Abstract 4784: Regulation of ovarian cancer stem cell population by DDB2

Abstract

Abstract Cancer stem cells (CSCs), representing the root of many solid tumors including ovarian cancer, have been implicated in disease recurrence, metastasis, and therapeutic resistance. Our previous study has demonstrated that DNA damage-binding protein 2 (DDB2) is able to reduce the abundance of CSCs in the bulk ovarian cancer cells, providing a novel mechanism to explain the DDB2-mediated suppression of tumorigenicity and metastasis, and also suggesting that low expression of DDB2 is required for the maintenance of CSCs. However, the underlying mechanisms still remain unclear. By using the Tet-On DDB2 modulation system, we have confirmed our previous finding that downregulation of DDB2 expands the CSC population in the 2008 ovarian cancer cell line. We also found that DDB2 is able to suppress non-CSC-to-CSC conversions in this cancer cell line. DDB2 has been recognized as a transcriptional regulator. Our microarray analysis has identified ALDH1A1 to be targeted and regulated by DDB2. The downregulation of ALDH1A1 expression by DDB2 at both mRNA and protein levels has been validated in various ovarian cancer cell lines. The mechanistic investigation demonstrated that DDB2 can bind to the promoter region of the ALDH1A1 gene, facilitating the enrichment of histone H3K27me3 by recruiting EZH2 to the promoter region, eventually inhibiting the promoter activity of the ALDH1A1 gene. In addition, we also found that DDB2 competes with transcription factor C/EBPβ for binding to the ALDH1A1 promoter, indirectly inhibiting the ALDH1A1 promoter activity. Finally, we knocked down the expression of DDB2 and ALDH1A1 individually or simultaneously in the 2008 ovarian cancer cell line, and analyzed their tumorigenicity. We found that downregulation of ALDH1A1 is able to block DDB2 silencing-induced expansion of the CSC population, indicating that ALDH1A1 plays a critical role in DDB2-mediated suppression of the CSC population in ovarian cancer cells. In summary, our data demonstrated that DDB2, functioning as a transcription repressor, is able to abrogate ovarian CSC properties by downregulating ALDH1A1 expression. This study provides a novel mechanism underlying the regulation of the CSC population, and would facilitate the development of efficient strategies for eliminating CSCs to prevent tumor relapse and metastasis in ovarian cancers. (Supported by NIH R01CA151248) Citation Format: Tiantian Cui, Amit Kumar Srivastava, Chunhua Han, Zhiqin Gao, Xiaoli Zhang, Altaf A. Wani, Qi-En Wang. Regulation of ovarian cancer stem cell population by DDB2 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4784. doi:10.1158/1538-7445.AM2017-4784