title: Cellular requirements for bovine immunodeficiency virus Vif-mediated inactivation of bovine APOBEC3 proteins.
abstract: Human immunodeficiency virus type 1 (HIV-1) and simian immunodeficiency virus (SIV) viral infectivity factor (Vif) form a CRL5 E3 ubiquitin ligase complex to suppress virus restriction by host APOBEC3 (A3) proteins. The primate lentiviral Vif complex is composed of the unique cofactor core binding factor β (CBF-β) and canonical ligase components Cullin 5 (CUL5), Elongin B/C (ELOB/C), and RBX2. However, the mechanism by which the Vif protein of the related lentivirus bovine immunodeficiency virus (BIV) overcomes its host A3 proteins is less clear. In this study, we show that BIV Vif interacts with Cullin 2 (CUL2), ELOB/C, and RBX1, but not with CBF-β or CUL5, to form a CRL2 E3 ubiquitin ligase and degrade the restrictive bovine A3 proteins (A3Z2Z3 and A3Z3). RNA interference-mediated knockdown of ELOB or CUL2 inhibited BIV Vif-mediated degradation of these A3 proteins, whereas knockdown of CUL5 or CBF-β did not. BIV Vif with mutations in the BC box (Vif SLQ-AAA) or putative VHL box (Vif YI-AA), which cannot interact with ELOB/C or CUL2, respectively, lost the ability to counteract bovine A3 proteins. Moreover, CUL2 and UBE2M dominant negative mutants competitively inhibited the BIV Vif-mediated degradation mechanism. Thus, although the general strategy for inhibiting A3 proteins is conserved between HIV-1/SIV and BIV, the precise mechanisms can differ substantially, with only the HIV-1/SIV Vif proteins requiring CBF-β as a cofactor, HIV-1/SIV Vif using CUL5-RBX2, and BIV Vif using CUL2-RBX1.
  
  
  OBJECTIVE
  Primate lentivirus HIV-1 and SIV Vif proteins form a ubiquitin ligase complex to target host antiviral APOBEC3 proteins for degradation. However, the mechanism by which the nonprimate lentivirus BIV Vif inhibits bovine APOBEC3 proteins is unclear. In the present study, we determined the mechanism for BIV Vif-mediated degradation of bovine APOBEC3 proteins and found that it differs from the mechanism of HIV-1/SIV Vif by being CBF-β independent and requiring different ubiquitin ligase scaffolding proteins (CUL2-RBX1 instead of CUL5-RBX2). BIV Vif is the only known retroviral protein that can interact with CUL2. This information broadens our understanding of the distinct mechanisms by which the Vif proteins of different lentiviruses facilitate viral infection. This novel mechanism for assembly of the BIV Vif-APOBEC3 ubiquitin ligase complex advances our understanding of viral hijacking of host E3 ubiquitin ligases and illustrates the evolutionary flexibility of lentiviruses.
authors.affiliation: First Hospital of Jilin University, Institute of Virology and AIDS Research, Changchun, Jilin, China Department of Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, USA.
authors.forename: Wenyan
authors.initials: W
authors.lastname: Zhang
authors.affiliation: First Hospital of Jilin University, Institute of Virology and AIDS Research, Changchun, Jilin, China.
authors.forename: Hong
authors.initials: H
authors.lastname: Wang
authors.affiliation: First Hospital of Jilin University, Institute of Virology and AIDS Research, Changchun, Jilin, China.
authors.forename: Zhaolong
authors.initials: Z
authors.lastname: Li
authors.affiliation: First Hospital of Jilin University, Institute of Virology and AIDS Research, Changchun, Jilin, China.
authors.forename: Xin
authors.initials: X
authors.lastname: Liu
authors.affiliation: First Hospital of Jilin University, Institute of Virology and AIDS Research, Changchun, Jilin, China.
authors.forename: Guanchen
authors.initials: G
authors.lastname: Liu
authors.affiliation: Department of Biochemistry, Molecular Biology and Biophysics, Institute for Molecular Virology, University of Minnesota, St. Paul, Minnesota, USA.
authors.forename: Reuben S
authors.initials: RS
authors.lastname: Harris
authors.affiliation: First Hospital of Jilin University, Institute of Virology and AIDS Research, Changchun, Jilin, China Department of Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, USA Collaborative Innovation Center of Chemical Science and Engineering, School of Life Sciences, Tianjin University, Tianjin, China xyu2@jhu.edu.
authors.forename: Xiao-Fang
authors.initials: XF
authors.lastname: Yu
mesh_terms: D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D002417:Cattle; D044842:Cullin Proteins / Q000378:metabolism*; D043525:Cytosine Deaminase / Q000037:antagonists & inhibitors*; D016346:Gene Products, vif / Q000378:metabolism*; D054884:Host-Pathogen Interactions; D057131:Immune Evasion; D007108:Immune Tolerance; D016087:Immunodeficiency Virus, Bovine / Q000502:physiology*; D011485:Protein Binding; D025941:Protein Interaction Mapping; D059748:Proteolysis; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D044842:Cullin Proteins; D016346:Gene Products, vif; D044767:Ubiquitin-Protein Ligases; D043525:Cytosine Deaminase