title: Thioredoxin (Trx1) regulates CD4 membrane domain localization and is required for efficient CD4-dependent HIV-1 entry.
abstract: CD4 is a glycoprotein expressed on the surfaces of certain immune cells. On lymphocytes, an important function of CD4 is to co-engage Major Histocompatibility Complex (MHC) molecules with the T Cell Receptor (TCR), a process that is essential for antigen-specific activation of T cells. CD4 localizes dynamically into distinct membrane microdomains, an important feature of its immunoregulatory function that has also been shown to influence the efficiency of HIV replication. However, the mechanism by which CD4 localization is regulated and the biological significance of this is incompletely understood.
  
  
  
  In this study, we used confocal microscopy, density-gradient centrifugation and flow cytometry to analyze dynamic redox-dependent effects on CD4 membrane domain localization.
  
  
  
  Blocking cell surface redox exchanges with both a membrane-impermeable sulfhydryl blocker (DTNB) and specific antibody inhibitors of Thioredoxin-1 (Trx1) induces translocation of CD4 into detergent-resistant membrane domains (DRM). In contrast, Trx1 inactivation does not change the localization of the chemokine receptor CCR5, suggesting that this effect is targeted. Moreover, DTNB treatment and Trx1 depletion coincide with strong inhibition of CD4-dependent HIV entry, but only moderate reductions in the infectivity of a CD4-independent HIV pseudovirion.
  
  
  
  Changes in the extracellular redox environment, potentially mediated by allosteric consequences of functional disulfide bond oxidoreduction, may represent a signal for translocation of CD4 into DRM clusters, and this sequestration, another potential mechanism by which the anti-HIV effects of cell surface oxidoreductase inhibition are exerted.
  
  
  
  Extracellular redox conditions may regulate CD4 function by potentiating changes in its membrane domain localization.
authors.affiliation: HIV Pathogenesis Research Unit, Department of Molecular Medicine and Haematology, University of the Witwatersrand, Faculty of Health Sciences, 7 York Road Parktown, 2193 Johannesburg, South Africa.
authors.forename: Naazneen
authors.initials: N
authors.lastname: Moolla
authors.affiliation: HIV Pathogenesis Research Unit, Department of Molecular Medicine and Haematology, University of the Witwatersrand, Faculty of Health Sciences, 7 York Road Parktown, 2193 Johannesburg, South Africa.
authors.forename: Mark
authors.initials: M
authors.lastname: Killick
authors.affiliation: HIV Pathogenesis Research Unit, Department of Molecular Medicine and Haematology, University of the Witwatersrand, Faculty of Health Sciences, 7 York Road Parktown, 2193 Johannesburg, South Africa.
authors.forename: Maria
authors.initials: M
authors.lastname: Papathanasopoulos
authors.affiliation: HIV Pathogenesis Research Unit, Department of Molecular Medicine and Haematology, University of the Witwatersrand, Faculty of Health Sciences, 7 York Road Parktown, 2193 Johannesburg, South Africa. Electronic address: alexio.capovilla@gmail.com.
authors.forename: Alexio
authors.initials: A
authors.lastname: Capovilla
mesh_terms: D015704:CD4 Antigens / Q000378:metabolism*; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism* / Q000821:virology*; D004228:Dithionitrobenzoic Acid / Q000494:pharmacology; D015497:HIV-1 / Q000472:pathogenicity*; D006367:HeLa Cells; D006801:Humans; D008285:Major Histocompatibility Complex / Q000502:physiology; D021962:Membrane Microdomains / Q000378:metabolism*; D010084:Oxidation-Reduction / Q000187:drug effects; D019713:Receptors, CCR5 / Q000378:metabolism; D013601:T-Lymphocytes / Q000187:drug effects / Q000378:metabolism / Q000821:virology; D013879:Thioredoxins / Q000378:metabolism*; D053586:Virus Internalization / Q000187:drug effects
chemical_list: D015704:CD4 Antigens; D019713:Receptors, CCR5; D013879:Thioredoxins; D004228:Dithionitrobenzoic Acid
keywords: CD4; HIV-1; Lipid raft; Redox; Thioredoxin