Counteraction of innate sensing and retroviral restriction by patient-derived HIV-1 Vpr.

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Antiviral restriction factors (RFs) can be effector proteins of the type I interferon cascade induced by pathogen sensing. While RFs have the capacity to potently suppress HIV-1 replication, the virus has evolved multiple counteraction strategies which are exerted by the so-called viral accessory proteins. Vpr is the viral accessory protein with the highest abundance in the virion and is delivered directly into the cytoplasm of the infected cell before de novo production of viral proteins. Vpr has various described but still enigmatic functions related to the enhancement of HIV-1 integration and increased viral gene expression and recent studies suggested a role of Vpr in evasion of HIV-1 immune sensing. Hence, we postulate that HIV-1 Vpr might have important functions in the early viral cycle, potentially related to the counteraction of initial blocks in viral replication and productive gene expression. Furthermore, we hypothesize that such mechanisms are likely to be conserved in primary patient-derived HIV-1 Vpr alleles while they could be lost in lab-adapted strains. During the first two years of the SPP funding period (2/2017-02/2019) we challenged this hypothesis by isolation and characterization of Vpr proteins from a cohort of therapy naïve HIV-1-infected individuals differing in viral loads and CD4+ T cell counts. While we identified thus far unknown residues in Vpr associated with disease progression, we found no inhibitory effect of Vpr on the cGAS-pathway in myeloid cells. Furthermore, Vpr modestly enhanced rather than suppressed induction of ISGs in primary HIV-1-infected macrophages and in line with this, robust Vpr-mediated activation of NFAT and a pro-stimulatory effect on NF-κB was observed.Intriguingly, we recently identified a Vpr-degraded and chromatin-associated protein, PHF13, which is a transcriptional regulator that inhibits HIV-1 gene expression, highly reminiscent to the HUSH-complex that is degraded by SIV/HIV-2 Vpx. Vpr primes HIV-1-infected cells for productive infection by at least two mechanisms, i.e. (i) alleviation of transcriptional repression through degradation of PHF13 and (ii) cellular activation via induction of NFAT. Overall, our major hypothesis is that Vpr boosts productive infection of resting non-activated immune cells by generating a pro-inflammatory overall stimulating cellular environment. Thereby, Vpr overcomes the initial restriction to productive viral replication in resting non-activated primary HIV-1 target cells. We aim here to analyze the functional role of PHF13 in this process and elucidate Vpr-targets and their functional role early in HIV-1 infection of primary CD4+ T cells. Based on RNAseq data and our own preliminary work we furthermore put forward the hypothesis that PHF13 interconnects DNA-damage and alterations of the chromatin to immune activation and innate immune response.