Inhibition of the NF-κB transcription factor increases Bax expression in cancer cell lines (original) (raw)
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Oncogene
The NF-kB transcription factor has been shown to inhibit apoptosis in several experimental systems. We therefore investigated whether the expression of the Bax proapoptotic protein could be in¯uenced by NF-kB activity. Increased Bax protein expression was detected in HCT116, OVCAR-3 and MCF7 cells stably expressing a mutated unresponsive IkB-a inhibitory protein that blocks NF-kB activity. Northern blots showed that bax mRNA expression was increased as a consequence of mutated IkB-a expression in HCT116 cells. A careful examination of the human bax gene promoter sequence showed three putative binding sites for NF-kB, and the kB2 site at position -687 could indeed bind NF-kB complexes in vitro. Transient transfection of a bax promoter luciferase construct in HCT116 cells showed that NF-kB proteins could partially inhibit the transactivation of the bax promoter by p53. Mutations or deletions of the kB sites, including kB2, indicated that this NF-kB-dependent inhibitory eect did not require NF-kB DNA-binding, and was thus an indirect eect. However, cotransfection of expression vectors for several known cofactors failed to identify a competition between p53 and NF-kB for a transcription coactivator. Our ®ndings thus demonstrate for the ®rst time that NF-kB regulates, through an indirect pathway, the bax gene expression. Oncogene (2001) 20, 2805 ± 2813.
NF-κB in cancer—a friend turned foe
Drug Resistance Updates, 2004
The nuclear factor of B (NF-B) family of heterodimeric transcription factors plays an instrumental role in immune, inflammatory, and stress responses. NF-B induces the expression of diverse target genes that promote cell cycle progression, regulate apoptosis, and facilitate cell adhesion, angiogenesis, and metastasis. Given the ability of NF-B to influence these cardinal features of neoplastic transformation, it is no surprise that tumor cells of almost every tissue type acquire the ability to constitutively activate NF-B via a host of diverse genetic alterations and viral proteins. The activation of NF-B not only enables malignant transformation and tumor progression, but also provides a mechanism by which tumor cells escape immune surveillance and resist therapy. NF-B may be inhibited by targeting either the apical signaling proteins responsible for its activation in specific types of cancer, the downstream kinases (IB kinase and casein kinase 2) at which NF-B-activating signaling pathways converge, the proteasome-mediated degradation of the inhibitor of B (IB) proteins, or the transcriptional activity of Rel proteins. Since NF-B inhibitors can sensitize tumor cells to apoptosis signaling pathways activated by death receptors, interferons, and immune effector cells, they hold enormous promise for the development of effective combinatorial regimens against a wide spectrum of hematologic and epithelial malignancies.
Significance of Bax Expression in Breast Cancer Patients
Polish Journal of Surgery, 2011
Bax protein, the proapoptotic member of Bcl-2 protein family, plays the key role in apoptosis pathway. the aim of the study was to assess the expression of Bax protein in breast cancer cells. material and methods. Sixty-two breast cancer patients were included in the study. The control group encompassed 11 fibroadenoma patients. Single cells were isolated from defrosted samples and prepared for flow cytometry measurement. Results. Median expression of Bax protein in study group was 7.9% (range: 0-49.4%) and was significantly lower than in control (median expression 15.8%; range 4.9-30.9%; p=0.034). Expression of Bax correlated with expression of p53 and caspase-3 proteins (p<0,01, rank Spearman test). In patients under 70 years old and with positive estrogen receptors status the expression of Bax protein was significantly higher (p=0.03 and p=0.01 respectively). conclusions. Lower expression of Bax protein in breast cancer cells may suggest the potential way of apoptosis avoidance of tumor cells. Correlations among Bax protein, p53 and caspase-3 are likely associated with active apoptotic mechanism in breast cancer cells expressing Bax protein. Further investigation with long time follow-up should be performed to establish the prognostic role of Bax protein expression in breast cancer patients.
