Suppression of tumor necrosis factor-induced cell death by inhibitor of apoptosis c-IAP2 is under NF-kappaB control

Protein kinase B regulates T lymphocyte survival, nuclear factor kappaB activation, and Bcl-X(L) levels in vivo

The serine/threonine kinase protein kinase B (PKB)/Akt mediates cell survival in a variety of systems. We have generated transgenic mice expressing a constitutively active form of PKB (gag-PKB) to examine the effects of PKB activity on T lymphocyte survival. Thymocytes and mature T cells overexpressing gag-PKB displayed increased active PKB, enhanced viability in culture, and resistance to a variety of apoptotic stimuli. PKB activity prolonged the survival of CD4(+)CD8(+) double positive (DP) thymocytes in fetal thymic organ culture, but was unable to prevent antigen-induced clonal deletion of thymocytes expressing the major histocompatibility complex class I-restricted P14 T cell receptor (TCR). In mature T lymphocytes, PKB can be activated in response to TCR stimulation, and peptide-antigen-specific proliferation is enhanced in T cells expressing the gag-PKB transgene. Both thymocytes and T cells overexpressing gag-PKB displayed elevated levels of the antiapoptotic molecule Bcl-X(L). In addition, the activation of peripheral T cells led to enhanced nuclear factor (NF)-kappaB activation via accelerated degradation of the NF-kappaB inhibitory protein IkappaBalpha. Our data highlight a physiological role for PKB in promoting survival of DP thymocytes and mature T cells, and provide evidence for the direct association of three major survival molecules (PKB, Bcl-X(L), and NF-kappaB) in vivo in T lymphocytes.

Elevated levels of RanBP7 mRNA in colorectal carcinoma are associated with increased proliferation and are similar to the transcription pattern of the proto-oncogene c-myc

We have used suppression subtractive hybridisation, "in silico" cloning and reverse Northern dot blot analysis to identify significant up-regulation of RanBP7 transcription in a human colorectal carcinoma. Quantitative RT-PCR analyses using the Taqman system demonstrated that RanBP7 mRNA levels were elevated in 47/75 colorectal tumours. There was no significant difference in 17 matched normal and tumour pairs and reduced levels in 11. Since RanBP7 specifies a key member of nuclear transport receptors responsible for the nuclear import of histone H1 and ribosomal proteins, we investigated whether this up-regulation might be proliferation-associated. RanBP7 mRNA copy numbers were significantly correlated with those of proliferating cell nuclear antigen in both normal and cancer tissue. Interestingly, the transcription pattern of the proto-oncogene c-myc showed a similar correlation with PCNA mRNA. Our results highlight the need for the careful interpretation of quantitative data that compare mRNA levels in normal and cancer tissue.

Proteasome inhibition: a new strategy in cancer treatment

The ubiquitin proteasome pathway is a highly conserved intracellular pathway for the degradation of proteins. Many of the short-lived regulatory proteins which govern cell division, growth, activation, signaling and transcription are substrates that are temporally degraded by the proteasome. In recent years, new and selective inhibitors of the proteasome have been employed in cell culture systems to examine the anti-tumor potential of these agents. This review covers the chemistry of selected proteasome inhibitors, possible mechanisms of action in cell culture and the in vivo examination of proteasome inhibitors in murine and human xenograft tumor models in mice. One inhibitor, PS-341, has recently entered Phase I clinical trials in cancer patients with advanced disease to further test the potential of this approach.

Evidence that de novo protein synthesis is dispensable for anti-apoptotic effects of NF-kappaB

The transcription factor NF-kappaB is a positive transcription factor for a number of genes and has been recognized as an anti-apoptotic regulator. However, the mechanism by which NF-kappaB blocks apoptosis is still controversial. Here, we demonstrate the evidence that NF-kappaB could attenuate the TNF-alpha-induced apoptosis without de novo protein synthesis using human pancreatic cancer cell lines, MIA PaCa-2 and Capan-2. The TNF-alpha-induced apoptosis was blocked by IL-1beta, a potent inducer of NF-kappaB activation. This inhibitory effect of IL-1beta was evident when cells were treated with protein synthesis inhibitors such as cycloheximide (CHX). Moreover, NF-kappaB decoy oligonucleotides could not block the anti-apoptotic effect of IL-1beta at doses sufficient to block the NF-kappaB-dependent transcription induced by IL-1beta. To confirm the role of NF-kappaB in blocking apoptosis, we generated stable cell lines expressing IkappaBdeltaN, a highly stable form of IkappaBalpha, a cytoplasmic inhibitor of NF-kappaB. In these stable transfectants, the antiapoptotic effect of IL-1beta was totally abolished, indicating that the anti-apoptotic action of IL-1beta could be ascribed to the NF-kappaB action. These findings show that de novo protein synthesis is dispensable for anti-apoptotic effects of NF-kappaB and support the possibility that NF-kappaB could exert its anti-apoptotic action through protein-protein interaction.

Mechanisms of liver cell injury

Liver cell death is triggered by a number of insults arising from the external environment or from within the cell. These insults may engage cell surface receptors with death domaines leading to a proteolytic cascade involving initiator and executioner caspases and an apoptotic demise. Alternatively, the insults may profoundly disrupt mitochondrial function and result in loss of homeostasis accompanied by activation of hydrolases and a necrotic or lytic demise. The distinction between apoptotic and necrotic cell death has become blurred recently by the recognition that the same stimuli can induce either form of cell death as well as caspase independent apoptosis. Mitochondria play a key role in the shape of cell death; selective release of mediators amplifies the apoptosis program and profound loss of mitochondrial function leads to necrosis. Reactive oxygen metabolites and nitric oxide participate as initiating factors and modulators. The extensive knowledge gained in recent years about the mechanisms of cell death will undoubtedly lead to new and exciting advances in the prevention and treatment of liver diseases. Important targets include death receptors, death signaling mechanisms, the mitochondrial permeability transition and approaches which selectively inhibit or activate cell death in parenchymal versus nonparenchymal cells.

Neuronal apoptosis inhibitory protein (NAIP)-like immunoreactivity in brains of adult patients with Down syndrome

In Down syndrome (DS), enhanced apoptosis (programmed cell death) may play a role in the pathogenesis of characteristic early mental retardation and precocious neurodegeneration of Alzheimer-type. The human IAP (inhibitor of apoptosis proteins) genes (NAIP, c-IAP-2/HIAP-1, c-IAP-1/Hiap-2, XIAP, survivin) are an evolutionary conserved family of proteins which prevent cell death across species, implying that they act at a central, highly conserved point in the cell death cascade. Evidence for downregulation of NAIP-mRNA in fetal DS (23rd week of gestation), as found by subtractive hybridization technique challenged studies at the protein level in adult DS brain specimen. NAIP-like immunoreactivity was determined in four different regions of cerebral cortex and cerebellum in 9 adult DS patients with Alzheimer-like neuropathologic lesions, 9 Alzheimer disease (AD) patients as compared to 9 controls. For the first time, NAIP-IR could be demonstrated in different cortical regions of the human brain. Compared to control subjects, western blotting demonstrated significantly decreased levels in parietal and occipital cortex in DS and in frontal and occipital cortex in AD. While the mode of NAIP action is unknown, inhibition of certain caspases has already been demonstrated for other IAP-family members (c-IAP1, c-IAP2 and XIAP). Although decreased NAIP-IR of certain brain regions in DS and AD awaits further confirmation, the results suggest that alterations of apoptosis regulatory (inhibitory) proteins may be another feature of neurodegeneration in DS and AD.

