Interactions of Histone Deacetylase 6 with DNA Damage Repair Factors Strengthen its Utility as a Combination Drug Target in High-Grade Serous Ovarian Cancer

High-grade serous ovarian cancer (HGSOC) is the deadliest gynecologic malignancy in women. The low survival rate is largely due to drug resistance. Approximately 80% of patients who initially respond to treatment relapse and become drug-resistant. The lack of effective second-line therapeutics remains a substantial challenge for BRCA-1/2 wild-type HGSOC patients. Histone Deacetylases (HDACs) are promising targets in HGSOC treatment; however, the mechanism and efficacy of HDAC inhibitors are understudied in HGSOC. In order to consider HDACs as a treatment target, an improved understanding of their function within HGSOC is required. This includes elucidating HDAC6-specific protein–protein interactions. In this study, we carried out substrate trapping followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) to elucidate HDAC6 catalytic domain (CD)-specific interactors in the context of BRCA-1/2 wild-type HGSOC. Overall, this study identified new HDAC6 substrates that may be unique to HGSOC. The HDAC6-CD1 mutant condition contained the largest number of significant proteins compared to the CD2 mutant and the CD1/2 mutant conditions, suggesting the HDAC6-CD1 domain has catalytic activity that is independent of CD2. Among the identified substrates were proteins involved in DNA damage repair including PARP proteins. These findings further justify the use of HDAC inhibitors as a combination treatment with platinum chemotherapy agents and PARP inhibitors in HGSOC.高级别浆液性卵巢癌（High-grade serous ovarian cancer, HGSOC）是女性群体中致死率最高的妇科恶性肿瘤。其低生存率在很大程度上源于肿瘤耐药性：约80%初始对治疗产生应答的患者会出现复发，并进展为耐药性肿瘤。对于BRCA-1/2野生型高级别浆液性卵巢癌患者而言，缺乏有效的二线治疗方案仍是一项重大挑战。组蛋白去乙酰化酶（Histone Deacetylases, HDACs）是高级别浆液性卵巢癌治疗中颇具前景的靶点，但组蛋白去乙酰化酶抑制剂在该疾病中的作用机制与疗效仍有待深入探究。若要将组蛋白去乙酰化酶确立为治疗靶点，需进一步明晰其在高级别浆液性卵巢癌中的生物学功能，其中包括阐明HDAC6特异性的蛋白质-蛋白质相互作用。在本研究中，我们采用底物捕获技术结合液相色谱-串联质谱（liquid chromatography-tandem mass spectrometry, LC-MS/MS），在BRCA-1/2野生型高级别浆液性卵巢癌的背景下，解析了HDAC6催化结构域（catalytic domain, CD）特异性的相互作用蛋白。总体而言，本研究鉴定出了可能仅在高级别浆液性卵巢癌中特异存在的新型HDAC6底物。与CD2突变体组及CD1/2双突变体组相比，HDAC6-CD1突变体组中显著差异蛋白的数量最多，这表明HDAC6的CD1结构域拥有独立于CD2结构域的催化活性。在本次鉴定得到的底物蛋白中，包含了参与DNA损伤修复的各类蛋白质，其中就包括PARP家族蛋白。上述研究结果进一步证实了将组蛋白去乙酰化酶抑制剂与铂类化疗药物及PARP抑制剂联合应用于高级别浆液性卵巢癌治疗的合理性。