title: The PKR activator, PACT, becomes a PKR inhibitor during HIV-1 replication.
abstract: BACKGROUND
  HIV-1 translation is modulated by the activation of the interferon (IFN)-inducible Protein Kinase RNA-activated (PKR). PKR phosphorylates its downstream targets, including the alpha subunit of the eukaryotic translation Initiation Factor 2 (eIF2α), which decreases viral replication. The PKR Activator (PACT) is known to activate PKR after a cellular stress. In lymphocytic cell lines, HIV-1 activates PKR only transiently and not when cells replicate the virus at high levels. The regulation of this activation is due to a combination of viral and cellular factors that have been only partially identified.
  
  
  RESULTS
  PKR is transiently induced and activated in peripheral blood mononuclear cells after HIV-1 infection. The addition of IFN reduces viral replication, and induces both the production and phosphorylation of PKR. In lymphocytic Jurkat cells infected by HIV-1, a multiprotein complex around PKR contains the double-stranded RNA binding proteins (dsRBPs), adenosine deaminase acting on RNA (ADAR)1 and PACT. In HEK 293T cells transfected with an HIV-1 molecular clone, PACT unexpectedly inhibited PKR and eIF2α phosphorylation and increased HIV-1 protein expression and virion production in the presence of either endogenous PKR alone or overexpressed PKR. The comparison between different dsRBPs showed that ADAR1, TAR RNA Binding Protein (TRBP) and PACT inhibit PKR and eIF2α phosphorylation in HIV-infected cells, whereas Staufen1 did not. Individual or a combination of short hairpin RNAs against PACT or ADAR1 decreased HIV-1 protein expression. In the astrocytic cell line U251MG, which weakly expresses TRBP, PACT mediated an increased HIV-1 protein expression and a decreased PKR phosphorylation. In these cells, a truncated PACT, which constitutively activates PKR in non-infected cells showed no activity on either PKR or HIV-1 protein expression. Finally, PACT and ADAR1 interact with each other in the absence of RNAs.
  
  
  CONCLUSIONS
  In contrast to its previously described activity, PACT contributes to PKR dephosphorylation during HIV-1 replication. This activity is in addition to its heterodimer formation with TRBP and could be due to its binding to ADAR1. HIV-1 has evolved to replicate in cells with high levels of TRBP, to induce the expression of ADAR1 and to change the function of PACT for PKR inhibition and increased replication.
authors.affiliation: Lady Davis Institute for Medical Research, 3999 Côte Ste Catherine, Montréal, QC H3T 1E2, Canada. anne.gatignol@mcgill.ca.
authors.forename: Guerline
authors.initials: G
authors.lastname: Clerzius
authors.forename: Eileen
authors.initials: E
authors.lastname: Shaw
authors.forename: Aïcha
authors.initials: A
authors.lastname: Daher
authors.forename: Samantha
authors.initials: S
authors.lastname: Burugu
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Gélinas
authors.forename: Thornin
authors.initials: T
authors.lastname: Ear
authors.forename: Lucile
authors.initials: L
authors.lastname: Sinck
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Routy
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Mouland
authors.forename: Rekha C
authors.initials: RC
authors.lastname: Patel
authors.forename: Anne
authors.initials: A
authors.lastname: Gatignol
mesh_terms: D000243:Adenosine Deaminase / Q000378:metabolism; D002460:Cell Line; D015497:HIV-1 / Q000502:physiology*; D054884:Host-Pathogen Interactions; D006801:Humans; D010766:Phosphorylation; D011485:Protein Binding; D055503:Protein Multimerization; D011499:Protein Processing, Post-Translational; D016601:RNA-Binding Proteins / Q000378:metabolism*; D014779:Virus Replication; D019892:eIF-2 Kinase / Q000037:antagonists & inhibitors*; D000099253:Trans-Activation Responsive RNA-Binding Protein
