Class I HDACs介导的DNA损伤修复和转录重编程在肝癌发生中的作用研究

The development of cancers is commonly associated with DNA damage caused by various genotoxic stress, particularly with insufficient DNA damage repair mechanism. Class I histone deacetylases (HDACs) are essential in DNA damage control and are often aberrantly expressed in diverse malignances including hepatocellular carcinoma (HCC). The activation of proto-oncogenes, often accompanied by the inactivation of tumor suppressor genes, represents a typical example of transcriptional reprogramming and serves as a distinctive character of malignancies. However, the intrinsic link between the initial factors of transcriptional reprogramming and DNA damage is still unclear. We have observed that loss of HDAC3 in mouse liver leads to severe DNA injury and the early-onset spontaneous HCC. HDAC3 selectively targets histone H3K9 and HDAC3 ablation leads to a defect in the H3K9ac (acetylated H3K9) to H3K9me3 (trimethylated H3K9) transition, which ultimately disturbs DNA repair. In addition, severing as an important epigenetic factor, the downregulated HDAC3 promotes the malignant transform of hepatocytes through the persistent acetylation of H3K9 which enhances the transcription of a great number of tumor related genes. It appears that the aberrant expression of HDACs are critical in the malignant transformation than DNA damage itself. We also found that among the class I HDAC members, HDAC1 and HDAC2 are increased variously whereas HDAC8 is overwhelmingly decreased in human HCC tissues; HDAC3 can either be increased or decreased in HCC tissues. All these members exert overlapping but distinct functions in regulating diverse pathophysiological processes. Moreover, these members can regulate the expression of each other, making their role in DNA damage repair and transcriptional reprogramming more complicated which requires further investigation. In this study, we aim to explore the significant role of HDACs in the transcriptional reprogramming and malignant transformation of hepatocytes triggered by DNA damage. Our work will be helpful to discover the pathophysiology of the carcinogenesis of HCC and develop novel strategies for HCC prevention and treatment.

肿瘤常肇始于DNA损伤及修复机制失效。组蛋白去乙酰化酶家族I（class I HDACs）在DNA修复中至关重要，也常在肝细胞肝癌（HCC）等肿瘤中异常表达。细胞恶性转化涉及大量基因的活化或失活，即所谓“转录重编程”，但其始动因素及与DNA损伤的关系仍不清楚。我们此前发现HDAC3选择性作用于H3K9位点，其缺失导致H3K9ac/H3K9me3转换失败，阻碍DNA修复；同时作为表观遗传学调控蛋白，下调的HDAC3依靠过表达H3K9ac参与重编程促进恶性转化。可见HDACs等修复机制异常导致的重编程可能比DNA损伤本身更为重要。HDAC成员在HCC中表达趋势并不一致，有一定功能互补，还可相互调控彼此表达，在DNA修复和重编程中的作用极为复杂。本研究将探讨DNA损伤与HDACs异常表达的相互关系及其在肝细胞重编程和恶性转化中的作用，从新的角度阐明HCC发生机制，为HCC防治提供理论支持。

肿瘤常肇始于DNA损伤及修复机制失效。我们此前发现HDAC3选择性作用于H3K9位点，其缺失导致H3K9ac/H3K9me3转换失败，阻碍DNA修复；同时作为表观遗传学调控蛋白，下调的HDAC3依靠过表达H3K9ac参与重编程促进恶性转化。我们的发现提示HDACs等修复机制异常导致的重编程可能比DNA损伤本身更为重要。本研究我们探讨了DNA损伤与HDACs异常表达的相互关系及其在肝细胞重编程和恶性转化中的作用。我们发现在DNA辐照或化学药物诱导损伤后，HDAC3维持在相对稳定水平，但另一个重要的表观遗传调控机制（SWI/SNF复合体）的关键活性蛋白Brg1的表达水平迅速升高，后者在DNA损伤修复中发挥着更加重要且直接的关系。我们在HDAC3肝脏特异基因敲除小鼠中，发现HDAC3的缺失，并非一来就导致转录重编程的发生。在DNA损伤积累到一定程度之前，肝细胞仍能维持相对正常的形态、功能以及增殖分化，提示HDAC3缺失导致的自发HCC，可能更多依赖于DNA稳态的丢失。而DNA损伤的出现除了前面我们发现的H3K9ac异常，还引起Brg1的高表达，后者同样作为转录调控蛋白，促进转录重编程和细胞恶性转化。我们还发现HDAC3的缺失通过调控FOXa1/2，在雌性小鼠中更早诱发HCC的发生。HDAC3缺失时，大量肝脏前体细胞（HPC）扩增，其Numb的缺失表达，促进小鼠自发ICC。.在本项目研究基础上，我们提出新的设想，获批新的国家自然科学基金面上项目一项（HDAC3-BRG1介导DNA损伤快速低精度修复促进肝癌异质化，82072689，2021.01-2024.12），将帮助我们进一步探索HDAC3及Brg1协同在肝癌发生发展中的关键作用。同时，由于二者协调促进DNA损伤后的快速修复，我们已针对Brg1关键活性区域，筛选出小分子抑制剂，初步实验已证实该小分子抑制剂特异性阻断Brg1溴区结构域同乙酰化组蛋白的结合，抑制DDR复合体的组装，能非常显著增加放化疗的敏感性。本项目已在国际高水平期刊发表论文3篇，接收发表1篇，另有2篇已修回。项目完成全部计划任务，达到预期目标。