Apoptosis promotes a caspase-induced amino-terminal truncation of IkappaBalpha that functions as a stable inhibitor of NF-kappaB

Shedding Light on NF-κB Functions in Cellular Organelles

NF-κB is diffusely recognized as a transcriptional factor able to modulate the expression of various genes involved in a broad spectrum of cellular functions, including proliferation, survival and migration. NF-κB is, however, also acting outside the nucleus and beyond its ability to binds to DNA. NF-κB is indeed found to localize inside different cellular organelles, such as mitochondria, endoplasmic reticulum, Golgi and nucleoli, where it acts through different partners in mediating various biological functions. Here, we discuss the relationship linking NF-κB to the cellular organelles, and how this crosstalk between cellular organelles and NF-κB signalling may be evaluated for anticancer therapies.

Synonymous mutations in oncogenesis and apoptosis versus survival unveiled by network modeling

Synonymous mutations, which do not alter the encoded amino acid, have been routinely assumed to be ‘neutral’ and would have no effect on phenotype or fitness. Yet increasing observations have emerged to overturn this conventional concept. However, convicted elucidation of how synonymous mutations exert biological consequences in oncogenesis is still lacking. By performing systematic analysis of the TNF-α signaling network model, we identify the critical dose which separates the cell survival and apoptosis regions and define the sensitive parameters with single-parameter sensitivity analysis. Combining with the cancer-related mutation spectra obtained from 9 cancers, our results hint that, similar as missense and nonsense mutations, synonymous mutations are also strongly correlated with the parameter sensitivity of the critical dose, providing possible causal mechanism of the mutations in cancer development. Based on such a correlation, we furthermore dissect that members of caspases family proteases (caspase3, 6, 8) could jointly inhibit NFκB activation, providing efficient pro-apoptotic behavior. Thus, we argue that apoptosis module could suppress survival module through negative feedback of caspases family on NFκB.

The multifunctional polydnavirus TnBVANK1 protein: impact on host apoptotic pathway

Toxoneuron nigriceps (Hymenoptera, Braconidae) is an endophagous parasitoid of the larval stages of the tobacco budworm, Heliothis virescens (Lepidoptera, Noctuidae). The bracovirus associated with this wasp (TnBV) is currently being studied. Several genes expressed in parasitised host larvae have been isolated and their possible roles partly elucidated. TnBVank1 encodes an ankyrin motif protein similar to insect and mammalian IκB, an inhibitor of the transcription nuclear factor κB (NF-κB). Here we show that, when TnBVank1 was stably expressed in polyclonal Drosophila S2 cells, apoptosis is induced. Furthermore, we observed the same effects in haemocytes of H. virescens larvae, after TnBVank1 in vivo transient transfection, and in haemocytes of parasitised larvae. Coimmunoprecipitation experiments showed that TnBVANK1 binds to ALG-2 interacting protein X (Alix/AIP1), an interactor of apoptosis-linked gene protein 2 (ALG-2). Using double-immunofluorescence labeling, we observed the potential colocalization of TnBVANK1 and Alix proteins in the cytoplasm of polyclonal S2 cells. When Alix was silenced by RNA interference, TnBVANK1 was no longer able to cause apoptosis in both S2 cells and H. virescens haemocytes. Collectively, these results indicate that TnBVANK1 induces apoptosis by interacting with Alix, suggesting a role of TnBVANK1 in the suppression of host immune response observed after parasitisation by T. nigriceps.

Non-mutagenic Suppression of Enterocyte Ferroportin 1 by Chemical Ribosomal Inactivation via p38 Mitogen-activated Protein Kinase (MAPK)-mediated Regulation: EVIDENCE FOR ENVIRONMENTAL HEMOCHROMATOSIS

Iron transfer across the basolateral membrane of an enterocyte into the circulation is the rate-limiting step in iron absorption and is regulated by various pathophysiological factors. Ferroportin (FPN), the only known mammalian iron exporter, transports iron from the basolateral surface of enterocytes, macrophages, and hepatocytes into the blood. Patients with genetic mutations in FPN or repeated blood transfusion develop hemochromatosis. In this study, non-mutagenic ribosomal inactivation was assessed as an etiological factor of FPN-associated hemochromatosis in enterocytes. Non-mutagenic chemical ribosomal inactivation disrupted iron homeostasis by regulating expression of the iron exporter FPN-1, leading to intracellular accumulation in enterocytes. Mechanistically, a xenobiotic insult stimulated the intracellular sentinel p38 MAPK signaling pathway, which was positively involved in FPN-1 suppression by ribosomal dysfunction. Moreover, ribosomal inactivation-induced iron accumulation in Caenorhabditis elegans as a simplified in vivo model for gut nutrition uptake was dependent on SEK-1, a p38 kinase activator, leading to suppression of FPN-1.1 expression and iron accumulation. In terms of gene regulation, ribosomal stress-activated p38 signaling down-regulated NRF2 and NF-κB, both of which were positive transcriptional regulators of FPN-1 transcription. This study provides molecular evidence for the modulation of iron bioavailability by ribosomal dysfunction as a potent etiological factor of non-mutagenic environmental hemochromatosis in the gut-to-blood axis.

Disruptions of Host Immunity and Inflammation by Giardia Duodenalis: Potential Consequences for Co-Infections in the Gastro-Intestinal Tract

Giardia duodenalis (syn. G. intestinalis, or G. lamblia) is a leading cause of waterborne diarrheal disease that infects hundreds of millions of people annually. Research on Giardia has greatly expanded within the last few years, and our understanding of the pathophysiology and immunology on this parasite is ever increasing. At peak infection, Giardia trophozoites induce pathophysiological responses that culminate in the development of diarrheal disease. However, human data has suggested that the intestinal mucosa of Giardia-infected individuals is devoid of signs of overt intestinal inflammation, an observation that is reproduced in animal models. Thus, our understanding of host inflammatory responses to the parasite remain incompletely understood and human studies and experimental data have produced conflicting results. It is now also apparent that certain Giardia infections contain mechanisms capable of modulating their host’s immune responses. As the oral route of Giardia infection is shared with many other gastrointestinal (GI) pathogens, co-infections may often occur, especially in places with poor sanitation and/or improper treatment of drinking water. Moreover, Giardia infections may modulate host immune responses and have been found to protect against the development of diarrheal disease in developing countries. The following review summarizes our current understanding of the immunomodulatory mechanisms of Giardia infections and their consequences for the host, and highlights areas for future research. Potential implications of these immunomodulatory effects during GI co-infection are also discussed.

Direct and indirect anti-inflammatory effects of tulathromycin in bovine macrophages: inhibition of CXCL-8 secretion, induction of apoptosis, and promotion of efferocytosis

Recent evidence indicates that immunomodulation by antibiotics may enhance their clinical efficacy. Specifically, drug-induced leukocyte apoptosis and macrophage efferocytosis have been shown to promote the resolution of inflammation in a variety of disease settings. Tulathromycin is a new macrolide antibiotic for the treatment of bovine respiratory disease. The direct antimicrobial effects of the drug alone do not fully justify its superior clinical efficacy, and we hypothesize that tulathromycin may have immunomodulating properties. We recently reported that tulathromycin promotes apoptosis and inhibits proinflammatory NF-κB signaling in bovine neutrophils. In this study, we investigated the direct and indirect anti-inflammatory effects of tulathromycin in bovine macrophages. The findings indicate that bovine monocyte-derived macrophages and alveolar macrophages readily phagocytose tulathromycin-induced apoptotic neutrophils both in vitro and in the airways of Mannheimia haemolytica-infected calves. Moreover, tulathromycin promotes delayed, concentration-dependent apoptosis, but not necrosis, in bovine macrophages in vitro. Activation of caspase-3 and detection of mono- and oligonucleosomes in bovine monocyte-derived macrophages treated with tulathromycin was observed 12 h posttreatment; pretreatment with a pan-caspase inhibitor (ZVAD) blocked the proapoptotic effects of the drug. Lastly, tulathromycin inhibited the secretion of proinflammatory CXCL-8 in lipopolysaccharide (LPS)-stimulated bovine macrophages; this effect was independent of caspase activation or programmed cell death. Taken together, these immunomodulating effects observed in bovine macrophages help further elucidate the mechanisms through which tulathromycin confers anti-inflammatory and proresolution benefits. Furthermore, these findings offer novel insights on how antibiotics may offer anti-inflammatory benefits by modulating macrophage-mediated events that play a key role in inflammation.