Pro-apoptotic role of NF-κB: Implications for cancer therapy
Biochimica et Biophysica Acta (BBA) - Reviews on Cancer, 2006
Nuclear factor-κB (NF-κB) is generally viewed as anti-apoptotic and oncogenic, leading to a quest for its inhibitors. However, recent evidence suggests that in some situations NF-κB may promote apoptosis. Depending on the specific cell type and the stimulus involved, NF-κB activation may lead to either anti-or pro-apoptotic response. Both these effects can be mediated by NF-κB in a context-dependent manner by selectively regulating its target genes. In this review, we discuss the evidence for NF-κB's pro-apoptotic role and explore the possible mechanisms behind it. We emphasize that rather than trying to inhibit NF-κB in cancer therapy, agents should be developed to unleash its pro-apoptotic ability.
Biochimica et Biophysica Acta (BBA) - Molecular Cell Research, 2013
TNFα can promote either cell survival or cell death. The activation of NF-κB plays a central role in cell survival while its inhibition makes TNFα-triggered cytotoxicity possible. Here, we report that the overexpression of a non-degradable mutant of the inhibitor of NF-κB (super-repressor (SR)-IκBα) sensitizes HeLa cells towards TNFα-induced apoptosis, involving caspases activation and cytocrome C release from the mitochondria. Interestingly, we describe that the specific knockdown of Bcl-x L , but not that of Bcl-2, Bcl-w or Mcl-1, renders cells sensitive to TNFα-induced apoptosis. This cytotoxic effect occurs without altering the activation of NF-κB. Then, the activation of the NF-κB pathway is not sufficient to protect Bcl-x L -downregulated cells from TNFα-induced cell death, meaning that TNFα is not able to promote cell survival in the absence of Bcl-x L . In addition, Bcl-x L silencing does not potentiate the cytotoxicity afforded by the cytokine in SR-IκBα-overexpressing cells. This indicates that TNFα-induced apoptosis in SR-IκBα-overexpressing cells relies on the protein levels of Bcl-x L . We have corroborated these findings using RD and DU-145 cells, which also become sensitive to TNFα-induced apoptosis after Bcl-x L knockdown despite that NF-κB remains activated. Altogether, our results point out that the impairment of the anti-apoptotic function of Bcl-x L should make cells sensitive towards external insults circumventing the TNFα-triggered NF-κB-mediated cytoprotective effect. Hence, the specific inhibition of Bcl-x L could be envisaged as a promising alternative strategy against NF-κB-dependent highly chemoresistant proliferative malignancies.
Oncogene
The early response gene IEX-1 is involved in the regulation of cellular growth and survival, and its expression is related to stress-, growth-and deathinducing signals. Addressing the role of IEX-1 in the promotion of apoptosis, we investigated the effect of IEX-1 on nuclear factor-jB (NF-jB) activation. Stably transfected HEK-293 cells conditionally overexpressing IEX-1 exhibit decreased levels of NF-jB activity, either basal or TNFa induced, as shown by gel-shift and luciferase reporter gene assay. Furthermore, activated p65 accumulated in the nuclei of 293 cells to a lower degree, if IEX-1 expression was increased. This inhibited NF-jB activation was preceded by an altered turnover of IjBa and phospho-IjBa. In addition, IEX-1 expression also inhibited the activity of the 26S-proteasome, as shown by a fluorometric proteasome assay. Conversely, disruption of IEX-1 expression in 293 cells by stable transfection with specific anti-IEX-1 hammerhead ribozymes increased NF-jB activity, and accelerated the degradation of IjBa. Along with these opposite effects of IEX-1 expression and IEX-1 disruption on NF-jB activation, the sensitivity of 293 cells towards various apoptotic stimuli also changed. In contrast to ribozymetransduced 293 cells that were significantly less sensitive to apoptosis, this sensitivity was enhanced if IEX-1 expression was increased. Our data suggest that IEX-1itself an NF-jB target gene -inhibits the activation of this transcription factor, and hereby may counteract the antiapoptotic potential of NF-jB.