PKC-zeta-associated CK2 participates in the turnover of free IkappaBalpha

The atypical PKC isoenzymes, zeta and iota, activate NF-kappaB, a mechanism thought to mediate the anti-apoptotic and proliferative features of these kinases. PKC-zeta has been shown to be associated with an IkappaBalpha kinase in resting cells. In this study, we have sought to identify the PKC-zeta associated kinase and understand how PKC-zeta mediates basal IkappaBalpha turnover in vivo. We demonstrate that the PKC-zeta-associated IkappaBalpha kinase is CK2. This kinase, previously shown to phosphorylate the PEST domain of IkappaB molecules, co-precipitates with PKC-zeta in resting cells. In vitro, PKC-zeta interacts with CK2-beta. The in vivo PKC-zeta-associated CK2 preferentially phosphorylates S293 of IkappaBalpha as compared to non-associated CK2. The functional relevance of this observation is supported by the fact that the turnover of free IkappaBalpha in resting cells is S293-dependent. Moreover, overexpressing PKC-zeta results in lower steady-state protein levels of free IkappaBalpha, which is dependent on S293. Lastly, it is shown that PKC-zeta wt but not kinase dead leads to the in vitro phosphorylation of both CK2-alpha and beta. These studies demonstrate that the association between CK2 and PKC-zeta may play a major role in the control of the basal turnover of free IkappaBalpha, in the absence of extracellular stimuli.

Transcription of the inositol polyphosphate 1-phosphatase gene (INPP1) is upregulated in human colorectal cancer

We have used suppression subtractive hybridization to demonstrate significant overexpression of the inositol polyphosphate 1-phosphatase gene (INPP1) in colorectal cancer compared with matched normal colon epithelium. Its gene product catalyses the hydrolysis of inositol 1,3,4-trisphosphate and inositol 1, 4-bisphosphate, a key molecule in the phosphoinositide metabolic and signaling pathways. Following confirmation of the differential expression by reverse Northern dot blot analysis, fully quantitative Taqman reverse transcriptase-polymerase chain reaction assays showed that its transcription was upregulated in 42/49 colorectal tumors. There was no significant difference in four tumors and reduced transcription was observed in three. This is the first study to report the upregulation of the INPP1 gene in a human cancer and should facilitate further studies looking at the role of phosphatidylinositol signaling reactions in human colorectal cancer.

The Rel/NF-kappaB family directly activates expression of the apoptosis inhibitor Bcl-x(L)

The transcription factors of the Rel/NF-kappaB family are key regulators of immune and inflammatory responses and contribute to lymphocyte proliferation, survival, and oncogenesis. The absolute correlation between the antiapoptotic and oncogenic activities of the Rel/NF-kappaB oncoprotein v-Rel emphasizes the importance of characterizing the death antagonists under NF-kappaB control. Our recent finding that the prosurvival Bcl-2 homolog Bfl-1 (also called A1) is a direct transcriptional target of NF-kappaB raised the issue of whether NF-kappaB is a specific or global regulator of death antagonists in the Bcl-2 family. Here, we demonstrate that NF-kappaB differentially regulates the expression of particular Bcl-2-related death inhibitors and that it directly activates the expression of Bcl-x(L). While Bcl-x(L) was significantly upregulated by c-Rel and RelA, Bcl-2 was not. Importantly, stimuli that activate endogenous NF-kappaB factors also upregulated bcl-x gene expression and this effect was antagonized by an inhibitor of NF-kappaB activity. The expression of bcl-x suppressed apoptosis in the presence or absence of NF-kappaB activity. Functional analysis of the bcl-x promoter demonstrated that it is directly controlled by c-Rel. These results establish that NF-kappaB directly regulates the expression of distinct prosurvival factors in the Bcl-2 family, such as Bcl-x(L) and Bfl-1/A1. These findings raise the possibility that some of these factors may contribute to oncogenesis associated with aberrant Rel/NF-kappaB activity.

NF-kappaB activation by camptothecin. A linkage between nuclear DNA damage and cytoplasmic signaling events

Activation of the transcription factor NF-kappaB by extracellular signals involves its release from the inhibitor protein IkappaBalpha in the cytoplasm and subsequent nuclear translocation. NF-kappaB can also be activated by the anticancer agent camptothecin (CPT), which inhibits DNA topoisomerase (Topo) I activity and causes DNA double-strand breaks during DNA replication to induce S phase-dependent cytotoxicity. Here we show that CPT activates NF-kappaB by a mechanism that is dependent on initial nuclear DNA damage followed by cytoplasmic signaling events. NF-kappaB activation by CPT is dramatically diminished in cytoplasts and in CEM/C2 cells expressing a mutant Topo I protein that fails to bind CPT. This response is intensified in S phase cell populations and is prevented by the DNA polymerase inhibitor aphidicolin. In addition, CPT activation of NF-kappaB involves degradation of cytoplasmic IkappaBalpha by the ubiquitin-proteasome pathway in a manner that depends on the IkappaB kinase complex. Finally, inhibition of NF-kappaB activation augments CPT-induced apoptosis. These findings elucidate the progression of signaling events that initiates in the nucleus with CPT-Topo I interaction and continues in the cytoplasm resulting in degradation of IkappaBalpha and nuclear translocation of NF-kappaB to attenuate the apoptotic response.

Inhibition of tumor necrosis factor-alpha transcription in macrophages exposed to febrile range temperature. A possible role for heat shock factor-1 as a negative transcriptional regulator

We previously reported that expression of tumor necrosis factor-alpha (TNFalpha) was attenuated in macrophages exposed to febrile range temperatures. In this study, we analyzed the influence of temperature on TNFalpha transcription in the Raw 264.7 macrophage cell line during incubation at 37 and 39.5 degrees C. The initial activation of TNFalpha transcription in response to endotoxin (LPS) was comparable in the 37 and 39.5 degrees C cell cultures, peaking within 10 min of LPS stimulation. However, the duration of transcriptional activation was markedly reduced in the 39.5 degrees C cells (30-60 min) compared with the 37 degrees C cells (2-4 h). Deletion mapping of the TNFalpha gene revealed that the proximal 85-nucleotide promoter sequence and the 5'-untranslated region were sufficient for temperature sensitivity. This sequence contains six heat shock response element (HRE) half-sites but no complete HREs. Electrophoretic mobility shift and immunoblot assays demonstrated that nuclear transclocation of heat shock factor (HSF) and its activation to a DNA-binding form occurred in the 39.5 degrees C cells in the absence of heat shock protein-70 gene activation. The proximal TNFalpha promoter/5'-untranslated region sequence competed for HSF binding to a classic HRE. Overexpression of HSF-1 reduced activity of the TNFalpha promoter. These data suggest that partial activation of HSF-1 during exposure to febrile, sub-heat shock temperatures may block TNFalpha transcription by binding to its proximal promoter or 5'-untranslated region.

Nerve growth factor activation of nuclear factor kappaB through its p75 receptor is an anti-apoptotic signal in RN22 schwannoma cells

Recent evidence indicates that nerve growth factor (NGF) produces its effects through signaling contributions from both TrkA and the p75 receptor. In contrast to its trophic actions through TrkA, NGF binding to p75 has been shown to activate programmed cell death through a mechanism involving the stress kinase JNK. However, this receptor also activates nuclear factor kappaB (NF-kappaB), the role of which has yet to be determined. We investigated the function of p75-mediated NF-kappaB stimulation in regulating cell survival in the rat schwannoma cell line RN22, which expresses p75, but not TrkA. Gel shift assays demonstrated activation of NF-kappaB in response to NGF within 30 min and lasting at least 4 h. NGF also stimulated JNK in the cells (detected by in vitro kinase assays) with a similar time course. Preventing activation of NF-kappaB with the specific inhibitor SN50 resulted in NGF-induced cell loss. Similarly, transfection of the cells with a mutant form of the endogenous NF-kappaB inhibitor (IkappaBalphaDeltaN), which cannot be degraded and therefore remains bound to NF-kappaB, preventing its activation, resulted in a significant increase in the number of apoptotic cells following NGF treatment. These results suggest that NGF activation of NF-kappaB through the p75 receptor promotes survival, counterbalancing the pro-apoptotic signal.

