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Interactions with DCAF1 and DDB1 in the CRL4 E3 ubiquitin ligase are required for Vpr-mediated G2 arrest.

ABSTRACT: HIV-1 Vpr-mediated G2 cell cycle arrest is dependent on the interaction of Vpr with an E3 ubiquitin ligase that contains damage-specific DNA binding protein 1 (DDB1), Cullin 4A (Cul4A), DDB1 and Cul4-associated factor 1 (DCAF1), and Rbx1. Vpr is thought to associate directly with DCAF1 in the E3 ubiquitin ligase complex although the exact interaction pattern of the proteins in the complex is not completely defined. The Vpr of SIVagm induces G2 arrest of cognate African Green Monkey (AGM) cells but not human cells. The molecular mechanism by which SIVagm Vpr exhibits its species-specific function remained unknown.Physical interaction of proteins in the E3 ubiquitin ligase complex was assessed by co-immunoprecipitation followed by western blotting. In addition, co-localization of the proteins in cells was investigated by confocal microscopy. The cell cycle was analyzed by propidium iodide staining and flow cytometry. DNA damage response elicited by Vpr was evaluated by detecting phosphorylation of H2AX, a marker for DNA damage response.We show that RNAi knock-down of DCAF1 prevented the co-immunoprecipitation of DDB1 with HIV-1 Vpr while DDB1 knock-down did not influence the binding of Vpr to DCAF1. HIV-1 Vpr mutants with a L64P or a R90K mutation maintained the ability to associate with DCAF1 but did not appear to be in a complex with DDB1. SIVagm Vpr associated with AGM DCAF1 and DDB1 while, in human cells, it binds to human DCAF1 but hardly binds to human DDB1, resulting in the reduced activation of H2AX.The identification of Vpr mutants which associate with DCAF1 but only poorly with DDB1 suggests that DCAF1 is necessary but the simple binding of Vpr to DCAF1 is not sufficient for the Vpr association with DDB1-containing E3 ligase complex. Vpr may interact both with DCAF1 and DDB1 in the E3 ligase complex. Alternatively, the interaction of Vpr and DCAF1 may induce a conformational change in DCAF1 or Vpr that promotes the interaction with DDB1. The ability of SIVagm Vpr to associate with DDB1, but not DCAF1, can explain the species-specificity of SIVagm Vpr-mediated G2 arrest.

SUBMITTER: Hakata Y

PROVIDER: S-EPMC4058697 | biostudies-literature | 2014 Jun

REPOSITORIES: biostudies-literature

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Interactions with DCAF1 and DDB1 in the CRL4 E3 ubiquitin ligase are required for Vpr-mediated G2 arrest.

Hakata Yoshiyuki Y Miyazawa Masaaki M Landau Nathaniel R NR

Virology journal 20140609

<h4>Background</h4>HIV-1 Vpr-mediated G2 cell cycle arrest is dependent on the interaction of Vpr with an E3 ubiquitin ligase that contains damage-specific DNA binding protein 1 (DDB1), Cullin 4A (Cul4A), DDB1 and Cul4-associated factor 1 (DCAF1), and Rbx1. Vpr is thought to associate directly with DCAF1 in the E3 ubiquitin ligase complex although the exact interaction pattern of the proteins in the complex is not completely defined. The Vpr of SIVagm induces G2 arrest of cognate African Green M ...[more]

