Phenylarsine Oxide Blocks Interleukin-1β–Induced Activation of the Nuclear Transcription Factor NF-κB, Inhibits Proliferation, and Induces Apoptosis of Acute Myelogenous Leukemia Cells

The human herpes virus 8-encoded viral FLICE inhibitory protein protects against growth factor withdrawal-induced apoptosis via NF-kappa B activation

The human herpes virus 8 (HHV8)-encoded viral FLICE (Fas-associating protein with death domain-like interleukin-1-converting enzyme) inhibitory protein (vFLIP) is believed to protect cells against death receptor-mediated apoptosis. In the present study we demonstrate that expression of HHV8 vFLIP in a growth factor-dependent TF-1 leukemia cell line protects against growth factor withdrawal-induced apoptosis. Unlike vector-expressing cells, those expressing HHV8 vFLIP maintain their mitochondrial membrane potential upon withdrawal from growth factor and also exhibit a block in the activation of caspases. The protective effect of HHV8 vFLIP is associated with its ability to activate the nuclear factor-kappa B (NF-kappaB) pathway and is missing in the vFLIP encoded by equine herpes virus 2 that lacks this activity. Inhibition of the NF-kappaB pathway by IkappaB superrepressor, lactacystin, MG132, arsenic trioxide, and phenylarsine oxide reverse the protection against growth factor withdrawal-induced apoptosis conferred by HHV8 vFLIP. HHV8 vFLIP up-regulates the expression of Bcl-x(L), an antiapoptotic member of the Bcl2 family, which is a known target of the NF-kappaB pathway. Collectively, the above results suggest that HHV8 vFLIP-induced NF-kappaB activation may contribute to cellular transformation seen in association with HHV8 infection by preventing the apoptosis of cells destined to die because of growth factor deprivation.

Curcumin (diferuloylmethane) down-regulates the constitutive activation of nuclear factor-kappa B and IkappaBalpha kinase in human multiple myeloma cells, leading to suppression of proliferation and induction of apoptosis

Because of the central role of the transcription factor nuclear factor-kappaB (NF-kappaB) in cell survival and proliferation in human multiple myeloma (MM), we explored the possibility of using it as a target for MM treatment by using curcumin (diferuloylmethane), an agent known to have very little or no toxicity in humans. We found that NF-kappaB was constitutively active in all human MM cell lines examined and that curcumin, a chemopreventive agent, down-regulated NF-kappaB in all cell lines as indicated by electrophoretic mobility gel shift assay and prevented the nuclear retention of p65 as shown by immunocytochemistry. All MM cell lines showed consitutively active IkappaB kinase (IKK) and IkappaBalpha phosphorylation. Curcumin suppressed the constitutive IkappaBalpha phosphorylation through the inhibition of IKK activity. Curcumin also down-regulated the expression of NF-kappaB-regulated gene products, including IkappaBalpha, Bcl-2, Bcl-x(L), cyclin D1, and interleukin-6. This led to the suppression of proliferation and arrest of cells at the G(1)/S phase of the cell cycle. Suppression of NF-kappaB complex by IKKgamma/NF-kappaB essential modulator-binding domain peptide also suppressed the proliferation of MM cells. Curcumin also activated caspase-7 and caspase-9 and induced polyadenosine-5'-diphosphate-ribose polymerase (PARP) cleavage. Curcumin-induced down-regulation of NF-kappaB, a factor that has been implicated in chemoresistance, also induced chemosensitivity to vincristine and melphalan. Overall, our results indicate that curcumin down-regulates NF-kappaB in human MM cells, leading to the suppression of proliferation and induction of apoptosis, thus providing the molecular basis for the treatment of MM patients with this pharmacologically safe agent.

Increased IkappaB kinase activity is associated with activated NF-kappaB in acute myeloid blasts

NF-kappaB/Rel transcription factors are modulators of immune and inflammatory processes and are also involved in malignancy. Phosphorylation of the IkappaB inhibitors by the IkappaB kinase (IKK) complex leads to their proteasomal degradation, resulting in activated NF-kappaB. Here, we investigated the activation status of NF-kappaB and the IKK complex in acute myeloid leukemia (AML). Gelshift assays revealed an increased level of activated nuclear NF-kappaB in myeloid blasts. Both bone marrow and peripheral blood blasts from AML patients showed enhanced IKK activity relative to controls, whereas the IKK protein concentrations were comparable. In addition, an increased level of IkappaB-alpha was detected in AML blast cells, although this appeared to be insufficient to block nuclear translocation of NF-kappaB, also confirmed by immunofluorescence. In subtype M4 and M5 AML cells a more extensive NF-kappaB activation and higher IKK activity was found than in M1/M2 specimens. Isolated AML blasts cultured ex vivo responded to external stimulation (TNF, LPS) by further IKK activation, IkappaB degradation and NF-kappaB activation. Preincubation with the proteasome inhibitor PSI inhibited the NF-kappaB system in isolated AML blasts. This study established for the first time a dysregulation of IKK signaling in AML leading to increased NF-kappaB activity suggesting potential therapeutic avenues.

