Role of HIV-1 Tat Protein Interactions with Host Receptors in HIV Infection and Pathogenesis

Abstract

Each time the virus starts a new round of expression/replication, even under effective antiretroviral therapy (ART), the transactivator of viral transcription Tat is one of the first HIV-1 protein to be produced, as it is strictly required for HIV replication and spreading. At this stage, most of the Tat protein exits infected cells, accumulates in the extracellular matrix and exerts profound effects on both the virus and neighbor cells, mostly of the innate and adaptive immune systems. Through these effects, extracellular Tat contributes to the acquisition of infection, spreading and progression to AIDS in untreated patients, or to non-AIDS co-morbidities in ART-treated individuals, who experience inflammation and immune activation despite virus suppression. Here, we review the role of extracellular Tat in both the virus life cycle and on cells of the innate and adaptive immune system, and we provide epidemiological and experimental evidence of the importance of targeting Tat to block residual HIV expression and replication. Finally, we briefly review vaccine studies showing that a therapeutic Tat vaccine intensifies ART, while its inclusion in a preventative vaccine may blunt escape from neutralizing antibodies and block early events in HIV acquisition.

Keywords: HIV functional cure; HIV preventative vaccine; HIV therapeutic vaccine; HIV vaccine; HIV-1 Env; HIV-1 Tat protein; HIV-1 Tat/Env complex; HIV-1 infection; HIV-1 pathogenesis; extracellular Tat protein.

Figure 1

HIV-1 Tat sequence (HXBc2 strain) and functional domains. See text for Tat domains’ detailed description.

Figure 2

Effects of extracellular Tat on cells that are key players of the innate and adaptative immune response. Arrows indicate increase (blue) or decrease (red) of the markers shown. AICDA: Activation-induced cytidine deaminase; Bcl-2, -6: B-cell lymphoma 2, 6; Blimp-1: B lymphocyte-induced maturation protein-1; CCR2: C-C chemokine receptor type 2; CCR3: C-C chemokine receptor type 3; CCL-2, -3, -4: chemokine (C-C motif) ligand 2, 3, 4; HLA-ABC: Human leukocyte antigens A, B, C; HLA-DR: HLA class II cell surface receptor; ICAM-1: Intercellular Adhesion Molecule 1; IDO-1: Indoleamine 2,3-dioxygenase; IL: Interleukin; IFN-γ: Interferon gamma; MMP-9: Matrix metalloproteinase-9; mROS: mitochondrial reactive oxygen species; mTORC1: mammalian target of rapamycin complex 1; PD-L1: Programmed death-ligand 1; T-bet: T-box transcription factor TBX21; VEGF: Vascular endothelial growth factor; VEGFR-1: Vascular endothelial growth factor receptor 1; VCAM-1: Vascular cell adhesion protein 1.