Cell Death-Inducing DFFA-Like Effector b Is Required for Hepatitis C Virus Entry into Hepatocytes
JOURNAL OF VIROLOGY
Authors: Wu, Xianfang; Lee, Emily M.; Hammack, Christy; Robotham, Jason M.; Basu, Mausumi; Lang, Jianshe; Brinton, Margo A.; Tang, Hengli
The molecular mechanism of the hepatic tropism of hepatitis C virus (HCV) remains incompletely defined. In vitro hepatic differentiation of pluripotent stem cells produces hepatocyte-like cells (HLCs) permissive for HCV infection, providing an opportunity for studying liver development and host determinants of HCV susceptibility. We previously identified the transition stage of HCV permissiveness and now investigate whether a host protein whose expression is induced during this transition stage is important for HCV infection. We suppressed the expression of a liver-specific protein, cell death-inducing DFFA-like effector b (CIDEB), and performed hepatocyte function and HCV infection assays. We also used a variety of cell-based assays to dissect the specific step of the HCV life cycle that potentially requires CIDEB function. We found CIDEB to be an essential cofactor for HCV entry into hepatocytes. Genetic interference with CIDEB in stem cells followed by hepatic differentiation leads to HLCs that are refractory to HCV infection, and infection time course experiments revealed that CIDEB functions in a late step of HCV entry, possibly to facilitate membrane fusion. The role of CIDEB in mediating HCV entry is distinct from those of the well-established receptors, as it is not required for HCV pseudoparticle entry. Finally, HCV infection effectively downregulates CIDEB protein through a posttranscriptional mechanism. IMPORTANCE This study identifies a hepatitis C virus (HCV) entry cofactor that is required for HCV infection of hepatocytes and potentially facilitates membrane fusion between viral and host membranes. CIDEB and its interaction with HCV may open up new avenues of investigation of lipid droplets and viral entry.
Cell death-inducing DNA fragmentation factor A-like effector A and fat-specific protein 27 beta coordinately control lipid droplet size in brown adipocytes
JOURNAL OF BIOLOGICAL CHEMISTRY
Authors: Nishimoto, Yuki; Nakajima, Shinsuke; Tateya, Sanshiro; Saito, Masayuki; Ogawa, Wataru; Tamori, Yoshikazu
Adipose tissue stores neutral lipids and is a major metabolic organ involved in regulating whole-body energy homeostasis. Triacylglycerol is stored as unilocular large lipid droplets (LDs) in white adipocytes and as multilocular small LDs in brown adipocytes. Proteins of the cell death-inducing DNA fragmentation factor A-like effector (Cide) family include CideA, CideB, and fat-specific protein of 27 (FSP27). Of these, FSP27 has been shown to play a crucial role in the formation of unilocular large LDs in white adipocytes. However, the mechanisms by which brown adipocytes store small and multilocular LDs remain unclear. An FSP27 isoform, FSP27 beta, was recently identified. We herein report that CideA and FSP27 beta are mainly expressed in brown adipose tissue and that FSP27 beta overexpression inhibits CideA-induced LD enlargements in a dose-dependent manner in COS cells. Furthermore, RNAi-mediated FSP27 beta depletion resulted in enlarged LDs in HB2 adipocytes, which possess the characteristics of brown adipocytes. Brown adipocytes in FSP27-knock-out mice that express CideA, but not FSP27 beta, had larger and fewer LDs. Moreover, we confirmed that FSP27 beta and CideA form a complex in brown adipose tissue. Our results suggest that FSP27 beta negatively regulates CideA-promoted enlargement of LD size in brown adipocytes. FSP27 beta appears to be responsible for the formation of small and multilocular LDs in brown adipose tissue, a morphology facilitating free fatty acid transport to mitochondria adjacent to LDs for oxidation in brown adipocytes.