Abstract 750: Negative regulation of bcl-2 transcription by DNA damage-binding protein complex in human ovarian cancer cells.

Abstract

Abstract Elevated expression of the anti-apoptotic factor Bcl-2 is believed to be one of the contributing factors to an increased relapse rate associated with multiple cisplatin-resistant cancers. DNA damage-binding protein 2 (DDB2) has recently been revealed to play an important role in sensitizing human ovarian cancer cells to cisplatin-induced apoptosis through the down-regulation of Bcl-2, but the underlying molecular mechanism remains poorly defined. Here, we report that DDB2 functions as a transcriptional repressor for Bcl-2. DDB2 binds to a specific response element at the 5’-end of bcl-2 P1 promoter, concomitant with marked losses of histone H3 acetylation along the bcl-2 promoter and enhancer regions. Quantitative chromatin immunoprecipitation analysis revealed that HDAC1 was locally enriched in the bcl-2 P1 core promoter following DDB2 over-expression. Lysine 244 in DDB2 is essential for the transcriptional regulation of bcl-2, evidenced by the fact that the K244E mutant failed to inhibit bcl-2 promoter activity. Interestingly, the simultaneous DDB1 knock-down and DDB2 over-expression are required to potentiate bcl-2 promoter activity in the human ovarian cancer cell line CP70, while the knockdown of DDB1 alone failed to produce any significant effect. Furthermore, quantitative analysis of DDB2 and Bcl-2 expression in ovarian cancers provides clinical evidence that DDB2 and Bcl-2 are inversely correlated. Collectively, our data supports a model in which DDB2 and DDB1 function cooperatively in repressing bcl-2 transcription by recruiting HDAC1 to deacetylate histone H3 across bcl-2 regulatory regions, with DDB2 being responsible for binding to a specific cis-acting element in the bcl-2 P1 promoter. These findings have immediate implications for clinical trial designs of DDB2-based therapies for diverse cisplatin-resistant malignancies.(Supported by NIH grant CA151248 to QEW, and CA93413 to AAW) Citation Format: Ran Zhao, Chunhua Han, Eric Eisenhauer, John Kroger, Li Gong, Qianzheng Zhu, Weiqiang Zhao, Jianhua Yu, Selvendiran Karuppaiyah, Xingluo Liu, Altaf Ahmad Wani, Qi-En Wang. Negative regulation of bcl-2 transcription by DNA damage-binding protein complex in human ovarian cancer cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 750. doi:10.1158/1538-7445.AM2013-750