Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_45_библиотеки_им_акад_М_И_Перельмана

infection systems and accessible animal models of HBV infection has signiicantly hindered the identiication of cellular factors mediating the early steps of HBV infection in human hepatocytes. The irst step in HBV infection involves a non-cell-type speciic primary attachment to the cell­associated heparan sulfate proteoglycans (Schulze 2007). T his irst reversible attachment step is then followed by an irreversible binding of the virus to a speciic hepatocyte-speciic receptor (Urban 2014). Using mutational analysis, important determinants for infectivity were identiied within the HBV envelope proteins. These include 75 amino acids of the preS1 domain of the HBV L-protein, its myristoylation and the integrity of a region in the antigenic loop of the S domain (Gripon 2005, Engelke 2006, Meier 2013). Of note, HBV and HDV infection can be blocked by a small myristoylated lipopeptide (Myrcludex-B) containing the same aminoacid sequence of the preS1 domain of the HBV-L protein (Petersen 2008, Lütgehetmann 2012). Although cell polarisation, in addition to the diferentiation status of the hepatocytes, was shown to play an essential role in the infection process (Schulze 2011), the identity of the receptor has remained a mystery for many years. By using a method called zero-length photo cross-linking and tandem ainity puriication, the preS1 peptide was seen to speciically interact with a sodium taurocholate cotransporting polypeptide (NTCP), a multiple transmembrane transporter localised to the basolateral membrane of highly diferentiated primary hepatocytes (Yan 2012). NTCP mediates the transport of conjugated bile acids and some drugs from portal blood to the liver. Based on the discovery that NTCP functions as viral entry receptor by interacting with the large surface protein of HBV, cell lines susceptible to HBV infection could be established demonstrating that both HBV and HDV infection can be established in human hepatoma cell lines (Yan 2012, Nkongolo 2013). Although large amounts of input viruses (MOI >1000) are generally used to achieve eicient HBV infection in these culture systems, the availability of in vitro assays permitting investigation of the early steps of infection as well as rapid screening of new anti-HBV agents has opened new opportunities in HBV research. Such in vitro studie s showed for instance that HBV entry is inhibited by cyclosporins and oxysterols, which are known to bind to NTCP, in hNTCP-transfected hepatoma cells (Nkongolo 2013, Watashi 2013). In addition, binding of HBV or of Myrcludex-B to the cellular receptor NTCP was shown to limit its function, thus altering the hepatocellular uptake of bile salts and the expression proile of genes of the bile acid metabolism (Oehler 2014).