Abstract
BackgroundVpr is exclusively expressed in primate lentiviruses and contributes to viral replication and disease progression in vivo. HIV-1 Vpr has two major activities in vitro: arrest of cell cycle in the G2 phase (G2 arrest), and enhancement of viral replication in macrophages. Previously, we reported a potent HIV-1 restriction in the human CD4+ CEM.NKR (NKR) T cells, where wild-type (WT) HIV-1 replication was inhibited by almost 1,000-fold. From the parental NKR cells, we isolated eight clones by limiting dilution. These clones showed three levels of resistance to the WT HIV-1 infection: non-permissive (NP), semi-permissive (SP), and permissive (P). Here, we compared the replication of WT, Vif-defective, Vpr-defective, and Vpu-defective viruses in these cells.ResultsAlthough both WT and Vpu-defective viruses could replicate in the permissive and semi-permissive clones, the replication of Vif-defective and Vpr-defective viruses was completely restricted. The expression of APOBEC3G (A3G) cytidine deaminase in NKR cells explains why Vif, but not Vpr, was required for HIV-1 replication. When the Vpr-defective virus life cycle was compared with the WT virus life cycle in the semi-permissive cells, it was found that the Vpr-defective virus could enter the cell and produce virions containing properly processed Gag and Env proteins, but these virions showed much less efficiency for reverse transcription during the next-round of infection. In addition, although viral replication was restricted in the non-permissive cells, treatment with arsenic trioxide (As2O3) could completely restore WT, but not Vpr-defective virus replication. Moreover, disruption of Vpr binding to its cofactor DCAF1 and/or induction of G2 arrest activity did not disrupt the Vpr activity in enhancing HIV-1 replication in NKR cells.ConclusionsThese results demonstrate that HIV-1 replication in NKR cells is Vpr-dependent. Vpr promotes HIV-1 replication from the 2nd cycle likely by overcoming a block at early stage of viral replication; and this activity does not require DCAF1 and G2 arrest. Further studies of this mechanism should provide new understanding of Vpr function in the HIV-1 life cycle.
Highlights
Viral protein regulatory (Vpr) is exclusively expressed in primate lentiviruses and contributes to viral replication and disease progression in vivo
Vpr binds to the DDB1-Cullin 4A (Cul4A)-associated-factor-1 (DCAF1) protein, which is recognized by the Cullin (Cul) 4A E3 ligase consisting of Cul4A, RING H2 finger protein homolog (RBX1), and DNA damage-binding protein 1 (DDB1)
Vpr is required for HIV-1 replication in the permissive and semi-permissive the parental CEM.NKR cells (NKR) clones Previously, we reported a potent HIV-1 restriction in the human CD4+ CEM.NKR (NKR) T cells [42]
Summary
Vpr is exclusively expressed in primate lentiviruses and contributes to viral replication and disease progression in vivo. Inactivated vpr genes quickly revert back to the active form after infecting a human subject, chimpanzees, and rhesus monkeys, indicating that vpr is under strong positive selection [9,10]; vpr mutations are frequently found in HIV-1 patients with slow disease progression [11,12,13,14]; vpr/vpx double-deletion mutation markedly attenuates SIV replication in rhesus monkeys [15,16]; vpx singledeletion mutation significantly attenuates SIV replication in pig-tailed monkeys [17,18] These results suggest that vpr and vpx are very important for viral replication and disease progression in vivo. All these downstream events may induce killing of infected cells and contribute to viral pathogenesis in vivo
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