Activation of apoptosis and its inhibition

The induction of apoptosis, or controlled cell death, by various stimuli has been shown to activate a cascade of endoproteases, called caspases, that cleave numerous cellular proteins necessary for cellular homeostasis. This review discusses this family of proteases together with a variety of mammalian and viral regulatory proteins that act to control this activation.

NFkappaB mediates apoptosis through transcriptional activation of Fas (CD95) in adenoviral hepatitis

NFkappaB is an essential survival factor in several physiological conditions such as embryonal liver development and liver regeneration. However, NFkappaB is also a main mediator of the cellular response to a variety of extracellular stress stimuli, and it has been shown that some viral-induced host cell apoptosis appears to be dependent on NFkappaB activation. The activation of NFkappaB upon viral infection may be a rapid way of initiating an innate immune response against the viral particles. We have assessed the role of NFkB during the early phase of adenoviral hepatitis in a nude mouse model using an adenoviral vector expressing a mutant form of IkappaBalpha. Administration of a LacZ-expressing adenoviral vector induces NFkB DNA and correlates with the up-regulation of Fas (CD95) mRNA, but not FasL (CD95L) mRNA, during the early phase of adenoviral hepatitis. The rapid increase in NFkappaB DNA binding after adenoviral infection of the liver could be very effectively inhibited by IkappaBalpha. Compared with the LacZ control virus, the IkappaBalpha-expressing adenoviral vector inhibits the increase of Fas (CD95) mRNA expression, in particular in the very early phase of the hepatitis. Reporter gene experiments in hepatoma cell lines with a Fas promoter-luciferase construct indicated that the repression of Fas (CD95) mRNA by IkappaBalpha was transcriptionally mediated. The functional relevance of the NFkappaB-dependent increase in Fas (CD95) transcription was assessed by caspase 3 assays and terminal dUTP nick-end labeling tests. Compared with the control, IkappaBalpha adenoviral infection resulted in reduced caspase 3 activity during the early phase of viral hepatitis and in a prevention of liver cell apoptosis 24 h after adenoviral administration. Therefore our study demonstrates a new pro-apoptotic function of NFkappaB in Fas (CD95)-mediated apoptosis of hepatocytes. Interestingly, NFkappaB mediates liver cell apoptosis upon viral infection even in a phase where tumor necrosis factor-alpha is already induced, as shown by the time curves of tumor necrosis factor-alpha serum levels. Therefore, the pro- or anti-apoptotic role of NFkappaB appears to be more determined by the nature of the death stimulus than by the origin of the tissue.

Akt suppresses apoptosis by stimulating the transactivation potential of the RelA/p65 subunit of NF-kappaB

It is well established that cell survival signals stimulated by growth factors, cytokines, and oncoproteins are initiated by phosphoinositide 3-kinase (PI3K)- and Akt-dependent signal transduction pathways. Oncogenic Ras, an upstream activator of Akt, requires NF-kappaB to initiate transformation, at least partially through the ability of NF-kappaB to suppress transformation-associated apoptosis. In this study, we show that oncogenic H-Ras requires PI3K and Akt to stimulate the transcriptional activity of NF-kappaB. Activated forms of H-Ras and MEKK stimulate signals that result in nuclear translocation and DNA binding of NF-kappaB as well as stimulation of the NF-kappaB transactivation potential. In contrast, activated PI3K or Akt stimulates NF-kappaB-dependent transcription by stimulating transactivation domain 1 of the p65 subunit rather than inducing NF-kappaB nuclear translocation via IkappaB degradation. Inhibition of IkappaB kinase (IKK), using an IKKbeta dominant negative protein, demonstrated that activated Akt requires IKK to efficiently stimulate the transactivation domain of the p65 subunit of NF-kappaB. Inhibition of endogenous Akt activity sensitized cells to H-Ras(V12)-induced apoptosis, which was associated with a loss of NF-kappaB transcriptional activity. Finally, Akt-transformed cells were shown to require NF-kappaB to suppress the ability of etoposide to induce apoptosis. Our work demonstrates that, unlike activated Ras, which can stimulate parallel pathways to activate both DNA binding and the transcriptional activity of NF-kappaB, Akt stimulates NF-kappaB predominantly by upregulating of the transactivation potential of p65.

Selective activation of NF-kappa B subunits in human breast cancer: potential roles for NF-kappa B2/p52 and for Bcl-3

Members of the NF-kappa B/Rel transcription factor family have been shown recently to be required for cellular transformation by oncogenic Ras and by other oncoproteins and to suppress transformation-associated apoptosis. Furthermore, NF-kappa B has been shown to be activated by several oncoproteins including HER2/Neu, a receptor tyrosine kinase often expressed in human breast cancer. Human breast cancer cell lines, human breast tumors and normal adjacent tissue were analysed by gel mobility shift assay, immunoblotting of nuclear extracts and immunohistochemistry for activation of NF-kappa B. Furthermore, RNA levels for NF-kappa B-activated genes were analysed in order to determine if NF-kappa B is functionally active in human breast cancer. Our data indicate that the p65/RelA subunit of NF-kappa B is activated (i.e., nuclear) in breast cancer cell lines. However, breast tumors exhibit an absence or low level of nuclear p65/RelA but show activated c-Rel, p50 and p52 as compared to nontumorigenic adjacent tissue. Additionally, the I kappa B homolog Bcl-3, which functions to stimulate transcription with p50 or p52, was also activated in breast tumors. There was no apparent correlation between estrogen receptor status and levels of nuclear NF-kappa B complexes. Transcripts of NF-kappa B-regulated genes were found elevated in breast tumors, as compared to adjacent normal tissue, indicating functional NF-kappa B activity. These data suggest a potential role for a subset of NF-kappa B and I kappa B family proteins, particularly NF-kappa B/p52 and Bcl-3, in human breast cancer. Additionally, the activation of functional NF-kappa B in these tumors likely involves a signal transduction pathway distinct from that utilized by cytokines.

NF-kappa B is required for H-ras oncogene induced abnormal cell proliferation and tumorigenesis

Oncogenic mutations in ras lead to constitutive activation of downstream signaling pathways that modulate the activities of transcription factors. In turn, these factors control the expression of a subset of genes responsible for neoplastic cell transformation. Recent studies suggest that transcription factor NF-kappa B contributes to cell transformation by inhibiting the cell death signal activated by oncogenic Ras. In this study, inhibition of NF-kappa B activity by forced expression of a super-repressor form of I kappa B alpha, the major inhibitor of NF-kappa B, markedly decreased the growth rate, saturation density and tumorigenicity of oncogenic H-Ras transformed rat embryo fibroblasts. Such clonally isolated cells overexpressing I kappa B alpha super-repressor not only were viable but also exhibited no sign of spontaneous apoptosis. Inhibition of NF-kappa B in these cells was functionally demonstrated by both the loss of cytokine induced DNA binding activity and a profoundly increased sensitivity to cell death in response to TNF-alpha treatment. In contrast, inhibition of NF-kappa B activity in non-transformed fibroblasts had minimal effect on growth, but rendered the cells resistant to a subsequent transformation by H-ras oncogene. Similar results were also obtained with rat intestinal epithelial cells harboring an inducible ras oncogene. Taken together, these findings suggest that NF-kappa B activity is essential for abnormal cell proliferation and tumorigenicity activated by the ras oncogene and highlight an alternative functional role for NF-kappa B in oncogenic Ras-mediated cell transformation that is distinct from its anti-apoptotic activity. Oncogene (2000) 19, 841 - 849.

