Abstract 4321: Epigenetic regulation of TP73 expression in HCC and GI cancer

Abstract

Tumorigenesis results from an accumulation of mutational and epigenetic changes that alter normal cell growth and survival pathways. TP73 is the homologue of the master tumor suppressor TP53 involved in cellular responses to stress and development. The TP73 gene encodes two different protein isoforms, TAp73 and ΔNp73, and maps to a region on chromosome 1p36 that is frequently deleted in neuroblastoma and other tumors, and is thought to contain multiple tumor suppressor genes. However, the analysis of p73-knockout mice yielded conflicting results with respect to tumor suppression. World-wide efforts in sequencing the TP73 gene in patient tumor samples have not provided evidence for genetic alterations as a common cause of TP73 inactivation in human cancer. The role of TP73 in tumorigenesis has remained elusive to date. In this study, we isolated two stem cell lines from normal young and old human liver tissues to determine TP73 expression in normal human liver stem cell and hepatocellular cancer (HCC) cell lines (HepG2, SNU398, SNU449 & SNU475), gastrointestinal cancer (GI) cell lines (Caco2 & HCT116) and a normal skin fibroblast cell line (HS27). The results show that TP73 only expresses in cancer cell lines. Further immunohistochemistry studies on human normal liver tissues as well as adjacent normal and cancerous liver tissues from HCC patients confirm that TP73 only expresses in the cancerous tissues. Moreover, methylation-specific PCR and bisulfite sequencing studies revealed that TP73 promoter is activated only in cancer cell lines by DNA methylation. Furthermore, ChIP assay results demonstrated that CTCF (a chromosomal networking protein CCCTC binding factor) binds to TP73 promoter and regulates TP73 expression. Our observation may prove significant for the development of future therapeutic and diagnostic applications. Citation Format: Zhixing Yao, Cristina Di Poto, Habtom W. Ressom, Zaki A. Sherif. Epigenetic regulation of TP73 expression in HCC and GI cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4321.