Combined deletion and DNA methylation result in silencing of FAM107A gene in laryngeal tumors

Larynx squamous cell carcinoma (LSCC) is characterized by complex genotypes, with numerous abnormalities in various genes. Despite the progress in diagnosis and treatment of this disease, 5-year survival rates remain unsatisfactory. Therefore, the extended studies are conducted, with the aim to find genes, potentially implicated in this cancer. In this study, we focus on the FAM107A (3p14.3) gene, since we found its significantly reduced expression in LSCC by microarray profiling (Affymetrix U133 Plus 2.0 array). By RT-PCR we have confirmed complete FAM107A downregulation in laryngeal cancer cell lines (15/15) and primary tumors (21/21) and this finding was further supported by FAM107A protein immunohistochemistry (15/15). We further demonstrate that a combined two hit mechanism including loss of 3p and hypermethylation of FAM107A promoter region (in 9/15 cell lines (p p FAM107A expression (5 to 6 fold increase) in the UT-SCC-29 cell line, characterized by high DNA methylation. Therefore, we report the recurrent inactivation of FAM107A in LSCC, what may suggest that the gene is a promising tumor suppressor candidate involved in LSCC development.</p

Recurrent epigenetic silencing of the PTPRD tumor suppressor in laryngeal squamous cell carcinoma

Cellular processes like differentiation, mitotic cycle, and cell growth are regulated by tyrosine kinases with known oncogenic potential and tyrosine phosphatases that downmodulate the first. Therefore, tyrosine phosphatases are recurrent targets of gene alterations in human carcinomas. We and others suggested recently a tumor suppressor function of the PTPRD tyrosine phosphatase and reported homozygous deletions of the PTPRD locus in laryngeal squamous cell carcinoma. In this study, we investigated other gene-inactivating mechanisms potentially targeting PTPRD, including loss-of-function mutations and also epigenetic alterations like promoter DNA hypermethylation. We sequenced the PTPRD gene in eight laryngeal squamous cell carcinoma cell lines but did not identify any inactivating mutations. In contrast, by bisulfite pyrosequencing of the gene promoter region, we identified significantly higher levels of methylation (p = 0.001 and p = 0.0002, respectively) in 9/14 (64%) laryngeal squamous cell carcinoma cell lines and 37/79 (47%) of primary laryngeal squamous cell carcinoma tumors as compared to normal epithelium of the upper aerodigestive tract. There was also a strong correlation (p = 0.0001) between methylation and transcriptional silencing for the PTPRD gene observed in a cohort of 497 head and neck tumors from The Cancer Genome Atlas dataset suggesting that DNA methylation is the main mechanism of PTPRD silencing in these tumors. In summary, our data provide further evidence of the high incidence of PTPRD inactivation in laryngeal squamous cell carcinoma. We suggest that deletions and loss-of-function mutations are responsible for PTPRD loss only in a fraction of cases, whereas DNA methylation is the dominating mechanism of PTPRD inactivation.</p