Infection by the human immunodeficiency virus (HIV) either upregulates or downregulates the expression of several cytokines and interferons (IFNs) that use the Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway for signal transduction. However, very little is known on the state of activation of the JAK/STAT pathway after HIV infection either in vivo or in vitro. In this regard, we report here that a constitutive activation of a C-terminal truncated STAT5 (STAT5▵) and of STAT1 occurs in the majority (∼75%) of individuals with progressive HIV disease. We have further demonstrated that, among peripheral blood mononuclear cells (PBMCs), STAT5▵ is activated preferentially in CD4+ T cells. In contrast to a published report, expression of STATs from PBMCs of infected individuals was comparable with that of seronegative donors. In addition, in vitro infection of mitogen-activated PBMCs with a panel of laboratory-adapted and primary HIV strains characterized by differential usage of chemokine coreceptors did not affect STAT protein levels. However, enhanced activation of STAT was observed after in vitro infection of resting PBMCs and nonadherent PBMCs by different viral strains. Thus, constitutive STAT activation in CD4+T lymphocytes represents a novel finding of interest also as a potential new marker of immunological reconstitution of HIV-infected individuals.

Infection by the human immunodeficiency virus (HIV) either upregulates or downregulates the expression of several cytokines and interferons (IFNs) that use the Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway for signal transduction. However, very little is known on the state of activation of the JAK/STAT pathway after HIV infection either in vivo or in vitro. In this regard, we report here that a constitutive activation of a C-terminal truncated STAT5 (STAT5▵) and of STAT1 occurs in the majority (∼75%) of individuals with progressive HIV disease. We have further demonstrated that, among peripheral blood mononuclear cells (PBMCs), STAT5▵ is activated preferentially in CD4+ T cells. In contrast to a published report, expression of STATs from PBMCs of infected individuals was comparable with that of seronegative donors. In addition, in vitro infection of mitogen-activated PBMCs with a panel of laboratory-adapted and primary HIV strains characterized by differential usage of chemokine coreceptors did not affect STAT protein levels. However, enhanced activation of STAT was observed after in vitro infection of resting PBMCs and nonadherent PBMCs by different viral strains. Thus, constitutive STAT activation in CD4+T lymphocytes represents a novel finding of interest also as a potential new marker of immunological reconstitution of HIV-infected individuals.

The susceptibility of HIV-1 to chemokine-mediated inhibition may be lost as a consequence of the expanded usage of chemokine co-receptors frequently occurring in clade B isolates obtained from individuals with advanced disease. Since chemokine-based immune intervention is under intense investigation, it is crucial to determine its potential effect on primary dualtropic HIV isolates characterized by simultaneous utilization of CCR5 and CXCR4 chemokine co-receptors (R5X4 viruses). In the present study, the CCR5 binding chemokine regulated upon activation normal T cell expressed and secreted (RANTES) strongly inhibited the replication of two of eight primary R5X4 viruses in mitogen-activated primary peripheral blood mononuclear cells (PBMC). The CXCR4 antagonist AMD3100 efficiently suppressed the replication of other two HIV isolates, whereas the remaining four viruses were partially inhibited by treatment with either RANTES or AMD3100. The potency of chemokine-mediated inhibition was influenced by PBMC donor variability, but it was usually independent from the levels of expression of CCR5 or CXCR4. Dual co-receptor usage was maintained by the viruses after two serial passages on U87.CD4 astrocytic cell lines expressing exclusively either CCR5 or CXCR4. The gp120 env variable domains were sequenced before and after passages on U87.CD4 cells. Virus replication into U87.CD4-CXCR4 cells did not result in changes in the V3 region but perturbed the dominant env V4 sequence. Interestingly, double passage onto U87.CD4-CXCR4 cells determined the loss of susceptibility to RANTES inhibition. In conclusion, interference with CCR5 may efficiently inhibit the replication of at least some dualtropic HIV-1 strains, whereas forced CXCR4 usage may result in viral escape from CCR5-dependent inhibitory effects.

Leader binding protein-1 (LBP-1)/late SV40 factor (LSF) and ying yang-1 (YY1) transcription factors are involved in the regulation of HIV expression. In particular, YY1 and LBP-1 have been shown to cooperate in repressing HIV-1-long terminal repeat reporter gene expression by in vitro cotransfection experiments. However, no information is available on the levels of expression and activation of these transcription factors in PBMC of HIV-infected individuals. Therefore, we have evaluated the expression and DNA binding activity of YY1 and LBP-1 (LSF) in PBMC of HIV-infected individuals before, during, and after administration of IL-2 in association with antiretroviral therapy (ART), a regimen under consideration for broad clinical use in this disease based on its ability to stably raise the absolute number of circulating CD4+ T lymphocytes. Both YY1- and LBP-1 (LSF)-DNA binding were profoundly down-modulated during administration of IL-2/ART, and a proteolytic activity probably responsible for the reduced expression of the two cellular transcription factors was found activated in PBMC of individuals receiving the immunotherapeutic regimen. This study is the first evidence of modulation of cellular transcription factors following IL-2/ART administration and provides a potential correlate of the transient raises in plasma viremia early reported in patients receiving IL-2 in the absence of ART, thus underscoring the importance of always administering this cytokine to HIV-infected individuals together with potent antiretrovirals.

IFN-γ induces transcription of several IFN-stimulated genes (ISGs). Recently, the IFN-γ-dependent Janus kinase (JAK)/STAT pathway has been shown to mediate the activation of some ISGs, by the sequential phosphorylation of two JAK kinases (JAK1 and JAK2) and of STAT1. Given that the JAK/STAT is the major, but not the only pathway linked to the IFN-γR, aim of our work was to investigate the signal-transduction pathway(s) by which IFN-γ exerts its effects on acute replication of HIV in monocytic cells. To this end, we utilized clones previously derived from the U937 promonocytic cell line, differing for their efficient (plus clones) or inefficient (minus clones) abilities of supporting HIV replication. Unlike IFN-α, IFN-γ did not inhibit HIV replication in plus clones, whereas virus production in minus cells was efficiently inhibited by both types of IFN. Plus clones generated a JAK/STAT signal-transduction pathway in response to IFN-α, but not IFN-γ. In contrast, minus clones responded to either cytokines. The functional defect of plus clones in response to IFN-γ was correlated to a selective defect of IFN-γR2, but not IFN-γR1, membrane expression. Surprisingly enough, IFN-γ stimulation of plus clones induced IFN-stimulated gene factor 3 (ISGF3γ). These results strongly support the hypothesis that the JAK/STAT pathway is responsible for the antiretroviral effect of IFN-γ, and further provide evidence for a potential second pathway triggered by IFN-γ in the absence of IFN-γR2 chain cell surface expression and involving ISGF3γ.