title: The PARP inhibitor PJ34 causes a PARP1-independent, p21 dependent mitotic arrest.
abstract: Poly(ADP)-ribose polymerase (PARP) inhibitors modify the enzymatic activity of PARP1/2. When certain PARP inhibitors are used either alone or in combination with DNA damage agents they may cause a G2/M mitotic arrest and/or apoptosis in a susceptible genetic context. PARP1 interacts with the cell cycle checkpoint proteins Ataxia Telangectasia Mutated (ATM) and ATM and Rad3-related (ATR) and therefore may influence growth arrest cascades. The PARP inhibitor PJ34 causes a mitotic arrest by an unknown mechanism in certain cell lines, therefore we asked whether PJ34 conditionally activated the checkpoint pathways and which downstream targets were necessary for mitotic arrest. We found that PJ34 produced a concentration dependent G2/M mitotic arrest and differentially affected cell survival in cells with diverse genetic backgrounds. p53 was activated and phosphorylated at Serine15 followed by p21 gene activation through both p53-dependent and -independent pathways. The mitotic arrest was caffeine sensitive and UCN01 insensitive and did not absolutely require p53, ATM or Chk1, while p21 was necessary for maintaining the growth arrest. Significantly, by using stable knockdown cell lines, we found that neither PARP1 nor PARP2 was required for any of these effects produced by PJ34. These results raise questions and cautions for evaluating PARP inhibitor effectiveness, suggesting whether effects should be considered not only on PARP's diverse ADP-ribosylation independent protein interactions but also on homologous proteins that may be producing either overlapping or distinct effect.
authors.affiliation: Division of Endocrinology, L-607, Department of Medicine, Oregon Health and Sciences University, 3181 SW Sam Jackson Park Rd, Portland, OR 97239, USA. Madisond@ohsu.edu
authors.forename: Dana L
authors.initials: DL
authors.lastname: Madison
authors.forename: Daniel
authors.initials: D
authors.lastname: Stauffer
authors.forename: James R
authors.initials: JR
authors.lastname: Lundblad
mesh_terms: D017209:Apoptosis; D064007:Ataxia Telangiectasia Mutated Proteins; D002110:Caffeine / Q000494:pharmacology; D059447:Cell Cycle Checkpoints; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D000071877:Checkpoint Kinase 1; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D005260:Female; D020868:Gene Silencing; D006367:HeLa Cells; D006801:Humans; D008938:Mitosis / Q000187:drug effects*; D010616:Phenanthrenes / Q000494:pharmacology*; D010766:Phosphorylation; D000071137:Poly (ADP-Ribose) Polymerase-1; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D011065:Poly(ADP-ribose) Polymerases / Q000235:genetics / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: C493956:CDKN1A protein, human; D018797:Cell Cycle Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D004268:DNA-Binding Proteins; C434926:N-(oxo-5,6-dihydrophenanthridin-2-yl)-N,N-dimethylacetamide hydrochloride; D010616:Phenanthrenes; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; D002110:Caffeine; C499320:PARP1 protein, human; C483041:PARP2 protein, human; D000071137:Poly (ADP-Ribose) Polymerase-1; D011065:Poly(ADP-ribose) Polymerases; D011494:Protein Kinases; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; C000605867:CHEK1 protein, human; D000071877:Checkpoint Kinase 1; D017346:Protein Serine-Threonine Kinases