Nuclear factor-kappa B and cancer: its role in prevention and therapy

Cancer is a hyperproliferative disorder in which invasion and angiogenesis lead to tumor metastasis. Several genes that mediate tumorigenesis and metastasis are regulated by a nuclear transcription factor, nuclear factor kappa B (NF-kappaB). A heterotrimeric complex consisting of p50, p65, and IkappaBalpha, NF-kappaB is present in its inactive state in the cytoplasm. When NF-kappaB is activated, IkappaBalpha is degraded and p50-p65 heterodimer is translocated to the nucleus, binds the DNA (at the promoter region), and activates gene. Research within the last few years has revealed that NF-kappaB is activated by carcinogens, tumor promoters, inflammatory cytokines, and by chemotherapeutic agents. The activation of NF-kappaB can suppress apoptosis, thus promoting chemoresistance and tumorigenesis. Interestingly, however, most chemopreventive agents appear to suppress the activation of the NF-kappaB through inhibition of NF-kappaB signaling pathway. These chemopreventive agents also sensitize the tumors to chemotherapeutic agents through abrogation of NF-kappaB activation. Overall, these observations suggest that NF-kappaB is an ideal target for chemoprevention and chemosensitization. This article reviews evidence supporting this hypothesis.

In vitro and in vivo effectiveness of arsenic trioxide against murine T-cell prolymphocytic leukaemia

T-cell prolymphocytic leukaemia (T-PLL) is a rare form of mature T-cell leukaemia that is generally resistant to conventional chemotherapy. Mice transgenic for MTCP1 develop leukaemia similar to human T-PLL, providing a model useful for testing therapeutics. We here evaluated the potential effectiveness of arsenic trioxide (ATO) in murine T-PLL. In vitro, ATO consistently reduced the viability of murine T-PLL cells at a clinically achievable concentration (1 micromol/l). The percentage of viable cells after 24 h was 77 +/- 4%, 56 +/- 6%, 31 +/- 7% with 0 micromol/l, 0.5 micromol/l and 1 micromol/l ATO respectively. ATO cytotoxicity was enhanced by ascorbic acid (125 micromol/l). Mice were then treated with ATO (5 microg/g/d intra peritoneally, 5 d per week) or saline for 4 weeks, starting 14 d after tumoral engraftment. The appearance of lymphocytosis and splenomegaly was delayed in the group treated with ATO and survival was significantly prolonged (mean survival in days: 57.6 +/- 0.8 for ATO versus 45 +/- 0 for saline, P < 10-4). No additional effect was observed in vivo by combining ATO with ascorbic acid (500 microg/g/d, 5 d per week, intra peritoneally). These findings provide support for clinical trials to test therapeutic effects of ATO for human T-PLL.

NF-kappa B activates prostate-specific antigen expression and is upregulated in androgen-independent prostate cancer

The transcription factor NF-kappa B regulates gene expression involved in cell growth and survival and has been implicated in progression of hormone-independent breast cancer. By expressing a dominant-active form of mitogen-activated protein kinase kinase kinase 1, by exposure to tumor necrosis factor alpha, or by overexpression of p50/p65, we show that NF-kappa B activates a transcription regulatory element of the prostate-specific antigen (PSA)-encoding gene, a marker for prostate cancer development, treatment, and progression. By DNase I footprinting, we identified four NF-kappa B binding sites in the PSA core enhancer. We also demonstrate that androgen-independent prostate cancer xenografts have higher constitutive NF-kappa B binding activity than their androgen-dependent counterparts. These results suggest a role of NF-kappa B in prostate cancer progression.

Glucosamine modulates IL-1-induced activation of rat chondrocytes at a receptor level, and by inhibiting the NF-kappa B pathway

We recently reported that glucosamine reversed the decrease in proteoglycan synthesis and in UDP-glucuronosyltransferase I mRNA expression induced by interleukin-1 beta (IL-1 beta) [Arthritis Rheum. 44 (2001) 351-360]. In the present work, we show that glucosamine does not exert the same effects when chondrocytes were stimulated with reactive oxygen species (ROS). In order to better understand its mechanism of action, we determined if glucosamine could prevent the binding of IL-1 beta to its cellular receptors or could interfere with its signaling pathway at a post-receptor level. Addition of glucosamine to rat chondrocytes treated with IL-1 beta or with ROS decreased the activation of the nuclear factor kappa B, but not the activator protein-1. After treatment with IL-1 beta, glucosamine increased the expression of mRNA encoding the type II IL-1 beta receptor. These results emphasize the potential role of two regulating proteins of the IL-1 beta signaling pathway that could account for the beneficial effect of glucosamine in osteoarthritis.

