Sylvie Delhalle

Nuclear factor-kappa B, cancer, and apoptosis.

The role of nuclear factor (NF)-kappa B in the regulation of apoptosis in normal and cancer cells has been extensively studied in recent years. Constitutive NF-kappa B activity in B lymphocytes as well as in Hodgkins disease and breast cancer cells protects these cells against apoptosis. It has also been reported that NF-kappa B activation by tumor necrosis factor (TNF)-alpha, chemotherapeutic drugs, or ionizing radiations can protect several cell types against apoptosis, suggesting that NF-kappa B could participate in resistance to cancer treatment. These observations were explained by the regulation of antiapoptotic gene expression by NF-kappa B. However, in our experience, inhibition of NF-kappa B activity in several cancer cell lines has a very variable effect on cell mortality, depending on the cell type, the stimulus, and the level of NF-kappa B inhibition. Moreover, in some experimental systems, NF-kappa B activation is required for the onset of apoptosis. Therefore, it is likely that the NF-kappa B antiapoptotic role in response to chemotherapy is cell type- and signal-dependent and that the level of NF-kappa B inhibition is important. These issues will have to be carefully investigated before considering NF-kappa B as a target for genetic or pharmacological anticancer therapies.

Mechanisms of Persistent Nf-Kappa B Activity in the Bronchi of an Animal Model of Asthma

In most cells trans-activating NF-κB induces many inflammatory proteins as well as its own inhibitor, IκB-α, thus assuring a transient response upon stimulation. However, NF-κB-dependent inflammatory gene expression is persistent in asthmatic bronchi, even after allergen eviction. In the present report we used bronchial brushing samples (BBSs) from heaves-affected horses (a spontaneous model of asthma) to elucidate the mechanisms by which NF-κB activity is maintained in asthmatic airways. NF-κB activity was high in granulocytic and nongranulocytic BBS cells. However, NF-κB activity highly correlated to granulocyte percentage and was only abrogated after granulocytic death in cultured BBSs. Before granulocytic death, NF-κB activity was suppressed by simultaneous addition of neutralizing anti-IL-1β and anti-TNF-α Abs to the medium of cultured BBSs. Surprisingly, IκB-β, whose expression is not regulated by NF-κB, unlike IκB-α, was the most prominent NF-κB inhibitor found in BBSs. The amounts of IκB-β were low in BBSs obtained from diseased horses, but drastically increased after addition of the neutralizing anti-IL-1β and anti-TNF-α Abs. These results indicate that sustained NF-κB activation in asthmatic bronchi is driven by granulocytes and is mediated by IL-1β and TNF-α. Moreover, an imbalance between high levels of IL-1β- and TNF-α-mediated IκB-β degradation and low levels of IκB-β synthesis is likely to be the mechanism preventing NF-κB deactivation in asthmatic airways before granulocytic death.

Induction of apoptosis by curcumin: mediation by glutathione S-transferase P1-1 inhibition

Expression of glutathione S-transferase P1-1 (GSTP1-1) is correlated to carcinogenesis and resistance of cancer cells against chemotherapeutic agents. Curcumin, a natural compound extracted from Curcuma longa, has shown strong antioxidant and anticancer properties and also the ability to regulate a wide variety of genes that require activating protein 1 and nuclear factor kappaB (NF-kappaB) activation. In the present study, we examined the inhibitory effect of curcumin on the expression of GSTP1-1 mRNA as well as protein, and we correlated this inhibition with the apoptotic effect of curcumin on K562 leukemia cells. Curcumin efficiently inhibited the tumour necrosis factor alpha- and phorbol ester-induced binding of AP-1 and NF-kappaB transcription factors to sites located on the GSTP1-1 gene promoter. TNFalpha-induced GSTP1-1 promoter activity was also inhibited by curcumin as shown by reporter gene assay. In parallel, curcumin induced pro-caspases 8 and 9 as well as poly ADP ribose polymerase cleavage and thus leading to apoptosis in K562 cells. Our results overall add a novel role for curcumin as this chemoprotective compound could contribute to induce apoptosis by its ability to inhibit the GSTP1-1 expression at the level of transcription.