Cell death at the millennium. Implications for liver diseases

Cell death occurs by apoptosis or necrosis. Although these are morphologically distinct, they share similar initiating events (death receptor ligation, chemicals, drug hypoxia, oxidative stress), and usually involve the participation of mitochondria. The ultimate shape of cell death depends on the extent of functional collapse of mitochondria, which either leads to a rapid loss of ATP, swelling and lysis, or a more selective release of cytochrome c in the presence of sufficient ATP to activate executioner caspases, leading to the development of apoptosis. Apoptosis and necrosis participate in the pathogenesis of most liver diseases. Therapies targeting the death receptors, initiator caspases and mitochondria show potential promise in various liver disease, whereas targeting inhibition of executioner caspases may rapidly or in delayed fashion switch from apoptotic to necrotic cell death.

Tumor necrosis factor-alpha-induced lung cell expression of antiapoptotic genes TRAF1 and cIAP2

Tumor necrosis factor (TNF) receptor (TNFR)-associated factors 1 and 2 (TRAF1 and TRAF2) and inhibitor of apoptosis proteins cIAP1 (MIHB) and cIAP2 (MIHC) were recently identified as proteins that associate with the TNF-alpha receptors TNFRI (p55) and TNFRII (p75) and inhibit TNF-alpha-induced programmed cell death or apoptosis. In the original reports, TRAF1 expression, unlike the ubiquitous TRAF2, was restricted to specific tissues in the lung, spleen, and testis. TNF-alpha is increased in the lung in many forms of pulmonary disease. In the current study, Western analysis, immunohistochemistry, and ribonuclease protection assays were used to determine whether TNF-alpha regulates the expression of these TNFR-associated proteins in lung cells. We demonstrate for the first time TNF-alpha dose-dependent induction of TRAF1 protein and messenger RNA (mRNA) in human H441 and A549 pulmonary adenocarcinoma cell lines, as well as in lung cells of C57BL/6J mice after intratracheal administration of TNF-alpha. In contrast to the epithelial cells, TRAF1 was not induced by TNF-alpha in U937 cells, a human monocytic cell line, suggesting cell type-specific regulation. Similarly, cIAP2 mRNA was induced by TNF-alpha in both H441 and A549 pulmonary epithelial cells but not in U937 cells. TNF-alpha is a primary mediator of acute pulmonary inflammation and contributes to the pathophysiology of chronic lung diseases such as bronchopulmonary dysplasia (BPD), a fibrotic disease of prematurely born infants. Immunohistochemical staining of human neonatal lung tissue demonstrated increased TRAF1 in lungs of infants dying of pneumonia or BPD in comparison with those dying of congenital malformation. These studies support the hypothesis that the TRAF1 and cIAP2 genes are highly regulated in pulmonary cells and may play a role in human lung disease.

Roles of nuclear factor kappaB in neuronal survival and plasticity

The transcription factor nuclear factor kappaB (NF-kappaB) is moving to the forefront of the fields of apoptosis and neuronal plasticity because of recent findings showing that activation of NF-kappaB prevents neuronal apoptosis in various cell culture and in vivo models and because NF-kappaB is activated in association with synaptic plasticity. Activation of NF-kappaB was first shown to mediate antiapoptotic actions of tumor necrosis factor in cultured neurons and was subsequently shown to prevent death of various nonneuronal cells. NF-kappaB is activated by several cytokines and neurotrophic factors and in response to various cell stressors. Oxidative stress and elevation of intracellular calcium levels are particularly important inducers of NF-kappaB activation. Activation of NF-kappaB can interrupt apoptotic biochemical cascades at relatively early steps, before mitochondrial dysfunction and oxyradical production. Gene targets for NF-kappaB that may mediate its antiapoptotic actions include the antioxidant enzyme manganese superoxide dismutase, members of the inhibitor of apoptosis family of proteins, and the calcium-binding protein calbindin D28k. NF-kappaB is activated by synaptic activity and may play important roles in the process of learning and memory. The available data identify NF-kappaB as an important regulator of evolutionarily conserved biochemical and molecular cascades designed to prevent cell death and promote neuronal plasticity. Because NF-kappaB may play roles in a range of neurological disorders that involve neuronal degeneration and/or perturbed synaptic function, pharmacological and genetic manipulations of NF-kappaB signaling are being developed that may prove valuable in treating disorders ranging from Alzheimer's disease to schizophrenia.

NF-kappaB determines localization and features of cell death in epidermis

Specialized forms of physiologic cell death lacking certain characteristic morphologic features of apoptosis occur in terminally differentiating tissues, such as in the outer cell layers of epidermis. In these cell layers, NF-kappaB translocates from the cytoplasm to the nucleus and induces target gene expression. In light of its potent role in regulating apoptotic cell death in other tissues, NF-kappaB activation in these cells suggests that this transcription factor regulates cell death during terminal differentiation. Here, we show that NF-kappaB protects normal epithelial cells from apoptosis induced by both TNFalpha and Fas, whereas NF-kappaB blockade enhances susceptibility to death via both pathways. Expression of IkappaBalphaM under control of keratin promoter in transgenic mice caused a blockade of NF-kappaB function in the epidermis and provoked premature spontaneous cell death with apoptotic features. In normal tissue, expression of the known NF-kappaB-regulated antiapoptotic factors, TRAF1, TRAF2, c-IAP1, and c-IAP2, is most pronounced in outer epidermis. In transgenic mice, NF-kappaB blockade suppressed this expression, whereas NF-kappaB activation augmented it, consistent with regulation of cell death by these NF-kappaB effector proteins. These data identify a new role for NF-kappaB in preventing premature apoptosis in cells committed to undergoing physiologic cell death and indicate that, in stratified epithelium, such cell death normally proceeds via a distinct pathway that is resistant to NF-kappaB and its antiapoptotic target effector genes.

Cytokine-induced nuclear factor kappa B activation promotes the survival of developing neurons

Ciliary neurotrophic factor (CNTF), leukemia inhibitory factor (LIF), cardiotrophin-1 (CT-1), and interleukin 6 (IL-6) comprise a group of structurally related cytokines that promote the survival of subsets of neurons in the developing peripheral nervous system, but the signaling pathways activated by these cytokines that prevent neuronal apoptosis are unclear. Here, we show that these cytokines activate NF-kappaB in cytokine-dependent developing sensory neurons. Preventing NF-kappaB activation with a super-repressor IkappaB-alpha protein markedly reduces the number of neurons that survive in the presence of cytokines, but has no effect on the survival response of the same neurons to brain-derived neurotrophic factors (BDNF), an unrelated neurotrophic factor that binds to a different class of receptors. Cytokine-dependent sensory neurons cultured from embryos that lack p65, a transcriptionally active subunit of NF-kappaB, have a markedly impaired ability to survive in response to cytokines, but respond normally to BDNF. There is increased apoptosis of cytokine- dependent neurons in p65(-/)- embryos in vivo, resulting in a reduction in the total number of these neurons compared with their numbers in wild-type embryos. These results demonstrate that NF-kappaB plays a key role in mediating the survival response of developing neurons to cytokines.

