Functional competition between poly(ADP-ribose) polymerase and its 24-kDa apoptotic fragment in DNA repair and transcription.
Poly(ADP-ribose) polymerase is a 113-kDa nuclear enzyme that binds to both damaged DNA and to RNA associated with actively transcribed regions of chromatin. Binding of poly(ADP-ribose) polymerase to DNA lesions activates it, catalyzing the covalent addition of multiple ADP-ribose polymers to the enzyme (automodification). During apoptosis, poly(ADP-ribose) polymerase is cleaved by caspase-3, resulting in the formation of an N-terminal 24-kDa fragment, containing the DNA binding domain, and a C-terminal 89-kDa catalytic fragment. The functional relevance of this cleavage is not well understood. We therefore prepared a recombinant 24-kDa poly(ADP-ribose) polymerase fragment and investigated the role of this fragment in DNA repair and transcription. The 24-kDa fragment retained its binding affinity for both DNA breaks and RNA. In an in vitro cell-free DNA repair assay, this fragment inhibited rejoining of DNA breaks and suppressed ADP-ribose polymer formation by competing with poly(ADP-ribose) polymerase in binding to DNA breaks. With regard to transcription, it has recently been demonstrated that binding of poly(ADP-ribose) polymerase to transcribed RNA reduces the rate of transcript elongation and that automodification of poly(ADP-ribose) polymerase bound to DNA breaks results in up-regulation of transcription. We tested the 24-kDa fragment for its ability to suppress transcript elongation, and we found that it competed against the up-regulation of transcription mediated by full-length poly(ADP-ribose) polymerase. The ability of the 24-kDa fragment to inhibit DNA repair, ADP-ribose polymer formation, and damage-dependent up-regulation of transcription may contribute to the apoptotic shift from cell survival to cell death mode.
Yung
T M
TM
DNA Repair Group, Health and Environment Unit, Laval University Medical Centre, CHUQ, Faculty of Medicine, Laval University, Ste-Foy, Quebec G1V 4G2, Canada.
Satoh
M S
MS
D017209:Apoptosis / Q000235:genetics*; D002460:Cell Line; D004260:DNA Repair; D006801:Humans; D010446:Peptide Fragments / Q000235:genetics / Q000378:metabolism; D011065:Poly(ADP-ribose) Polymerases / Q000235:genetics* / Q000378:metabolism*; D014158:Transcription, Genetic
D010446:Peptide Fragments; D011065:Poly(ADP-ribose) Polymerases