Cells lacking an intact ATM gene are hypersensitive to ionizing radiation and show multiple defects in the cell cycle-coupled checkpoints. DNA damage usually triggers cell cycle arrest through, among other things, the activation of p53. Another DNA-damage responsive factor is NF-kB. It is activated by various stress situations, including oxidative stress, and by DNAdamaging compounds such as topoisomerase poisons. We found that cells from Ataxia Telangiectasia patients exhibit a defect in NF-kB activation in response to treatment with camptothecin, a topoisomerase I poison. In AT cells, this activation is shortened or suppressed, compared to that observed in normal cells. Ectopic expression of the ATM protein in AT cells increases the activation of NF-kB in response to camptothecin. MO59J glioblastoma cells that do not express the DNA-PK catalytic subunit respond normally to camptothecin. These results support the hypothesis that NFkB is a DNA damage-responsive transcription factor and that its activation pathway by DNA damage shares some components with the one leading to p53 activation.

The nuclear factor kappaB (NF-kappaB) is involved in T cell activation and enhances HIV-1 gene expression. It is activated in response to numerous stimuli, including oxidative stress. Oxidative stress damages membrane lipids, proteins and nucleic acids. We have shown previously that oxidative DNA damage generated by photosensitization could trigger activation of NF-kappaB. We now show that a series of topoisomerase poisons (actinomycin D, camptothecin, daunomycin and etoposide) also activate NF-kappaB (NFKB1/RelA dimer) in ACH-2 and CEM cells. This activation is inhibited by pyrrolidine dithiocarbamate. In ACH-2 cells latently infected by HIV-1, camptothecin, daunomycin and etoposide are able to enhance virus production. Since topoisomerase poisons cause the formation of single- and double-strand breaks in DNA, these lesions might be capable of triggering NF-kappaB activation. Indeed, DNA damaging agents generating adducts (trans-platin and 4-nitroquinoline 1-oxide) and/or crosslinks in DNA (cisplatin and mitomycin C) do not or only weakly activate NF-kappaB in T cell lines.

A large body of work has been devoted to tumor necrosis factor α or interleukin‐1β (IL‐1β) signaling leading to the activation of the transcription factor nuclear factor‐κ B (NF‐κ B) in various cell types. Several studies have indicated that NF‐κ B activation depends strictly on the production of reactive oxygen intermediates. In this report, we first demonstrated that IL‐1β is a potent activator of NF‐κ B in various epithelial transformed ccll lines (OVCAR‐3, SKOV‐3, MCF7 A/Z). In these cells, IL‐1β rapidly induces NF‐κ B through a complete degradation of Iκ B‐α while H2O2 activates NF‐κ B with slower kinetics through a partial degradation of IkB‐α, p100 and p105. We showed that IL‐1β‐mediated induction of NF‐κ B in OVCAR‐3 and in other epithelial cell lines does not proceed through the production of reactive oxygen intermediates, while the same cytokine activates NF‐kB in lymphoid cells through the intracellular generation of H2O2. Our study demonstrated that several signaling pathways lead to the activation of NF‐κ B, following IL‐1β treatment in different cell types.

Reactive oxygen intermediates like hydrogen peroxide (H2O2) have been shown to serve as messengers in the induction of NF-kappa B and, then, in the activation and replication of human immunodeficiency virus (HIV)-1 in human cells. Because H2O2 can be converted into the highly reactive OH. at various locations inside the cells, we started to investigate the generation of Reactive oxygen intermediates by photosensitization. This technique is based on the use of a photosensitizer which is a molecule absorbing visible light and which can be located at various sites inside the cell depending on its physicochemical properties. In this work, we used proflavine (PF), a cationic molecule having a high affinity for DNA, capable of intercalating between DNA base pairs. Upon visible light irradiation, intercalated PF molecules oxidize guanine residues and generate DNA single-strand breaks. In lymphocytes or monocytes latently infected with HIV-1 (ACH-2 or U1, respectively), this photosensitizing treatment induced a cytotoxicity, an induction of NF-kappa B, and a reactivation of HIV-1 in cells surviving the treatment. NF-kappa B induction by PF-mediated photosensitization was not affected by the presence of N-acetyl-L-cysteine while strong inhibition was recorded when the induction was triggered by H2O2 or by phorbol 12-myristate 13-acetate. Another transcription factor like AP-1 is less activated by this photosensitizing treatment. In comparison with other inducing treatments, such as phorbol 12-myristate 13-acetate or tumor necrosis factor alpha, the activation of NF-kappa B is slow, being optimal 120 min after treatment. These kinetic data were obtained by following, on the same samples, both the appearance of NF-kappa B in the nucleus and the disappearance of I kappa B-alpha in cytoplasmic extracts. These data allow us to postulate that signaling events, initiated by DNA oxidative damages, are transmitted into the cytoplasm where the inactive NF-kappa B factor is resident and allow the translocation of p50/p65 subunits of NF-kappa B to the nucleus leading to HIV-1 gene expression.

NFKB, a nuclear transcription factor, was induced in the brain nuclear fraction of naive rats after an acute injection of ethanol, 2 g/kg. In contrast, rats which had been chronically alcoholised showed the constitutively active NFKB-like complex only after a further acute dose of ethanol. Hepatic nuclear fractions did not exhibit the specific NFKB-like complex during the first 45 min after acute ethanol injection, beyond that which was normally constitutively present. Such activation of NFKBlike complex in the brains of the naive rats may play an important role in the cellular protective response.