Abstract
Abstract
Gene silencing associated with aberrant methylation of promoter region CpG islands is an acquired epigenetic alteration. It serves as an alternative to genetic defects in the inactivation of tumor suppressor and other genes in human cancers. Several genes have been shown to be epigenetically inactivated in a wide range of tumors and most neoplasms show hypermethylation of one or more genes. Concurrent methylation status of the CpG islands of 24 genes were determined in 40 PTC cases and in a panel of PTC cell lines, using methylation specific PCR. Seven genes demonstrated a relatively high frequency of aberrant methylation: RASF1 (95%), HIC1 (55%), GSTP1 (26%), P14 (25%), TMS1 (24%), DCR1 (17%) and SERF (15%). Five genes (BRACA1, P15INK4B, MGMT, BLU and APC) showed a low frequency (2-6%) of methylation, and no methylation was detected for the remaining twelve genes (P16INK4A, APAF1, FANCF, FAS, MINT25, P73, MLH1, DAPK, RARB, CASP8, E-Cadherin and SOC1.
Statistical analysis demonstrated that frequency of methylated and unmethylated HIC1 was significant (p <0.05). Further clinical analysis demonstrated significant association of only HIC1 methylation with: age of patients, stage of disease and expression of HIC1 IHC data (p = <0.0001, <0.0173 and < 0.0448; respectively). HIC1 has been shown to be hypermethylated in different cancers and confers bad prognosis. HIC1 is a tumor suppressor gene which encodes a transcriptional repressor with five Kruppel-like Cys2-His2 zinc fingers in the C terminus and a protein-protein interaction domain called the BTB/POZ domain at the N terminus.
Analysis of BCPAP-1 and TPC1 (papillary thyroid cell lines) revealed that they are completely methylated for HIC1 gene. Treatment of methylated thyroid cell line with the methyltransferase inhibitor, 5-aza-2’deoxy-cytidine, resulted in partial demethylation and re-expression of HIC1 gene, suggesting the role of methylation in silencing of the gene. We further evaluated the role of HIC1 gene after demethylation for apoptosis. After demethylation of HIC1 gene with 5-aza-2’deoxy-cytidine we treated our PTC cell lines with increasing doses of TRAIL and evaluated its response by Annexin/PI dual staining. We found that after demethylation of HIC1 there was increase in percentage apoptosis following increasing doses of TRAIL suggesting that HIC1 gene plays a major role in inducing apoptosis in PTC.
In conclusion, HIC1 methylation may be a promising molecular marker to predict patient outcome in PTC, and may be used as therapeutic demethylating target.
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 2017. doi:10.1158/1538-7445.AM2011-2017