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NF-?B mediates radio-sensitization by the PARP-1 inhibitor, AG-014699.

ABSTRACT: The stress-inducible transcription factor, nuclear factor (NF)-?B induces genes involved in proliferation and apoptosis. Aberrant NF-?B 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-?B activation using p65 small interfering RNA (siRNA), PARP siRNA or the potent PARP-1 inhibitor, AG-014699. Survival and apoptosis assays showed that NF-?B 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-?B. 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-?B activation, and independent of SSB repair inhibition. PARP-1 catalytic activity was essential for IR-induced p65 DNA binding and NF-?B-dependent gene transcription, whereas for tumor necrosis factor (TNF)-?-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-?. Targeting DNA damage-activated NF-?B using AG-014699 may therefore overcome toxicity observed with classical NF-?B inhibitors without compromising other vital inflammatory functions. These data highlight the potential of PARP-1 inhibitors to overcome NF-?B-mediated therapeutic resistance and widens the spectrum of cancers in which these agents may be utilized.

SUBMITTER: Hunter JE

PROVIDER: S-EPMC3191117 | biostudies-literature | 2012 Jan

REPOSITORIES: biostudies-literature

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NF-κB mediates radio-sensitization by the PARP-1 inhibitor, AG-014699.

Hunter J E JE Willmore E E Irving J A E JA Hostomsky Z Z Veuger S J SJ Durkacz B W BW

Oncogene 20110627 2

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-014 ...[more]

PMID: 21706052

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Project description:BackgroundMultiple myeloma (MM) is an incurable hematological malignancy. Although proteasome inhibitors and immunomodulators have significantly improved patient outcomes, some patients respond poorly to treatment and almost all patients will relapse. Mechanisms of proteasome inhibitor resistance in multiple myeloma have not been fully elucidated. ZHX2 is a transcription regulator degraded via proteasome and presents both oncogenic or tumor suppressive effect in different cancers, however, it is still unknown that the role of ZHX2 in myeloma. In this study, we aim to demonstrate the effect and mechanism of ZHX2 on proteasome inhibitor resistance in MM.MethodsGSE24080 gene expression profile datasets from Gene Expression Omnibus (GEO) were analyzed to evaluate the relationship between ZHX2 expression level and survival in MM. Expression of ZHX2 in human MM cell lines at baseline and after bortezomib (BTZ) treatment was determined by Western blotting (WB). The proliferation and apoptosis rate of MM cells treated with BTZ after the knockdown of ZHX2 were analyzed by flow cytometry. Nuclear translocation of NF-κB after the knockdown of ZHX2 was evaluated by WB and immunofluorescence, and the expression of NF-κB target genes was measured by real-time quantitative PCR. Co-immunoprecipitation (Co-IP) and WB were used to detect the interaction of ZHX2 with NF-κB.ResultsWe found that higher ZHX2 expression was correlated with poorer clinical outcomes of patients. In addition, ZHX2 expression was relatively higher in RPMI-8226 and MM.1S cell lines and the level of ZHX2 protein was upregulated after BTZ treatment. Knockdown of ZHX2 significantly enhanced the sensitivity of MM cells to BTZ, inhibited nuclear translocation of NF-κB, and reduced mRNA expression of NF-κB target genes. It was also revealed that ZHX2 directly binds to NF-κB.ConclusionOur study showed that ZHX2 can promote proteasome inhibitor resistance in MM cells by regulating the nuclear translocation of NF-κB.

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NF-?B mediates radio-sensitization by the PARP-1 inhibitor, AG-014699.

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NF-κB mediates radio-sensitization by the PARP-1 inhibitor, AG-014699.

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