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  • Poster presentation
  • Open Access

HIV-1 replication changes the function of the PKR activator PACT

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Retrovirology201310 (Suppl 1) :P35

  • Published:


  • Adenosine Deaminase
  • eIF2a Phosphorylation
  • Cell Line U251MG
  • Astrocytic Cell Line
  • Pact Function


HIV-1 translation is modulated by the activation of the interferon-inducible Protein Kinase R (PKR), which phosphorylates its downstream target, the eukaryotic translation Initiation Factor 2 (eIF2a). Phosphorylated eIF2a blocks translation initiation and consequently viral replication. PKR is not activated in HIV-1-replicating lymphocytes. Inactivated PKR allows high HIV-1 translation and may contribute to HIV-1 persistence in several cell types.


Peripheral blood mononuclear cells (PBMCs) were infected with HIV-1 molecular clone pNL4-3. Viral kinetics were followed by reverse transcriptase (RT) assay. Expression of viral and cellular proteins were monitored by immunoprecipitation (IP) and western blots.


PKR is transiently induced and activated in PBMCs after HIV-1 infection and dephosphorylated during viral replication. The expression of two double-stranded RNA binding proteins, the RNA adenosine deaminase (ADAR) 1 and the PKR Activator (PACT) is induced during HIV-1 infection. By co-IP of HIV-1-infected lymphocytes with antibodies against PKR, we identified a multiprotein complex, which contains ADAR1 and PACT. PACT is known to activate PKR after a cellular stress. In cells transfected with an HIV-1 molecular clone, PACT unexpectedly inhibited PKR and eIF2a phosphorylation and increased HIV-1 protein expression and virion production. Short hairpin RNAs against PACT decreased HIV-1 protein expression. Furthermore, ADAR1, the TAR RNA binding protein, TRBP, and PACT all inhibit PKR and eIF2a phosphorylation in HIV-1-expressing cells. In the astrocytic cell line U251MG that weakly expresses TRBP, PACT also mediated an increased HIV-1 protein expression and a decreased PKR phosphorylation. Finally, PACT and ADAR1 interact with each other in the absence of RNA, which may mediate the change of PACT function in HIV-1 infected cells.


In contrast to its previously described activity, PACT contributes to PKR dephosphorylation during HIV-1 replication. This activity is in addition to the previously described inhibition of PACT by TRBP [1] and to the direct activity of ADAR1 on PKR [2]. The change in PACT function is likely due to its interaction with ADAR1 but does not exclude the contribution of another HIV-1 component or virally-induced cellular factor. PKR inactivation likely contributes to HIV-1 persistence in several cell types.



This work was supported by grants from the Canadian Institutes for Health Research and by the Réseau-SIDA Maladies Infectieuses from the Fond de la Recherche du Québec en Santé.

Authors’ Affiliations

Virus-Cell Interactions Laboratory, Lady Davis Institute for Medical Research, Montréal, QC, Canada
Department of Medicine, Division of Experimental Medicine, McGill University, Montréal, QC, Canada
Department of Microbiology and Immunology, McGill University, Montréal, QC, Canada
Chronic Viral Illness Service and Division of Hematology, McGill University Health Centre, Montréal, QC, Canada
Department of Biological Sciences, University of South Carolina, Columbia, SC, USA


  1. Daher A, Laraki G, Singh M, Melendez-Peña CE, Bannwarth S, Peters AH, Meurs EF, Braun RE, Patel RC, Gatignol A: TRBP control of PACT-induced phosphorylation of PKR is reversed by stress. Mol Cell Biol. 2009, 29: 254-265. 10.1128/MCB.01030-08.PubMed CentralView ArticlePubMedGoogle Scholar
  2. Clerzius G, Gélinas JF, Daher A, Bonnet M, Meurs EF, Gatignol A: ADAR1 interacts with PKR during human immunodeficiency virus infection of lymphocytes and contributes to viral replication. J Virol. 2009, 83: 10119-10128. 10.1128/JVI.02457-08.PubMed CentralView ArticlePubMedGoogle Scholar


© Clerzius et al; licensee BioMed Central Ltd. 2013

This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.