title: NF-κB mediates radio-sensitization by the PARP-1 inhibitor, AG-014699.
abstract: The stress-inducible transcription factor, nuclear factor (NF)-κB induces genes involved in proliferation and apoptosis. Aberrant NF-κB activity is common in cancer and contributes to therapeutic-resistance. Poly(ADP-ribose) polymerase-1 (PARP-1) is activated during DNA strand break repair and is a known transcriptional co-regulator. Here, we investigated the role of PARP-1 function during NF-κB activation using p65 small interfering RNA (siRNA), PARP siRNA or the potent PARP-1 inhibitor, AG-014699. Survival and apoptosis assays showed that NF-κB p65(-/-) cells were more sensitive to ionizing radiation (IR) than p65(+/+) cells. Co-incubation with p65 siRNA, PARP siRNA or AG-014699 radio-sensitized p65(+/+), but not p65(-/-) cells, demonstrating that PARP-1 mediates its effects on survival via NF-κB. Single-strand break (SSB) repair kinetics, and the effect SSB repair inhibition by AG-014699 were similar in p65(+/+) and p65(-/-) cells. As preventing SSB repair did not radio-sensitize p65(-/-) cells, we conclude that radio-sensitization by AG-014699 is due to downstream inhibition of NF-κB activation, and independent of SSB repair inhibition. PARP-1 catalytic activity was essential for IR-induced p65 DNA binding and NF-κB-dependent gene transcription, whereas for tumor necrosis factor (TNF)-α-treated cells, PARP-1 protein alone was sufficient. We hypothesize that this stimulus-dependent differential is mediated via stimulation of the poly(ADP-ribose) polymer, which was induced following IR, not TNF-α. Targeting DNA damage-activated NF-κB using AG-014699 may therefore overcome toxicity observed with classical NF-κB inhibitors without compromising other vital inflammatory functions. These data highlight the potential of PARP-1 inhibitors to overcome NF-κB-mediated therapeutic resistance and widens the spectrum of cancers in which these agents may be utilized.
authors.affiliation: Newcastle Cancer Centre at the Northern Institute for Cancer Research, Newcastle University, Tyneside, UK.
authors.forename: J E
authors.initials: JE
authors.lastname: Hunter
authors.forename: E
authors.initials: E
authors.lastname: Willmore
authors.forename: J A E
authors.initials: JA
authors.lastname: Irving
authors.forename: Z
authors.initials: Z
authors.lastname: Hostomsky
authors.forename: S J
authors.initials: SJ
authors.lastname: Veuger
authors.forename: B W
authors.initials: BW
authors.lastname: Durkacz
mesh_terms: D000818:Animals; D002460:Cell Line; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D007211:Indoles / Q000494:pharmacology*; D007259:Infrared Rays; D051379:Mice; D016328:NF-kappa B / Q000378:metabolism*; D000071137:Poly (ADP-Ribose) Polymerase-1; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D011065:Poly(ADP-ribose) Polymerases / Q000235:genetics; D034741:RNA, Small Interfering; D011836:Radiation Tolerance; D014409:Tumor Necrosis Factor-alpha / Q000008:administration & dosage
chemical_list: D004791:Enzyme Inhibitors; D007211:Indoles; D016328:NF-kappa B; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D034741:RNA, Small Interfering; D014409:Tumor Necrosis Factor-alpha; C531549:rucaparib; C499321:Parp1 protein, mouse; D000071137:Poly (ADP-Ribose) Polymerase-1; D011065:Poly(ADP-ribose) Polymerases