Stress proteins induced by arsenic

The elevated expression of stress proteins is considered to be a universal response to adverse conditions, representing a potential mechanism of cellular defense against disease and a potential target for novel therapeutics. Exposure to arsenicals either in vitro or in vivo in a variety of model systems has been shown to cause the induction of a number of the major stress protein families such as heat shock proteins (Hsp). Among them are members with low molecular weight, such as metallotionein and ubiquitin, as well as ones with masses of 27, 32, 60, 70, 90, and 110 kDa. In most of the cases, the induction of stress proteins depends on the capacity of the arsenical to reach the target, its valence, and the type of exposure, arsenite being the biggest inducer of most Hsp in several organs and systems. Hsp induction is a rapid dose-dependent response (1-8 h) to the acute exposure to arsenite. Thus, the stress response appears to be useful to monitor the sublethal toxicity resulting from a single exposure to arsenite. The present paper offers a critical review of the capacity of arsenicals to modulate the expression and/or accumulation of stress proteins. The physiological consequences of the arsenic-induced stress and its usefulness in monitoring effects resulting from arsenic exposure in humans and other organisms are discussed.

Functional expression of receptor activator of nuclear factor kappaB in Hodgkin disease cell lines

The malignant Hodgkin and Reed-Sternberg (H/RS) cells of Hodgkin disease (HD) express several members of the tumor necrosis factor (TNF) receptor family, including CD30 and CD40, and secrete several cytokines and chemokines. However, little is known about what regulates cytokine and chemokine secretion in H/RS cells. Although H/RS cells are predominantly of B-cell origin, they frequently share phenotypic and functional features with dendritic cells (DCs). Previous studies reported that receptor activator of nuclear factor kappaB (NF-kappaB) (RANK), a member of the TNF receptor family, is expressed on DCs, and that RANK ligand (RANKL) enhances DC survival and induces them to secrete cytokines. This study reports that, similar to DCs, cultured H/RS cells expressed RANK. However, unlike DCs, H/RS cells also expressed RANKL. Soluble RANKL activated NF-kappaB and induced messenger RNA expression of interferon-gamma, interleukin-8 (IL-8), IL-13, IL-9, IL-15, and RANTES, in addition to the receptors for IL-9, IL-13, IL-15, and CCR4. RANKL increased IL-8 and IL-13 levels in the supernatants of H/RS cell lines, an effect that was blocked by soluble RANK. Furthermore, soluble RANK decreased the basal level of IL-8 in one cell line, suggesting that IL-8 was induced by an autocrine RANKL/RANK loop. RANKL had no effect on H/RS cell survival in culture, and it did not modulate the expression of bcl-2, bcl-xL, bax, or inhibitors of apoptosis proteins. These data provide evidence of further functional similarities between DCs and H/RS cells. The coexpression of RANK and RANKL in H/RS cells suggests that they may regulate cytokine and chemokine secretion in H/RS cells by an autocrine mechanism.

Opposite effect of NF-kappa B and c-Jun N-terminal kinase on p53-independent GADD45 induction by arsenite

Cell cycle checkpoint, a major genomic surveillance mechanism, is an important step in maintaining genomic stability and integrity in response to environmental stresses. Using cells derived from human bronchial epithelial cells, we demonstrate that NF-kappaB and c-Jun N-terminal kinase (JNK) reciprocally regulate arsenic trioxide (arsenite)-induced, p53-independent expression of GADD45 protein, a cell cycle checkpoint protein that arrests cells at the G(2)/M phase transition. Inhibition of NF-kappaB activation by stable expression of a kinase-mutated form of IkappaB kinase caused increased and prolonged induction of GADD45 by arsenite. In contrast, the induction of GADD45 by arsenite was transient and less potent in cells where the NF-kappaB activation pathway was normal. Analysis of the cell cycle profile by flow cytometry indicated that NF-kappaB inhibition potentiates arsenite-induced G(2)/M cell cycle arrest. Abrogation of JNK activation, on the other hand, decreased GADD45 expression induced by arsenite, suggesting a role for JNK activation in GADD45 induction. These results indicate a molecular mechanism by which NF-kappaB and JNK may differentially contribute to cell cycle regulation in response to arsenite.

