HDAC1 Inactivation Induces Mitotic Defect and Caspase-Independent Autophagic Cell Death in Liver Cancer

Histone deacetylases (HDACs) are known to play a central role in the regulation of several cellular properties interlinked with the development and progression of cancer. Recently, HDAC1 has been reported to be overexpressed in hepatocellular carcinoma (HCC), but its biological roles in hepatocarcinogenesis remain to be elucidated. In this study, we demonstrated overexpression of HDAC1 in a subset of human HCCs and liver cancer cell lines. HDAC1 inactivation resulted in regression of tumor cell growth and activation of caspase-independent autophagic cell death, via LC3B-II activation pathway in Hep3B cells. In cell cycle regulation, HDAC1 inactivation selectively induced both p21WAF1/Cip1 and p27Kip1 expressions, and simultaneously suppressed the expression of cyclin D1 and CDK2. Consequently, HDAC1 inactivation led to the hypophosphorylation of pRb in G1/S transition, and thereby inactivated E2F/DP1 transcription activity. In addition, we demonstrated that HDAC1 suppresses p21WAF1/Cip1 transcriptional activity through Sp1-binding sites in the p21WAF1/Cip1 promoter. Furthermore, sustained suppression of HDAC1 attenuated in vitro colony formation and in vivo tumor growth in a mouse xenograft model. Taken together, we suggest the aberrant regulation of HDAC1 in HCC and its epigenetic regulation of gene transcription of autophagy and cell cycle components. Overexpression of HDAC1 may play a pivotal role through the systemic regulation of mitotic effectors in the development of HCC, providing a particularly relevant potential target in cancer therapy.

组蛋白去乙酰化酶（Histone deacetylases, HDACs）已知在多种与癌症发生发展密切相关的细胞特性调控中发挥核心作用。近期有研究显示，组蛋白去乙酰化酶1（HDAC1）在肝细胞癌（hepatocellular carcinoma, HCC）中存在过表达现象，但其在肝癌发生过程中的生物学功能仍有待阐明。本研究证实，在部分人类肝细胞癌组织及肝癌细胞系中，HDAC1存在过表达。在Hep3B细胞中，HDAC1失活可通过激活LC3B-II通路，诱导肿瘤细胞生长阻滞以及不依赖半胱天冬酶的自噬性细胞死亡。在细胞周期调控层面，HDAC1失活可选择性上调p21WAF1/Cip1与p27Kip1的表达，同时抑制细胞周期蛋白D1（cyclin D1）与细胞周期蛋白依赖性激酶2（CDK2）的表达。由此，HDAC1失活可导致G1/S转换过程中视网膜母细胞瘤蛋白（pRb）的低磷酸化，进而灭活E2F/DP1的转录活性。此外，本研究证实HDAC1可通过p21WAF1/Cip1启动子区域的Sp1结合位点，抑制p21WAF1/Cip1的转录活性。进一步实验显示，持续抑制HDAC1可削弱体外细胞集落形成能力，并在小鼠异种移植模型中抑制体内肿瘤生长。综上，本研究表明HDAC1在肝细胞癌中存在异常调控，并可通过表观遗传机制调控自噬及细胞周期相关基因的转录。HDAC1过表达可能通过系统性调控有丝分裂效应分子，在肝细胞癌的发生发展中发挥关键作用，为癌症治疗提供了极具潜力的靶点。