The early autophagic pathway is activated by hepatitis B virus and required for viral DNA replication

Abstract

Autophagy is a catabolic process by which cells remove long-lived proteins and damaged organelles for recycling. Viral infections may also induce autophagic response. Here we show that hepatitis B virus (HBV), a pathogen that chronically infects ≈350 million people globally, can enhance autophagic response in cell cultures, mouse liver, and during natural infection. This enhancement of the autophagic response is not coupled by an increase of autophagic protein degradation and is dependent on the viral X protein, which binds to and enhances the enzymatic activity of phosphatidylinositol 3-kinase class III, an enzyme critical for the initiation of autophagy. Further analysis indicates that autophagy enhances HBV DNA replication, with minimal involvement of late autophagic vacuoles in this process. Our studies thus demonstrate that a DNA virus can use autophagy to enhance its own replication and indicate the possibility of targeting the autophagic pathway for the treatment of HBV patients.autophagy | hepatitis B virus DNA replication | hepatitis B virus X protein | PI3KC3A utophagy is a catabolic process by which long-lived proteins and damaged organelles are sequestered in the cytoplasm and removed for recycling. It is important for maintaining cellular homeostasis. During autophagy, membrane crescents appear in the cytoplasm. These membranes will eventually form a double-membrane structure known as autophagosomes, which will mature by fusing with lysosomes to form autolysosomes. The contents of autophagosomes will subsequently be degraded by lysosomal enzymes. Autophagy has also been implicated in innate and adaptive immune responses to the infection of microbial pathogens (1, 2). A number of viruses have been shown to induce autophagy, either completely or partially, and often with either a destructive or beneficial result to themselves. For examples, several single-stranded RNA viruses such as poliovirus, coronavirus, dengue virus, and hepatitis C virus all seem to induce the accumulation of autophagic vacuoles and use these membrane vesicles to benefit their replication (3-6). In contrast, other viruses such as herpes simplex virus-1 (HSV-1), cytomegalovirus (CMV), and Kaposi's sarcoma herpes virus (KSHV) have evolved mechanisms to suppress autophagy and, in the case of HSV-1, for its own survival (2).Hepatitis B virus (HBV) belongs to the Hepadnavirus family. This virus has a 3.2-kb circular and partially double-stranded DNA genome that contains four genes named S, C, P, and X genes. The S gene codes for the surface antigens (i.e., envelope proteins), the C gene codes for the core protein and a related protein termed precore protein, the P gene codes for the viral DNA polymerase, and the X gene codes for a multifunctional regulatory protein. After its synthesis, the core protein packages its own mRNA, which is also known as the pregenomic RNA (pgRNA), to form the core particle. The pgRNA will be converted to the DNA genome in the core particle by the viral DNA polymerase, which is also a reverse transcriptase...

Regulation of lipid stores and metabolism by lipophagy

“…The two major hepatitis viruses, both of which are significant causes of chronic human liver disease, alter host cell autophagic function by unknown mechanisms. The RNA hepatitis C virus (HCV) 60,61 and the DNA hepatitis B virus 62,63 upregulate autophagy, which acts to promote rather than to block viral replication. HCV has a well-established association with LDs and the core protein of HCV attaches to LD for the apparent purpose of promoting viral assembly through a mechanism that is unknown.…”

Autophagy Modulation As a Potential Therapeutic Target for Liver Diseases

“…However, there is increase in protein degradation in HBV infected cells. 71 In HBV infection, the HBVencoding protein, HBx, plays a crucial role in subverting the autophagy functions in infected cells. Autophagy enhances viral replication at most steps of HBV replication.…”

Role of autophagy in the pathogenesis of liver diseases

“…A HBV fokozza az autophagosoma-képződést a májsejtekben, amelyet in vitro, in vivo és HBV-fertőzött betegekben is igazoltak [30]. Ellentétben a HCV-vel, a HBV fokozza az autofagolizoszóma-képződést, de a fertőzött sejtekben a fehérjék lebontása nem nő.…”

“…Ellentétben a HCV-vel, a HBV fokozza az autofagolizoszóma-képződést, de a fertőzött sejtekben a fehérjék lebontása nem nő. A HBx fontos szerepet játszik az autophagia fokozásában, amelyhez a fehérje expressziója is elegendő [30,31]. A HBx kötődik a PI3K III-hoz (phosphatidylinositol 3-kinase class III), amely az autophagia fontos szabá-lyozója, valamint serkenti a Beclin-1 transzkripcióját [30,31].…”

“…A HBx fontos szerepet játszik az autophagia fokozásában, amelyhez a fehérje expressziója is elegendő [30,31]. A HBx kötődik a PI3K III-hoz (phosphatidylinositol 3-kinase class III), amely az autophagia fontos szabá-lyozója, valamint serkenti a Beclin-1 transzkripcióját [30,31]. A HBV kis felületi fehérje (SHB s = small surface protein) az LC3 fehérjén keresztül segíti elő az autophagia növelését [32].…”