Endothelial cell activation by myeloblasts: molecular mechanisms of leukostasis and leukemic cell dissemination

Leukostasis and tissue infiltration by leukemic cells are poorly understood life-threatening complications of acute leukemia. This study has tested the hypothesis that adhesion receptors and cytokines secreted by blast cells play central roles in these reactions. Immunophenotypic studies showed that acute myeloid leukemia (AML) cells (n = 78) of the M0 to M5 subtypes of the French-American-British Cooperative Group expressed various amounts of adhesion receptors, including CD11a, b, c/CD18, CD49d, e, f/CD29, CD54, sCD15, and L-selectin. The presence of functional adhesion receptors was evaluated using a nonstatic adhesion assay. The number of blast cells attached to unactivated endothelium increased by 7 to 31 times after a 6-hour exposure of endothelium to tumor necrosis factor (TNF)-alpha. Inhibition studies showed that multiple adhesion receptors--including L-selectin, E-selectin, VCAM-1, and CD11/CD18--were involved in blast cell adhesion to TNF-alpha-activated endothelium. Leukemic cells were then cocultured at 37 degrees C on unactivated endothelial cell monolayers for time periods up to 24 hours. A time-dependent increase in the number of blasts attached to the endothelium and a concomitant induction of ICAM-1, VCAM-1, and E-selectin were observed. Additional experiments revealed that endothelial cell activation by leukemic myeloblasts was caused by cytokine secretion by blast cells, in particular TNF-alpha and IL-1 beta, and direct contacts between adhesion receptors expressed by blast cells and endothelial cells. Thus, leukemic cells have the ability to generate conditions that promote their own adhesion to vascular endothelium, a property that may have important implications for the pathophysiology of leukostasis and tissue infiltration by leukemic blast cells. (Blood. 2001;97:2121-2129)

Apoptosis and nuclear factor-kappa B: a tale of association and dissociation

It is not clear why on treatment with certain killer cytokines or chemotherapeutic agents, some cells undergo apoptosis while others do not. The delineation of sensitivity/resistance pathways should provide a more specific therapy for cancer and other hyperproliferative diseases. Most cells die either by apoptosis or by necrosis. The biochemical pathway that mediates these two modes of cell death has recently been described. The nuclear factor (NF)-kappa B and the genes regulated by this transcription factor have been shown to play a critical role in induction of resistance to killer agents. Thus, inhibitors of NF-kappa B activation have a potential in overcoming resistance to apoptosis induced by various agents. The evidence for and against such a notion is discussed.

Arsenic inhibits NF-kappaB-mediated gene transcription by blocking IkappaB kinase activity and IkappaBalpha phosphorylation and degradation

The inflammatory cytokine, TNF-alpha, induces IL-8 gene transcription via a mechanism involving proteasome-mediated IkappaBalpha degradation and NF-kappaB activation. Here, we investigated whether arsenic, which has been shown to inhibit the ubiquitin-proteasome pathway, could inhibit TNF-alpha-mediated increases in IL-8 expression. Using RT-PCR, we show that the addition of TNF-alpha to human bronchial epithelial (BEAS 2B) or embryonic kidney (HEK293) cells resulted in increased steady-state levels of IL-8 mRNA. This was preceded by a rapid decrease in cellular IkappaBalpha levels, as demonstrated by Western analysis, and an increase in nuclear levels of NF-kappaB, as demonstrated by gel shift analysis. Further demonstrating the activation of NF-kappaB, TNF-alpha induced the transcription of a NF-kappaB-dependent reporter gene. Exposing the cells to 500 microM arsenite, prior to adding TNF-alpha, completely inhibited IkappaBalpha degradation, NF-kappaB translocation, NF-kappaB-dependent gene transcription, and transcription of the endogenous gene for IL-8. In comparison with the proteasome inhibitor MG-132, which does not affect the phosphorylation and ubiquitination of IkappaBalpha, arsenite inhibited the phosphorylation of IkappaBalpha. Furthermore, arsenite directly blocked the activity of IKK, the kinase responsible for IkappaBalpha phosphorylation. These studies demonstrate that high levels of arsenic may inhibit NF-kappaB-mediated gene transcription by specifically blocking IKK activity, thereby limiting the phosphorylation and subsequent degradation of the NF-kappaB inhibitor, IkappaBalpha.

Apoptosis induction by arsenic: mechanisms of action and possible clinical applications for treating therapy-resistant cancers

Arsenic, a known carcinogen, may be useful in cancer treatment. Arsenic may be effective in counteracting drug resistance because it appears to induce apoptosis in tumor cells independently of p53 activation, thereby allowing it to be directed against p53-defective cancers. The role of MAP kinases in arsenic-induced apoptosis in tumor cells is important and may be influenced by reactive oxygen species or glutathione. This review focuses on recent findings from this and other laboratories regarding the mechanism(s) of arsenic-induced apoptosis in tumor cells and considers their relevance in the clinical treatment of therapy-resistant cancers. Copyright 2000 Harcourt Publishers Ltd.