protein mgmt is peculiar once it acts alone and not in complexes like other DNA repair proteins. Hypermethylation of these genes is already described in a large variety of tumors, leads to gene silencing and has an important role in tumoregenesis. Here, we determined the frequency of hypermethylation among penile carcinoma samples and the percentage of aberrant methylation for each sample. The samples were submitted to bisulfite conversion, amplification and sequencing employing the pyrosequencing methodology, which is a quantitative methodology allowing percentage determination of each CpG dinucleotide analyzed. The hypermethylation status and methylation levels were evaluated in 33 squamous cell penile carcinoma samples. We observed P16 hypermethylation in 9% of the samples and MGMT was methylated in 27%, with levels of methylation varying from 10.71% to 35.43% and 12.20% to 62.60%, respectively. The low frequency of samples showing P16 hypermethylation could be explained by the presence of HPV infection, which is described in approximately 70.00% to 80.00% of penile carcinomas. It is well known that in the presence of HPV there is no P16 DNA methylation, suggesting that the HPV E7 protein influences the Rb pathway in these samples. MGMT hypermethylation frequency is in accordance with what was described by other groups and that showed no association to clinical characters of the samples analysed. Little is known about the influence of DNA hypermethylation on penile carcinoma tumorigenesis but our results show that the epigenetic alteration of P16 and MGMT genes are not tumor markers for penile carcinoma. To our knowledge it is the first study describing the epigenetic status of penile carcinomas in the Brazilian population. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4807. doi:10.1158/1538-7445.AM2011-4807