NF-κB-dependent MnSOD expression protects adenocarcinoma cells from TNF-α-induced apoptosis

NF-κB is known to exert a cytoprotective action against TNF-α-induced apoptosis. To study the role of NF-κB in various TNF-α-treated epithelial cell lines, we generated stable transfectants overexpressing a mutated unresponsive form of the IκBα inhibitor (MT cells). As NF-κB prevented TNF-α-induced apoptosis in various epithelial cancer cell lines, we searched for NF-κB target gene products responsible for this difference of sensitivity. We observed an increased Bcl-XL expression level in OVCAR-3 cells compared with OVCAR-3 cells expressing a mutated IκBα inhibitor (MT cells). Induction of the antioxidant enzyme MnSOD was detected only in TNF-α-treated OVCAR, MCF7A/Z and HCT116 cells but not in MT cells. Moreover, reactive oxygen species were involved in TNF-α-induced apoptosis, as various antioxidants partially protected these cells from apoptosis. At last, transfection of the MnSOD cDNA in MT cells, which do not express this protein after TNF-α stimulation, partially restored resistance to TNF-α-induced cell death, as observed by clonogenic assays. However, transfection of the Bcl-XL cDNA did not induce any protective effect. Therefore, MnSOD expression is induced by NF-κB in epithelial cancer cells in response to TNF-α, and is at least partially responsible for their resistance to TNF-α-induced apoptosis, presumably through the clearance of death-inducing ROS.

A Beginner's Guide to NF-κB Signaling Pathways

Abstract: Nuclear factor κB (NF‐κB) belongs to a family of heterodimeric transcription factors that play a key role in inflammatory and stress responses as well as in tumor cell resistance to apoptosis. These effects are due to the NF‐κB‐dependent transcription of many proinflammatory and antiapoptotic genes, whose products ensure various cell responses to environmental conditions. The signal transduction pathways leading to NF‐κB activation are well characterized, and the different steps implicated in these pathways involve proteins that could constitute targets for NF‐κB inhibition. Several inhibitors aiming to prevent NF‐κB activity and thus the transcription of target genes are studied, and a few compounds seem particularly promising. We try here to summarize the advantages that can issue from various studies on NF‐κB.

An introduction to the molecular mechanisms of apoptosis.

Abstract: Apoptosis is a type of cell death that has been observed and studied for more than a century. The process of apoptosis was described as “programmed cell death” in 1964, and the term apoptosis, from a Greek word meaning “to fall away from” and describing the fall of dead leaves from trees in autumn, was only coined in 1972. During the last 30 years, this type of cell death has been extensively investigated and the molecular mechanisms underlying this cell suicide well characterized. Apoptosis is a physiological phenomenon necessary to tissue and body genesis and homeostasis, but defects in its regulation may cause numerous diseases, including cancer. Investigating the mechanisms of apoptosis is thus important to discover new cellular regulators that could be potential targets for new death‐inducing drugs.

Curcumin-Induced Cell Death in Two Leukemia Cell Lines: K562 and Jurkat

Abstract: Curcumin presents strong antioxidant and anticancer properties. However, molecular mechanisms leading to curcumin‐induced cell death are poorly understood. The effect of curcumin was compared in two different leukemia cell lines: K562 and Jurkat. Cell death was induced in both cell lines, and apoptosis pathways were investigated by Western blot analysis. Decreases in pro‐caspase 8 and 9 levels were observed. BH3 interacting domain death agonist (Bid) was also cleaved. Jurkat cells appeared to be more sensitive to curcumin, and apoptosis takes place earlier.

Identification of cytokine-induced nuclear factor-kappaB target genes in ovarian and breast cancer cells.

NF-kappaB is a pleiotropic transcription factor controlling the expression of many genes and viruses. NF-kappaB plays a role in immune response, cellular adhesion or acute phase response. It also inhibits apoptosis and favors cancer cell survival. We studied the expression of genes controlled by NF-kappaB in ovarian and breast adenocarcinoma cancer cells. We stably transfected OVCAR-3 and MCF7 A/Z cells with an expression vector coding for the mutated inhibitor IkappaBalpha, which sequesters NF-kappaB in the cytoplasm. We stimulated control and IkappaBalpha expressing cells with IL-1beta or TNF-alpha and extracted the RNA, which was reverse-transcribed and hybridized to DNA microarrays. Several of the genes identified were not known as NF-kappaB target genes. Among them, we confirmed the differential expression of ephrin-A1 and caveolin-1 by quantitative real-time polymerase chain reaction. Our results showed an NF-kappaB-dependent induction of ephrin-A1 and caveolin-1 mRNAs after stimulation with TNF-alpha and IL-1beta, confirming that NF-kappaB controls target genes implied in tumor angiogenesis and cell transformation.

Curcumin Stability and Its Effect on Glutathione S-Transferase P1-1 mRNA Expression in K562 Cells

Abstract: To investigate the stability of curcumin in physiological media, the absorption variation of a curcumin solution was measured in 0.1% and 10% FCS. Under daylight conditions, curcumin degraded very rapidly in 0.1% FCS and was found to be more stable in higher serum concentrations. Under dark conditions, almost no decomposition could be observed after 2 h, whether the measurements were performed in 0.1% or 10% FCS. Furthermore, depending on the medium concentration, differential glutathione S‐transferase P1‐1 mRNA expression could be observed in K562 cells after incubation with curcumin. Indeed, incubation in 0.1% FCS led to a decrease of mRNA expression, whereas incubation in 10% FCS induced an increase of mRNA production.