Abstract 4089: Regulation of cancer-specific microRNA by aberrant DNA methylation in laryngeal cancer

DNA methylation plays an essential role in the regulation of gene expression during development and differentiation, and furthermore has been reported to be involved in various diseases such as diabetes, schizophrenia and cancers. The majority of CpG islands are normally unmethylated, but a sizeable fraction is prone to become methylated in various cell types and pathological situations. The down-regulation of tumor suppressor genes has been reported to be linked to the hypermethylation of CpG sites located within CpG islands with promoter activity. The same mechanism could play an important role in silencing of tumor-suppressive microRNAs (miRNAs) in tumors. Head and neck cancer (HNC) is a major cause of cancer-related mortality and morbidity, comprising roughly 6% of all malignancies worldwide, and laryngeal cancer has the highest incidence in it. However, although to date its relevance to smoking has been well documented, the molecular mechanism involved in laryngeal cancer development and its highly sensitive biomarkers as well as promising therapeutic targets remain to be known. Thus, we have focused on the down-regulated miRNAs in laryngeal cancers and their neighboring methylated DNA sites on the genome as potential novel biomarkers or therapeutic targets with clinical applicability. In this study, we used an approach with a series of sequential analyses using clinical samples to clarify DNA methylation loci and examine the relationship between miRNA down-regulation and DNA methylation in laryngeal cancer. First, we analyzed the methylation levels at 27,578 CpG dinucleotides in 14,495 genes in 8 laryngeal tissues (1 dysplasia, 4 laryngeal cancers) using HumanMethylation27 BeadChip® (Illumina), in which AVG_Beta Methylation Values were used to quantify methylation levels at specific loci on the genome of each patient. We have compared dysplasia samples with laryngeal cancer samples and found that 198 hypermethylation loci within CpG islands were specific for laryngeal cancers, and also clarified 72 miRNAs on/around these CpG sites using the human genome database. Next, we have examined the expression patterns of 723 human miRNAs in 8 laryngeal tissues (1 polyp, 2 dysplasias, 3 laryngeal cancers and 2 neighboring normal tissues matched to laryngeal cancers) using microarrays (Agilent Human miRNA V2) and found 88 miRNAs down-regulated in laryngeal cancers compared to others. Finally, we combined the results of these two analyses to reveal that 11 miRNAs were down-regulated together with DNA methylation status on/around their neighboring CpG islands. Our study suggested that tumor-specific DNA methylation could be an important molecular mechanism for the down-regulation of miRNA expression. These novel findings may lead to the identification of methylated DNAs associated with down-regulated miRNAs specific to laryngeal cancer and the future elucidation of the molecular mechanism of HNC development. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4089.