chemical_list: D000243:Adenosine Deaminase; D016601:RNA-Binding Proteins; D019892:eIF-2 Kinase; D000099253:Trans-Activation Responsive RNA-Binding Protein; C104647:PRKRA protein, human; C567955:ADARB1 protein, human
references.citation: Nat Med. 2008 Oct;14(10):1077-87
references.pmid: 18806803
references.citation: J Biol Chem. 2000 Dec 1;275(48):37993-8
references.pmid: 10988289
references.citation: Retrovirology. 2008 May 22;5:41
references.pmid: 18498651
references.citation: AIDS Res Hum Retroviruses. 2003 Sep;19(9):767-78
references.pmid: 14585207
references.citation: Virology. 2011 Aug 15;417(1):27-36
references.pmid: 21612809
references.citation: J Biol Chem. 2006 Nov 17;281(46):35129-36
references.pmid: 16982605
references.citation: RNA Biol. 2008 Apr-Jun;5(2):92-103
references.pmid: 18421256
references.citation: Retrovirology. 2009 Jan 24;6:8
references.pmid: 19166625
references.citation: J Virol. 2007 Jan;81(2):917-23
references.pmid: 17079286
references.citation: Nat Rev Immunol. 2008 Jul;8(7):559-68
references.pmid: 18575461
references.citation: J Biol Chem. 2007 Jun 15;282(24):17649-57
references.pmid: 17452327
references.citation: J Virol. 2007 May;81(9):4664-76
references.pmid: 17329338
references.citation: Mol Ther. 2005 May;11(5):717-23
references.pmid: 15851010
references.citation: J Virol. 2007 Mar;81(5):2221-30
references.pmid: 17166899
references.citation: Biochemistry. 2011 May 31;50(21):4550-60
references.pmid: 21526770
references.citation: Front Biosci. 2008 May 01;13:5693-707
references.pmid: 18508616
references.citation: J Biol Chem. 2001 Sep 7;276(36):33899-905
references.pmid: 11438532
references.citation: Methods Mol Biol. 2014;1103:31-43
references.pmid: 24318884
references.citation: Science. 1991 Mar 29;251(5001):1597-600
references.pmid: 2011739
references.citation: Proc Natl Acad Sci U S A. 2013 Apr 16;110(16):6536-41
references.pmid: 23550157
references.citation: Eur J Biochem. 1999 Sep;264(3):806-15
references.pmid: 10491127
references.citation: Virology. 1994 Nov 1;204(2):823-7
references.pmid: 7524241
references.citation: J Mol Biol. 2006 Feb 3;355(5):898-910
references.pmid: 16343534
references.citation: Mol Cell Biol. 2004 May;24(10):4502-12
references.pmid: 15121867
references.citation: J Virol. 1994 Nov;68(11):7008-20
references.pmid: 7933083
references.citation: Microbiol Mol Biol Rev. 2006 Dec;70(4):1032-60
references.pmid: 17158706
references.citation: J Virol. 2010 Sep;84(17):8446-59
references.pmid: 20554776
references.citation: Arch Biochem Biophys. 2000 Jan 15;373(2):361-7
references.pmid: 10620360
references.citation: Nucleic Acids Res. 2009 Sep;37(17):5848-58
references.pmid: 19651874
references.citation: Virol J. 2005 Feb 28;2:17
references.pmid: 15737233
references.citation: J Virol. 2008 Jun;82(11):5145-52
references.pmid: 18385227
references.citation: Mol Cell Biol. 2000 Feb;20(4):1278-90
references.pmid: 10648614
references.citation: J Virol. 2002 Feb;76(3):1004-14
references.pmid: 11773376
references.citation: J Cell Biochem. 2012 Aug;113(8):2754-64
references.pmid: 22473766
references.citation: Nucleic Acids Res. 2008 Feb;36(3):998-1008
references.pmid: 18096616
references.citation: Microbiol Mol Biol Rev. 2012 Sep;76(3):652-66
references.pmid: 22933564
references.citation: J Biol Chem. 2003 Feb 14;278(7):4440-8
references.pmid: 12475984
references.citation: Nucleic Acids Res. 2005 Aug 26;33(15):4797-812
references.pmid: 16126845
references.citation: J Biol Chem. 2004 Oct 8;279(41):42687-93
references.pmid: 15299031
references.citation: Cell Signal. 2006 Nov;18(11):1865-75
references.pmid: 16600570
