Thiol/disulfide exchange is a prerequisite for CXCR4-tropic HIV-1 envelope-mediated T-cell fusion during viral entry

Uniformed Services University of the Health Sciences, 베서스다, Maryland, United States
Blood (Impact Factor: 10.45). 04/2004; 103(5):1586-94. DOI: 10.1182/blood-2003-05-1390
Source: PubMed


Attachment of gp120 to CD4 during HIV-1 entry triggers structural rearrangement in gp120 that enables binding to an appropriate coreceptor. Following coreceptor engagement, additional conformational changes occur in the envelope (Env), resulting in fusion of virion and cell membranes. Catalysts with redox-isomerase activity, such as protein disulfide isomerase (PDI), facilitate Env conversion from its inactive to its fusion-competent conformation. We report here that anti-PDI agents effectively block CXCR4 Env-mediated fusion and spread of virus infection. Exogenously added PDI, in turn, can rescue fusion from this blockade. We further find that PDI facilitates thiol/disulfide rearrangement in gp120 during conformational change, whereas inhibition of this redox shuffling prevents gp41 from assuming the fusogenic 6-helix bundle conformation. At the virus-cell contact site, gp120 induces assembly of PDI, CD4, and CXCR4 into a tetramolecular protein complex serving as a portal for viral entry. Our findings support the hypothesis that Env conformational change depends on a well-coordinated action of a tripartite system in which PDI works in concert with the receptor and the coreceptor to effectively lower the activation energy barrier required for Env conformational rearrangement.

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Available from: Christopher Broder, Feb 03, 2015
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    • "It is also found on the cell membrane and may be actively secreted by various cell types [32], [33]. Extracellular PDI has been shown to regulate numerous activities, including cellular adhesion [34], pathogen entry [35], [36], platelet aggregation and secretion [37], intracellular nitric oxide delivery [38], and insulin degradation [39], [40]. Lymphocytes (especially CD4+ T cells) increase the availability of cell surface thiols after immune activation [41]. "
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    PLoS ONE 12/2013; 8(12):e81662. DOI:10.1371/journal.pone.0081662 · 3.23 Impact Factor
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    • "Activation of fusogenicity can result from precise thiol/disulfide rearrangements mediated by either an endogenous redox autocatalytic isomerase or a cell-associated oxidoreductase [1]. In addition thiol/disulfide exchange in the HIV-1 envelope protein is a prerequisite for CXCR4-tropic HIV-1 envelope-mediated T-cell fusion [6]. "
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    PLoS ONE 06/2013; 8(6):e66073. DOI:10.1371/journal.pone.0066073 · 3.23 Impact Factor
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    • "DTNB was able to suppress infection by all three isolates with levels of reverse transcriptase activity approaching those observed for uninfected control MDM, indicating that its effect was not strain specific (Figure 3A,B,C). To identify the disulfide reductases/isomerases involved in HIV-1 infection of MDM and serving as potential targets for DTNB, the effects of specific monoclonal antibodies (mAbs) against PDI and/or Trx, two enzymes previously implicated in HIV-1 Env disulfude bond rearrangements [16-20] were evaluated. The mAbs were applied before and during virus adsorption/fusion; HIV-1 infection was monitored by measuring RT activity at various time points throughout the course of infection. "
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    ABSTRACT: Background The role of disulfide bond remodeling in HIV-1 infection is well described, but the process still remains incompletely characterized. At present, the data have been predominantly obtained using established cell lines and/or CXCR4-tropic laboratory-adapted virus strains. There is also ambiguity about which disulfide isomerases/ reductases play a major role in HIV-1 entry, as protein disulfide isomerase (PDI) and/or thioredoxin (Trx) have emerged as the two enzymes most often implicated in this process. Results We have extended our previous findings and those of others by focusing on CCR5-using HIV-1 strains and their natural targets - primary human macrophages and CD4+ T lymphocytes. We found that the nonspecific thiol/disulfide exchange inhibitor, 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB), significantly reduced HIV-1 entry and infection in cell lines, human monocyte-derived macrophages (MDM), and also phytohemagglutinin (PHA)-stimulated peripheral blood mononuclear cells (PBMC). Subsequent studies were performed using specific anti-PDI or Trx monoclonal antibodies (mAb) in HIV-1 envelope pseudotyped and wild type (wt) virus infection systems. Although human donor-to-donor variability was observed as expected, Trx appeared to play a greater role than PDI in HIV-1 infection of MDM. In contrast, PDI, but not Trx, was predominantly involved in HIV-1 entry and infection of the CD4+/CCR5+ T cell line, PM-1, and PHA-stimulated primary human T lymphocytes. Intriguingly, both PDI and Trx were present on the surface of MDM, PM-1 and PHA-stimulated CD4+ T cells. However, considerably lower levels of Trx were detected on freshly isolated CD4+ lymphocytes, compared to PHA-stimulated cells. Conclusions Our findings clearly demonstrate the role of thiol/disulfide exchange in HIV-1 entry in primary T lymphocytes and MDM. They also establish a cell-type specificity regarding the involvement of particular disulfide isomerases/reductases in this process and may provide an explanation for differences among previously published studies. More importantly, from an in vivo perspective, the preferential utilization of PDI may be relevant to the HIV-1 entry and establishment of virus reservoirs in resting CD4+ cells, while the elevated levels of Trx reported in the chronic stages of HIV-1 infection may facilitate the virus entry in macrophages and help to sustain high viremia during the decline of T lymphocytes.
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