Involvement of host cellular multivesicular body functions in hepatitis B virus budding

Abstract

Hepatitis B virus (HBV) is a major human pathogen that chronically infects Ϸ350 million people, causing liver disease and liver cancer. HBV virions bud into an endoplasmic reticulum (ER)-associated intracellular compartment, but the mechanisms of HBV assembly, budding, and release remain poorly understood. Budding of retroviruses and some other enveloped RNA viruses from plasma membranes requires host functions involved in protein sorting into late endosomal multivesicular bodies (MVBs). To determine whether budding of DNA-containing HBV virions at intracellular membranes also involves MVB functions, we used immunofluorescence to show that, in human hepatoma cells, HBV envelope protein colocalizes with MVB proteins AIP1/ALIX and VPS4B. We also found that a dominant negative (DN) AIP1 mutant inhibited production and/or release of enveloped virions without significant effects on intracellular nucleocapsid formation, whereas DN VPS4B inhibited both nucleocapsid production and budding. By contrast, DN AIP1 and VPS4 had no effect on the efficiency of release of enveloped, nucleocapsid-lacking HBV subviral particles, which are produced in vast excess over virions, and dramatically increased the release of unenveloped, naked nucleocapsids by an apparently nonlytic route. Thus, host MVB functions are required for efficient budding and release of enveloped HBV virions and may be a valuable target for HBV control. Moreover, HBV enveloped virions, enveloped subviral particles, and unenveloped nucleocapsids are all released by distinct pathways with separate host factor requirements.antiviral control ͉ hepadnavirus ͉ vacuolar protein sorting ͉ virus replication ͉ virus-host interaction

Ultrastructural Evidences of Hepatitis B Infection in Human Liver Biopsies Disclose Complex Assembly and Morphogenesis Pathways for Hepatitis B Virus

“…Nevertheless, results from this work showed that Dane's-like particles and SVP localize in different cellular compartments. This is in agreement with recent evidences showing that the viral and subviral HBV assembly pathways seemingly differ in their requirement for cell functions and trafficking routes [25,26] . While HBV virions budding required the involvement of MVB functions, the mechanisms of SVP production showed to be clearly distinct and likely independent of MVB functions [25,26] .…”

“…Most of these viruses access the MVB machinery through its virusencoded late assembly domains and bud through the plasma membrane. In addition, recent communications have reported the involvement of MVB functions in HBV virion maturation and egress using virusreplicating liver cell lines [25,26] . HBV virions have been suggested to bud into internal MVB-related compartments and exit the cell by the exosome pathway.…”

HBV secretion is regulated through the activation of endocytic and autophagic compartments via Rab7 stimulation

“…Based on the findings of others, HBV appears to utilize the MVB (Kian Chua et al, 2006;Lambert et al, 2007;Watanabe et al, 2007) and autophagic compartments (Li et al, 2011;Sir et al, 2010;Tian et al, 2011) during assembly, maturation and release. As Rab7 is known to regulate the dynamics and traffic between these late endocytic compartments and the lysosome (Cantalupo et al, 2001;Jäger et al, 2004;Stenmark, 2009), we tested whether alterations in Rab7 expression and/or function might interfere with the viral life cycle.…”

“…Recently, a compartment of the late endocytic pathway, the multivesicular body (MVB), has been shown to participate in the final stages of HBV maturation and release. The HBV appears to reside transiently in the MVB and disruption of this compartment results in a decrease of released HBV (Kian Chua et al, 2006;Lambert et al, 2007;Stieler and Prange, 2014;Watanabe et al, 2007). Although the structural interactions between the HBV and this organelle remain unclear, it appears that virus buds inwards into invaginations of the MVB limiting membrane, forming intraluminal vesicles (ILVs), a process that is topologically equivalent to enveloped viral budding from the cell surface (Prange, 2012).…”

Serological and molecular epidemiological outcomes after two decades of universal infant hepatitis B virus (HBV) vaccination in Nunavut, Canada

“…Positive-sense strand synthesis by viral polymerase and pregenomic mRNA degradation by a ribonuclease follows. The encapsidated viral genome may now be enveloped by a lipid envelope containing embedded HBsAg and be secreted from the host hepatocyte [47][48][49].…”