C型肝炎病毒非結構性蛋白質NS3對於c-Jun表現量及轉錄活性之調節

Abstract

C型肝炎病毒為單股正向RNA病毒，感染宿主後可在內質網上轉譯成一多蛋白質前驅物，藉由細胞及病毒本身的蛋白酶切割後產生結構性和非結構性蛋白質；非結構性蛋白質NS3由631個胺基酸組成。過去研究指出NS3可造成細胞轉型，也讓細胞可以在低血清的環境生長。實驗室先前研究發現，NS3蛋白質在NS4A蛋白質的輔助下會發生內部截切，且主要內部截切產物NS3(1-402)，相較於全長NS3有更高轉型能力。過去也有報導指出，由肝癌病人所分離出的肝細胞有JNK過度活化的現象。JNK的下游轉錄調控因子c-Jun屬於致癌蛋白質，可促使細胞轉型，與肝癌的發生有關。c-Jun的活化可促使與細胞增生、生長和凋亡相關的基因表現。本研究的目的在進一步探討NS3造成的細胞轉型能力是否藉由影響c-Jun的表現或是功能所致。由免疫沉澱及GST pull down的分析，發現NS3可與c-Jun形成複合物。當同時表現c-Jun及NS3全長或NS3(1-402)時，c-Jun表現量有下降的情況，而NS3(369-631)對c-Jun表現量則無明顯影響。另一方面，在冷光酶報導基因分析實驗中則見到NS3(1-402)及NS3 RNA binding domain NS3(327-484)對於c-Jun轉錄功能有抑制的作用，但NS3全長及NS3(369-631)則無明顯差異。分析細胞表現NS3的過程中對於JNK訊息路徑的影響時觀察到，相較於控制組，表現NS3的細胞JNK活化的時間較長，而內生性c-Jun的表現量則有下降的趨勢，可看出NS3可對JNK及c-Jun造成影響。因此推測，NS3可藉由影響JNK的活化，干擾下游c-Jun的功能，而影響細胞內JNK-c-Jun訊息傳遞路徑。

Hepatitis C virus (HCV) is a single-stranded, positive-sense RNA virus that encodes a polyprotein precursor at endoplasmic reticulum. The precursor is further processed into structural and nonstructural proteins by cellular signal peptidase and viral proteases. The nonstructural protein 3 (NS3) consists of 631 amino acids. Previous studies have shown that NS3 can transform cells and help them growth under low serum condition. Studies in our laboratory have demonstrated an internal NS3 cleavage activity, the major cleavage product NS3(1-402) has a higher transforming activity than the full-length NS3. In addition, JNK activity was remarkably increased in hepatocytes isolated from hepatocellular carcinoma patients. The downstream effector c-Jun possesses a transforming activity and is an oncogenic protein associated with hepatocellular carcinomas. C-Jun is a transcription factor that can induce gene expression involved in cell proliferation, growth, and apoptosis. To investigate whether NS3 affects the expression and transcriptional regulation of c-Jun, co-immunoprecipitation and GST pull down assay were performed. The results demonstrated interactions between c-Jun and both the full-length NS3 and its subdomains. Co-expression of NS3 or its subdomain NS3(1-402) significantly reduced the expression level of c-Jun, but NS3(369-631) had only a little effect. On the other hand, the transcription activity of c-Jun was reduced by NS3(1-402) and NS3(327-484) but neither the full-length NS3 nor the NS3(369-631). In addition, cell expressing NS3 showed a prolonged activation of JNK as compared to the control cells, the endogenous downstream effector c-Jun was also reduced. These results indicate a role of NS3 in regulating JNK-c-Jun signaling pathway.