Regulation of cell death and autophagy by IKK and NF-κB: critical mechanisms in immune function and cancer

The cellular response to survive or to undergo death is fundamental to the benefit of the organism, and errors in this process can lead to autoimmunity and cancer. The transcription factor nuclear factor κB (NF-κB) functions to block cell death through transcriptional induction of genes encoding anti-apoptotic and antioxidant proteins. This is essential for survival of activated cells of the immune system and for cells undergoing a DNA damage response. In Ras-transformed cells and tumors as well as other cancers, NF-κB functions to suppress apoptosis--a hallmark of cancer. Critical prosurvival roles for inhibitor of NF-κB kinase (IKK) family members, including IKKε and TBK1, have been reported, which are both NF-κB-dependent and -independent. While the roles of NF-κB in promoting cell survival in lymphocytes and in cancers is relatively clear, evidence has been presented that NF-κB can promote cell death in particular contexts. Recently, IKK was shown to play a critical role in the induction of autophagy, a metabolic response typically associated with cell survival but which can lead to cell death. This review provides an historical perspective, along with new findings, regarding the roles of the IKK and NF-κB pathways in regulating cell survival.

Crosstalk in NF-κB signaling pathways

NF-κB transcription factors are critical regulators of immunity, stress responses, apoptosis and differentiation. A variety of stimuli coalesce on NF-κB activation, which can in turn mediate varied transcriptional programs. Consequently, NF-κB-dependent transcription is not only tightly controlled by positive and negative regulatory mechanisms but also closely coordinated with other signaling pathways. This intricate crosstalk is crucial to shaping the diverse biological functions of NF-κB into cell type- and context-specific responses.

Hydrogen peroxide modulates immunoglobulin expression by targeting the 3'Igh regulatory region through an NFκB-dependent mechanism

Reactive oxygen species such as hydrogen peroxide (H(2)O(2)) appear to play a role in signal transduction in immune cells and have been shown to be synthesized upon antigen-mediated activation and to facilitate cellular activation in B- and T-cells. However, an effect of H(2)O(2) on B-cell function (i.e. immunoglobulin (Ig) expression) has been less well-characterized. The effects of H(2)O(2) exposure on lymphocytes may be partly mediated by oxidative modulation of the NFκB signal transduction pathway, which also plays a role in Ig heavy chain (Igh) gene expression. Igh transcription in B lymphocytes is an essential step in antibody production and is governed through a complex interaction of several regulatory elements, including the 3'Igh regulatory region (3'IghRR). Utilizing an in vitro mouse B-cell line model, this study demonstrates that exposure to low μM concentrations of H(2)O(2) can enhance 3'IghRR-regulated transcriptional activity and Igh gene expression, while either higher concentrations of H(2)O(2) or the expression of a degradation resistant inhibitory κB (IκBα super-repressor) can abrogate this effect. Furthermore, suppressive H(2)O(2) concentrations increased protein levels of the p50 NFκB sub-unit, IκBα, and an IκBα immunoreactive band which was previously characterized as an IκBα cleavage product exhibiting stronger inhibitory function than native IκBα. Taken together, these observations suggest that exposure of B lymphocytes to H(2)O(2) can alter Igh transcriptional activity and Ig expression in a complex biphasic manner which appears to be mediated by NFκB and altered 3'IghRR activity. These results may have significant implications to disease states previously associated with the 3'IghRR.

Insulin-like growth factor-binding protein-3 suppresses tumor growth via activation of caspase-dependent apoptosis and cross-talk with NF-κB signaling

Nuclear factor-kappaB (NF-κB) is constitutively activated in a variety of human cancers including prostate cancer and involved in tumorigenesis, tumor progression and chemo-resistance. Insulin-like growth factor-binding protein-3 (IGFBP-3) is a potent tumor suppressor and is significantly suppressed in a variety of cancers. Diverse biological effects of IGFBP-3 have been reported to be both dependent and independent of the IGF/IGF-I receptor (IGF-IR) axis. The precise underlying mechanisms of IGF/IGF-IR-independent, antiproliferative actions of IGFBP-3 are yet to be elucidated. We found an inverse correlation between NF-κB activity and IGFBP-3 expression during prostate cancer progression using an in vitro prostate cancer progression model. Restoration of IGFBP-3 resulted in significant inhibition of constitutively elevated NF-κB activity in prostate cancer cells. IGFBP-3 further inhibited the expression of NF-κB-regulated angiogenic factors such as VEGF and IL-8, and cell adhesion molecules, ICAM-1 and VCAM-1. This inhibitory action of IGFBP-3 was IGF/IGF-IR-independent since IGFBP-3 mutant devoid of IGF binding affinity had a similar inhibitory effect. We identified that IGFBP-3 degrades the key NF-κB regulatory molecules-IκBα and p65-NF-κB proteins through activation of caspase-8 and -3/-7, thereby inhibiting elevated NF-κB activity in prostate cancer. Finally intratumoral administration of IGFBP-3 resulted in significant tumor suppression as well as sensitization of antitumor effect of doxorubicin. Our findings indicate that IGFBP-3 exerts antitumor effects via IGF-independent mechanisms which involve activation of caspase-dependent apoptosis and cross-talk with NF-κB signaling. The use of IGFBP-3 as a cancer therapeutic with this distinctive suppression mechanism may offer alternate means to treat chemotherapy resistant tumors.

Anti-Inflammatory benefits of antibiotic-induced neutrophil apoptosis: tulathromycin induces caspase-3-dependent neutrophil programmed cell death and inhibits NF-kappaB signaling and CXCL8 transcription

Clearance of apoptotic neutrophils is a central feature of the resolution of inflammation. Findings indicate that immuno-modulation and induction of neutrophil apoptosis by macrolide antibiotics generate anti-inflammatory benefits via mechanisms that remain obscure. Tulathromycin (TUL), a new antimicrobial agent for bovine respiratory disease, offers superior clinical efficacy for reasons not fully understood. The aim of this study was to identify the immuno-modulating effects of tulathromycin and, in this process, to establish tulathromycin as a new model for characterizing the novel anti-inflammatory properties of antibiotics. Bronchoalveolar lavage specimens were collected from Holstein calves 3 and 24 h postinfection, challenged intratracheally with live Mannheimia haemolytica (2 × 10(7) CFU), and treated with vehicle or tulathromycin (2.5 mg/kg body weight). Terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling (TUNEL) staining and enzyme-linked immunosorbent assay (ELISA) revealed that tulathromycin treatment significantly increased leukocyte apoptosis and reduced levels of proinflammatory leukotriene B(4) in M. haemolytica-challenged calves. In vitro, tulathromycin concentration dependently induced apoptosis in freshly isolated bovine neutrophils from healthy steers in a capase-3-dependent manner but failed to induce apoptosis in bovine fibroblasts, epithelial cells, and endothelial cells, as well as freshly isolated bovine blood monocytes and monocyte-derived macrophages. The proapoptotic effects of TUL were also, in part, drug specific; equimolar concentrations of penicillin G, oxytetracycline, and ceftiofur failed to cause apoptosis in bovine neutrophils. In addition, tulathromycin significantly reduced levels of phosphorylated IκBα, nuclear translocation of NF-κB p65, and mRNA levels of proinflammatory interleukin-8 in lipopolysaccharide (LPS)-stimulated bovine neutrophils. The findings illustrate novel mechanisms through which tulathromycin confers anti-inflammatory benefits.

