title: Proteolytic cleavage of the catalytic subunit of DNA-dependent protein kinase during poliovirus infection.
abstract: DNA-dependent protein kinase (DNA-PK) is a serine/threonine kinase that has critical roles in DNA double-strand break repair, as well as B- and T-cell antigen receptor rearrangement. The DNA-PK enzyme consists of the Ku regulatory subunit and a 450-kDa catalytic subunit termed DNA-PK(CS). Both of these subunits are autoantigens associated with connective tissue diseases such as systemic lupus erythematosus (SLE) and scleroderma. In this report, we show that DNA-PK(CS) is cleaved during poliovirus infection of HeLa cells. Cleavage was visible as early as 1.5 h postinfection (hpi) and resulted in an approximately 40% reduction in the levels of native protein by 5.5 hpi. Consistent with this observation, the activity of the DNA-PK(CS) enzyme was also reduced during viral infection, as determined by immunoprecipitation kinase assays. Although it has previously been shown that DNA-PK(CS) is a substrate of caspase-3 in vitro, the protein was still cleaved during poliovirus infection of the caspase-3-deficient MCF-7 cell line. Cleavage was not prevented by infection in the presence of a soluble caspase inhibitor, suggesting that cleavage in vivo was independent of host caspase activation. DNA-PK(CS) is directly cleaved by a picornaviral 2A protease in vitro, producing a fragment similar in size to the cleavage product observed in vivo. Taken together, our results indicate that DNA-PK(CS) is cleaved by the 2A protease during poliovirus infection. Proteolytic cleavage of DNA-PK(CS) during poliovirus infection may contribute to inhibition of host immune responses. Furthermore, cleavage of autoantigens by viral proteases may target these proteins for the autoimmune response by generating novel, or "immunocryptic," protein fragments.
authors.affiliation: Division of Immunology and Rheumatology, Stanford University School of Medicine, Stanford University School of Medicine, CCSR Building, Room 2215A, 269 Campus Drive, Stanford, CA 94305, USA.
authors.forename: Kareem L
authors.initials: KL
authors.lastname: Graham
authors.forename: Kurt E
authors.initials: KE
authors.lastname: Gustin
authors.forename: Carlos
authors.initials: C
authors.lastname: Rivera
authors.forename: N Muge
authors.initials: NM
authors.lastname: Kuyumcu-Martinez
authors.forename: Sunny S
authors.initials: SS
authors.lastname: Choe
authors.forename: Richard E
authors.initials: RE
authors.lastname: Lloyd
authors.forename: Peter
authors.initials: P
authors.lastname: Sarnow
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Utz
mesh_terms: D053148:Caspase 3; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism; D020134:Catalytic Domain / Q000502:physiology*; D002460:Cell Line; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D051747:DNA-Activated Protein Kinase; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006367:HeLa Cells; D006801:Humans; D009687:Nuclear Proteins; D017955:Poliovirus / Q000472:pathogenicity*; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry / Q000378:metabolism*; D014764:Viral Proteins
chemical_list: D061945:Caspase Inhibitors; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D009687:Nuclear Proteins; D014764:Viral Proteins; D051747:DNA-Activated Protein Kinase; C497263:PRKDC protein, human; D017346:Protein Serine-Threonine Kinases; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases; D003546:Cysteine Endopeptidases; C057400:picornain 2A, Picornavirus