Cell death in the oligodendrocyte lineage: a molecular perspective of life/death decisions in development and disease

Cell death in the oligodendrocyte lineage occurs during development and in pathological conditions as the result of a balance between opposing molecular signals. This review focuses on the molecular mechanisms of activation of signal transduction pathways affecting life/death decisions in progenitor cells and in mature oligodendrocytes. Loss of trophic support, cytokine receptor activation, and oxidative stress may differentially contribute to the induction of cell death at specific stages of development and to the pathogenesis of demyelinating disorders. The execution of the death program leading to the morphological changes of apoptosis and/or necrosis is then determined by the generation of reactive oxygen species and the level of impairment of mitochondrial function. The final decision of a cell to die or survive is determined by a competition between survival and death signals. Depending on ligand availability, type, and levels of receptor expression and downstream cross-talks between distinct signaling pathways, the cell may activate a death execution program that will be affected by its stage of differentiation and its energetic metabolism.

Inhibition of proteasome function induces programmed cell death in proliferating endothelial cells

Proteolysis mediated by the ubiquitin-proteasome system has been implicated in the regulation of programmed cell death. Here we investigated the differential effects of proteasomal inhibitors on the viability of proliferating and quiescent primary endothelial cells in vitro and in vivo. Subconfluent, proliferating cells underwent carbobenzoxy-L-isoleucyl-gamma-t-butyl-L-glutamyl-L-alanyl-L-leucinal (PSI) -induced apoptosis at low concentrations (EC(50)=24 nM), whereas at least 340-fold higher concentrations of PSI were necessary to obtain the same effect in confluent, contact-inhibited cells. PSI-mediated cell death could be blocked by a caspase-3 inhibitor (Ac-DEVD-H), but not by a caspase-1 inhibitor (Ac-YVAD-H), suggesting that a caspase-3-like enzyme is activated during PSI-induced apoptosis. When applied to the embryonic chick chorioallantoic membrane, a rapidly expanding tissue, PSI induced massive apoptosis also in vivo. PSI treatment of the CAM led to the formation of areas devoid of blood flow due to the induction of apoptosis in endothelial and other cells and to the collapse of capillaries and first order vessels. Our results demonstrate that proteasomal inhibitors such as PSI may prove effective as novel anti-angiogenic and anti-neoplastic substances.

Nuclear factor-κB activation by the photochemotherapeutic agent verteporfin

The nuclear factor-kappa B (NF-κB) gene transactivator serves in the formation of immune, inflammatory, and stress responses. In quiescent cells, NF-κB principally resides within the cytoplasm in association with inhibitory κ (IκB) proteins. The status of IκB and NF-κB proteins was evaluated for promyelocytic leukemia HL-60 cells treated at different intensities of photodynamic therapy (PDT). The action of the potent photosensitizer, benzoporphyrin derivative monoacid ring A (verteporfin), and visible light irradiation were assessed. At a verteporfin concentration that produced the death of a high proportion of cells after light irradiation, evidence of caspase-3 and caspase-9 processing and of poly(ADP-ribose) polymerase cleavage was present within whole cell lysates. The general caspase inhibitor Z-Val-Ala-Asp-fluoromethylketone (ZVAD.fmk) effectively blocked these apoptosis-related changes. Recent studies indicate that IκB proteins may be caspase substrates during apoptosis. However, the level of IκBβ was unchanged for HL-60 cells undergoing PDT-induced apoptosis. IκB levels decreased during PDT-induced apoptosis, though ZVAD.fmk did not affect this change. At a less intensive level of photosensitization, cellular IκB levels were transiently depressed after PDT. At these times, p50 and RelA NF-κB species were increased within nuclear extracts, as revealed by electrophoretic mobility supershift assays. HL-60 cells transiently transfected with a κB-luciferase reporter construct exhibited elevated luciferase activity after PDT or treatment with tumor necrosis factor-, a well-characterized NF-κB activator. Productive NF-κB activation and associated gene transcription may influence the phenotype and behavior of cells exposed to less intensive PDT regimens. However, IκB is not subject to caspase-mediated degradation as a component of PDT-induced apoptosis. (Blood. 2000;95:256-262)

Nuclear factor-κB activation by the photochemotherapeutic agent verteporfin

The nuclear factor-kappa B (NF-κB) gene transactivator serves in the formation of immune, inflammatory, and stress responses. In quiescent cells, NF-κB principally resides within the cytoplasm in association with inhibitory κ (IκB) proteins. The status of IκB and NF-κB proteins was evaluated for promyelocytic leukemia HL-60 cells treated at different intensities of photodynamic therapy (PDT). The action of the potent photosensitizer, benzoporphyrin derivative monoacid ring A (verteporfin), and visible light irradiation were assessed. At a verteporfin concentration that produced the death of a high proportion of cells after light irradiation, evidence of caspase-3 and caspase-9 processing and of poly(ADP-ribose) polymerase cleavage was present within whole cell lysates. The general caspase inhibitor Z-Val-Ala-Asp-fluoromethylketone (ZVAD.fmk) effectively blocked these apoptosis-related changes. Recent studies indicate that IκB proteins may be caspase substrates during apoptosis. However, the level of IκBβ was unchanged for HL-60 cells undergoing PDT-induced apoptosis. IκB levels decreased during PDT-induced apoptosis, though ZVAD.fmk did not affect this change. At a less intensive level of photosensitization, cellular IκB levels were transiently depressed after PDT. At these times, p50 and RelA NF-κB species were increased within nuclear extracts, as revealed by electrophoretic mobility supershift assays. HL-60 cells transiently transfected with a κB-luciferase reporter construct exhibited elevated luciferase activity after PDT or treatment with tumor necrosis factor-, a well-characterized NF-κB activator. Productive NF-κB activation and associated gene transcription may influence the phenotype and behavior of cells exposed to less intensive PDT regimens. However, IκB is not subject to caspase-mediated degradation as a component of PDT-induced apoptosis. (Blood. 2000;95:256-262)

CD40 and B chronic lymphocytic leukemia cell response to fludarabine: the influence of NF-kappaB/Rel transcription factors on chemotherapy-induced apoptosis

The levels of tumour necrosis factor receptor (TNF-R) superfamily members can be altered in lymphoid leukemias, indicating a possible role of such molecules in the biology of these neoplasias. In B chronic lymphocytic leukemia cells, the CD40/CD40L system has been shown to be effective in inhibiting the apoptotic response to fludarabine. The modulation of apoptosis relied on the CD40-induced activity of NF-kappaB/Rel transcription factors. The anti-apoptotic effect of CD40 was abolished using a phosphorothioate kappaB decoy oligodeoxynucleotide. These findings illustrate an example of the biological activity of TNF-R-like molecules in leukemias. They also show the influence of NF-kappaB/Rel activity on leukemic cell response to apoptogenic agents.

Biochemical pathways of caspase activation during apoptosis

Caspase activation plays a central role in the execution of apoptosis. The key components of the biochemical pathways of caspase activation have been recently elucidated. In this review, we focus on the two most well-studied pathways of caspase activation: the cell surface death receptor pathway and the mitochondria-initiated pathway. In the cell surface death receptor pathway, activation of caspase-8 following its recruitment to the death-inducing signaling complex (DISC) is the critical event that transmits the death signal. This event is regulated at several different levels by various viral and mammalian proteins. Activated caspase-8 can activate downstream caspases by direct cleavage or indirectly by cleaving Bid and inducing cytochrome c release from the mitochondria. In the mitochondrial-initiated pathway, caspase activation is triggered by the formation of a multimeric Apaf-1/cytochrome c complex that is fully functional in recruiting and activating procaspase-9. Activated caspase-9 will then cleave and activate downstream caspases such as caspase-3, -6, and -7. This pathway is regulated at several steps, including the release of cytochrome c from the mitochondria, the binding and hydrolysis of dATP/ATP by Apaf-1, and the inhibition of caspase activation by the proteins that belong to the inhibitors of apoptosis (IAP).

