TLR-MyD88信号通路在慢性炎症诱导肝癌发生中的分子机制研究

MyD88 (Myeloid differentiation primary response gene 88) is the key factor of Toll-like receptor pathway, which play the core role in the carcinogenesis, progression and metastasis of hepatocarcinoma (HCC). However, the detail mechanism is unclear. Aim to explore the role of MyD88 pathway in inflammation-associated HCC, we conducted Mdr2-/- mice as a model of inflammation-induced HCC, and we found a significant tumor reduction when MyD88+/+ or MyD88-/- bone marrow was transferred into MyD88-/-Mdr2-/- recipients. Furthermore, we generated Albumin-Cre+MyD88flox/floxMdr2-/- mice that deficiency of MyD88 in hepatocytes (MyD88∆hepMdr2-/-), and liver-specific deletion of MyD88 resulted in marked delay in HCC development, which suggesting an essential role of hepatocyte-intrinsic MyD88 signaling in the development of HCC. MyD88 is the most important adaptor of TLR family, we found heparan sulfate, an endogenous TLR4 ligand was elevated during the course of cholestatic hepatitis and hepatocarcinogenesis in Mdr2-/- mice. Therefore, we hypothesize that HS released during the inflammation promotes HCC via the TLR4-MyD88 signaling pathway. To test this hypothesis, we generated TLR4-/-Mdr2-/- mice to investigate the underlying mechanisms by which hepatocyte-intrinsic TLR-MyD88 signaling promotes HCC formation. By providing molecular basis for inflammation-related HCC, these studies will substantially increase knowledge of critical factors governing pathways leading to inflammation-induced cancer.

MyD88是Toll样家族受体激活NF-kB信号通路的关键蛋白分子，在肝细胞肝癌（HCC）发生、发展中起了重要作用，但其作用机制尚不清楚。我们前期利用缺乏多药耐药基因2（Mdr2-/-）小鼠建立慢性炎症介导的HCC模型，进一步将Mdr2-/-小鼠肝细胞的MyD88基因条件性敲除后发现小鼠HCC发生率显著降低、存活率明显提高，提示MyD88对非骨髓衍生细胞促Mdr2-/-小鼠发生HCC至关重要。据此我们提出假设，肝细胞固有TLR4-MyD88信号可能通过PI3K-AKT-Epiregulin通路促进HCC发生。本项目中我们拟进行TLR4-/-Mdr2-/-、MyD88∆hepMdr2-/-等多种转基因动物HCC模型的遗传学表型分析及体外细胞功能研究，从动物、细胞及分子机制三个层次，深入研究肝细胞TLR-MyD88信号参与HCC癌变的机制，从而为HCC的防治提供新的理论依据。

肝细胞癌（简称肝癌）是世界范围内最常见恶性肿瘤之一，我国肝癌发病率及死亡率高居恶性肿瘤第5位和第2位，是威胁我国人民健康的重要因素之一。超过80%的肝癌患者在初次诊断时已处于中晚期，失去根治性治疗的机会。肝癌的诱发因素包括乙型病毒性肝炎（HBV）、丙型病毒性肝炎（HCV）、酒精性肝病、非酒精性脂肪肝以及黄曲霉素摄入等。新近的研究表明慢性炎症在肿瘤发生中起到重要作用，肝癌是炎症相关性肿瘤的代表，约90%的肝癌伴随有慢性感染相关的非可控炎症。但炎症反应及其引起的免疫应答反应在肝癌发生中的具体作用尚未完全阐明。我们前期利用缺乏多药耐药基因2（Mdr2-/-）小鼠建立慢性炎症介导的肝癌模型，进一步将Mdr2-/-小鼠肝细胞的MyD88基因条件性敲除后发现肝癌发生率显著降低，而小鼠存活率明显提高，提示MyD88对非骨髓衍生细胞促Mdr2-/-小鼠发生肝癌至关重要。本项目中我们拟从动物、细胞及分子机制三个层次，深入研究肝细胞TLR-MyD88信号参与肝癌癌变的机制，从而为肝癌的防治提供新的理论依据。本项目：①证实去泛素化酶USP13在肝癌中表达上调，其阳性表达与恶性临床病理特征及预后不良密切相关；②发现干扰USP13显著抑制肝癌细胞体外增殖、侵袭和上皮间质转化（EMT），并抑制小鼠体内肝癌生长和肺转移；③揭示了USP13通过去泛素化和稳定TLR4增强MyD88/NF-κB通路活化；④明确USP13是一个缺氧反应基因，其介导缺氧激活的TLR4/MyD88/NF-κB通路；⑤发现LINC01123在肝癌中表达升高，其高表达与恶性临床病理特征及预后不良显著相关；⑥发现LINC01123促进肝癌细胞增殖和侵袭，并增强小鼠体内肝癌生长；⑦证实LINC01123通过竞争性结合miR-34a-5p促进TUFT1表达。本项目结果为预测肝癌转移和术后复发的标志物和靶治疗药物的研发等具有挑战性的问题提供了新的思路和可能的解决方案。