核受体PXR信号通路在HBV感染和黄曲霉毒素暴露协同致原发性肝癌发生中的机制研究

Hepatitis B virus (HBV) infections and xenobiotics exposure are considered to be two major etiological factors for hepatocellular carcinoma (HCC) in China. Previous data has suggested a strong statistical interaction between HBV infection and Aflatoxin B1 (AFB1) exposure in etiology of HCC by epidemiological studies. However, molecular mechanism of the synergistic interaction in HCC was still poorly understood. We found that the ectopic models of Pregnane X receptor (PXR) signaling are associates with pathological progression in HBV infection associated liver diseases, and the expression level of PXR is high might be an early event in hepatocarcinogenesis. We further confirmed that HBx is a novel co-factor of PXR. In addition, HBx can significantly enhance the PXR transcriptional activity in the ligand and dose dependent manner, and the recruitment of HBx to the cytochrome P450-3A4 (CYP3A4) chromatin by PXR is in promoter dependent fashion. Notably, HBx-PXR signaling regulates the expression of key enzymes responsible for AFB1 metabolism of detoxification and carcinogenic activation, in PXR dependent manner. Especially in the presence of PXR agonist, HBx can significantly enhance the cytotoxicity of AFB1.So, the goal of this project is to investigate the link among sPXR (small PXR, a new truncated PXR isofrom)-(HBx-PXR signaling)-(AFB1 metabolizing enzymes)-(AFB1-DNA conjunction) or TP53 mutation-hepatocellular carcinogenesis in HBV infection associated hepatocarcinogenesis and to discover the mechanisms of synergistic effect of chemical and infectious carcinogens.

HBV病毒感染和化学致癌物黄曲霉毒素AFB1暴露是我国原发性肝细胞癌(Hepatocellular Carcinoma, HCC)发生的两大主要危险因素，二者协同致HCC发生机制不清。我们前期发现，核受体PXR通路异常与HBV感染相关HCC发生有关；HBx是PXR的一个新Co-factor；HBx增加AFB1肝毒性呈PXR依赖模式；HBx以配体依赖和剂量依赖方式调控PXR转录活性及AFB1肝内代谢关键酶谱（AFB1代谢为AFBO及AFBO分解的关键酶）的表达；HBx knock in小鼠瞬时毒性和AFB1慢性诱瘤预实验证实AFB1肝内代谢与PXR通路激活相关。综上，本课题拟以sPXR-(HBx-PXR signaling)-AFB1代谢酶谱-（AFB1-DNA加合物）/TP53突变-HCC发生为主线，深入研究HCC中AFB1与HBV暴露的关系，以期揭示二者协同致HCC发生的分子机制。

原发性肝细胞癌HCC是我国及世界范围内常见的恶性肿瘤。HBV感染和黄曲霉毒素AFB1摄入是HCC发生的两大主要危险因素，且两者间具有协同作用。现有理论多认为二者共暴露可能与增加AFB1诱导的遗传物质突变及DNA修复酶基因抑制有关。然而，HBV如何协同AFB1导致TP53突变的机制并不清楚，故我们假设“HCC是HBV感染协同AFB1暴露致肝癌是HBx-PXR Signaling相互作用干扰AFB1在肝内的代谢而导致AFB1肝毒性及遗传毒性增加的结果” 。.核受体PXR，是机体清除外源异物、毒物，及大多数临床用药体内代谢的核心调节因子。近年来研究发现PXR与结肠癌、乳腺癌、食管癌等多种肿瘤密切相关。我们在HBV感染相关的新鲜的临床组织标本中PXR 及PXRsignaling分析发现，PXR及CYP3A4在癌组织中多显著低表达。随后，在104例HBV感染相关的肝脏疾病临床组织芯片中做了验证。结果提示，PXR或PXR signaling异常与HBV感染相关HCC相关。鉴于HBx是PXR的一个辅因子，且考虑到AFB1的关系，我们先后通过过表达或敲降PXR的手段，证实HBx增加AFB1肝毒性是PXR通路依赖的；p21-HBx敲入鼠的AFB1瞬时毒性及14个月的慢性长期诱瘤实验证实HBx-PXR-CYP3A4/GSTM1-KRAS-IL11: IL11RA信号通路轴与HBV感染及AFB1共暴露诱导HCC相关。并提出，HBx调控PXR信号通路影响AFB1在肝内的代谢可能是HCC发生病因网络中外源性致癌因素中生物因素和化学因素协同致癌的关键环节；针对性“HBx-PXR-CYP3A4/GSTM1-KRAS-IL11:IL11RA信号通路轴”深入探讨HCC病因链，发展有效的预防措施和治疗手段，具有重要的科学意义和社会应用价值。