title: HIV-1 Vpu utilizes both cullin-RING ligase (CRL) dependent and independent mechanisms to downmodulate host proteins.
abstract: BACKGROUND
  Hijacking of the cullin-RING E3 ubiquitin ligase (CRL) machinery is a common mechanism employed by diverse groups of viruses for the efficient counteraction and degradation of host proteins. In particular, HIV-1 Vpu usurps the SCF(β-TrCP) E3 ubiquitin ligase complex to mark CD4 for degradation by the 26S proteasome. Vpu also interacts with and downmodulates a number of other host proteins, including the restriction factor BST-2. However, whether Vpu primarily relies on a cullin-dependent or -independent mechanism to antagonize its cellular targets has not been fully elucidated.
  
  
  RESULTS
  We utilized a sulphamate AMP analog, MLN4924, to effectively block the activation of CRLs within infected primary CD4(+) T cells. MLN4924 treatment, in a dose dependent manner, efficiently relieved surface downmodulation and degradation of CD4 by NL4-3 Vpu. MLN4924 inhibition was highly specific, as this inhibitor had no effect on Nef's ability to downregulate CD4, which is accomplished by a CRL-independent mechanism. In contrast, NL4-3 Vpu's capacity to downregulate BST-2, NTB-A and CCR7 was not inhibited by the drug. Vpu's from both a transmitted founder (T/F) and chronic carrier (CC) virus preserved the ability to downregulate BST-2 in the presence of MLN4924. Finally, depletion of cellular pools of cullin 1 attenuated Vpu's ability to decrease CD4 but not BST-2 surface levels.
  
  
  CONCLUSIONS
  We conclude that Vpu employs both CRL-dependent and CRL-independent modes of action against host proteins. Notably, we also establish that Vpu-mediated reduction of BST-2 from the cell surface is independent of β-TrCP and the CRL- machinery and this function is conserved by Vpu's from primary isolates. Therefore, potential therapies aimed at antagonizing the activities of Vpu may need to address these distinct mechanisms of action in order to achieve a maximal effect.
authors.affiliation: Division of Microbiology and Immunology, Department of Pathology, University of Utah School of Medicine, Salt Lake City, UT, 84112, USA. peter.ramirez@path.utah.edu.
authors.forename: Peter W
authors.initials: PW
authors.lastname: Ramirez
authors.affiliation: Division of Microbiology and Immunology, Department of Pathology, University of Utah School of Medicine, Salt Lake City, UT, 84112, USA. bea.silva@path.utah.edu.
authors.forename: Ana Beatriz
authors.initials: AB
authors.lastname: DePaula-Silva
authors.affiliation: Division of Microbiology and Immunology, Department of Pathology, University of Utah School of Medicine, Salt Lake City, UT, 84112, USA. matthew.szaniawski@path.utah.edu.
authors.forename: Matt
authors.initials: M
authors.lastname: Szaniawski
authors.affiliation: Department of Immunology and Microbiology, Rush University Medical Center, Chicago, IL, 60612, USA. Edward_Barker@rush.edu.
authors.forename: Edward
authors.initials: E
authors.lastname: Barker
authors.affiliation: Division of Microbiology and Immunology, Department of Pathology, University of Utah School of Medicine, Salt Lake City, UT, 84112, USA. alberto.bosque@path.utah.edu.
authors.forename: Alberto
authors.initials: A
authors.lastname: Bosque
authors.affiliation: Division of Microbiology and Immunology, Department of Pathology, University of Utah School of Medicine, Salt Lake City, UT, 84112, USA. vicente.planelles@path.utah.edu.
authors.forename: Vicente
authors.initials: V
authors.lastname: Planelles
mesh_terms: D015704:CD4 Antigens / Q000378:metabolism; D015496:CD4-Positive T-Lymphocytes / Q000187:drug effects / Q000821:virology; D002478:Cells, Cultured; D044842:Cullin Proteins / Q000378:metabolism*; D003517:Cyclopentanes / Q000037:antagonists & inhibitors / Q000494:pharmacology; D015536:Down-Regulation; D015497:HIV-1 / Q000235:genetics / Q000378:metabolism; D054298:Human Immunodeficiency Virus Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D011743:Pyrimidines / Q000037:antagonists & inhibitors / Q000494:pharmacology; D054400:Receptors, CCR7 / Q000235:genetics; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*; D054334:Viral Regulatory and Accessory Proteins / Q000235:genetics / Q000378:metabolism*; D044844:beta-Transducin Repeat-Containing Proteins / Q000235:genetics / Q000378:metabolism; D000086082:Viroporin Proteins
chemical_list: D015704:CD4 Antigens; D044842:Cullin Proteins; D003517:Cyclopentanes; D054298:Human Immunodeficiency Virus Proteins; D011743:Pyrimidines; D054400:Receptors, CCR7; D044767:Ubiquitin-Protein Ligases; D054334:Viral Regulatory and Accessory Proteins; D044844:beta-Transducin Repeat-Containing Proteins; C515370:CCR7 protein, human; C100318:Cullin 1; C514859:vpu protein, Human immunodeficiency virus 1; D000086082:Viroporin Proteins; C539933:pevonedistat