I-IBV life cycle is restricted in mouse hepatocytes .~xpressing human NTCP

Recent studies have revealed that human sodium taurocholate cotransporting polypeptide （SLC10A1 or NTCP） is a functional cellular receptor for hepatitis B virus （HBV）. However, whether human NTCP can support HBV infection in mouse hepatocyte cell lines has not been clarified. Because an HBV-permissible mouse model would be helpful for the study of HBV pathogenesis, it is necessary to investigate whether human NTCP supports the susceptibility of mouse hepatocyte cell lines to HBV. The results show that exogenous human NTCP expression can render non-susceptible HepG2 （human）, Huh7 （human）, Hepal-6 （mouse）, AML-12 （mouse） cell lines and primary mouse hepatocyte （PMH） cells susceptible to hepatitis D virus （HDV） which employs HBV envelope proteins. However, human NTCP could only introduce HBV susceptibility in human-derived HepG2 and Huh7 cells, but not in mouse-derived Hepal-6, AML-12 or PMH cells. These data suggest that although human NTCP is a functional receptor that mediates HBV infection in human cells, it cannot support HBV infection in mouse hepatocytes. Our study indicated that the restriction of HBV in mouse hepatocytes likely occurs after viral entry but prior to viral transcription. We have excluded the role of mouse hepatocyte nuclear factors in the restriction of the HBV life cycle and showed that knockdown or inhibition of Sting, TBK1, IRF3 or IRF7, the components of the anti-viral signaling pathways, had no effect on HBV infection in mouse hepatocytes. Therefore, murine restriction factors that limit HBV infection need to be identified before a HBV-permissible mouse line can be created.

ZBP1 mediates interferon-induced necroptosis

Interferons(IFNs)play an important role in immunomodulatory and antiviral functions.IFN-induced necroptosis has been reported in cells deficient in receptor-interacting protein kinase 1(RIPK1),Fas-associated protein with death domain(FADD),or caspase-8,but the mechanism is largely unknown.Here,we report that the DNA-dependent activator of IFN regulatory factors(ZBP1,also known as DAI)is required for both type Ⅰ(β)and type Ⅱ(γ)IFN-induced necroptosis.We show that L929 fibroblast cells became susceptible to IFN-induced necroptosis when RIPK1,FADD,or Caspase-8 was genetically deleted,confirming the antinecroptotic role of these proteins in IFN signaling.We found that the pronecroptotic signal from IFN stimulation depends on new protein synthesis and identified ZBP1,an IFN-stimulated gene(ISG)product,as the de novo synthesized protein that triggers necroptosis in IFN-stimulated cells.The N-terminal domain(ND)of ZBP1 is important for ZBP1–ZBP1 homointeraction,and its RHIM domain in the C-terminal region interacts with RIPK3 to initiate RIPK3-dependent necroptosis.The antinecroptotic function of RIPK1,FADD,and caspase-8 in IFN-treated cells is most likely executed by caspase-8-mediated cleavage of RIPK3,since the inhibitory effect on necroptosis was eliminated when the caspase-8 cleavage site in RIPK3 was mutated.ZBP1-mediated necroptosis in IFN-treated cells is likely physiologically relevant,as ZBP1 KO mice were significantly protected against acute systemic inflammatory response syndrome(SIRS)induced by TNF+IFN-γ.