Basal shuttle of NF-κB/IκBα in resting T lymphocytes regulates HIV-1 LTR dependent expression

Universidad Autónoma de Madrid, Madrid, Madrid, Spain
Retrovirology (Impact Factor: 4.19). 02/2007; 4(1):56. DOI: 10.1186/1742-4690-4-56
Source: PubMed


In HIV-infected T lymphocytes, NF-κB/Rel transcription factors are major elements involved in the activation of LTR-dependent transcription from latency. Most NF-κB heterodimer p65/p50 is sequestered as an inactive form in the cytoplasm of resting T lymphocytes via its interaction with IκB inhibitors. In these cells, both absolute HIV latency and low level ongoing HIV replication have been described. These situations could be related to differences in the balance between NF-κB and IκBα ratio. Actually, control of IκBα by cellular factors such as Murr-1 plays a critical role in maintaining HIV latency in unstimulated T lymphocytes. Formerly, our group demonstrated the presence of nuclear IκBα in T cells after PMA activation. Now we attempt to determine the dynamics of NF-κB/IκBα nucleocytosolic transport in absence of activation as a mechanism to explain both the maintenance of latency and the existence of low level ongoing HIV replication in resting CD4+ T lymphocytes.

Results and conclusion
We show that the inhibition of the nuclear export by leptomycin B in resting CD4+ T cells resulted in nuclear accumulation of both IκBα and p65/RelA, as well as formation of NF-κB/IκBα complexes. This proves the existence of a rapid shuttling of IκBα between nucleus and cytosol even in absence of cellular activation. The nuclear accumulation of IκBα in resting CD4+ T lymphocytes results in inhibition of HIV-LTR dependent transcription as well as restrains HIV replication in CD4+ T lymphocytes. On the other hand, basal NF-κB activity detected in resting CD4+ T lymphocytes was related to low level HIV replication in these cells.

Download full-text


Available from: María Mittelbrunn
  • Source
    • "Indeed, the NFκB and SP1 sites of the LTR have been implicated in controlling stochastic HIV-1 gene expression noise [42]. Other potential mechanisms of NFκB fluctuation include oscillatory behavior in response to TNFα signaling [43], and rapid nuclear shuttling of NFκB p65 and IκBα [44]. NFκB p65 shuttling was shown to provide low-level basal HIV-1 transcription in infected resting CD4+ T-cells [44], while shuttling of IκBα was shown to dampen leaky NFκB signaling by removing active NFκB p65 from the nucleus [44,45]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Molecular latency allows HIV-1 to persist in resting memory CD4+ T-cells as transcriptionally silent provirus integrated into host chromosomal DNA. Multiple transcriptional regulatory mechanisms for HIV-1 latency have been described in the context of progressive epigenetic silencing and maintenance. However, our understanding of the determinants critical for the establishment of latency in newly infected cells is limited. In this study, we used a recently described, doubly fluorescent HIV-1 latency model to dissect the role of proviral integration sites and cellular activation state on direct non-productive infections at the single cell level. Proviral integration site mapping of infected Jurkat T-cells revealed that productively and non-productively infected cells are indistinguishable in terms of genomic landmarks, surrounding epigenetic landscapes, and proviral orientation relative to host genes. However, direct non-productive infections were inversely correlated with both cellular activation state and NFkappaB activity. Furthermore, modulating NFkappaB with either small molecules or by conditional overexpression of NFkappaB subunits was sufficient to alter the propensity of HIV-1 to directly enter a non-productive latent state in newly infected cells. Importantly, this modulatory effect was limited to a short time window post-infection. Taken together, our data suggest that cellular activation state and NFkappaB activity during the time of infection, but not the site of proviral integration, are important regulators of direct HIV-1 non-productive infections.
    Full-text · Article · Feb 2014 · Retrovirology
  • Source
    • "The IκB genes themselves are targets of NF-κB resulting in upregulation of IκB, which upon removal of the activating stimulus results in accumulation of IκB in the cytoplasm once more. In addition, a nuclear role for IκBα in regulating NF-κB has more recently become apparent [38], with shuttling of IκBα between the cytoplasm and nucleus previously described in a range of cell types, including T cells [27], [28], [39]. Here we show that IκBα accumulates in the nucleus of T cells following the removal of the activating signal. "
    [Show abstract] [Hide abstract]
    ABSTRACT: The role of the Nuclear Factor κB (NF-κB) transcription factor family in T cell function has been well described. The c-Rel family member is of particular importance in initiating T cell responses to antigen and regulating activation of inflammatory cytokine genes, including the Interleukin-2 (IL-2) and Granulocyte macrophage colony stimulating factor (GM-CSF) genes. c-Rel is required for chromatin remodeling of these gene promoters, which involves depletion of histones from the promoters in response to T cell activating signals. These chromatin remodeling events precede transcriptional activation of the genes. The subsequent down-regulation of cytokine gene expression is important in the termination of an immune response and here we examine this process at the murine GM-CSF and IL-2 genes. We show that the cytokine mRNA levels rapidly return to basal levels following stimulus removal and this is associated with reassembly of histones onto the promoter. Histone reassembly at the GM-CSF and IL-2 promoters occurs concomitantly with depletion of RelA, c-Rel and RNA polymerase II from the promoters. Furthermore we show that transcriptional down-regulation and chromatin reassembly is dependent on depletion of c-Rel from the nucleus, and that this is regulated by the nuclear translocation of the NF-κB inhibitor, IκBα. The nuclear activation of c-Rel therefore not only regulates the initiation of GM-CSF and IL-2 gene activation in response to T cell activation, but also the termination of these gene responses following the removal of the activating signal.
    Full-text · Article · Jul 2012 · PLoS ONE
  • Source
    • "The 5′LTR functions as an HIV-1 promoter and contains several DNA binding sites for various cellular transcription factors such as SP1 and NF-κB which are required for viral replication, whereas other sites, such as those binding NFAT, LEF-1, COUP-TF, ets-1, USF, and AP-1, enhance transcription without being indispensable [56–58]. The p50/p65 NF-κB heterodimer is sequestered into the cytoplasm in unstimulated cells through its interaction with an inhibitory protein of the family of NF-κB inhibitors (IκBs) [59]. Following cellular activation, phosphorylation of IκB by IκB kinase (IKK) results in its dissociation from NF-κB, NF-κB translocation into the nucleus, and transcription of NF-κB-dependent genes [60]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: The introduction of highly active antiretroviral therapy (HAART) has been an important breakthrough in the treatment of HIV-1 infection and has also a powerful tool to upset the equilibrium of viral production and HIV-1 pathogenesis. Despite the advent of potent combinations of this therapy, the long-lived HIV-1 reservoirs like cells from monocyte-macrophage lineage and resting memory CD4+ T cells which are established early during primary infection constitute a major obstacle to virus eradication. Further HAART interruption leads to immediate rebound viremia from latent reservoirs. This paper focuses on the essentials of the molecular mechanisms for the establishment of HIV-1 latency with special concern to present and future possible treatment strategies to completely purge and target viral persistence in the reservoirs.
    Full-text · Article · Apr 2012 · Advances in Virology
Show more