Amifostine Inhibits Hematopoietic Progenitor Cell Apoptosis by Activating NF-κB/Rel Transcription Factors

We investigated the involvement of NF-κB/Rel transcription factors that reportedly can inhibit apoptosis in various cell types in the antiapoptotic mechanism of the cytoprotectant amifostine. In the nontumorigenic murine myeloid progenitor 32D cells incubated with amifostine, we detected a reduction of the IκB cytoplasmic levels by Western blotting and a raising of nuclear NF-κB/Rel complexes by electrophoretic mobility shift assay. Amifostine inhibited by more than 30% the growth factor deprivation-induced apoptosis, whereas its effect failed when we blocked the NF-κB/Rel activity with an NF-κB/Rel-binding phosphorothioate decoy oligodeoxynucleotide. In human cord blood CD34+ cells, the NF-κB/Rel p65 subunit was detectable (using immunofluorescence analysis) mainly in the cytoplasm in the absence of amifostine, whereas its presence was appreciable in the nuclei of cells incubated with the cytoprotectant. In 4 CD34+ samples incubated for 3 days in cytokine-deficient conditions, cell apoptosis was reduced by more than 30% in the presence of amifostine (or amifostine plus a control oligo); the effect of amifostine was abolished in cultures with the decoy oligo. These findings indicate that the inhibition of hematopoietic progenitor cell apoptosis by amifostine requires the induction of NF-κB/Rel factors and that the latter can therefore exert an antiapoptotic activity in the hematopoietic progenitor cell compartment. Furthermore, the identification of this specific mechanism underlying the survival-promoting activity of amifostine lends support to the possible use of this agent in apoptosis-related pathologies, such as myelodysplasias.

Amifostine Inhibits Hematopoietic Progenitor Cell Apoptosis by Activating NF-κB/Rel Transcription Factors

We investigated the involvement of NF-κB/Rel transcription factors that reportedly can inhibit apoptosis in various cell types in the antiapoptotic mechanism of the cytoprotectant amifostine. In the nontumorigenic murine myeloid progenitor 32D cells incubated with amifostine, we detected a reduction of the IκB cytoplasmic levels by Western blotting and a raising of nuclear NF-κB/Rel complexes by electrophoretic mobility shift assay. Amifostine inhibited by more than 30% the growth factor deprivation-induced apoptosis, whereas its effect failed when we blocked the NF-κB/Rel activity with an NF-κB/Rel-binding phosphorothioate decoy oligodeoxynucleotide. In human cord blood CD34+ cells, the NF-κB/Rel p65 subunit was detectable (using immunofluorescence analysis) mainly in the cytoplasm in the absence of amifostine, whereas its presence was appreciable in the nuclei of cells incubated with the cytoprotectant. In 4 CD34+ samples incubated for 3 days in cytokine-deficient conditions, cell apoptosis was reduced by more than 30% in the presence of amifostine (or amifostine plus a control oligo); the effect of amifostine was abolished in cultures with the decoy oligo. These findings indicate that the inhibition of hematopoietic progenitor cell apoptosis by amifostine requires the induction of NF-κB/Rel factors and that the latter can therefore exert an antiapoptotic activity in the hematopoietic progenitor cell compartment. Furthermore, the identification of this specific mechanism underlying the survival-promoting activity of amifostine lends support to the possible use of this agent in apoptosis-related pathologies, such as myelodysplasias.

Pharmacological manipulation of granulocyte apoptosis: potential therapeutic targets

Resolution of inflammation involves the clearance of excess or effete inflammatory cells by a process of physiological programmed cell death (apoptosis) and the subsequent recognition and removal of apoptotic cells by phagocytes. The therapeutic induction of apoptosis for the resolution of chronic inflammation and the general pharmacology of apoptosis have become subjects of increasing interest. In this article, some of the unique and important differences in the control of apoptosis of various inflammatory cells (particularly neutrophil and eosinophil granulocytes) are highlighted. It is suggested that apoptosis can be specifically regulated pharmacologically and could be exploited to develop new drug therapies.

Discovering novel chemotherapeutic drugs for the third millennium

There is enormous potential for the discovery of innovative cancer drugs with improved efficacy and selectivity for the third millennium. In this review we show how novel mechanism-based agents are being discovered by focusing on the molecular targets and pathways that are causally involved in cancer formation, maintenance and progression. We also show how new technologies, from genomics through high through-put bioscience, combinatorial chemistry, rational drug design and molecular pharmacodynamic and imaging techniques, are accelerating the pace of cancer drug discovery. The process of contemporary small molecule drug discovery is described and progress and current issues are reviewed. New and potential targets and pathways for therapeutic intervention are illustrated. The first examples of a new generation of molecular therapeutics are now entering hypothesis-testing clinical trials and showing activity. The early years of the new millennium will see a range of exciting new agents moving from bench to bedside and beginning to impact on the management and cure of cancer.

Control of apoptosis by Rel/NF-kappaB transcription factors

Apoptosis is a physiological process critical for organ development, tissue homeostasis, and elimination of defective or potentially dangerous cells in complex organisms. Apoptosis can be initiated by a wide variety of stimuli, which activate a cell suicide program that is constitutively present in most vertebrate cells. In diverse cell types, Rel/NF-kappaB transcription factors have been shown to have a role in regulating the apoptotic program, either as essential for the induction of apoptosis or, perhaps more commonly, as blockers of apoptosis. Whether Rel/NF-kappaB promotes or inhibits apoptosis appears to depend on the specific cell type and the type of inducer. An understanding of the role of Rel/NF-kappaB transcription factors in controlling apoptosis may lead to the development of therapeutics for a wide variety of human diseases, including neurodegenerative and immune diseases, and cancer.

Aberrant rel/nfkb genes and activity in human cancer

Rel/NF-kappaB transcription factors are key regulators of immune, inflammatory and acute phase responses and are also implicated in the control of cell proliferation and apoptosis. Remarkable progress has been made in understanding the signal transduction pathways that lead to the activation of Rel/NF-kappaB factors and the consequent induction of gene expression. Evidence linking deregulated Rel/NF-kappaB activity to oncogenesis in mammalian systems has emerged in recent years, consistent with the acute oncogenicity of the viral oncoprotein v-Rel in animal models. Chromosomal amplification, overexpression and rearrangement of genes coding for Rel/NF-kappaB factors have been noted in many human hematopoietic and solid tumors. Persistent nuclear NF-kappaB activity was also described in several human cancer cell types, as a result of constitutive activation of upstream signaling kinases or mutations inactivating inhibitory IkappaB subunits. Studies point to a correlation between the activation of cellular gene expression by Rel/NF-kappaB factors and their participation in the malignant process. Experiments implicating NF-kappaB in the control of the apoptotic response also support a role in oncogenesis and in the resistance of tumor cells to chemotherapy. This review focuses on the status of the rel, nfkb and ikb genes and their activity in human tumors and their association with the onset or progression of malignancies.

