The role of the deubiquitinase CYLD for liver injury and hepatocarcinogenesis

CYLD是一种去泛素化酶，可从靶蛋白中去除k63连接的泛素链，例如参与NF-kB， Wnt/ß-catenin和BCL-3信号通路。在不同类型的人类癌症中已经观察到CYLD表达的缺失。在人类肝细胞癌（HCC）中，CYLD表达水平降低，我们在小鼠CYLD敲除模型中证实了自发性慢性肝损伤和致癌物质诱导的HCC增加，缺乏全长CYLD，但表达自然发生的剪接变体（CYLDex7/8 xAlbCre）。该项目的目的是揭示由CYLD活性降低引起的肝损伤和肝癌发生的机制，并分析通过操纵CYLD使HCC对治疗诱导的细胞死亡敏感的方法。具体来说，我们将分析小鼠CYLD敲除模型中HCC的发展，这些模型在剪接变体的表达方面存在差异。这将有助于阐明是否缺乏全长CYLD或剪接变异体的表达是小鼠HCC发展的关键。在肝细胞中进行cyld介导的去泛素化的靶蛋白将被确定。由于我们在CYLDex7/8 xAlbCre小鼠中观察到NF-kB家族成员RelB和原癌基因BCL-3的活性增加，我们将分析CYLD和BCL-3或RelB在肝细胞特异性双敲除中的肝损伤和HCC发展。由于我们有证据表明CYLD对小鼠肝细胞的凋亡信号传导有重要调节作用，并可能因此影响肝癌的发生，因此我们将探索促进CYLD阴性肝细胞对死亡受体介导的凋亡的抗性增加的信号事件。我们还将进一步说明，CYLD表达降低如何促进人类HCC细胞对靶向药物（如索拉非尼和c-MET抑制剂）的耐药性。此外，我们计划确定在HCC细胞和人类HCC重要组织培养物中触发CYLD表达的方法，以进一步发展HCC治疗的翻译工作。我们相信CYLD的重建是治疗慢性肝病和HCC细胞对治疗诱导的细胞死亡的敏感化的一种有希望的方法。

CYLD is a deubiquitinating enzyme that removes K63-linked ubiquitin chains from target proteins, e.g. involved in NF-kB, Wnt/ß-catenin and BCL-3 signalling pathways. Loss of CYLD expression has been observed in different types of human cancer. Together with decreased levels of CYLD expression in human hepatocellular carcinoma (HCC), we have demonstrated spontaneous chronic liver injury and increased carcinogen-induced HCC in a murine CYLD knockout model, lacking full length CYLD, but expressing a naturally occurring splice variant (CYLDex7/8 xAlbCre). The aim of the project is to unravel the mechanisms of liver injury and hepatocarcinogenesis caused by reduced CYLD activity and to analyse approaches to sensitize HCC to therapy-induced cell death by manipulating CYLD. Specifically, we will analyse HCC development in murine CYLD knockout models which differ regarding expression of splice variants. This will help to clarify whether the lack of full length CYLD or the expression of splice variants is pivotal for HCC development in mice. Target proteins undergoing CYLD-mediated deubiquitination in hepatocytes, will be identified. Since we observed increased activity of the NF-kB family member RelB as well as the protooncogene BCL-3 in CYLDex7/8 xAlbCre mice, we will analyse liver injury and HCC development in hepatocyte-specific double knockouts of CYLD and BCL-3 or RelB. As we have evidence that CYLD critically regulates apoptosis signalling in murine hepatocytes and may thereby influence hepatocarcinogenesis, signalling events contributing to increased resistance of CYLD-negative hepatocytes towards death-receptor mediated apoptosis will be explored. We will also further specify, how decreased CYLD expression contributes to the resistance of human HCC cells towards targeted agents, such as sorafenib and c-MET inhibitors. In addition, we plan to identify ways to trigger CYLD expression in HCC cells and vital tissue cultures of human HCC to further develop translational efforts for HCC treatment. We believe that reconstitution of CYLD is a promising approach for the treatment of chronic liver diseases and the sensitization of HCC cells towards therapy-induced cell death.