references.citation: J Biol Chem. 2001 Dec 28;276(52):48803-13
references.pmid: 11641396
references.citation: RNA. 2012 Mar;18(3):519-29
references.pmid: 22286970
references.citation: J Cell Sci. 2010 Feb 1;123(Pt 3):369-83
references.pmid: 20053637
references.citation: Clin Immunol. 2007 May;123(2):121-8
references.pmid: 17112786
references.citation: Mol Cell Biol. 2001 Mar;21(6):1908-20
references.pmid: 11238927
references.citation: Nucleic Acids Res. 2008 Jan;36(1):30-40
references.pmid: 17984074
references.citation: Biochem J. 2002 Aug 15;366(Pt 1):175-86
references.pmid: 11985496
references.citation: J Leukoc Biol. 2006 Nov;80(5):984-93
references.pmid: 16916960
references.citation: EMBO J. 1997 Feb 3;16(3):611-24
references.pmid: 9034343
references.citation: Virology. 2012 Jun 5;427(2):208-16
references.pmid: 22381929
references.citation: RNA Biol. 2011 Mar-Apr;8(2):343-53
references.pmid: 21422817
references.citation: J Virol. 1999 Nov;73(11):9021-8
references.pmid: 10516008
references.citation: J Virol. 2005 Oct;79(20):12763-72
references.pmid: 16188979
references.citation: Adv Pharmacol. 2007;55:137-59
references.pmid: 17586314
references.citation: J Virol. 2008 Nov;82(21):10864-72
references.pmid: 18753201
references.citation: Mol Cell Biol. 2009 Jan;29(1):254-65
references.pmid: 18936160
references.citation: Rev Med Virol. 2011 Jan;21(1):42-53
references.pmid: 21294215
references.citation: Cell Host Microbe. 2011 Apr 21;9(4):299-309
references.pmid: 21501829
references.citation: Cell. 1990 Jul 27;62(2):379-90
references.pmid: 1695551
references.citation: J Virol. 2009 Jan;83(2):961-8
references.pmid: 19004947
references.citation: J Virol. 2007 Jun;81(12):6216-30
references.pmid: 17428849
references.citation: Biochimie. 2007 Jun-Jul;89(6-7):799-811
references.pmid: 17451862
references.citation: Viruses. 2012 Oct 29;4(11):2598-635
references.pmid: 23202496
references.citation: Curr Top Microbiol Immunol. 2007;316:253-92
references.pmid: 17969452
references.citation: J Virol. 2012 Apr;86(7):3787-94
references.pmid: 22278222
references.citation: Blood. 2006 Aug 1;108(3):821-9
references.pmid: 16861340
references.citation: Cancer Gene Ther. 2008 Oct;15(10):636-44
references.pmid: 18535617
references.citation: J Virol. 2012 Oct;86(19):10347-58
references.pmid: 22787234
references.citation: Proc Natl Acad Sci U S A. 1992 Aug 1;89(15):7149-53
references.pmid: 1496009
references.citation: Mol Cell Biol. 2004 Apr;24(7):2637-48
references.pmid: 15024055
references.citation: J Virol. 2011 Sep;85(17):8460-6
references.pmid: 21490091
references.citation: FEBS J. 2005 Mar;272(6):1425-39
references.pmid: 15752359
references.citation: Proc Natl Acad Sci U S A. 1985 Jul;82(13):4341-5
references.pmid: 3859866
references.citation: J Virol. 2011 Dec;85(23):12614-21
references.pmid: 21937648
references.citation: Virology. 2003 Oct 25;315(2):283-91
references.pmid: 14585331
references.citation: Mol Cell Biol. 1999 Mar;19(3):2220-30
references.pmid: 10022909
references.citation: EMBO J. 1998 Aug 3;17(15):4379-90
references.pmid: 9687506
references.citation: Curr HIV Res. 2005 Jan;3(1):61-71
references.pmid: 15638724
references.citation: J Biol Chem. 1999 May 28;274(22):15427-32
references.pmid: 10336432
references.citation: J Virol. 2007 May;81(10):5121-31
references.pmid: 17360756
references.citation: J Virol. 2003 Apr;77(7):3939-49
references.pmid: 12634354
references.citation: J Virol. 2009 Oct;83(19):10119-28
references.pmid: 19605474
references.citation: J Interferon Cytokine Res. 2005 Jun;25(6):345-60
references.pmid: 15957958
references.citation: J Gen Virol. 2011 May;92(Pt 5):1228-1232
references.pmid: 21289159
references.citation: BMC Mol Biol. 2009 May 07;10:38
references.pmid: 19422693