Modulation of apoptosis and immune signaling pathways by the Hantaan virus nucleocapsid protein

Herein, we show a direct relationship between the Hantaan virus (HTNV) nucleocapsid (N) protein and the modulation of apoptosis. We observed an increase in caspase-7 and -8, but not -9 in cells expressing HTNV N protein mutants lacking amino acids 270-330. Similar results were observed for the New World hantavirus, Andes virus. Nuclear factor kappa B (NF-kappaB) was sequestered in the cytoplasm after tumor necrosis factor receptor (TNFR) stimulation in cells expressing HTNV N protein. Further, TNFR stimulated cells expressing HTNV N protein inhibited caspase activation. In contrast, cells expressing N protein truncations lacking the region from amino acids 270-330 were unable to inhibit nuclear import of NF-kappaB and the mutants also triggered caspase activity. These results suggest that the HTNV circumvents host antiviral signaling and apoptotic response mediated by the TNFR pathway through host interactions with the N protein.

Control of NF-κB activity by proteolysis

NF-κB transcription factors are critical regulators of many biological processes such as innate and adaptive immune responses, inflammation, cell proliferation and programmed cell death. This versatility necessitates a highly complex and tightly coordinated control of the signaling pathways leading to their activation. Here, we review the role of proteolysis in the regulation of NF-κB activity, more specifically the contribution of the well-known ubiquitin-proteasome system and the involvement of proteolytic activity of caspases and calpains.

Oligomerized tumor necrosis factor-related apoptosis inducing ligand strongly induces cell death in myeloma cells, but also activates proinflammatory signaling pathways

The oligomerization status of soluble tumor necrosis factor-related apoptosis inducing ligand (TRAIL) trimers has an overwhelming impact on cell death induction in a cell-type dependent fashion. Thus, we evaluated the ability of single and oligomerized TRAIL trimers to induce cell death in human myeloma cells. In all myeloma cell lines analyzed, oligomerized TRAIL trimers induced caspase activation and complete cell death, whereas non-oligomerized TRAIL trimers showed no or only a modest effect. Caspase activation induced by oligomerized TRAIL was blocked in all cell lines by the pan-caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp(OMe)-fluoromethylketone (z-VAD-fmk). Cell death induction was largely blocked in two cell lines by z-VAD-fmk, but was only marginally attenuated in three other cell lines, indicating that TRAIL induces caspase-dependent and caspase-independent cell death in myeloma cells. Preceding cell death, TRAIL activated nuclear factor kappaB, c-Jun N-terminal kinase, p38 and p42/44. Although TRAIL-induced stimulation of c-Jun N-terminal kinase and p38 was caspase-dependent in a cell type-specific fashion, activation of nuclear factor kappaB and p42/44 was caspase-independent in all cases. In accordance with activation of the nuclear factor kappaB pathway, we observed transcriptional up-regulation of several well established nuclear factor kappaB target genes. Furthermore, we found that TRAIL activates proinflammatory pathways in approximately 50% of primary myeloma samples. Taken together, our data suggest (a) that oligomerized TRAIL variants are necessary to ensure maximal cell death induction in myeloma cells and (b) TRAIL should be used in combination with anti-inflammatory drugs for treatment of myeloma to avoid and/or minimize any potential side-effects arising from the proinflammatory properties of the molecule.

Caspases and kinases in a death grip

The complex process of apoptosis is orchestrated by caspases, a family of cysteine proteases with unique substrate specificities. Accumulating evidence suggests that cell death pathways are finely tuned by multiple signaling events, including direct phosphorylation of caspases, whereas kinases are often substrates of active caspases. Importantly, caspase-mediated cleavage of kinases can terminate prosurvival signaling or generate proapoptotic peptide fragments that help to execute the death program and facilitate packaging of the dying cells. Here, we review caspases as kinase substrates and kinases as caspase substrates and discuss how the balance between cell survival and cell death can be shifted through crosstalk between these two enzyme families.

Roles of MAPK and NF-kappaB in interleukin-6 induction by lipopolysaccharide in vascular smooth muscle cells

Toll-like receptor (TLR)-4 signaling promotes cytokine synthesis in vascular smooth muscle cells (VSMC). However, it is unknown how TLR-4 regulates interleukin-6 (IL-6) in VSMC. Therefore, the present study investigated cellular factors involved in TLR-4-mediated IL-6 in VSMC in terms of MAPK and transcription elements. Exposure of aortic smooth muscle cells to TLR4-specific lipopolysaccharide (LPS) not only enhanced IL-6 release but also induced IL-6 transcript via promoter activation. The promoter activation was attenuated by dominant-negative MKK1 and to a lesser extent by dominant-negative MKK3, but not by dominant-negative MKK4. IL-6 promoter activity was diminished by U0126 or SB202190, but not by SP600125. Co-transfection with dominant negative CCAAT/enhancer binding protein or with IkappaB suppressed LPS-induced promoter activation, whereas the promoter activity was not influenced by dominant negative c-Jun. Mutation in the IL-6 promoter region at the binding site of NF-kappaB or C/EBP impaired promoter activation in response to LPS. Further impairment occurred when both NF-kappaB- and C/EBP-binding sites were mutated. LPS-induced IL-6 promoter activation was also prevented by pretreatment with epigallocatechin 3-gallate, curcumin, and resveratrol. The present study reports that TLR4-agonistic LPS induces IL-6 through transcriptional activation in VSMC and ERK1/2, p38 MAPK, NF-kappaB, and C/EBP play active roles in that process.

Cystic fibrosis transmembrane conductance regulator controls lung proteasomal degradation and nuclear factor-kappaB activity in conditions of oxidative stress

Cystic fibrosis is a lethal inherited disorder caused by mutations in a single gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR) protein, resulting in progressive oxidative lung damage. In this study, we evaluated the role of CFTR in the control of ubiquitin-proteasome activity and nuclear factor (NF)-kappaB/IkappaB-alpha signaling after lung oxidative stress. After a 64-hour exposure to hyperoxia-mediated oxidative stress, CFTR-deficient (cftr(-/-)) mice exhibited significantly elevated lung proteasomal activity compared with wild-type (cftr(+/+)) animals. This was accompanied by reduced lung caspase-3 activity and defective degradation of NF-kappaB inhibitor IkappaB-alpha. In vitro, human CFTR-deficient lung cells exposed to oxidative stress exhibited increased proteasomal activity and decreased NF-kappaB-dependent transcriptional activity compared with CFTR-sufficient lung cells. Inhibition of the CFTR Cl(-) channel by CFTR(inh-172) in the normal bronchial immortalized cell line 16HBE14o- increased proteasomal degradation after exposure to oxidative stress. Caspase-3 inhibition by Z-DQMD in CFTR-sufficient lung cells mimicked the response profile of increased proteasomal degradation and reduced NF-kappaB activity observed in CFTR-deficient lung cells exposed to oxidative stress. Taken together, these results suggest that functional CFTR Cl(-) channel activity is crucial for regulation of lung proteasomal degradation and NF-kappaB activity in conditions of oxidative stress.

