Abstract 575: NKX6.1 functions as a tumor suppressor in hepatocellular carcinoma

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA In addition to genetic alterations, epigenetic alterations have been increasingly recognized as a key event for carcinogenesis. Methylation of CpG islands in promoter regions is almost associated with transcriptional silencing and is implicated in tumor suppressor gene (TSG) inactivation in cancer cells. Our previous data showed that NKX6.1 promoter is hypermethylated and downregulated in hepatocellular carcinoma (HCC) cell lines. The goal of this study was to elucidate whether NKX6.1 is a tumor suppressor gene in HCC. All HCC samples with NKX6.1 promoter hypermethylation showed downregulation of NKX6.1 expression using quantitative methylation-specific PCR and quantitative RT-PCR analysis. In addition, the expression of NKX6.1 in HCC cell lines can be restored by treatment with DNA methyltransferase (DNMT) inhibitor, 5-aza-2′-deoxycytidine. These findings indicate that NKX6.1 is frequently silenced in HCC via promoter methylation. We then cloned and determined the putative promoter of NKX6.1 by luciferase reporter assay. The Sp1 site in the NKX6.1 promoter region is important for the promoter activity. When we treated cells with Trichostatin A (TSA), a histone deacetylase inhibitor (HDACi), the NKX6.1 promoter activity increased. These data suggest that promoter methylation and histone modification may take part in the epigenetic silencing of NKX6.1 in HCC. Overexpression of NKX6.1 significantly suppressed transformation in HepG2 and SK-Hep1 cells; however, there is no significant effect on cell viability. Moreover we use a xenograft model to demonstrate the suppressor effects of NKX6.1 on tumor formation in vivo. Taken together, these data suggest that NKX6.1 might be a candidate tumor suppressor in HCC in vitro and in vivo. Citation Format: Hsin-Jung Li, Yu-Lueng Shih, Ming-De Yan, Pei-Ning Yu, Ya-Wen Lin. NKX6.1 functions as a tumor suppressor in hepatocellular carcinoma. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 575. doi:10.1158/1538-7445.AM2014-575