Multifactorial Role of HIV-Vpr in Cell Apoptosis Revealed by a Naturally Truncated 54aa Variant
Human immunodeficiency virus type 1 (HIV-1) remains a significant global public health challenge despite the effectiveness of antiretroviral therapy (ART) in suppressing viral replication. Among the various proteins encoded by HIV-1, the viral protein R (Vpr) is a multifunctional accessory protein known for its role in regulating cellular apoptosis. This study investigates the multifactorial role of Vpr in apoptosis, focusing on a naturally truncated 54-amino acid (aa) variant (∗54Vpr) identified in HIV patients during the acquired immunodeficiency syndrome (AIDS) phase. The research reveals novel insights into the apoptosis-regulating domains of Vpr and its interaction with distinct adenine nucleotide translocator (ANT) isoforms, shedding light on the cell-dependent pro- and antiapoptotic effects of Vpr.
The Role of Vpr in Apoptosis Regulation
Vpr is a critical protein in the HIV-1 life cycle, with its primary function being the regulation of cellular apoptosis. Previous studies have identified the C-terminal region of Vpr, specifically the aa positions 52–96, as the apoptosis-regulating domain. However, this study uncovers a novel apoptosis-regulating domain located in the N-terminus of Vpr, spanning aa positions 23–37. The discovery of this domain in the N-terminus adds a new layer of complexity to the understanding of Vpr’s multifunctional role in apoptosis.
Identification and Characterization of the Truncated ∗54Vpr Variant
The study focuses on a naturally occurring truncated variant of Vpr, ∗54Vpr, which lacks the C-terminal apoptosis-regulating domain. The ∗54Vpr variant was isolated from HIV patients in the AIDS phase, and its effects on apoptosis were compared with those of the full-length Vpr. The researchers used two distinct isolates of HIV-1: the CRF07_BC ∗54Vpr and the B subtype ∗54Vpr (pNL4-3_54Stop), along with their corresponding full-length Vpr counterparts (XJN0084_54W and pNL4-3).
To investigate the apoptosis-inducing effects of Vpr, the researchers constructed green fluorescent protein (GFP)-tagged Vpr expression vectors and transfected them into 293T and TZM-bl cells. Apoptosis was measured using Annexin-V staining and fluorescence-activated cell sorting (FACS) analysis. The results showed that both the full-length Vpr and the ∗54Vpr variant induced significant apoptosis in TZM-bl cells but not in 293T cells, indicating that the proapoptotic effects of Vpr are cell line dependent.
Interaction of Vpr with ANT Isoforms
The study further explored the mechanism underlying the cell-dependent proapoptotic activity of Vpr by examining its interaction with ANT isoforms. ANT is a mitochondrial membrane protein involved in the regulation of apoptosis. The researchers analyzed the RNA expression levels of three ANT isoforms (ANT1, ANT2, and ANT3) in 293T, TZM-bl, and HeLa cells using quantitative PCR. The results revealed that ANT3 was highly expressed in TZM-bl cells compared to 293T and HeLa cells, while ANT1 and ANT2 were expressed at very low levels in all three cell lines.
To investigate the role of ANT isoforms in Vpr-mediated apoptosis, the researchers cotransfected ANT1, ANT2, and ANT3 expression vectors with GFP-Vpr into 293T and TZM-bl cells. The results demonstrated that the overexpression of ANT1 or ANT3 in 293T cells significantly increased apoptosis in the presence of Vpr. In contrast, the overexpression of ANT2 in TZM-bl cells reduced apoptosis in the presence of Vpr. These findings suggest that the proapoptotic activity of Vpr is dependent on the expression levels of specific ANT isoforms in different cell lines.
Identification of a Novel Apoptosis-Regulating Domain in the N-Terminus of Vpr
The study identified a potential new apoptosis-regulating domain in the N-terminus of Vpr, spanning aa positions 23–37. To characterize this domain, the researchers introduced a series of site-directed mutations in the GFP-Vpr expression vector, truncating Vpr at various aa positions (43, 38, 34, 30, 27, and 23). These mutated Vpr variants were transfected into TZM-bl cells, and their proapoptotic activities were assessed using FACS analysis.
The results showed that Vpr variants truncated at aa positions 34, 38, and 43 induced significant apoptosis in TZM-bl cells, similar to the full-length Vpr and the ∗54Vpr variant. In contrast, Vpr variants truncated at aa positions 30, 27, and 23 did not induce significant apoptosis. These findings suggest that the first helix of Vpr, spanning aa positions 23–37, contains a critical proapoptotic motif.
Confirmation of the Proapoptotic Activity of the Vpr23-37aa Domain
To confirm the proapoptotic activity of the Vpr23-37aa domain, the researchers compared the apoptosis-inducing effects of the Vpr23-37aa domain with the well-known cell death domain in the C-terminus of Vpr (aa positions 71–92). The results showed that both domains induced significant apoptosis in TZM-bl cells, further supporting the role of the Vpr23-37aa domain as a novel apoptosis-regulating motif.
Multifactorial Roles of Vpr in Apoptosis Regulation
The study highlights the multifactorial roles of Vpr in regulating apoptosis through its interaction with distinct ANT isoforms. The data suggest that the proapoptotic effects of Vpr are mediated by its interaction with ANT1 and ANT3, while the antiapoptotic effects are mediated by its interaction with ANT2. This differential interaction with ANT isoforms explains the cell-dependent proapoptotic activity of Vpr and provides new insights into the complex regulatory mechanisms of apoptosis in HIV-1-infected cells.
Implications for HIV-1 Pathogenesis and Therapeutic Strategies
The findings of this study have significant implications for understanding HIV-1 pathogenesis and developing therapeutic strategies. The identification of a novel apoptosis-regulating domain in the N-terminus of Vpr and its interaction with distinct ANT isoforms provide new targets for therapeutic intervention. Understanding the multifactorial roles of Vpr in apoptosis regulation could lead to the development of novel therapies that modulate apoptosis in HIV-1-infected cells, potentially reducing viral persistence and latency.
Conclusion
This study provides a comprehensive analysis of the multifactorial role of HIV-1 Vpr in regulating cellular apoptosis. The identification of a naturally truncated 54aa variant (∗54Vpr) and the discovery of a novel apoptosis-regulating domain in the N-terminus of Vpr (aa positions 23–37) add new dimensions to the understanding of Vpr’s function. The interaction of Vpr with distinct ANT isoforms reveals the cell-dependent pro- and antiapoptotic effects of Vpr, highlighting the complex regulatory mechanisms of apoptosis in HIV-1-infected cells. These findings open new avenues for research into HIV-1 pathogenesis and the development of targeted therapeutic strategies.
doi.org/10.1097/CM9.0000000000001297
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