Inhibition of the NF-kappaB survival pathway via caspase-dependent cleavage of the IKK complex scaffold protein and NF-kappaB essential modulator NEMO

Apoptosis is mediated by cysteine-dependent, aspartate-directed proteases of the caspase family that proteolyse strategic intracellular substrates to induce cell suicide. We describe here that engagement of apoptotic processes by Fas triggering or by staurosporine stimulation leads to the caspase-dependent inactivation of the nuclear factor kappa B (NF-kappaB) pathway after cleavage of IKK1 (IkappaB kinase 1) and NEMO (NF-kappaB essential modulator), which are needed to transduce NF-kappaB activation signals. In this study, we have analyzed in more detail, the role of NEMO cleavage, as NEMO, but not IKK1, is important for the pro-survival actions of NF-kappaB. We demonstrate that NEMO is cleaved after Asp355 to remove the last 64 C-terminal amino acids. This short form was unable to rescue NF-kappaB activation by tumor necrosis factor-alpha (TNF-alpha) when transfected in NEMO-deficient cells. Consequently, inactivation of NEMO resulted in an inhibition of the expression of antiapoptotic NF-kappaB-target genes coding for caspase inhibitors (cIAP-1, cIAP-2) or adaptors of the TNF receptor family. NEMO-deficient Jurkat cells transiently expressing a non-cleavable mutant of NEMO were less sensitive to TNF-alpha-induced apoptosis. Therefore, downmodulation of NF-kappaB activation via the proteolytic cleavage of NEMO could represent an amplification loop for apoptosis.

Combined effects of histone deacetylase inhibitor and rituximab on non-Hodgkin's B-lymphoma cells apoptosis

OBJECTIVE

The anti-CD20 monoclonal antibody rituximab has shown promising results in the clinical treatment of patients with B-cell non-Hodgkin's lymphoma (B-NHL). However, its therapeutic effect could still be improved.

METHODS

This study examined the anti-tumor activity of rituximab combined with histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA) in CD20-positive B-NHL cell lines, as well as in primary B-NHL cells and a murine B-NHL model.

RESULTS

The combination treatment sensitized B-NHL cells to apoptosis in a synergistic manner, concomitant with mitochondrial instability and Bcl-2/Bcl-XL downregulation. Particularly in Daudi cells relatively resistant to rituximab, these events were associated with nuclear factor-kappaB (NF-kappaB) inactivation and c-Myc degradation. SAHA presented functional complementation with rituximab, through decreasing IKKalpha/beta and IkappaBalpha phosphorylation, thus preventing NF-kappaB nuclear translocation. In addition, SAHA induced IkappaBalpha cleavage to a stable inhibitory form and caused NF-kappaB degradation in response to caspase-3 activation. More importantly, rituximab-SAHA combination significantly promoted primary B-NHL cells apoptosis and improved survival time of a severe combined immunodeficient mouse lymphoma model established with intravenous injection of Daudi cells.

CONCLUSION

These findings emphasized the value of targeting apoptosis signaling pathway in lymphoma therapy. Rituximab in conjunction with histone deacetylase inhibitor may represent a novel strategy in treating patients with B-NHL.

Characterization of the IkappaB-like gene family in polydnaviruses associated with wasps belonging to different Braconid subfamilies

Polydnaviruses (PDVs) are obligate symbionts of hymenopteran parasitoids of lepidopteran larvae that induce host immunosuppression and physiological redirection. PDVs include bracoviruses (BVs) and ichnoviruses (IVs), which are associated with braconid and ichneumonid wasps, respectively. In this study, the gene family encoding IkappaB-like proteins in the BVs associated with Cotesia congregata (CcBV) and Toxoneuron nigriceps (TnBV) was analysed. PDV-encoded IkappaB-like proteins (ANK) are similar to insect and mammalian IkappaB, an inhibitor of the transcription factor nuclear factor kappaB (NF-kappaB), but display shorter ankyrin domains and lack the regulatory domains for signal-mediated degradation and turnover. Phylogenetic analysis of ANK proteins indicates that those of IVs and BVs are closely related, even though these two taxa are believed to lack a common ancestor. Starting from a few hours after parasitization, the transcripts of BV ank genes were detected, at different levels, in several host tissues. The structure of the predicted proteins suggests that they may stably bind NF-kappaB/Rel transcription factors of the tumour necrosis factor (TNF)/Toll immune pathway. Accordingly, after bacterial challenge of Heliothis virescens host larvae parasitized by T. nigriceps, NF-kappaB immunoreactive material failed to enter the nucleus of host haemocytes and fat body cells. Moreover, transfection experiments in human HeLa cells demonstrated that a TnBV ank1 gene product reduced the efficiency of the TNF-alpha-induced expression of a reporter gene under NF-kappaB transcriptional control. Altogether, these results suggest strongly that TnBV ANK proteins cause retention of NF-kappaB/Rel factors in the cytoplasm and may thus contribute to suppression of the immune response in parasitized host larvae.

Viral protease cleavage of inhibitor of kappaBalpha triggers host cell apoptosis

Apoptosis is an innate immune response to viral infection that limits viral replication. However, the mechanisms by which cells detect viral infection and activate apoptosis are not completely understood. We now show that during Coxsackievirus infection, the viral protease 3C(pro) cleaves inhibitor of kappaBalpha (IkappaBalpha). A proteolytic fragment of IkappaBalpha then forms a stable complex with NF-kappaB, translocates to the nucleus, and inhibits NF-kappaB transactivation, increasing apoptosis and decreasing viral replication. In contrast, cells with reduced IkappaBalpha expression are more susceptible to viral infection, with less apoptosis and more viral replication. IkappaBalpha thus acts as a sensor of viral infection. Cleavage of host proteins by pathogen proteases is a novel mechanism by which the host recognizes and responds to viral infection.

Successful allogeneic hemopoietic stem cell transplantation in a child who had anhidrotic ectodermal dysplasia with immunodeficiency

Anhidrotic ectodermal dysplasia with immunodeficiency is associated with multiple infections and a poor clinical outcome. Hypomorphic mutations in nuclear factor kappaB essential modulator (NEMO)/IkappaB kinase complex and a hypermorphic mutation in inhibitor alpha of nuclear factor kappaB (IkappaBalpha) both result in impaired nuclear factor kappaB activation and are associated with X-recessive and autosomal-dominant forms of anhidrotic ectodermal dysplasia with immunodeficiency, respectively. Autosomal-dominant anhidrotic ectodermal dysplasia with immunodeficiency is also associated with a severe T-cell phenotype. It is not known whether hematopoietic stem cell transplantation can cure immune deficiency in children with anhidrotic ectodermal dysplasia with immunodeficiency. A boy with autosomal-dominant anhidrotic ectodermal dysplasia with immunodeficiency and a severe T-cell immunodeficiency underwent transplantation at 1 year of age with haploidentical T-cell-depleted bone marrow after myeloablative conditioning. Engraftment occurred, with full hematopoietic chimerism. Seven years after transplantation, clinical outcome is favorable, with normal T-cell development. As expected, the developmental features of the anhidrotic ectodermal dysplasia syndrome have appeared and persisted. This is the first report of successful hematopoietic stem cell transplantation in a child with anhidrotic ectodermal dysplasia with immunodeficiency. Hematopoietic stem cell transplantation is well tolerated and efficiently cures the profound immunodeficiency associated with autosomal-dominant anhidrotic ectodermal dysplasia with immunodeficiency.

