Abstract:
Human immunodeficiency virus type 1 (HIV-1), the lentiviral pathogen behind the global AIDS
pandemic, preferentially infects CD4+ T lymphocytes, leading to their progressive depletion via both direct viral cytotoxicity and through increased rates of apoptosis. To achieve full pathogenicity in vivo, HIV-1 encodes multiple accessory proteins, most of which play defined roles at various steps of the viral replication cycle. In contrast, the 96-amino acid Viral Protein R (Vpr) is implicated in disrupting host cell physiology through a variety of mechanisms, such as facilitating the nuclear import of viral pre-integration complexes, as well as significantly boosting viral production by enhancing the transcriptional activity of viral LTRs. Further, Vpr is actively encapsidated into HIV-1 virions, allowing its direct delivery into host cells upon de novo infection. Collectively, these characteristics epitomize Vpr as a crucial supporting element in the establishment of a productive HIV-1 infection. Nevertheless, multiple gaps exist in the understanding of the mechanisms whereby Vpr allows HIV-1 to exert control over its host cell at various organizational levels, and many studies still fail to answer these questions in physiologically relevant models, such as donor-derived CD4+ T lymphocytes. To address these issues, HIV-1 infection assays employing inhibitors for various signaling pathways were performed on T cell-derived models and primary CD4+ T cells alike, focusing on Vpr’s role in the induction of NF-AT signaling. Consecutively, a thorough bioinformatic analysis was executed on an RNA-Seq dataset derived from HIV-1-infected primary T lymphocytes, aiming to identify how Vpr presence can influence the transcriptomic footprint left by HIV-1 on its host. Finally, Vpr’s ability to hijack and redirect its host’s proteasomal activity was studied in the context of two putative protein targets previously identified through non-targeted proteomics: TCF7 and G3BP1. The present work demonstrated that the role virion-delivered Vpr plays in supporting the establishment of a productive HIV-1 infection is highly reliant on its ability to induce the activation of NF-AT, as artificially inhibiting this transcriptional factor completely curtailed Vpr’s characteristic boost in viral productivity and spread. The aforementioned bioinformatic analyses revealed that Vpr-mediated NF-AT induction leads to the transcriptional reprogramming of the host T cell, differentially affecting a variety of physiological processes, including cell cycle progression, ribosome assembly, protein translation, immune & inflammatory function, intracellular signaling, and cell proliferation, amongst others. In addition, this study established the mechanism whereby Vpr leads to the proteasomal degradation of TCF7, a trans-acting factor of central relevance towards T cell development, differentiation, and survival. Taken together, these results establish Vpr-mediated NF-AT activation as a central mechanism through which HIV-1 reprograms T cell physiology to enhance viral replication, expanding Vpr’s array of virus-supporting roles and illustrating their eventual outcome on T cell physiology. Future work ought to prioritize validating many of these phenomena in primary CD4+ T cells, in parallel exploring the downstream effects of Vpr-targeted protein degradation on T cell differentiation, exhaustion, as well as in the establishment and reactivation of potential HIV-1 reservoir populations.
NF-AT