State Key Laboratory of Virology, Wuhan Institute of Virology, Chinese Academy of Sciences, Wuhan 430071, China; University of Chinese Academy of Sciences, Beijing, China.
State Key Laboratory of Molecular and Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China.
Biochim Biophys Acta Mol Cell Biol Lipids. 2017 Jul;1862(7):692-705. doi: 10.1016/j.bbalip.2017.03.007. Epub 2017 Mar 21.
Lipid droplet (LD) accumulation in hepatocytes is a typical character of steatosis. Hepatitis C virus (HCV) infection, one of the risk factors related to steatosis, induced LD accumulation in cultured cells. However, the mechanisms of which HCV induce LD formation are not fully revealed. Previously we identified cytosolic phospholipase A2 gamma (PLA2G4C) as a host factor upregulated by HCV infection and involved in HCV replication. Here we further revealed that PLA2G4C plays an important role in LD biogenesis and refined the functional analysis of PLA2G4C in LD biogenesis and HCV assembly. LD formation upon fatty acid and HCV stimulation in PLA2G4C knockdown cells was impaired and could not be restored by complementation with PLA2G4A. PLA2G4C was tightly associated in the membrane with the domain around the amino acid residues 260-292, normally in ER but relocated into LDs upon oleate stimulation. Mutant PLA2G4C without enzymatic activity was not able to restore LD formation in PLA2G4C knockdown cells. Thus, both the membrane attachment and the enzymatic activity of PLA2G4C were required for its function in LD formation. The participation of PLA2G4C in LD formation is correlated with its involvement in HCV assembly. Finally, PLA2G4C overexpression itself led to LD formation in hepatic cells and enhanced LD accumulation in the liver of high-fat diet (HFD)-fed mice, suggesting its potential role in fatty liver disease.
肝细胞中脂滴（LD）的积累是脂肪变性的典型特征。丙型肝炎病毒（HCV）感染是脂肪变性的相关危险因素之一，它可诱导培养细胞中 LD 的积累。然而，HCV 诱导 LD 形成的机制尚未完全阐明。先前我们鉴定了细胞质磷脂酶 A2γ（PLA2G4C）作为 HCV 感染上调的宿主因子，并参与 HCV 复制。在这里，我们进一步揭示了 PLA2G4C 在 LD 生物发生中的重要作用，并对 PLA2G4C 在 LD 生物发生和 HCV 组装中的功能进行了精细化分析。在 PLA2G4C 敲低的细胞中，脂肪酸和 HCV 刺激引起的 LD 形成受损，并且不能通过与 PLA2G4A 的互补来恢复。PLA2G4C 与 ER 中围绕氨基酸残基 260-292 附近的区域紧密结合，但在油酸盐刺激下会重新定位到 LD 中。没有酶活性的突变 PLA2G4C 不能恢复 PLA2G4C 敲低细胞中的 LD 形成。因此，PLA2G4C 在 LD 形成中的功能既需要其膜结合，也需要其酶活性。PLA2G4C 参与 LD 形成与其参与 HCV 组装有关。最后，PLA2G4C 的过表达本身导致肝细胞中形成 LD，并增强高脂肪饮食（HFD）喂养小鼠肝脏中 LD 的积累，表明其在脂肪性肝病中具有潜在作用。