Eriocalyxin B induces apoptosis of t(8;21) leukemia cells through NF-κB and MAPK signaling pathways and triggers degradation of AML1-ETO oncoprotein in a caspase-3-dependent manner

Diterpenoids isolated from Labiatae family herbs have strong antitumor activities with low toxicity. In this study, Eriocalyxin B (EriB), a diterpenoid extracted from Isodon eriocalyx, was tested on human leukemia/lymphoma cells and murine leukemia models. Acute myeloid leukemia cell line Kasumi-1 was most sensitive to EriB. Significant apoptosis was observed, concomitant with Bcl-2/Bcl-XL downregulation, mitochondrial instability and caspase-3 activation. AML1-ETO oncoprotein was degraded in parallel to caspase-3 activation. EriB-mediated apoptosis was associated with NF-kappaB inactivation by preventing NF-kappaB nuclear translocation and inducing IkappaBalpha cleavage, and disturbance of MAPK pathway by downregulating ERK1/2 phosphorylation and activating AP-1. Without affecting normal hematopoietic progenitor cells proliferation, EriB was effective on primary t(8;21) leukemia blasts and caused AML1-ETO degradation. In murine t(8;21) leukemia models, EriB remarkably prolonged the survival time or decreased the xenograft tumor size. Together, EriB might be a potential treatment for t(8;21) leukemia by targeting AML1-ETO oncoprotein and activating apoptosis pathways.

Zinc at pharmacologic concentrations affects cytokine expression and induces apoptosis of human peripheral blood mononuclear cells

OBJECTIVE

The present study examined the effect of zinc at concentrations of the apoptotic signaling pathway and immune function of peripheral blood mononuclear cells (PBMCs).

METHODS

PBMCs from healthy subjects were treated in vitro with various zinc concentrations to imitate different serum statuses of physiologic (2 to 15 microM) and pharmacologic (15 to 100 microM) concentrations to higher than 100 microM and analyzed their expressions of cytokines and apoptotically related factors.

RESULTS

Although a normal physiologic concentration of zinc had no effect on immunologic function or apoptosis of PBMCs, a pharmacologic concentration (100 microM) or higher affected both functions. Zinc decreased cell proliferation at concentrations higher than 100 microM and stimulated cytokine expression at concentrations of at least 100 microM. Further, at concentrations of at least 100 microM, apoptosis was induced, and expressions of caspase-3 and proapoptotic genes, including Fas (FasL) and c-fos, which trigger apoptosis through receptor-mediated extrinsic and mitochondrion-mediated apoptotic pathways, respectively, were increased. At concentrations at least 300 microM, expressions of antiapoptotic factors nuclear factor-kappaB, Bcl-2, and Bcl-X(L) were markedly decreased.

CONCLUSIONS

Zinc stimulates cytokine expression and induces apoptosis of PBMCs from healthy subjects only at concentrations equal to or greater than the serum pharmacologic range. Receptor-mediated extrinsic and mitochondrial-mediated intrinsic pathways are involved in this zinc-induced apoptosis.

Physalis angulata induced G2/M phase arrest in human breast cancer cells

Physalis angulata (PA) is employed in herbal medicine around the world. It is used to treat diabetes, hepatitis, asthma and malaria in Taiwan. We have evaluated PA as a cancer chemopreventive agent in vitro by studying the role of PA in regulation of proliferation, cell cycle and apoptosis in human breast cancer cell lines. PA inhibited cell proliferation and induced G2/M arrest and apoptosis in human breast cancer MAD-MB 231 and MCF-7 cell lines. In this study, under treatment with various concentrations of PA in MDA-MB 231 cell line, we checked mRNA levels for cyclin A and cyclin B1 and the protein levels of cyclin A and cyclin B1, Cdc2 (cyclin-dependent kinases), p21(waf1/cip1) and P27(Kip1) (cyclin-dependent kinase inhibitors), Cdc25C, Chk2 and Wee1 kinase (cyclin-dependent kinase relative factors) in cell cycle G2/M phase. From those results, we determined that PA arrests MDA-MB 231 cells at the G2/M phase by (i) inhibiting synthesis or stability of mRNA and their downstream protein levels of cyclin A and cyclin B1, (ii) increasing p21(waf1/cip1) and P27(kip1) levels, (iii) increasing Chk2, thus causing an increase in Cdc25C phosphorylation/inactivation and inducing a decrease in Cdc2 levels and an increase in Wee1 level. According to the results obtained, PA appears to possess anticarcinogenic properties; these results suggest that the effect of PA on the levels of phosphorylated/inactivated Cdc25C are mediated by Chk2 activation, at least in part, via p21(waf1/cip1) and P27(kip1) cyclin-dependent kinase inhibitors pathway to arrest cells at G2/M phase in breast cancer carcinoma cells.

The Anti-Death Machinery in IKK/NF-κB Signaling

The most extensively studied function of NF-kappaB is its ability to promote cell survival through induction of target genes, whose products inhibit various aspects of the apoptotic machinery in both normal and malignant cells. Recent studies, however, indicate that NF-kappaB activation can also suppress programmed necrosis through induction of genes encoding anti-oxidant proteins. Since tumor cells often use NF-kappaB pathway as a shield to escape the killing of conventional anti-cancer therapies, intervention of IKK/NF-kappaB signaling would be a promising option to improve the efficacy of cancer treatment.

IKK/NF-kappaB signaling: balancing life and death--a new approach to cancer therapy

IkappaB kinase/NF-kappaB (IKK/NF-kappaB) signaling pathways play critical roles in a variety of physiological and pathological processes. One function of NF-kappaB is promotion of cell survival through induction of target genes, whose products inhibit components of the apoptotic machinery in normal and cancerous cells. NF-kappaB can also prevent programmed necrosis by inducing genes encoding antioxidant proteins. Regardless of mechanism, many cancer cells, of either epithelial or hematopoietic origin, use NF-kappaB to achieve resistance to anticancer drugs, radiation, and death cytokines. Hence, inhibition of IKK-driven NF-kappaB activation offers a strategy for treatment of different malignancies and can convert inflammation-induced tumor growth to inflammation-induced tumor regression.

Pectinesterase inhibitor from jelly fig (Ficus awkeotsang Makino) achene induces apoptosis of human leukemic U937 cells

The antitumor activity of pectinesterase inhibitor (PEI), a group of cationic polypeptides, from jelly fig (Ficus awkeotsang Makino) achene was first examined as a treatment for leukemia in this study. PEI displayed strong growth inhibition against human leukemic U937 cells via induction of apoptosis in a dose- and time-dependent manner. At a level of 50 microg/mL, PEI inhibited 90% of cell growth, and the concentration of PEI required to induce 50% of cell viability (LC50) was about 180 microg/mL. Meanwhile, cell cycle arrest at G2/M phase was observed when cells were incubated with 100 microg PEI/mL for 24 h. PEI displayed a dose-dependent influence on mitochondria transmembrane potential (MTP, delta psi m) of cells when detected by a flow cytometry. MTP of more than 50% cells was reduced when cells were incubated with PEI at levels higher than 50 microg PEI/mL for 24 h. In addition, PEI upregulated caspase-3 activity. Taken together, PEI potently inhibited the proliferation of human leukemic U937 cells via cell cycle arrest and apoptosis in association with MTP reduction and caspase-3 activation, respectively, and showed therapy potential for U937 cells.

