title: Rab33B and its autophagic Atg5/12/16L1 effector assist in hepatitis B virus naked capsid formation and release.
abstract: Hepatitis B virus morphogenesis is accompanied by the production and release of non-enveloped capsids/nucleocapsids. Capsid particles are formed inside the cell cytosol by multimerization of core protein subunits and ultimately exported in an uncommon coatless state. Here, we investigated potential roles of Rab GTPases in capsid formation and trafficking by using RNA interference and overexpression studies. Naked capsid release does not require functions of the endosome-associated Rab5, Rab7 and Rab27 proteins, but depends on functional Rab33B, a GTPase participating in autophagosome formation via interaction with the Atg5-Atg12/Atg16L1 complex. During capsid formation, Rab33B acts in conjunction with its effector, as silencing of Atg5, Atg12 and Atg16L1 also impaired capsid egress. Analysis of capsid maturation steps revealed that Rab33B and Atg5/12/16L1 are required for proper particle assembly and/or stability. In support, the capsid protein was found to interact with Atg5 and colocalize with Atg5/12/16L1, implicating that autophagy pathway functions are involved in capsid biogenesis. However, a complete and functional autophagy pathway is dispensable for capsid release, as judged by knockdown analysis of Atg8/LC3 family members and pharmaceutical ablation of canonical autophagy. Experiments aimed at analysing the capsid release-stimulating activity of the Alix protein provide further evidence for a link between capsid formation and autophagy.
authors.affiliation: Department of Medical Microbiology and Hygiene, University Medical Center of the Johannes Gutenberg University Mainz, Mainz, D-55101, Germany.
authors.forename: Tatjana
authors.initials: T
authors.lastname: Döring
authors.forename: Reinhild
authors.initials: R
authors.lastname: Prange
mesh_terms: D000071192:Autophagy-Related Protein 12; D000071187:Autophagy-Related Protein 5; D000071183:Autophagy-Related Proteins; D002213:Capsid / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism*; D002460:Cell Line; D015870:Gene Expression; D055785:Gene Knockdown Techniques; D006515:Hepatitis B virus / Q000502:physiology*; D022781:Hepatocytes / Q000821:virology; D054884:Host-Pathogen Interactions; D006801:Humans; D008869:Microtubule-Associated Proteins / Q000378:metabolism*; D025941:Protein Interaction Mapping; D025841:Small Ubiquitin-Related Modifier Proteins / Q000378:metabolism*; D019065:Virus Assembly; D057074:Virus Release; D020691:rab GTP-Binding Proteins / Q000378:metabolism*
chemical_list: C466624:ATG12 protein, human; C518959:ATG16L1 protein, human; C502778:ATG5 protein, human; D000071192:Autophagy-Related Protein 12; D000071187:Autophagy-Related Protein 5; D000071183:Autophagy-Related Proteins; D002352:Carrier Proteins; D008869:Microtubule-Associated Proteins; D025841:Small Ubiquitin-Related Modifier Proteins; C486397:RAB33B protein, human; D020691:rab GTP-Binding Proteins