The pro- or anti-apoptotic function of NF-κB is determined by the nature of the apoptotic stimulus
European Journal of Biochemistry, 2000
To test whether the behaviour of transcription factor NF-kB as a promoter or antagonist of apoptosis depends on the apoptotic stimulus, we determined the influence of NF-kB on cell killing elicited by a variety of inducers within a given cell type. Inhibition of NF-kB by genetic and pharmacological approaches rendered HeLa cells more susceptible to TNF-a-induced cell killing, but protected them almost completely from H 2 O 2 -and pervanadate-induced apoptosis. TNF-a was unable to protect HeLa from H 2 O 2 -and pervanadate-induced apoptosis and further enhanced the cytotoxicity induced by these two adverse agents. Supernatants from HeLa cells stably overexpressing a transdominant negative form of IkB-a selectively increased the cytotoxicity of TNF-a for HeLa cells, suggesting that the enhanced susceptibility of these cells can be attributed to one or more secretable factors. Supershift experiments showed that the various apoptotic stimuli induced the same subset of DNA-binding subunits. Therefore, the nature of the signals elicited by the respective death inducers determines whether NF-kB induction leads to apoptosis or survival, suggesting that the manipulation of NF-kB activity may provide a new approach to adjuvant therapy in cancer treatment.
Oncogene, 2003
The early response gene IEX-1 is involved in the regulation of cellular growth and survival, and its expression is related to stress-, growth-and deathinducing signals. Addressing the role of IEX-1 in the promotion of apoptosis, we investigated the effect of IEX-1 on nuclear factor-jB (NF-jB) activation. Stably transfected HEK-293 cells conditionally overexpressing IEX-1 exhibit decreased levels of NF-jB activity, either basal or TNFa induced, as shown by gel-shift and luciferase reporter gene assay. Furthermore, activated p65 accumulated in the nuclei of 293 cells to a lower degree, if IEX-1 expression was increased. This inhibited NF-jB activation was preceded by an altered turnover of IjBa and phospho-IjBa. In addition, IEX-1 expression also inhibited the activity of the 26S-proteasome, as shown by a fluorometric proteasome assay. Conversely, disruption of IEX-1 expression in 293 cells by stable transfection with specific anti-IEX-1 hammerhead ribozymes increased NF-jB activity, and accelerated the degradation of IjBa. Along with these opposite effects of IEX-1 expression and IEX-1 disruption on NF-jB activation, the sensitivity of 293 cells towards various apoptotic stimuli also changed. In contrast to ribozymetransduced 293 cells that were significantly less sensitive to apoptosis, this sensitivity was enhanced if IEX-1 expression was increased. Our data suggest that IEX-1itself an NF-jB target gene -inhibits the activation of this transcription factor, and hereby may counteract the antiapoptotic potential of NF-jB.
Role of Bax in apoptosis of IL-3-dependent cells
Oncogene, 2001
IL-3 removal was reported to induce membrane association of the apoptotic eector Bax. This report demonstrates that IL-3-dependent cells from Bax-null mice failed to activate caspases after IL-3 removal and survived in an 10-fold lower concentration of IL-3. As IL-3 removal also down-regulates expression of Bcl-X, we examined the relationship between Bcl-X decrease and Bax membrane association. IL-3 removal from BAF-3 cells, followed by sorting caspase-active and caspase-inactive populations, showed that both expressed similar levels of Bcl-X. Inhibition of IL-3 signalling via PI-3 kinase and MEK1/2 resulted in cells with minimal Bcl-X, which remained viable with soluble Bax. However BAF-3-derived cells, which maintained Bcl-X expression without IL-3, also remained viable with soluble Bax on IL-3 removal. Therefore a decrease in Bcl-X is necessary, though not sucient, for Bax membrane association on IL-3 removal. In contrast, treatment of BAF-3 cells with hydroxyurea induced apoptosis in the absence of a Bcl-X decrease. Furthermore, IL-3dependent cells from Bax-null mice activated caspases after hydroxyurea treatment and show the same sensitivity to a variety of cytotoxic drugs. Thus, apoptosis after IL-3 removal requires a decrease in Bcl-X and Bax membrane association, whereas that induced by cytotoxic drugs does not. Oncogene (2001) 20, 4476 ± 4483.
Bcl-2 Suppresses Apoptosis Resulting from Disruption of the NF-κB Survival Pathway☆
Experimental Cell Research, 1997
anisms can result in profound and damaging conse-A role has been delineated for both bcl-2 and NF-kB quences and have been shown to directly contribute to in mediating an adaptive survival response to the TNF-multistep carcinogenesis [2]. It is now recognized that a signaling pathway for apoptosis. Additionally, we the bcl-2 oncoprotein can inhibit cellular pathways for and others have demonstrated a role for bcl-2 upregudeath that are seemingly independent, including, but lation during progression of prostate cancer and acnot limited to, TNF-a-mediated cytotoxicity [3].