Dixit Updesh, Pandey Ashutosh K, Liu Zhihe, Kumar Sushil, Neiditch Matthew B, Klein Kenneth M, Pandey Virendra N
Department of Microbiology, Biochemistry, and Molecular Genetics, Rutgers New Jersey Medical School, Rutgers, the State University of New Jersey, Newark, New Jersey, USA.
Department of Pathology and Laboratory Medicine, Rutgers New Jersey Medical School, Rutgers, the State University of New Jersey, Newark, New Jersey, USA.
J Virol. 2015 Aug;89(15):7905-21. doi: 10.1128/JVI.00729-15. Epub 2015 May 20.
Hepatitis C virus (HCV) is a leading cause of chronic hepatitis C (CHC), liver cirrhosis, and hepatocellular carcinoma (HCC). Immunohistochemistry of archived HCC tumors showed abundant FBP1 expression in HCC tumors with the CHC background. Oncomine data analysis of normal versus HCC tumors with the CHC background indicated a 4-fold increase in FBP1 expression with a concomitant 2.5-fold decrease in the expression of p53. We found that FBP1 promotes HCV replication by inhibiting p53 and regulating BCCIP and TCTP, which are positive and negative regulators of p53, respectively. The severe inhibition of HCV replication in FBP1-knockdown Huh7.5 cells was restored to a normal level by downregulation of either p53 or BCCIP. Although p53 in Huh7.5 cells is transcriptionally inactive as a result of Y220C mutation, we found that the activation and DNA binding ability of Y220C p53 were strongly suppressed by FBP1 but significantly activated upon knockdown of FBP1. Transient expression of FBP1 in FBP1 knockdown cells fully restored the control phenotype in which the DNA binding ability of p53 was strongly suppressed. Using electrophoretic mobility shift assay (EMSA) and isothermal titration calorimetry (ITC), we found no significant difference in in vitro target DNA binding affinity of recombinant wild-type p53 and its Y220C mutant p53. However, in the presence of recombinant FBP1, the DNA binding ability of p53 is strongly inhibited. We confirmed that FBP1 downregulates BCCIP, p21, and p53 and upregulates TCTP under radiation-induced stress. Since FBP1 is overexpressed in most HCC tumors with an HCV background, it may have a role in promoting persistent virus infection and tumorigenesis.
It is our novel finding that FUSE binding protein 1 (FBP1) strongly inhibits the function of tumor suppressor p53 and is an essential host cell factor required for HCV replication. Oncomine data analysis of a large number of samples has revealed that overexpression of FBP1 in most HCC tumors with chronic hepatitis C is significantly linked with the decreased expression level of p53. The most significant finding is that FBP1 not only physically interacts with p53 and interferes with its binding to the target DNA but also functions as a negative regulator of p53 under cellular stress. FBP1 is barely detectable in normal differentiated cells; its overexpression in HCC tumors with the CHC background suggests that FBP1 has an important role in promoting HCV infection and HCC tumors by suppressing p53.
丙型肝炎病毒（HCV）是慢性丙型肝炎（CHC）、肝硬化和肝细胞癌（HCC）的主要病因。对存档的HCC肿瘤进行免疫组织化学分析显示，在具有CHC背景的HCC肿瘤中FBP1表达丰富。对具有CHC背景的正常肿瘤与HCC肿瘤进行Oncomine数据分析表明，FBP1表达增加了4倍，同时p53表达下降了2.5倍。我们发现FBP1通过抑制p53并调节BCCIP和TCTP来促进HCV复制，BCCIP和TCTP分别是p53的正向和负向调节因子。在FBP1敲低的Huh7.5细胞中，HCV复制的严重抑制通过下调p53或BCCIP恢复到正常水平。尽管由于Y220C突变，Huh7.5细胞中的p53转录无活性，但我们发现Y220C p53的激活和DNA结合能力受到FBP1的强烈抑制，但在FBP1敲低后显著激活。在FBP1敲低的细胞中瞬时表达FBP1完全恢复了对照表型，其中p53的DNA结合能力受到强烈抑制。使用电泳迁移率变动分析（EMSA）和等温滴定量热法（ITC），我们发现重组野生型p53及其Y220C突变型p53的体外靶DNA结合亲和力没有显著差异。然而，在重组FBP1存在的情况下，p53的DNA结合能力受到强烈抑制。我们证实在辐射诱导的应激下，FBP1下调BCCIP、p21和p53并上调TCTP。由于FBP1在大多数具有HCV背景的HCC肿瘤中过表达，它可能在促进持续性病毒感染和肿瘤发生中起作用。
我们的新发现是，FUSE结合蛋白1（FBP1）强烈抑制肿瘤抑制因子p53的功能，并且是HCV复制所需的必需宿主细胞因子。对大量样本的Oncomine数据分析表明，在大多数慢性丙型肝炎相关的HCC肿瘤中，FBP1的过表达与p53表达水平的降低显著相关。最显著的发现是，FBP1不仅与p53发生物理相互作用并干扰其与靶DNA的结合，而且在细胞应激下作为p53的负调节因子发挥作用。在正常分化细胞中几乎检测不到FBP1；它在具有CHC背景的HCC肿瘤中的过表达表明FBP1通过抑制p53在促进HCV感染和HCC肿瘤中起重要作用。
