Nos études actuelles sur la protéine Vpr du VIH-1 visent à déterminer si cette protéine recrute le complexe DDB1-CUL4A-DCAF1 E3 ligase pour promouvoir la dégradation de une ou plusieurs protéines des cellules hôtes intervenant dans les réponses aux stress/dommages dans l’ADN ou dans la restriction de la réplication virale à l’intérieur des macrophages.
Quelques-unes des questions examinées par nos études en cours :
Viral protein R (Vpr): a viral protein inducing genotoxic stress Viral protein R (Vpr) is a 96 amino-acids protein that is packaged into mature HIV-1 virions. Vpr contributes to HIV-1 infection and persistence by playing a critical role in two distinct aspects of the interaction between HIV-1 and host target cells. First, Vpr arrests cells in the G2 phase of the cell-cycle by activating the DNA stress/damage-sensing kinase ATR. While G2 arrest by Vpr is believed to enhance HIV replication since viral transcription is more active in G2, it is also possible that ATR activation may have other functional consequences. We recently demonstrated that Vpr, like Vif and Vpu, engages a modular cullin-ring ubiquitin E3 ligase, in this case the DDB1-CUL4A-DCAF1 E3 ligase complex, via the substrate specificity receptor DCAF1 (DDB1- and CUL4-associated Factor), in order to induce a G2 arrest. This finding as well as more recent results raise the possibility that Vpr could act as a connector between the DDB1-CUL4A-DCAF1 E3 ligase complex and an unknown cellular factor(s) whose ubiquitination and degradation would lead to ATR activation and G2 arrest. A detailed understanding of Vpr-DCAF1 interactions and the identification of the substrate(s) targeted for degradation by Vpr remain central to understanding the effect of Vpr on ATR activation and its functional relevance. In addition to G2 arrest, HIV-1 Vpr facilitates infection of macrophages and dendritic cells (DC), which are considered critical viral reservoirs and major contributors of HIV pathogenesis. Interestingly, recent evidence indicates that HIV-2/SIVSM Vpx, a paralogue of HIV-1 Vpr, promotes infection of macrophage by antagonizing a host restriction, which prevents efficient reverse transcription. Importantly, Vpx, like Vpr, binds DCAF1 and the ability of SIV Vpx to interact with the DDB1-CUL4A-DCAF1 E3 ligase complex is essential for promoting HIV/SIVSM infection of macrophage. However, the identity of the Vpr/Vpx-regulated host cell restriction factor(s) that interferes with efficient virus replication in macrophage remains unknown. Finally, in addition to its function within infected cells, the role of extracellular Vpr as an effector of pathogenesis has also recently emerged. Vpr is packaged in significant amounts in infectious and defective virions and it can be detected in the serum and cerebrospinal fluid of HIV-infected patients. Importantly, in vitro studies implicate extracellular Vpr (virion-associated and soluble forms) as an effector of cellular responses, including G2-arrest, apoptosis and increased permissiveness of macrophages to Vpr-defective virus replication, through its ability to transduce into multiple cell types. Thus, the persistence of HIV-1 and ultimately its pathogenesis are in part intrinsically tied to the biological activities of Vpr.
Our current investigation on HIV-1 Vpr are aimed at investigating whether HIV-1 Vpr engages the DDB1-CUL4A-DCAF1 E3 ligase complex to promote degradation of host cell protein(s) that are involved in DNA stress/damage responses or/and in restricting virus replication in macrophages. Some questions addressed in ongoing studies: