title: Nicotinamide- and caspase-mediated inhibition of poly(ADP-ribose) polymerase are associated with p53-independent cell cycle (G2) arrest and apoptosis.
abstract: Poly(ADP-ribose) polymerase (PARP), which is activated by DNA strand breaks, is involved in DNA repair and replication but, during apoptosis, undergoes early caspase-mediated cleavage. Activation of programmed cell death in response to DNA damage may rely on functional p53 protein. Tumor cells are commonly deficient in this oncogene product resulting in resistance to many cytostatic drugs. Here we report that nicotinamide-induced inhibition of poly(ADP-ribosyl)ation and cytokine-induced nitric oxide production both result in a transient increase in p53 levels in pancreatic tumor RINm5F cells. These treatments also induce disruption of the mitochondrial membrane potential (delta psi(m)), as revealed using the mitochondrial probe JC-1, followed by PARP cleavage and apoptosis all of which are inhibited by the anti-apoptotic protein Bcl-2. Moreover, PARP-inhibition by nicotinamide or 3-aminobenzamide induces apoptosis and/or cell cycle arrest at the G2 checkpoint in all of four tested tumor cell lines of both mesenchymal and epithelial origin including mouse NIH-3T3 cells and p53 deficient human HeLa and Jurkat cells. Bcl-2 counteracts cytokine-, but not nicotinamide-induced G2 arrest. These findings indicate that both chemical and caspase-mediated inhibition of PARP activity, possibly by interfering with DNA replication and repair, may promote a p53-independent G2 arrest and apoptosis.
authors.affiliation: Department of Medical Cell Biology, Uppsala University, Uppsala, Sweden. johan.saldeen@medcellbiol.uu.se
authors.forename: Johan
authors.initials: J
authors.lastname: Saldeen
authors.forename: Linda
authors.initials: L
authors.lastname: Tillmar
authors.forename: Ella
authors.initials: E
authors.lastname: Karlsson
authors.forename: Nils
authors.initials: N
authors.lastname: Welsh
mesh_terms: D000818:Animals; D017209:Apoptosis; D001549:Benzamides / Q000494:pharmacology; D020169:Caspases / Q000494:pharmacology*; D002453:Cell Cycle; D002467:Cell Nucleus / Q000378:metabolism; D016207:Cytokines / Q000378:metabolism; D053938:DNA Fragmentation; D004305:Dose-Response Relationship, Drug; D016195:G2 Phase; D006367:HeLa Cells; D006801:Humans; D015151:Immunoblotting; D019169:Jurkat Cells; D008564:Membrane Potentials; D051379:Mice; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D041681:NIH 3T3 Cells; D009536:Niacinamide / Q000494:pharmacology*; D009569:Nitric Oxide / Q000378:metabolism; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology; D013997:Time Factors; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*; D014466:Ultraviolet Rays
chemical_list: D001549:Benzamides; D016207:Cytokines; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D019253:Proto-Oncogene Proteins c-bcl-2; D011838:Radiation-Sensitizing Agents; D016159:Tumor Suppressor Protein p53; D009536:Niacinamide; D009569:Nitric Oxide; C025160:3-aminobenzamide; D020169:Caspases