Abstract 1132: Regulation of CT120 gene as a new target of c-myc in head and neck squamous cell carcinoma (HNSCC)

Abstract

HNSCC is the sixth most common form of cancer and represents the third common cause of cancer-related deaths worldwide. Therefore, there is a need to understand the molecular mechanisms involved in the pathogenesis of HNSCC. The c-myc protein belongs to the myc family of transcription factors and plays a fundamental role in cell cycle progression, apoptosis and cellular transformation. In the human genome, the MYC gene is located on chromosome 8 and its protein product regulates expression of 15% of all genes through binding to the Enhancer box (E-box) sequences. An E-box is a DNA sequence found in the promoter regions of eukaryotic genes that acts as a protein binding site to regulate gene expression. The CANNTG consensus sequence of the E-box is known as the canonical E-boxes. There are several other non-canonical E-box motifs such as the GATGTG, CATGCG, CACGCG, CACGAG, CGCGAG and CAACGTG sequences. Amplification of the MYC gene is observed in many different types of cancers including HNSCC. CT120 is a novel gene which encodes a human trans-membrane plasma protein. It has been shown that up-regulation of CT120 is associated with lung and head and neck carcinogenesis. In this study we investigated the promoter region of the CT120 gene and identified 6 E-boxes. To test whether c-myc binds to these E-boxes we performed chromatin immunoprecipitation (ChIP) assays. We demonstrated that c-myc binds strongly to the E-boxes 2, 3 and 4. It is well known that the expression rates of the genes are under the control of epigenetic modifications. Methylation of the CpG islands which are found in the promoter regions is one of the most studied epigenetic modifications. We identified two putative CpG islands in the promoter of the CT120 gene. To investigate the possible epigenetic regulation of CT120 and the effect of the promoter methylation to the binding of c-myc, we also investigated the methylation levels of the two islands in the CT120 promoter by MS-PCR. We observed a slight decrease (3.1%) in the methylation level of the first CpG-rich region. In 56% (28/50) of the tumor tissues methylation was decreased compared to the non-cancerous tissues. However, there was no statistically significant correlation between the promoter methylation and CT120 mRNA level. Depending on these data we investigated the expression levels of the c-myc and CT120 in the 50 HNSCC and normal tissue samples by qRT-PCR and observed a direct correlation between the overexpression of the c-myc and CT120 genes. Overexpression of CT120 and c-myc were observed in 29 (58%) and 34 (68%) of the tumors, respectively, compared to non-cancerous tissues. A total of 24 (48%) patients out of 50 showed a concurrent pattern of either up- or down regulation. Our results indicate that the CT120 gene is a target of c-myc and that both proteins may participate in the progression of HNSCC. Citation Format: Onur Baykara, Elif Baltaci, Betul Seyhan, Nejat Dalay, Nur Buyru. Regulation of CT120 gene as a new target of c-myc in head and neck squamous cell carcinoma (HNSCC). [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1132.