Abstract 2090: TP73 expression may be influenced by DNA methylation in human tumorigenesis

Abstract

Abstract Epigenetic events that cause alterations in gene expression are common in human cancers. The connection between TP73 expression and its epigenetic functionality in tumorigenesis has scarcely been explored. As a transcription factor, TP73 (aka, p73) like its cousin, p53, is activated in response to DNA damage and regulates the expression of downstream genes involved in cell cycle arrest and apoptosis. However, there are other compounding functions of this gene that reflect its non-tumor-related characteristics, thus making it very difficult to assess its specific role in tumorigenesis. Our previous work showed that DNA methylation activates TP73 expression in hepatocellular carcinoma (HCC) and gastrointestinal cancer. In this study, we determined TP73 expression in normal human mammary epithelial cells (HMECs), human non-cancerous Li-Fraumeni Syndrome (LFS) skin fibroblast cells, human breast cancer cell lines (MCF7, MDA-MB-231 & MDA-MB-468), prostate cancer cell lines (LNCaP & MDA-PCa2b), lung cancer cell lines (A549 & NCI-H596), neuroblastoma cell lines (IMR32 & SK-N-SH) and normal human skin fibroblast cell line (HS27). The results show that TP73 was expressed solely in cancer cells. Subsequent immunohistochemical analyses of TP73 expression in cancerous and adjacent non-cancerous liver tissues of HCC patients clearly showed that TP73 expression was exclusively evident in cancerous tissues but not in the adjacent normal liver tissues. Mechanistically, methylation-specific PCR and bisulfite sequencing studies revealed that TP73 promoter is activated only in cancer cells and this activation occurs via DNA methylation. Moreover, ChIP assays demonstrated that a CTCF (a chromosomal networking protein CCCTC binding factor) and tumor protein p53 (TP53) bind to TP73 promoter and regulate TP73 expression. Our observations demonstrate that a positive correlation in tumorigenesis exists between TP73 expression and DNA methylation in promoter regions of TP73. These findings suggest that TP73's role in carcinogenesis may prove to be pivotal for the development of future diagnostic and therapeutic applications. Citation Format: Zhixing Yao, David R. Yao, William Yu, Ahmed Malki, Zaki A. Sherif. TP73 expression may be influenced by DNA methylation in human tumorigenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2090.