Zhao Ran, Han Chunhua, Eisenhauer Eric, Kroger John, Zhao Weiqiang, Yu Jianhua, Selvendiran Karuppaiyah, Liu Xingluo, Wani Altaf A, Wang Qi-En
Department of Radiology, The Ohio State University, Room 1014 BRT, 460 W. 12th Avenue, Columbus, OH 43210.
Mol Cancer Res. 2014 Mar;12(3):370-80. doi: 10.1158/1541-7786.MCR-13-0281. Epub 2013 Nov 18.
Elevated expression of the antiapoptotic 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 complex subunit 2 (DDB2) has recently been revealed to play an important role in sensitizing human ovarian cancer cells to cisplatin-induced apoptosis through the downregulation of Bcl-2, but the underlying molecular mechanism remains poorly defined. Here, it is report that DDB2 functions as a transcriptional repressor for Bcl-2 in combination with DDB1. Quantitative ChIP and EMSA analysis revealed that DDB2 binds to a specific cis-acting element at the 5'-end of Bcl-2 P1 promoter. Overexpression of DDB2 resulted in marked losses of histone H3K9,14 acetylation along the Bcl-2 promoter and enhancer regions, concomitant with a local enrichment of HDAC1 to the Bcl-2 P1 core promoter in ovarian cancer cells. Coimmunoprecipitation and in vitro binding analyses identified a physical interaction between DDB1 and HDAC1, whereas downregulation of HDAC1 significantly enhanced Bcl-2 promoter activity. Finally, in comparison with wild-type DDB2, mutated DDB2, which is unable to repress Bcl-2 transcription, mediates a compromised apoptosis upon cisplatin treatment. Taken together, these data support a model wherein DDB1 and DDB2 cooperate to repress Bcl-2 transcription. DDB2 recognizes and binds to the Bcl-2 P1 promoter, and HDAC1 is recruited through the DDB1 subunit associated with DDB2 to deacetylate histone H3K9,14 across Bcl-2 regulatory regions, resulting in suppressed Bcl-2 transcription.
Increasing the expression of DDB complex may provide a molecular strategy for cancer therapy.
抗凋亡因子Bcl-2的表达升高被认为是多种顺铂耐药癌症复发率增加的促成因素之一。DNA损伤结合蛋白复合体亚基2（DDB2）最近被发现通过下调Bcl-2在使人类卵巢癌细胞对顺铂诱导的凋亡敏感化过程中发挥重要作用，但其潜在分子机制仍不清楚。在此，报告DDB2与DDB1共同作为Bcl-2的转录抑制因子发挥作用。定量染色质免疫沉淀（ChIP）和电泳迁移率变动分析（EMSA）显示DDB2与Bcl-2 P1启动子5'端的一个特定顺式作用元件结合。DDB2的过表达导致Bcl-2启动子和增强子区域的组蛋白H3K9、14乙酰化显著丧失，同时卵巢癌细胞中HDAC1在Bcl-2 P1核心启动子局部富集。免疫共沉淀和体外结合分析确定了DDB1与HDAC1之间存在物理相互作用，而HDAC1的下调显著增强了Bcl-2启动子活性。最后，与野生型DDB2相比，无法抑制Bcl-2转录的突变型DDB2在顺铂处理后介导的凋亡受损。综上所述，这些数据支持一个模型，即DDB1和DDB2协同抑制Bcl-2转录。DDB2识别并结合Bcl-2 P1启动子，HDAC1通过与DDB2相关的DDB1亚基被招募，使Bcl-2调控区域的组蛋白H3K9、14去乙酰化，导致Bcl-2转录受抑制。
增加DDB复合体的表达可能为癌症治疗提供一种分子策略。
