Department of Biomedical Sciences, Unit of Oncology and Molecular Pathology, University of Cagliari, Cagliari, Italy.
Department of Oncology, University of Torino School of Medicine, Candiolo Cancer Institute - FPO, IRCCS, 10060 Candiolo (Torino), Italy.
J Hepatol. 2014 Nov;61(5):1088-96. doi: 10.1016/j.jhep.2014.06.033. Epub 2014 Jul 7.
BACKGROUND & AIMS: Although the growth suppressing Hippo pathway has been implicated in hepatocellular carcinoma (HCC) pathogenesis, it is unknown at which stage of hepatocarcinogenesis its dysregulation occurs. We investigated in rat and human preneoplastic lesions whether overexpression of the transcriptional co-activator Yes-associated protein (YAP) is an early event.
The experimental model used is the resistant-hepatocyte (R-H) rat model. Gene expression was determined by qRT-PCR or immunohistochemistry. Forward genetic experiments were performed in human HCC cells and in murine oval cells.
All foci of preneoplastic hepatocytes, generated in rats 4weeks after diethylnitrosamine (DENA) treatment, displayed YAP accumulation. This was associated with down-regulation of the β-TRCP ligase, known to mediate YAP degradation, and of microRNA-375, targeting YAP. YAP accumulation was paralleled by the up-regulation of its target genes. Increased YAP expression was also observed in human early dysplastic nodules and adenomas. Animal treatment with verteporfin (VP), which disrupts the formation of the YAP-TEAD complex, significantly reduced preneoplastic foci and oval cell proliferation. In vitro experiments confirmed that VP-mediated YAP inhibition impaired cell growth in HCC and oval cells; notably, oval cell transduction with wild type or active YAP conferred tumorigenic properties in vitro and in vivo.
These results suggest that (i) YAP overexpression is an early event in rat and human liver tumourigenesis; (ii) it is critical for the clonal expansion of carcinogen-initiated hepatocytes and oval cells, and (iii) VP-induced disruption of the YAP-TEAD interaction may provide an important approach for the treatment of YAP-overexpressing cancers.
尽管抑制 Hippo 通路的生长已被牵涉到肝细胞癌（HCC）的发病机制中，但尚不清楚其失调发生在肝癌发生的哪个阶段。我们在大鼠和人肝癌前病变中研究了转录共激活因子 Yes 相关蛋白（YAP）的过表达是否是早期事件。
使用的实验模型是耐肝细胞（R-H）大鼠模型。通过 qRT-PCR 或免疫组织化学测定基因表达。在人 HCC 细胞和鼠卵圆细胞中进行正向遗传实验。
在用二乙基亚硝胺（DENA）处理大鼠 4 周后产生的所有肝癌前肝细胞灶中，均观察到 YAP 积累。这与已知介导 YAP 降解的 β-TRCP 连接酶和靶向 YAP 的 microRNA-375 的下调有关。YAP 积累伴随着其靶基因的上调。在人类早期发育不良结节和腺瘤中也观察到 YAP 表达增加。用破坏 YAP-TEAD 复合物形成的维替泊芬（VP）处理动物，可显著减少肝癌前灶和卵圆细胞增殖。体外实验证实，VP 介导的 YAP 抑制可损害 HCC 和卵圆细胞的细胞生长；值得注意的是，野生型或活性 YAP 转导的卵圆细胞在体外和体内赋予了致瘤特性。
这些结果表明：（i）YAP 过表达是大鼠和人肝肿瘤发生的早期事件；（ii）它对于致癌物引发的肝细胞和卵圆细胞的克隆扩增至关重要；（iii）VP 诱导的 YAP-TEAD 相互作用的破坏可能为治疗 YAP 过表达的癌症提供重要方法。
