Limited proteolysis induces woodchuck hepatitis virus infectivity for human HepG2 cells

Previous work from our laboratory has shown that digestion of hepatitis B v irus (HBV) with V8 protease rendered the virus infectious for human hepatob lastoma cell line (HepG2). It was hypothesized that the cleavage exposes a 16 amino acid region that includes a consensus 'fusion' motif necessary to mediate infectivity. Since woodchuck hepatitis virus (WHV) and HBV possess significant homology in this region of their envelope proteins: including t he V8 protease cleavage site, the possibility that WHV infectivity for HepG 2 cells could be induced by V8 digestion was explored. WHV isolated from th e serum of chronically infected woodchucks, digested with V8 protease, was shown to loose its preS domain. V8 digested WHV eluted from gel filtration columns with a size similar to that of undigested virus, suggesting that di gestion with V8 protease did not cause significant changes in virion size. The amount of progeny virus secreted into the culture medium following infe ction of HepG2 cells with V8 digested WHV reached 2.5 pg/ml, after 8 days. Moreover, WHV DNA replicative intermediates could be detected in the cells following infection with protease digested, but not undigested, viruses. Th ese data suggest that protease modification of WHV: a non-human virus, indu ced infectivity for human tissue culture cells. These results are consisten t with the hypothesis that exposure of an amino acid region of the envelope polypeptide that contains a consensus fusion motif is important in Hepadna virus entry. (C) 2001 Elsevier Science B.V. All rights reserved.