Pathophysiological mechanisms of TNF during intoxication with natural or man-made toxins

Intoxication with different natural toxins or man-made toxicants has been associated with the induction of tumor necrosis factor alpha (TNF). These include endotoxin, superantigens, Pseudomonas aeruginosa exotoxin A, bacterial DNA, T cell stimulatory agents such as agonistic anti-CD3 mAbs or concanavalin A, alpha-amanitin, paracetamol, ethanol, carbon tetrachloride, dioxin, and dimethylnitrosamine. In this paper we compile and discuss the current knowledge on the pathophysiological role of TNF during intoxication with all mentioned toxins and toxicants. A possible role of gut-derived endotoxin in several TNF-dependent toxic events has been considered. The development of pharmaceuticals that selectively interfere with the detrimental pathways induced by TNF during intoxication with bacteria, viruses, drugs, or other chemicals requires detailed knowledge of the signaling pathways originating from the two TNF receptors (TNFR1 and TNFR2). Major characteristics of these signaling pathways are described and put together.

Transformation of leukocytes by Theileria parva and T. annulata

Theileria parva and T. annulata provide intriguing models for the study of parasite-host interactions. Both parasites possess the unique property of being able to transform the cells they infect; T. parva transforms T and B cells, whereas T. annulata affects B cells and monocytes/macrophages. Parasitized cells do not require antigenic stimulation or exogenous growth factors and acquire the ability to proliferate continuously. In vivo, parasitized cells undergo clonal expansion and infiltrate both lymphoid and non-lymphoid tissues of the infected host. Theileria-induced transformation is entirely reversible and is accompanied by the expression of a wide range of different lymphokines and cytokines, some of which may contribute to proliferation or may enhance spread and survival of the parasitized cell in the host. The presence of the parasite in the host-cell cytoplasm modulates the state of activation of a number of signal transduction pathways. This, in turn, leads to the activation of transcription factors, including nuclear factor-kappa B, which appear to be essential for the survival of Theileria-transformed T cells.

Role of progesterone receptor activation in pituitary adenylate cyclase activating polypeptide gene expression in rat ovary

It is well known that the pituitary gonadotropin surge induces progesterone receptor (PR) gene expression in luteinizing granulosa cells and that PR activation is critical for successful ovulation. To further understand the molecular mechanism(s) by which PR plays a role critical for granulosa cell functions, we wanted to identify progesterone-induced genes in granulosa cells. We employed a PCR-based subtraction cloning strategy to screen for genes expressed differentially in granulosa cells that were challenged with forskolin in the presence of progesterone or ZK98299. One such differentially expressed clone was identified as the pituitary adenylate cyclase activating polypeptide (PACAP). To begin to understand the relationship between PR activation and PACAP gene expression in luteinizing granulosa cells, we examined whether PR and PACAP messenger RNA (mRNA) expression is temporally correlated. In cultured granulosa cells, both human CG and forskolin induced PR and PACAP mRNA levels in a dose-dependent manner, as determined by semi-quantitative RT-PCR assays. However, the peak expression for PR and PACAP mRNAs was observed at 3 h and 6 h after hormone treatment, respectively. This time difference in cAMP-responsive expression of the PR and PACAP genes is due, at least in part, to the requirement of ongoing protein synthesis for PACAP expression, as demonstrated by the inhibitory effect of cycloheximide on cAMP-induced PACAP, but not PR, mRNA levels. To determine whether PR synthesis is prerequisite for PACAP expression, we examined the effect of ZK98299, a specific PR antagonist, on cAMP-induced PACAP mRNA expression. This compound blocked cAMP-induced PACAP mRNA expression in a dose-dependent manner, indicating that PR activation is required for PACAP gene expression in granulosa cells. We then compared cellular localization and hormonal regulation of ovarian PR and PACAP gene expression in immature rats treated with gonadotropins as well as in adult rats during the preovulatory period by using in situ hybridization and semiquantitative RT-PCR assays. Results show that both PR and PACAP mRNAs are induced in granulosa cells of preovulatory follicles by human CG, but that the PR gene is expressed before the PACAP gene. Taken together, these results demonstrate that PRs mediate the LH-induced PACAP gene expression in rat granulosa cells.

NF-kappaB as a primary regulator of the stress response

A myriad of unrelated exogenous or endogenous agents that represent a threat to the organism are capable of inducing NF-kappaB activity, including viral infection, bacterial lipids, DNA damage, oxidative stress and chemotherapuetic agents. Likewise, NF-kappaB regulates the expression of an equally diverse array of cellular genes. These findings are indicative of the widespread significance of NF-kappaB as a mediator of cellular stress. Remarkably, the NF-kappaB pathway displays the capacity to activate, in a cell- and stimulus-specific manner, only a subset of the total repertoire of NF-kappaB-responsive genes. The seemingly promiscuous nature of NF-kappaB activation poses a regulatory quagmire as to how specificity is achieved at the level of gene expression. The review will summarize recent findings and explore how they further our understanding of the mechanism by which stimulus-specific activation of NF-kappaB is achieved in response to cellular stress.

The role of NF-kappaB/IkappaB proteins in cancer: implications for novel treatment strategies

The nuclear factor-kappaB (NF-kappaB) family of transcription factors are involved in multiple cellular processes, including cytokine gene expression, cellular adhesion, cell cycle activation, apoptosis and oncogenesis. Constitutive activation of NF-kappaB has been described in a number of solid tumors and this activation appears to affect cancer cell survival. Inhibition of NF-kappaB has been shown to enhance the sensitivity of some cancer cell lines to antineoplastic- or radiation-induced apoptosis. Furthermore, suppression of NF-kappaB results in attenuation of cancer cachexia in a mouse tumor model. Studies are underway to further delineate the role of NF-kappaB in cancer cell survival, growth and resistance to standard chemotherapy and radiation regimens. Moreover, the effects of novel therapeutic agents which specifically target NF-kappaB proteins are currently being assessed in experimental models of cancer cell growth both in vitro and in vivo. In this review, we discuss the possible involvement of NF-kappaB in the growth of various solid tumors and potential future treatment strategies based on NF-kappaB inhibition.

Thymocyte apoptosis

Apoptosis is the fate of most thymocytes. Many molecules participate in the decision of whether a thymocyte is to live or to die, including cell surface receptors, such as the T cell receptor for antigen, Notch-1, and costimulatory receptors, ligand-regulated nuclear transcription factors such as the glucocorticoid receptor, signaling, and effector proteases, and direct regulators of the apoptotic machinery such IAPs. In this review we discuss recent data concerning these molecules and pathways and their implication for understanding the mechanisms underlying thymocyte death, survival, and the generation of inmmunocompetent T cells.

TNF-induced signaling in apoptosis

Out of the almost 17 members of the TNF superfamily, TNF is probably the most potent inducer of apoptosis. TNF activates both cell-survival and cell-death mechanisms simultaneously. Activation of NF-kB-dependent genes regulates the survival and proliferative effects pf TNF, whereas activation of caspases regulates the apoptotic effects. TNF-induced apoptosis is mediated primarily through the activation of type I receptors, the death domain of which recruits more than a dozen different signaling proteins, which together are considered part of an apoptotic cascade. This cascade does not, however, account for the role of reactive oxygen intermediates, ceramide, phospholipases, and serine proteases which are also implicated in TNF-induced apoptosis. This cascade also does not explain how type II TNF receptors which lack the death domain, induce apoptosis. Nevertheless, this review of apoptosis signaling will be limited to those proteins that makeup the cascade.