PMID: 24912982

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Project description:BackgroundVpr is a virion-associated protein that is encoded by lentiviruses and serves to counteract intrinsic immunity factors that restrict infection. HIV-1 Vpr mediates proteasome-dependent degradation of several DNA repair/modification proteins. Mechanistically, Vpr directly recruits cellular targets onto DCAF1, a substrate receptor of Cullin 4 RING E3 ubiquitin ligase (CRL4) for poly-ubiquitination. Further, Vpr can mediate poly-ubiquitination of DCAF1-interacting proteins by the CRL4. Because Vpr-mediated degradation of its known targets can not explain the primary cell-cycle arrest phenotype that Vpr expression induces, we surveyed the literature for DNA-repair-associated proteins that interact with the CRL4-DCAF1. One such protein is SIRT7, a deacetylase of histone 3 that belongs to the Sirtuin family and regulates a wide range of cellular processes. We wondered whether Vpr can mediate degradation of SIRT7 via the CRL4-DCAF1.MethodsHEK293T cells were transfected with cocktails of plasmids expressing DCAF1, DDB1, SIRT7 and Vpr. Ectopic and endogeneous levels of SIRT7 were monitered by immunoblotting and protein-protein interactions were assessed by immunoprecipitation. For in vitro reconstitution assays, recombinant CRL4-DCAF1-Vpr complexes and SIRT7 were prepared and poly-ubiqutination of SIRT7 was monitored with immunoblotting.ResultsWe demonstrate SIRT7 polyubiquitination and degradation upon Vpr expression. Specifically, SIRT7 is shown to interact with the CRL4-DCAF1 complex, and expression of Vpr in HEK293T cells results in SIRT7 degradation, which is partially rescued by CRL inhibitor MNL4924 and proteasome inhibitor MG132. Further, in vitro reconstitution assays show that Vpr induces poly-ubiquitination of SIRT7 by the CRL4-DCAF1. Importantly, we find that Vpr from several different HIV-1 strains, but not HIV-2 strains, mediates SIRT7 poly-ubiquitination in the reconstitution assay and degradation in cells. Finally, we show that SIRT7 degradation by Vpr is independent of the known, distinctive phenotype of Vpr-induced cell cycle arrest at the G2 phase, CONCLUSIONS: Targeting histone deacetylase SIRT7 for degradation is a conserved feature of HIV-1 Vpr. Altogether, our findings reveal that HIV-1 Vpr mediates down-regulation of SIRT7 by a mechanism that does not involve novel target recruitment to the CRL4-DCAF1 but instead involves regulation of the E3 ligase activity.

Project description:The lentiviral accessory proteins Vpx and Vpr are known to utilize CRL4 (DCAF1) E3 ligase to induce the degradation of the host restriction factor SAMHD1 or host helicase transcription factor (HLTF), respectively. Selective disruption of viral CRL4 (DCAF1) E3 ligase could be a promising antiviral strategy. Recently, we have determined that posttranslational modification (neddylation) of Cullin-4 is required for the activation of Vpx-CRL4 (DCAF1) E3 ligase. However, the mechanism of Vpx/Vpr-CRL4 (DCAF1) E3 ligase assembly is still poorly understood. Here, we report that zinc coordination is an important regulator of Vpx-CRL4 E3 ligase assembly. Residues in a conserved zinc-binding motif of Vpx were essential for the recruitment of the CRL4 (DCAF1) E3 complex and Vpx-induced SAMHD1 degradation. Importantly, altering the intracellular zinc concentration by treatment with the zinc chelator N,N,N'-tetrakis-(2'-pyridylmethyl)ethylenediamine (TPEN) potently blocked Vpx-mediated SAMHD1 degradation and inhibited wild-type SIVmac (simian immunodeficiency virus of macaques) infection of myeloid cells, even in the presence of Vpx. TPEN selectively inhibited Vpx and DCAF1 binding but not the Vpx-SAMHD1 interaction or Vpx virion packaging. Moreover, we have shown that zinc coordination is also important for the assembly of the HIV-1 Vpr-CRL4 E3 ligase. In particular, Vpr zinc-binding motif mutation or TPEN treatment efficiently inhibited Vpr-CRL4 (DCAF1) E3 ligase assembly and Vpr-mediated HLTF degradation or Vpr-induced G2 cell cycle arrest. Collectively, our study sheds light on a conserved strategy by the viral proteins Vpx and Vpr to recruit host CRL4 (DCAF1) E3 ligase, which represents a target for novel anti-human immunodeficiency virus (HIV) drug development.IMPORTANCE The Vpr and its paralog Vpx are accessory proteins encoded by different human immunodeficiency virus (HIV)/simian immunodeficiency virus (SIV) lentiviruses. To facilitate viral replication, Vpx has evolved to induce SAMHD1 degradation and Vpr to mediate HLTF degradation. Both Vpx and Vpr perform their functions by recruiting CRL4 (DCAF1) E3 ligase. In this study, we demonstrate that the assembly of the Vpx- or Vpr-CRL4 E3 ligase requires a highly conserved zinc-binding motif. This motif is specifically required for the DCAF1 interaction but not for the interaction of Vpx or Vpr with its substrate. Selective disruption of Vpx- or Vpr-CRL4 E3 ligase function was achieved by zinc sequestration using N,N,N'-tetrakis-(2'-pyridylmethyl)ethylenediamine (TPEN). At the same time, zinc sequestration had no effect on zinc-dependent cellular protein functions. Therefore, information obtained from this study may be important for novel anti-HIV drug development.

Dataset Information

Interactions with DCAF1 and DDB1 in the CRL4 E3 ubiquitin ligase are required for Vpr-mediated G2 arrest.

Publications

Interactions with DCAF1 and DDB1 in the CRL4 E3 ubiquitin ligase are required for Vpr-mediated G2 arrest.

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