BAP1/BARHR复合物在胰腺癌同源重组修复中的作用及机制研究

DNA breaks elicit homologous recombination (HR) repair pathways for repair of these lesions and maintain genomic stability, it is not surprising that germline mutations in many HR components, are associated with human cancers including pancreatic cancer. Since HR deficiencies have been frequently reported in pancreatic cancer, it is possible that other genes involved in HR repair pathway,, may be mutated or dysregulated in pancreatic cancer. The most exciting discovery in the field of HR repair is the establishment of synthetic lethality relationship between poly (ADP-ribose) polymerase (PARP) inhibition and HR deficiency. Our preliminary studies have revealed that a protein complex containing BAP1 interacts with BARHR (BAP1-associated protein required for homologus recombination) with central roles in HR repair. We will elucidate the mechanism of BAP1/BARHR complex in HR repair, and deficiency in this complex is involved in pancreatic cancer development or has implications in pancreatic cancer therapy. Using a series of complementary approaches including protein-protein interaction assay, HR repair assay, generating gene knockout mice model, etc., we will determine the functional significance of BAP1/BARHR complex in HR repair and pancreatic tumorigenesis. We will also examine the expression of BAP1/BARHR complex in pancreatic cancer and explore whether deficiency in BAP1/BARHR complex would lead to synthetic lethality impact in pancreatic cancer therapy using PARP inhibitors together with radiation and/or other chemotherapeutic agents. Our proposed project aims to answer several key questions, including whether there are yet-to-be-identified HR factors that are functionally inactivated in pancreatic cancers, whether deficiency in these new HR factors can be used to identify pancreatic cancer patients who would benefit from treatments including PARP inhibitors, and whether these new HR factors can be targeted directly for pancreatic cancer therapy. Our long-term goal is to discover biomarkers in pancreatic cancer with HR defects, and help to identify a larger proportion of pancreatic cancer patients, who may benefit from the treatment regimens designed for cancer patients with HR deficiencies.

DNA断裂能够诱导同源重组（HR）修复，从而保持基因组的完整性。HR修复缺陷在人类癌症（包括胰腺癌）患者中普遍存在，且HR缺陷患者应用多聚ADP-核糖聚合酶(PARP)抑制剂能够导致癌细胞的合成致死。我们前期发现，BARHR与BAP1形成复合物，并参与HR修复过程，在一些胰腺癌细胞中存在BARHR与BAP1表达下调。我们推测在胰腺癌中可能存在BAP1和BARHR突变从而导致蛋白功能缺失，引起HR修复缺陷，从而促进胰腺癌的发生发展。本研究通过一系列互补实验，包括蛋白与蛋白相互作用分析、HR修复分析、裸鼠移植瘤和基因敲除鼠等，明确BAP1/BARHR复合体在HR修复以及胰腺癌发生发展的具体分子作用，并评估BAP1和BARHR缺失联合PARP 抑制剂处理是否能够导致胰腺癌细胞的合成致死。本研究的完成，将有助于发现HR缺陷的胰腺癌患者的分子标志物，同时鉴定出受益于PARP抑制剂的胰腺癌亚群。

胰腺癌患者中存在同源重组（homologous recombination，HR）修复功能的缺陷，除BRCA1，BRCA2外，参与HR修复功能的其他基因可能在胰腺癌中存在突变或功能失调。最近的研究发现， BAP1基因突变患者患胰腺癌风险更高。本课题的研究表明 BAP1及BAP1相互作用蛋白（BAP1-associated protein required for homologous recombination，BARHR）参与了 HR修复功能。应用CRISPR/Cas9技术构建的BAP1和BARHR的基因敲除胰腺癌细胞株显示HR修复功能的缺陷。进一步研究发现BAP1和BARHR相互作用位点是其参与HR修复功能的重要基础。研究结果显示BAP1和BARHR在胰腺导管腺癌组织内呈现低表达，其表达水平和胰腺导管腺癌产生及发展可能具有一定相关性。意外的发现是去泛素化酶BAP1抑制BARHR的泛素化，为后期的机制研究提供新的思路。总之，我们的研究结果揭示了BAP和BARHR在胰腺癌HR修复缺陷中的分子机制，从而为胰腺癌的治疗手段提供了新的研究策略。