Aloe-emodin induced in vitro G2/M arrest of cell cycle in human promyelocytic leukemia HL-60 cells

In this study, we have evaluated the chemopreventive role of aloe-emodin in human promyelocytic leukemia HL-60 cells in vitro by studying the regulation of proliferation, cell cycle and apoptosis. Aloe-emodin inhibited cell proliferation and induced G2/M arrest and apoptosis in HL-60 cells. Investigation of the levels of cyclins B1, E and A by immunoblot analysis showed that cyclin E level was unaffected, whereas cyclin B1 and A levels increased with aloe-emodin in HL-60 cells. Investigation of the levels of cyclin-dependent kinases, Cdk1 and 2, showed increased levels of Cdk1 but the levels of Cdk2 were not effected with aloe-emodin in HL-60 cells. The levels of p27 were increased after HL-60 cells were cotreated with various concentrations of aloe-emodin. The increase of the levels of p27 may be the major factor for aloe-emodin to cause G2/M arrest in these examined cells. Flow cytometric assays and DNA fragmentation gel electrophoresis also confirmed aloe-emodin induced apoptosis in HL-60 cells. The levels of caspase-3 were increased after HL-60 cells were cotreated with 10 microM aloe-emodin for 12, 24, 48, and 72 hours. Taken together, aloe-emodin therefore appears to exert its anticarcinogenesis properties by inhibiting proliferation and inducing cell cycle arrest and apoptosis underwent activation of caspase-3 in human leukemia HL-60 cells.

An evolutionary conserved pathway of nuclear factor-kappaB activation involving caspase-mediated cleavage and N-end rule pathway-mediated degradation of IkappaBalpha

The Drosophila nuclear factor-kappaB (NF-kappaB)-like transcription factor Relish is activated by an endoproteolytic cleavage step mediated by the Drosophila caspase Dredd. We have examined the contribution of the caspase cascade to NF-kappaB activation via TRAIL, a mammalian tumor necrosis factor family ligand that is a potent activator of caspases. Our results demonstrate that TRAIL activates NF-kappaB in two phases as follows: an early caspase independent phase and a late caspase dependent phase. The late phase of the TRAIL-induced NF-kappaB is critically dependent on caspase 8 and can be blocked by pharmacological and genetic inhibitors of caspase 8 activation, such as benzyloxycarbonyl-VAD-fluoromethyl ketone, benzyloxycarbonyl-IETD-fluoromethyl ketone, and small interfering RNA targeting caspase 8 and FADD. Whereas caspase 3 is required for TRAIL-induced apoptosis, it is not involved in TRAIL-induced NF-kappaB activation. The late phase of TRAIL-induced NF-kappaB activation involves caspase mediated cleavage of IkappaBalpha between Asp(31) and Ser(32) residues to generate an N-terminal truncated fragment that is degraded by the proteasome via the N-end rule pathway. Our results demonstrate that caspases play an evolutionarily conserved role as regulated entry points to the N-end rule pathway and in NF-kappaB activation in mammalian cells.

Regulation of constitutive p50/c-Rel activity via proteasome inhibitor-resistant IkappaBalpha degradation in B cells

Constitutive NF-kappaB activity has emerged as an important cell survival component of physiological and pathological processes, including B-cell development. In B cells, constitutive NF-kappaB activity includes p50/c-Rel and p52/RelB heterodimers, both of which are critical for proper B-cell development. We previously reported that WEHI-231 B cells maintain constitutive p50/c-Rel activity via selective degradation of IkappaBalpha that is mediated by a proteasome inhibitor-resistant, now termed PIR, pathway. Here, we examined the mechanisms of PIR degradation by comparing it to the canonical pathway that involves IkappaB kinase-dependent phosphorylation and beta-TrCP-dependent ubiquitylation of the N-terminal signal response domain of IkappaBalpha. We found a distinct consensus sequence within this domain of IkappaBalpha for PIR degradation. Chimeric analyses of IkappaBalpha and IkappaBbeta further revealed that the ankyrin repeats of IkappaBalpha, but not IkappaBbeta, contained information necessary for PIR degradation, thereby explaining IkappaBalpha selectivity for the PIR pathway. Moreover, we found that PIR degradation of IkappaBalpha and constitutive p50/c-Rel activity in primary murine B cells were maintained in a manner different from B-cell-activating-factor-dependent p52/RelB regulation. Thus, our findings suggest that nonconventional PIR degradation of IkappaBalpha may play a physiological role in the development of B cells in vivo.

The liver-enriched inhibitory protein isoform of CCAAT/enhancer-binding protein beta, but not nuclear factor-kappaB, mediates the transcriptional inhibition of beta-casein by tumor necrosis factor-alpha

TNF-alpha is a physiological regulator of mammary gland development that stimulates the growth of both normal and malignant mammary epithelial cells in primary culture and inhibits functional differentiation. To understand how TNF exerts its effects, the current study examined the mechanism by which TNF down-regulates expression of the beta-casein and whey acidic protein (WAP) genes. TNF treatment markedly decreased activity of the beta-casein and WAP promoters in transiently transfected HC11 mammary epithelial cells. Overexpression of the nuclear factor-kappaB (NFkappaB) p50 and/or p65 proteins increased the transcriptional activity of the beta-casein and WAP promoters in HC11 cells, suggesting that the inhibitory effect of TNF on transcription of these genes is not mediated by NFkappaB. This was further confirmed in experiments in which an NFkappaB super-repressor was overexpressed, and by deletion of an NFkappaB binding site in the beta-casein promoter. In contrast, we found that TNF induced both nuclear expression and the DNA-binding activity of liver-enriched inhibitory protein (LIP) isoform of CCAAT/enhancer-binding protein beta. Moreover, cotransfection of LIP and beta-casein expression vectors showed that LIP suppressed the transcriptional activity of the beta-casein promoter. Together, these results suggest that LIP plays a critical role in mediating TNF-induced down-regulation of the beta-casein gene.

Apoptosis defects and chemotherapy resistance: molecular interaction maps and networks

Intrinsic (innate) and acquired (adaptive) resistance to chemotherapy critically limits the outcome of cancer treatments. For many years, it was assumed that the interaction of a drug with its molecular target would yield a lethal lesion, and that determinants of intrinsic drug resistance should therefore be sought either at the target level (quantitative changes or/and mutations) or upstream of this interaction, in drug metabolism or drug transport mechanisms. It is now apparent that independent of the factors above, cellular responses to a molecular lesion can determine the outcome of therapy. This review will focus on programmed cell death (apoptosis) and on survival pathways (Bcl-2, Apaf-1, AKT, NF-kappaB) involved in multidrug resistance. We will present our molecular interaction mapping conventions to summarize the AKT and IkappaB/NF-kappaB networks. They complement the p53, Chk2 and c-Abl maps published recently. We will also introduce the 'permissive apoptosis-resistance' model for the selection of multidrug-resistant cells.

Uncoupling of the Signaling and Caspase-inhibitory Properties of X-linked Inhibitor of Apoptosis

In addition to its well described function as an enzymatic inhibitor of specific caspases, X-linked inhibitor of apoptosis (X-linked IAP or XIAP) can function as a cofactor in Smad, NF-kappaB, and JNK signaling pathways. However, caspases themselves have been shown to regulate the activity of a number of signaling cascades, raising the possibility that the effect of XIAP in these pathways is indirect. Here we examine this question by introducing point mutations in XIAP predicted to disrupt the ability of the molecule to bind to and inhibit caspases. We show that whereas these mutant variants of XIAP lost caspase-inhibitory activity, they maintained their ability to activate Smad, NF-kappaB, and JNK signaling pathways. Indeed, the signaling properties of the molecule were mapped to domains not directly involved in caspase binding and inhibition. The activation of NF-kappaB by XIAP was dependent on the E3 ubiquitin ligase activity of the RING domain. On the other hand, the ability of XIAP to activate Smad-dependent signaling was mapped to the third baculoviral IAP repeat (BIR) and loop regions of the molecule. Thus, the anti-apoptotic and signaling properties of XIAP can be uncoupled.

