Department of Pathology, Saint Louis University, St. Louis, Missouri, USA.
J Virol. 2012 Aug;86(16):8705-12. doi: 10.1128/JVI.00616-12. Epub 2012 Jun 6.
Hepatitis C virus (HCV) induces autophagosome formation in infected human hepatocytes. We have previously reported that HCV exploits autophagic machinery in favor of virus growth and survival in host cells (S. Shrivastava et al., Hepatology 53:406-414, 2011); however, the mechanisms for autophagy induction is poorly understood. In the present study, we observed that HCV infection transcriptionally upregulates Beclin1, which forms complex with Vps34, the class III phosphatidylinositol 3-kinase, as a first step for autophagy initiation. Although Bcl-2 has an anti-autophagy effect by its association with Beclin1 in nutrient-deprived cells, our studies revealed that HCV-mediated autophagy occurs independent of Beclin1-Bcl-2 dissociation. Mammalian target of rapamycin (mTOR) is a positive regulator of cell growth and is recognized as an inhibitor of autophagy induction. Our results demonstrated that HCV infection enhances phospho-mTOR expression and its downstream target 4EBP1 activation, suggesting that mTOR is not a negative regulator of HCV-induced autophagy. On the other hand, HCV infection in autophagy-impaired cells reduced phospho-mTOR, mTOR, and phospho-4EBP1 expression. Together, these results suggested that HCV induces autophagy by upregulating Beclin1 and activates mTOR signaling pathway, which in turn may promote hepatocyte growth.
丙型肝炎病毒（HCV）在感染的人肝细胞中诱导自噬体形成。我们之前曾报道过，HCV 利用自噬机制有利于病毒在宿主细胞中的生长和存活（S. Shrivastava 等人，《Hepatology》53:406-414, 2011）；然而，自噬诱导的机制还知之甚少。在本研究中，我们观察到 HCV 感染转录上调 Beclin1，Beclin1 与 Vps34（III 类磷酸肌醇 3-激酶）形成复合物，作为自噬起始的第一步。虽然 Bcl-2 通过与营养缺乏细胞中的 Beclin1 结合具有抗自噬作用，但我们的研究表明，HCV 介导的自噬发生不依赖于 Beclin1-Bcl-2 解离。雷帕霉素靶蛋白（mTOR）是细胞生长的正调节剂，被认为是自噬诱导的抑制剂。我们的结果表明，HCV 感染增强了磷酸化 mTOR 的表达及其下游靶标 4EBP1 的激活，表明 mTOR 不是 HCV 诱导自噬的负调节剂。另一方面，自噬受损细胞中的 HCV 感染减少了磷酸化 mTOR、mTOR 和磷酸化 4EBP1 的表达。总之，这些结果表明，HCV 通过上调 Beclin1 诱导自噬，并激活 mTOR 信号通路，从而可能促进肝细胞生长。
