Abstract 3874: Loss of DDB2 enhances the tumorigenicity of ovarian cancer cells through expanding cancer stem-like cell population

Abstract

Abstract Ovarian cancer is an extremely aggressive disease associated with a high percentage of recurrence and chemotherapy resistance. DNA damage binding protein 2 (DDB2) is a 48-kDa protein originally identified as a component of the damage-specific DNA-binding heterodimeric complex DDB. Besides the known ability of DDB2 protein to bind ultraviolet (UV)-damaged DNA and serving as the initial damage recognition factor during nucleotide excision repair (NER), DDB2 was also reported to be involved in the promotion of apoptosis to reduce cisplatin resistance of ovarian cancer cells, control of cell migration, invasiveness and breast tumor progression, as well as suppression of metastasis of colon cancer through a transcriptional regulatory mechanism. Here we show that DDB2 is downregulated in human ovarian serous adenocarcinomas. DDB2 overexpression in human ovarian cancer cell line CP70 suppressed its capability to recapitulate tumors in athymic nude mice, as well as the growth of these cells cultured in semisolid media. Flow cytometry analyses indicate that DDB2 overexpression in CP70 cells reduced the abundance of ALDH+ cells, which are believed to be cancer stem-like cells (CSCs) in ovarian cancer. In contrast, downregulation of DDB2 in ovarian cancer cell line A2780 increased the percentage of ALDH+ cells. In addition, we analyzed the expression level of DDB2 in the putative CSCs isolated from various ovarian cancer cell lines, and demonstrated that DDB2 expression is downregulated in all tested CSCs in comparison with their parental bulk tumor cells. Overexpression of DDB2 in the ovarian CSCs reduced the expression of CSC marker Nanog, as well as inhibited the self-renewal of these CSCs. In addition, overexpression of DDB2 in CSCs isolated from ovarian cancer cell line SKOV-3 also decreased the tumorigenicity of these cells in NOD/SCID mice. Further analysis of publicly available gene expression array datasets revealed that low DDB2 expression correlates with poor outcomes among ovarian cancer patients, suggesting that loss of DDB2 may promote ovarian tumor relapse through expanding CSC population. Given that the DDB2 protein level is downregulated in ovarian tumor cells, targeting DDB2 expression could be a promising strategy to eradicate CSCs, and helps to halt ovarian cancer relapse. (Supported by NIH R01 grant CA151248 to QEW) Citation Format: Chunhua Han, Ran Zhao, Xingluo Liu, Amit Kumar Srivastava, Li Gong, Hsiaoyin Mao, Meihua Qu, Weiqiang Zhao, Jianhua Yu, Qi-En Wang. Loss of DDB2 enhances the tumorigenicity of ovarian cancer cells through expanding cancer stem-like cell population. [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 3874. doi:10.1158/1538-7445.AM2014-3874