Proteasome Inhibitors Induce Inhibitory κB (IκB) Kinase Activation, IκBα Degradation, and Nuclear Factor κB Activation in HT-29 Cells

The transcription factor nuclear factor kappaB (NF-kappaB) is activated and seems to promote oncogenesis in certain cancers. A major mechanism of NF-kappaB activation in cells involves cytoplasm-to-nucleus translocation of this transcription factor after hydrolysis of the cytoplasmic inhibitor inhibitory kappaB (IkappaB) by the 26S proteasome. Because selective proteasome inhibitors have been shown to block IkappaB degradation; consequently, NF-kappaB activation in a variety of cellular systems, proteasome inhibitors were proposed as potential therapeutic agents for the treatment of cancer. However, under certain conditions, IkappaB degradation and NF-kappaB activation are not mediated by the proteasome system. We investigated how proteasome inhibitors affected NF-kappaB activation in the intestinal epithelial cancer cell line HT-29, which has been documented to have an atypical NF-kappaB regulation. Treatment of cells with the selective proteasome inhibitors carbobenzoxy-L-leucyl-L-leucyl-L-norvalinal (MG-115), carbobenzoxy-L-leucyl-L-leucyl-L-leucinal (MG-132), or lactacystin induced NF-kappaB activation as indicated by both an increase in NF-kappaB DNA binding and transcriptional activity. This increase in NF-kappaB activation caused by proteasome inhibitors was accompanied by an increase in IkappaB kinase activation and a degradation of IkappaBalpha but not IkappaBbeta. Furthermore, proteasome inhibitors induced the expression of NF-kappaB target genes. In summary, these results demonstrate a unique effect of proteasome inhibitors on the IkappaB-NF-kappaB systems in HT-29 cells, in which proteasome inhibitors activate rather than deactivate the NF-kappaB system. We conclude that the use of proteasome inhibitors to block NF-kappaB activation in cancer cells may not always be a viable approach.

To be, or not to be: NF-kappaB is the answer--role of Rel/NF-kappaB in the regulation of apoptosis

During their lifetime, cells encounter many life or death situations that challenge their very own existence. Their survival depends on the interplay within a complex yet precisely orchestrated network of proteins. The Rel/NF-kappaB signaling pathway and the transcription factors that it activates have emerged as critical regulators of the apoptotic response. These proteins are best known for the key roles that they play in normal immune and inflammatory responses, but they are also implicated in the control of cell proliferation, differentiation, apoptosis and oncogenesis. In recent years, there has been remarkable progress in understanding the pathways that activate the Rel/NF-kappaB factors and their role in the cell's decision to either fight or surrender to apoptotic challenge. Whereas NF-kappaB is most commonly involved in suppressing apoptosis by transactivating the expression of antiapoptotic genes, it can promote programmed cell death in response to certain death-inducing signals and in certain cell types. This review surveys our current understanding of the role of NF-kappaB in the apoptotic response and focuses on many developments since this topic was last reviewed in Oncogene 4 years ago. These recent findings shed new light on the activity of NF-kappaB as a critical regulator of apoptosis in the immune, hepatic, epidermal and nervous systems, on the mechanisms through which it operates and on its role in tissue development, homoeostasis and cancer.

A JNK-dependent pathway is required for TNFalpha-induced apoptosis

Tumor necrosis factor (TNFalpha) receptor signaling can simultaneously activate caspase 8, the transcription factor, NF-kappaB and the kinase, JNK. While activation of caspase 8 is required for TNFalpha-induced apoptosis, and induction of NF-kappaB inhibits cell death, the precise function of JNK activation in TNFalpha signaling is not clearly understood. Here, we report that TNFalpha-mediated caspase 8 cleavage and apoptosis require a sequential pathway involving JNK, Bid, and Smac/DIABLO. Activation of JNK induces caspase 8-independent cleavage of Bid at a distinct site to generate the Bid cleavage product jBid. Translocation of jBid to mitochondria leads to preferential release of Smac/DIABLO, but not cytochrome c. The released Smac/DIABLO then disrupts the TRAF2-cIAP1 complex. We propose that the JNK pathway described here is required to relieve the inhibition imposed by TRAF2-cIAP1 on caspase 8 activation and induction of apoptosis. Further, our findings define a mechanism for crosstalk between intrinsic and extrinsic cell death pathways.

Genistein reduces NF-kappa B in T lymphoma cells via a caspase-mediated cleavage of I kappa B alpha

The transcription factor NF-kappa B is elevated in murine T-cell lymphoma lines compared with normal thymic lymphocytes, and may play a role in the neoplastic transformation of these cells. When T lymphoma cells were treated with the soy isoflavone genistein, a marked reduction in nuclear NF-kappa B levels was detectable predominantly for the p50/p50 homodimer and p50/p65 heterodimer. To examine the mechanism by which NF-kappa B is reduced by genistein, we analyzed the NF-kappa B inhibitor, I kappa B alpha, and detected a 34 kDa cleavage product Delta I kappa B alpha, which was induced by genistein in a dose-dependent manner. Our observation that a pan-caspase inhibitor could inhibit the induction of Delta I kappa B alpha by genistein suggested that caspase activity was responsible for this cleavage product. In support of this idea, we detected an increase in caspase-3 activity in response to increasing time of genistein exposure. When the induction of Delta I kappa B alpha was prevented, we detected no reduction of NF-kappa B levels by genistein. These results support a direct role for Delta I kappa B alpha in the reduction of NF-kappa B by genistein. To determine the effect of genistein on some NF-kappa B target gene products, we examined the antiapoptotic proteins Bcl-2, Bcl-X(L), A1, and cIAP-1. Only changes in A1 and cIAP-1 levels were affected with significant reductions in response to genistein. Generation of the repressive activity of Delta I kappa B alpha on NF-kappa B is a novel mechanism for the reduction of this transcription factor by genistein and the possible effect this may have on the ability of genistein to induce apoptosis in tumor cells.

Glycogen synthase kinase 3beta-mediated apoptosis of primary cortical astrocytes involves inhibition of nuclear factor kappaB signaling

Recent studies have revealed a positive correlation between astrocyte apoptosis and rapid disease progression in persons with neurodegenerative diseases. Glycogen synthase kinase 3beta (GSK-3beta) is a molecular regulator of cell fate in the central nervous system and a target of the phosphatidylinositol 3-kinase (PI-3K) pathway. We have therefore examined the role of the PI-3K pathway, and of GSK-3beta, in regulating astrocyte survival. Our studies indicate that inhibition of PI-3K leads to apoptosis in primary cortical astrocytes. Furthermore, overexpression of a constitutively active GSK-3beta mutant (S9A) is sufficient to cause astrocyte apoptosis, whereas an enzymatically inactive GSK-3beta mutant (K85M) has no effect. In light of reports on the interplay between GSK-3beta and nuclear factor kappaB (NF-kappaB), and because of the antiapoptotic activity of NF-kappaB, we examined the effect of GSK-3beta overexpression on NF-kappaB activation. These experiments revealed strong inhibition of NF-kappaB activation in astrocytes upon overexpression of the S9A, but not the K85M, mutant of GSK-3beta. This was accompanied by stabilization of the NF-kappaB-inhibitory protein, IkappaBalpha and down-regulation of IkappaB kinase (IKK) activity. These findings therefore implicate GSK-3beta as a regulator of NF-kappaB activation in astrocytes and suggest that the pro-apoptotic effects of GSK-3beta may be mediated at least in part through the inhibition of NF-kappaB pathway.