Endogenous inhibitors of caspases

Caspases are cysteine proteases that are specific for aspastic acid residues. These enzymes have been extensively characterized as integral and highly conserved components of a variety of cell death programs. Cowpox and several insect viruses have evolved mechanisms that counter host cell suicide by encoding proteins that directly inhibit caspases-thereby allowing propagation of viral progeny within the host cell. It has only recently been elucidated, however, that endogenous cellular inhibitors of the caspases exist. To date five members of the inhibitor of apoptosis (IAP) family of proteins has been identified in humans and at least three of these have been shown directly to inhibit specific caspases. Thus, members of the IAP family of proteins are the only endogenous inhibitors of caspases known in mammals. Here we discuss the caspase and IAP families of proteins and review the data concerning their relationship.

Insulin antiapoptotic signaling involves insulin activation of the nuclear factor kappaB-dependent survival genes encoding tumor necrosis factor receptor-associated factor 2 and manganese-superoxide dismutase

We recently showed that the antiapoptotic function of insulin requires nuclear factor kappaB (NF-kappaB) activation (Bertrand, F., Atfi, A., Cadoret, A., L'Allemain, G., Robin, H., Lascols, O., Capeau, J., and Cherqui, G. (1998) J. Biol. Chem. 273, 2931-2938). Here we sought to identify the NF-kappaB-dependent survival genes that are activated by insulin to mediate this function. Insulin increased the expression of tumor necrosis factor receptor-associated factor 2 (TRAF2) mRNA and protein in Chinese hamster ovary cells overexpressing insulin receptors (IRs). This effect required (i) IR activation since it was abrogated by IR mutation at tyrosines 1162 and 1163 and (ii) NF-kappaB activation since it was abolished by overexpression of dominant-negative IkappaB-alpha(A32/36) and mimicked by overexpression of the NF-kappaB c-Rel subunit. TRAF2 contributed to insulin protection against serum withdrawal-induced apoptosis since TRAF2 overexpression mimicked insulin protection, whereas overexpression of dominant-negative TRAF2-(87-501) reduced this process. Along with its protective effect, overexpressed TRAF2 increased basal and insulin-stimulated NF-kappaB activities. All effects were inhibited by IkappaB-alpha(A32/36), suggesting that an amplification loop involving TRAF2 activation of NF-kappaB is implicated in insulin antiapoptotic signaling. We also show that insulin increased manganese-superoxide dismutase (Mn-SOD) mRNA expression through NF-kappaB activation and that Mn-SOD contributed to insulin antiapoptotic signaling since expression of antisense Mn-SOD RNA decreased this process. This study provides the first evidence that insulin activates the NF-kappaB-dependent survival genes encoding TRAF2 and Mn-SOD and thereby clarifies the role of NF-kappaB in the antiapoptotic function of insulin.

Interleukin-1 protects transformed keratinocytes from tumor necrosis factor-related apoptosis-inducing ligand- and CD95-induced apoptosis but not from ultraviolet radiation-induced apoptosis

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), a new member of the tumor necrosis factor (TNF) family, induces apoptosis primarily of transformed cells. Interleukin-1 was previously found to protect the keratinocyte cell line KB from TRAIL-induced apoptosis, thus we studied whether interleukin-1 also protects from other apoptotic stimuli (ultraviolet radiation (UV), CD95-ligand). Interleukin-1 rescued KB cells from TRAIL- and CD95-induced apoptosis, which was critically dependent on nuclear factor kappaB, because cells transfected with a super-repressor form of the nuclear factor kappaB inhibitor IkappaB were less protected. In contrast, UV-mediated apoptosis was not only not prevented by interleukin-1 but even enhanced. This opposite effect of interleukin-1 was also observed for the expression of the inhibitor of apoptosis proteins (IAP). Whereas TRAIL- and CD95-mediated suppression of IAP expression was partially reversed by interleukin-1, UV-mediated down-regulation of IAPs was not reversed but even further enhanced. Increased apoptosis induced by interleukin-1 plus UV was accompanied by excessive TNFalpha release, implying that enhanced cytotoxicity is due to the additive effect of these two apoptotic stimuli. Accordingly, enhanced apoptosis was reduced by blocking the TNF receptor-1. The opposite effects of interleukin-1 indicate that different mechanisms are involved in UV-induced apoptosis compared with CD95- and TRAIL-mediated apoptosis. Furthermore, the data suggest that whether a signal acts in an antiapoptotic way or not does not only depend on the signal itself but also on the stimulus causing apoptosis.

NF-kappaB activation is required for human endothelial survival during exposure to tumor necrosis factor-alpha but not to interleukin-1beta or lipopolysaccharide

In the presence of a protein synthesis inhibitor, cycloheximide, tumor necrosis factor-alpha (TNF-alpha), interleukin 1-beta (IL-1beta), or lipopolysaccharide (LPS) induces human umbilical vein endothelial cells (HUVECs) to undergo apoptosis, suggesting that constitutive or inducible cytoprotective pathways are required for cell survival. We studied the correlation between nuclear factor-kappaB (NF-kappaB) activation and cell death induced by TNF-alpha, IL-1beta, or LPS. Adenovirus-mediated overexpression of a dominant-negative IkappaBalpha (inhibitor of kappaB) mutant blocked NF-kappaB activation by gel shift assay and blocked induction of vascular cell adhesion molecule-1 protein by TNF-alpha, IL-1beta, and LPS, a NF-kappaB-dependent response. In cells overexpressing the IkappaBalpha mutant, TNF-alpha induced cell death, whereas IL-1beta or LPS did not. We conclude that cell survival following TNF-alpha stimulation is NF-kappaB-dependent but that a constitutive or inducible NF-kappaB-independent pathway(s) protects IL-1beta- or LPS-treated HUVECs from cell death.

RING fingers mediate ubiquitin-conjugating enzyme (E2)-dependent ubiquitination

A RING finger-containing protein (AO7) that binds ubiquitin-conjugating enzymes (E2s) and is a substrate for E2-dependent ubiquitination was identified. Mutations of cation-coordinating residues within AO7's RING finger abolished ubiquitination, as did chelation of zinc. Several otherwise-unrelated RING finger proteins, including BRCA1, Siah-1, TRC8, NF-X1, kf-1, and Praja1, were assessed for their ability to facilitate E2-dependent ubiquitination. In all cases, ubiquitination was observed. The RING fingers were implicated directly in this activity through mutations of metal-coordinating residues or chelation of zinc. These findings suggest that a large number of RING finger-containing proteins, with otherwise diverse structures and functions, may play previously unappreciated roles in modulating protein levels via ubiquitination.

Sulindac inhibits activation of the NF-kappaB pathway

Sulindac is a non-steroidal anti-inflammatory agent that is related both structurally and pharmacologically to indomethacin. In addition to its anti-inflammatory properties, sulindac has been demonstrated to have a role in the prevention of colon cancer. Both its growth inhibitory and anti-inflammatory properties are due at least in part to its ability to decrease prostaglandin synthesis by inhibiting the activity of cyclooxygenases. Recently, we demonstrated that both aspirin and sodium salicylate, but not indomethacin, inhibited the activity of an IkappaB kinase beta (IKKbeta) that is required to activate the nuclear factor-kappaB (NF-kappaB) pathway. In this study, we show that sulindac and its metabolites sulindac sulfide and sulindac sulfone can also inhibit the NF-kappaB pathway in both colon cancer and other cell lines. Similar to our previous results with aspirin, this inhibition is due to sulindac-mediated decreases in IKKbeta kinase activity. Concentrations of sulindac that inhibit IKKbeta activity also reduce the proliferation of colon cancer cells. These results suggest that the growth inhibitory and anti-inflammatory properties of sulindac may be regulated in part by inhibition of kinases that regulate the NF-kappaB pathway.