Hepatitis B virus promotes autophagic degradation but not replication in autophagosome

Abstract

In this study, we investigate the relationship of hepatitis B virus (HBV) infection and autophagy. HepG2 cells and HepG2 cells infected with HBV (HepG2.2.15) were transfected with GFP-LC3 (green fluorescence protein conjugated with microtubule-associated protein 1 light chain 3) expression vector and autophagy status was then examined with confocal microscope. HepG2.2.15 cells were further treated with serum-free medium or 3-methyladenine (3-MA), and subjected to Hepatitis B core antigen (HBcAg), Hepatitis B surface antigen (HBsAg), or hepatitis B polymerase protein detection by immunohistochemistry. Localization of the GFP-LC3 and the HBV proteins was observed by confocal fluorescence microscope. The level of SQSTM1/p62 protein was also evaluated by Western blot analysis. In contrast to a diffuse distribution in HepG2 cells, GFP-LC3 formed distinct punctate dots, which were further enhanced by nutritional starvation, in HepG2.2.15 cells. The expression of hepatitis B polymerase and HBcAg, but not HBsAg, was positively correlated with the autophagic intensity. However, no co-localizations were observed between HBV proteins and autophagosomes. Suppression of autophagy reduced the expression of hepatitis B polymerase and HBcAg, but not HBsAg. Western blot showed that SQSTM1/p62 protein level was declined in HepG2.2.15 cells comparing HepG2 cells, and further reduced while upon serum starvation. In conclusion, HBV infection induces autophagic degradation and autophagy. Autophagy is critical for HBV replication. However HBV replication does not take place in autophagosomes.