NF-kappaB in cancer: a marked target

The imbalance between proliferation and programmed cell death (apoptosis) is one of the critical cellular events that lead to oncogenesis. While there is no doubt that uncontrolled cell proliferation is essential for the development of cancer, deregulation of apoptosis may play an equally important role in this process. Inhibition of apoptosis prevents the death of tumor cells with DNA damage either associated with carcinogenic initiation or cancer therapy. The transcription factor NF-kappaB is a key regulator in oncogenesis. By promoting proliferation and inhibiting apoptosis, NF-kappaB tips the balance between proliferation and apoptosis toward malignant growth in tumor cells.

Inhibition of IkappaB kinase by a new class of retinoid-related anticancer agents that induce apoptosis

The transcription factor NF-kappaB is overexpressed or constitutively activated in many cancer cells, where it induces expression of antiapoptotic genes correlating with resistance to anticancer therapies. Small molecules that inhibit the NF-kappaB signaling pathway could therefore be used to induce apoptosis in NF-kappaB-overexpressing tumors and potentially serve as anticancer agents. We found that retinoid antagonist MX781 inhibited the activation of NF-kappaB-dependent transcriptional activity in different tumor cell lines. MX781 was able to completely inhibit tumor necrosis factor alpha-mediated activation of IkappaB kinase (IKK), the upstream regulator of NF-kappaB. Inhibition of IKK activity resulted from direct binding of MX781 to the kinase, as demonstrated by in vitro inhibition studies. Two other molecules, MX3350-1 and CD2325, which are retinoic acid receptor gamma-selective agonists, were capable of inhibiting IKK in vitro, although they exerted variable inhibition of IKK and NF-kappaB activities in intact cells in a cell type-specific manner. However, N-(4-hydroxyphenyl)-retinamide, another apoptosis-inducing retinoid, and retinoic acid as well as other nonapoptotic retinoids did not inhibit IKK. Inhibition of IKK by the retinoid-related compounds and other small molecules correlated with reduced cell proliferation and increased apoptosis. Reduced cell viability was also observed after overexpression of an IKKbeta kinase-dead mutant or the IkappaBalpha superrepressor. The induction of apoptosis by the retinoid-related molecules that inhibited IKK was dependent on caspase activity but independent of the retinoid receptors. Thus, the presence of an excess of retinoic acid or a retinoid antagonist did not prevent the inhibition of IKK activation by MX781 and CD2325, indicating a retinoid receptor-independent mechanism of action.

Modulation by caspases of tumor necrosis factor-stimulated c-Jun N-terminal kinase activation but not nuclear factor-kappaB signaling

Tumour necrosis factor-alpha (TNF) is capable of activating many downstream signaling molecules via its two receptors TNFR1 and TNFR2. TNF can stimulate the proinflammatory transcription factor nuclear factor-kappaB (NF-kappaB) as well as the stress induced kinase c-Jun N-terminal kinase (JNK) through mechanisms that are not fully delineated. NF-kappaB becomes activated mainly through TNFR1 while JNK can be stimulated by either TNF receptor subtype. TNF can also induce apoptosis within cells due to its ability to recruit procaspase-8 to TNFR1, which in turn induces the caspase proteolytic cascade. We provide evidence here in human cells, that TNF-induced JNK activation is under the influence of caspases while NF-kappaB activity is not. By using pharmacological inhibitors of caspases, we have shown that JNK activity is reduced following caspase inhibition, especially when caspase-3 is targeted. NF-kappaB activity, as assessed by IkappaBalpha or IkappaBbeta degradation, electrophoretic mobility shift assay and NF-kappaB gene reporter assays, is shown to be unaffected by caspase inhibition. Therefore, downstream TNF receptor signaling events are differentially influenced by caspases.

Reactive nitrogen species and cell signaling: implications for death or survival of lung epithelium

Reactive nitrogen species such as nitric oxide, peroxynitrite, and nitrogen dioxide have been implicated in the pathophysiology of inflammatory lung diseases. Yet, the molecular mechanisms and cell signaling events responsible for cellular injury remain to be elucidated. Two major signaling pathways, co-ordinately regulated and responsible for cell survival and cell death, involve nuclear factor kappa B and c-Jun-N-terminal kinase, respectively. A review of these pathways, their modes of action, and their importance in executing oxidative stress responses in lung epithelial cells are discussed.

Aniracetam attenuates apoptosis of astrocytes subjected to simulated ischemia in vitro

The aim of the present study was to establish whether aniracetam is capable of protecting cultured rat astrocytes against ischemic injury. Treatment of the cultures with aniracetam (1, 10 and 100 mM) during 24 h ischemia simulated in vitro significantly decreased the number of apoptotic cells. The antiapoptotic effects of the drug were confirmed by the increase of intracellular ATP and phosphocreatine (PCr) levels and the inhibition of the caspase-3 activity. Aniracetam also attenuated cellular oxidative stress by decreased production of reactive oxygen species (ROS). These effects were associated with the decrease in levels of c-fos and c-jun mRNA in primary astrocyte cultures exposed to 24 h ischemia. When cultured astrocytes were incubated during 24 h simulated ischemia with wortmannin, a phosphatidylinositol 3-kinase (PI 3-kinase) inhibitor or PD98059, a mitogen-activated protein (MAP)/extracellular signal regulated kinase (ERK) (MEK) inhibitor the cell apoptosis was accelerated. This effect was antagonized by adding 100 mM aniracetam to the culture medium. These findings suggest that the protective effect of aniracetam is mediated by PI 3-kinase and MEK pathways in the downstream mechanisms.

Potential methods to circumvent blocks in apoptosis in lymphomas

We review our current understanding of the molecular determinants and mechanisms of lymphocyte apoptosis and identify the key regulators of these death-signaling pathways. In addition, we describe the key molecular aberrations that underlie the resistance of lymphomas to conventional therapy, and highlight the enormous promise of potential therapeutic strategies that could circumvent or overcome these genetic impediments to apoptosis.

Caspase cleavage product lacking amino-terminus of IkappaBalpha sensitizes resistant cells to TNF-alpha and TRAIL-induced apoptosis

In response to a diverse array of signals, IkappaBalpha is targeted for phosphorylation-dependent degradation by the proteasome, thereby activating NF-kappaB. Here we demonstrate a role of the cleavage product of IkappaBalpha in various death signals. During apoptosis of NIH3T3, Jurkat, Rat-1, and L929 cells exposed to tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), Fas, serum deprivation, or TNF-alpha, respectively, IkappaBalpha was cleaved in a caspase-dependent manner. In vitro and in vivo cleavage assays and site-directed mutagenesis showed that caspase-3 cleaved IkappaBalpha between Asp31 and Ser32. Expression of the cleavage product lacking amino-terminus (1-31), DeltaIkappaBalpha, sensitized otherwise resistant NIH3T3 fibroblast cells to apoptosis induced by TNF-alpha or TRAIL, and HeLa tumor cells to TNF-alpha. DeltaIkappaBalpha was more pro-apoptotic compared to wild type or cleavage-resistant (D31E)IkappaBalpha mutant and the sensitization elicited by DeltaIkappaBalpha was as effective as that by the dominant negative mutant, (S32,36A)IkappaBalpha, in NIH3T3 cells. DeltaIkappaBalpha suppressed the transactivation of NF-kappaB induced by TNF-alpha or TRAIL, as reflected by luciferase-reporter activity. Conversely, expression of the p65 subunit of NF-kappaB suppressed TNF-alpha-, TRAIL-, and serum deprivation-induced cell death. On the contrary, DeltaIkappaBalpha was less effective at increasing the death rate of HeLa cells that were already sensitive to death signals including TRAIL, etoposide, or taxol. These results suggest that DeltaIkappaBalpha generated by various death signals sensitizes cells to apoptosis by suppressing NF-kappaB activity.