HIV-1 Promotes the Degradation of Components of the Type 1 IFN JAK/STAT Pathway and Blocks Anti-viral ISG Induction

Abstract

Anti-retroviral therapy successfully suppresses HIV-1 infection, but fails to provide a cure. During infection Type 1 IFNs normally play an essential role in viral clearance, but in vivo IFN-α only has a modest impact on HIV-1 infection, suggesting its possible targeting by HIV. Here, we report that the HIV protein, Vif, inhibits effective IFN-α signalling via degradation of essential JAK/STAT pathway components. We found that STAT1 and STAT3 are specifically reduced in HEK293T cells expressing Vif and that full length, infectious HIV-1 IIIB strain promotes their degradation in a Vif-dependent manner. HIV-1 IIIB infection of myeloid ThP-1 cells also reduced the IFN-α-mediated induction of the anti-viral gene, ISG15, but not MxA, revealing a functional consequence of this HIV-1-mediated immune evasion strategy. Interestingly, while total STAT levels were not reduced upon in vitro IIIB infection of primary human PBMCs, IFN-α-mediated phosphorylation of STAT1 and STAT3 and ISG induction were starkly reduced, with removal of Vif (IIIBΔVif), partially restoring pSTATs, ISG15 and MxB induction. Similarly, pSTAT1 and pSTAT3 expression and IFN-α-induced ISG15 were reduced in PBMCs from HIV-infected patients, compared to healthy controls. Furthermore, IFN-α pre-treatment of a CEM T lymphoblast cells significantly inhibited HIV infection/replication (measured by cellular p24), only in the absence of Vif (IIIBΔVif), but was unable to suppress full length IIIB infection. When analysing the mechanism by which Vif might target the JAK/STAT pathway, we found Vif interacts with both STAT1 and STAT3, (but not STAT2), and its expression promotes ubiquitination and MG132-sensitive, proteosomal degradation of both proteins. Vif's Elongin-Cullin-SOCS-box binding motif enables the formation of an active E3 ligase complex, which we found to be required for Vif's degradation of STAT1 and STAT3. In fact, the E3 ligase scaffold proteins, Cul5 and Rbx2, were also found to be essential for Vif-mediated proteasomal degradation of STAT1 and STAT3. These results reveal a target for HIV-1-Vif and demonstrate how HIV-1 impairs the anti-viral activity of Type 1 IFNs, possibly explaining why both endogenous and therapeutic IFN-α fail to activate more effective control over HIV infection.

DHAV-1 Inhibits Type I Interferon Signaling to Assist Viral Adaption by Increasing the Expression of SOCS3

“…The innate immune system recognizes invasive viruses through pattern recognition receptors (PRRs) and then activates downstream pathways to produce IFNs; the IFNs then bind to corresponding receptors to activate the JAK-STAT signaling pathway, ultimately inducing antiviral responses to produce the antiviral proteins MX1, OASL, and others (31). Therefore, we wanted to further explore whether SOCS3 affected the expression of downstream antiviral proteins.…”

“…A variety of viruses disrupt the IFNα signaling pathway by degrading the major components of the JAK-STAT signaling pathway. For example, the HIV Vif protein achieves immune evasion by disrupting the IFNα-mediated phosphorylation of STAT1 and STAT3 and reducing the expression of ISG15 (31). However, enterovirus 71 (EV71) inhibits the intracellular type I IFN signaling pathway by downregulating the expression of the JAK1 protein (40).…”

Manipulation of Type I Interferon Signaling by HIV and AIDS-Associated Viruses

“…The protein Vif of HIV has been proposed to play a role in its own catalysis, in the ubiquitination and proteasomal degradation of STAT1 and STAT3 proteins of the JAK/STAT pathway, and in the degradation of monocytic cell lines, which allows HIV-1 to block the antiviral effects of IFN-I. More specifically, Vif-mediated STAT1 and STAT3 inhibition reduces IFN- α induction of ISG-15 [14]. On the other hand, another work has shown that Vpu and Nef are able to block the phosphorylation of Nef without the degradation of STAT1 in T-cell lines [15].…”

Zinc Finger CCCH-Type Antiviral Protein 1 Restricts the Viral Replication by Positively Regulating Type I Interferon Response

“…The interaction of IFNs with their receptors on the cell membrane initiates the Janus protein tyrosine kinase/signal transducers and activators of transcription (JAK/STAT) signaling cascade to regulate transcription of IFN-stimulated genes (ISGs) that generate an antiviral state within the cell. IFN-activated JAK/STAT signaling can also create an antiviral state in adjacent cells (Chen et al, 2018;Gargan et al, 2018).…”