Background

Chromosomal instability plays an important part in cancer, but its genetic basis in liver tumorigenesis remains largely unclear. We aimed to characterize the mechanistic significance and clinical implication of mitotic regulator microtubule-associated protein 9 (MAP9) in hepatocellular carcinoma (HCC).

Methods

The biological functions of MAP9 were determined by in vitro tumorigenicity assays. Systematic MAP9 knockout mouse (MAP9^∆/∆) and hepatocyte-specific MAP9 knockout mouse (MAP9^∆/∆hep) were generated to confirm the role of MAP9 in HCC. The clinical impact of MAP9 was assessed in primary HCC tissue samples.

Findings

We found that MAP9 was frequently silenced in HCC tissue samples. The transcriptional silence of MAP9 in liver cancer cell lines and tissue samples was mediated by its promoter hypermethylation. MAP9 promoter hypermethylation or downregulation was associated with poor survival and recurrence in patients with HCC. Mechanistically, ectopic expression of MAP9 in LO2 and HepG2 cell lines impaired cell proliferation, colony formation, migration and invasion, and induced cell apoptosis and cycle arrest, whereas knockdown of MAP9 in Miha cell line showed the opposite effects. We found that MAP9^∆/∆ mice spontaneously developed a liver hyperplastic nodule and MAP9^∆/∆hep accelerated diethylnitrosamine-induced HCC formation. The tumour suppressive effect of MAP9 in HCC was mediated by downregulating excision repair cross-complementation group 3 (ERCC3), a nucleotide excision repair gene. Restoration of ERCC3 expression possessed an oncogenic potency and abrogated the tumour suppressive effects of MAP9.

Interpretation

MAP9 is a novel tumour suppressor in HCC by inhibiting ERCC3 expression, and serves as a prognostic factor in HCC patients.

中文翻译：

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微管相关蛋白9通过抑制ERCC3抑制肝癌的发生

背景

染色体不稳定在癌症中起着重要的作用，但是其在肝肿瘤发生中的遗传基础仍然不清楚。我们旨在表征肝细胞癌（HCC）中有丝分裂调节剂微管相关蛋白9（MAP9）的力学意义和临床意义。

方法

通过体外致瘤性测定来确定MAP9的生物学功能。产生了系统性的MAP9基因敲除小鼠（MAP9 ^{∆ / ∆}）和肝细胞特异性MAP9基因敲除小鼠（MAP9 ^{∆ / ∆hep}），以确认MAP9在肝癌中的作用。在原发性肝癌组织样品中评估了MAP9的临床影响。

发现

我们发现MAP9在HCC组织样本中经常被沉默。MAP9在肝癌细胞系和组织样品中的转录沉默是由其启动子高甲基化介导的。MAP9启动子过度甲基化或下调与肝癌患者的不良生存和复发相关。从机制上讲，MAP9在LO2和HepG2细胞系中的异位表达会损害细胞增殖，集落形成，迁移和侵袭，并诱导细胞凋亡和周期停滞，而在Miha细胞系中敲除MAP9则显示相反的作用。我们发现MAP9 ^{∆ / ∆}小鼠自发形成了肝脏增生性结节和MAP9 ^{∆ / ∆hep}加速了二乙基亚硝胺诱导的肝癌的形成。MAP9在肝癌中的抑癌作用是通过下调核苷酸切除修复基因3号切除修复交叉互补组（ERCC3）介导的。ERCC3表达的恢复具有致癌作用，并废除了MAP9的抑癌作用。

解释

MAP9是通过抑制ERCC3表达而在肝癌中的新型肿瘤抑制因子，是肝癌患者的预后因素。