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

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.

Light-induced photoreceptor degeneration may involve the NF kappa B/caspase-1 pathway in vivo

PURPOSE

To determine the role of nuclear factor-kappaB (NFkappaB) in light-induced photoreceptor degeneration.

METHODS

Dark-adapted BALB/cJ mice, 4-8 weeks, were exposed to an intense green light (3.1-3.5 klux) for 1, 3, 6, 9, 12, or 24 h and killed immediately after exposure. The photoreceptor apoptosis was detected by TUNEL. Co-localization of NFkappaB p65 immunoreactivity and TUNEL in photoreceptor cells was detected by double immunolabeling. The protein levels of X-linked inhibitor of apoptosis protein (XIAP), Bcl-xL, caspase-1, and opsin after light exposure were analyzed by Western blot analysis. In addition, the initiation of NFkappaB activation was assessed by measuring the increase in phosphorylated IkappaBalpha (pIkappaBalpha). Immunohistochemical localization of caspase-1 was also performed on the mouse retinas.

RESULTS

Co-localization of NFkappaB p65 immunoreactivity with TUNEL was observed in scattered photoreceptor cells after 24 h of light exposure. The amount of pIkappaBalpha was increased after 1 h of light exposure, and in parallel, the amounts of XIAP and Bcl-xL were increased at 1 h. In contrast, caspase-1 did not increase until after 6 h of light exposure. Caspase-1-immunolabeling was observed in scattered photoreceptor cells after 3 h of light exposure but was markedly increased in many more cells at 6 h.

CONCLUSIONS

These findings suggest that NFkappaB may play an anti-apoptotic role in the early response to light stress and that photoreceptor apoptosis induced by light stress may be mediated through an NFkappaB/caspase-1 pathway.

Combination of tumor necrosis factor-alpha with sulindac augments its apoptotic potential and suppresses tumor growth of human carcinoma cells in nude mice

BACKGROUND

Resistance to apoptosis may be responsible for a principal mechanism by which cancer cells overcome anticancer therapies. Among antiapoptotic signals, the transcription factor, NF-kappaB, plays a pivotal role in the resistance because it is frequently activated in many primary carcinoma cells. However, NF-kappaB is also activated by several anticancer therapies, including tumor necrosis factor-alpha (TNF-alpha). The NF-kappaB-mediated survival signals are supposed to evade these therapies. Recently, a nonsteroidal antiinflammatory drug, sulindac, and its metabolites have been shown to inhibit the NF-kappaB pathway and to enhance TNF-alpha-mediated apoptosis in lung carcinoma cell lines. In the current study, the authors investigated whether sulindac can augment TNF-alpha-mediated apoptosis in other human carcinoma cells and whether it can be applied for in vivo clinical usage.

METHODS

Human gastric MKN45 and cervical HeLa carcinoma cells were treated with sulindac and/or TNF-alpha. Proapoptotic effects of these agents were evaluated by trypan blue exclusion assay, DNA fragmentation, and caspase-3 activity. The effect of sulindac on NF-kappaB activation was evaluated by luciferase reporter and gel-shift assays. The suppressive effects of these reagents on the subcutaneous tumor growth of MKN45 cells were evaluated by measuring tumor size in nude mice.

RESULTS

Sulindac inhibited TNF-alpha-mediated NF-kappaB activation and greatly sensitized MKN45 and HeLa cell lines to TNF-alpha. Moreover, in vivo tumor growth of MKN45 cells was inhibited most strongly by a combination of TNF-alpha with sulindac compared with TNF-alpha or sulindac alone.

CONCLUSIONS

The current study data strongly suggest that combination therapy of TNF-alpha with sulindac may sensitize tumor cells to TNF-alpha and augment its proapoptotic potential. Therefore, in combination with sulindac, TNF-alpha may become a potentially useful anticancer agent to suppress tumor growth in a wide range of carcinomas.

Inhibition of NF-kappa B activity in T and NK cells results in defective effector cell expansion and production of IFN-gamma required for resistance to Toxoplasma gondii

To define the role of NF-kappa B in the development of T cell responses required for resistance to Toxoplasma gondii, mice in which T cells are transgenic for a degradation-resistant (Delta N) form of I kappa B alpha, an inhibitor of NF-kappa B, were challenged with T. gondii and their response to infection compared with control mice. I kappa B alpha(Delta N)-transgenic (Tg) mice succumbed to T. gondii infection between days 12 and 35, and death was associated with an increased parasite burden compared with wild-type (Wt) controls. Analysis of the responses of infected mice revealed that IL-12 responses were comparable between strains, but Tg mice had a marked reduction in systemic levels of IFN-gamma, the major mediator of resistance to T. gondii. In addition, the infection-induced increase in NK cell activity observed in Wt mice was absent from Tg mice and this correlated with NK cell expression of the transgene. Infection-induced activation of CD4(+) T cells was similar in Wt and Tg mice, but expansion of activated CD4(+)T cells was markedly reduced in the Tg mice. This difference in T cell numbers correlated with a reduced capacity of these cells to proliferate after stimulation and was associated with a major defect in the ability of CD4(+) T cells from infected mice to produce IFN-gamma. Together, these studies reveal that inhibition of NF-kappa B activity in T and NK cells results in defective effector cell expansion and production of IFN-gamma required for resistance to T. gondii.

Mutations in the v-Rel transactivation domain indicate altered phosphorylation and identify a subset of NF-kappaB-regulated cell death inhibitors important for v-Rel transforming activity

Consistent with the constitutive activation of Rel/NF-kappaB in human hematopoietic tumors, the v-Rel oncoprotein induces aggressive leukemia/lymphomas in animal models. v-Rel is thus a valuable tool to characterize the role of Rel/NF-kappaB in cancer and the mechanisms involved. Prior studies by our group identified a serine-rich domain in v-Rel that was required for biological activity. Here, we investigated the molecular basis for the transformation defect of specific serine mutants. We show that the transforming efficiency of these mutants in primary lymphoid cells is correlated with their ability to mediate kappaB site-dependent transactivation and with specific changes in phosphorylation profiles. Interestingly, coexpression of the death antagonists Bcl-xL and Bcl-2 significantly increased their oncogenicity, whereas other NF-kappaB-regulated death inhibitors showed little or no effect. The fact that a subset of apoptosis inhibitors could rescue v-Rel transactivation mutants suggests that their reduced transcriptional activity may critically affect expression of defined death antagonists essential for oncogenesis. Consistent with this hypothesis, we observed selection for high endogenous expression of Bcl-2-related death antagonists in cells transformed by weakly transforming v-Rel mutants. These results emphasize the need for Rel/NF-kappaB to efficiently activate expression of a subset of antiapoptotic genes from the Bcl-2 family to manifest its oncogenic phenotype.

Suppression of RelA/p65 nuclear translocation independent of IkappaB-alpha degradation by cyclooxygenase-2 inhibitor in gastric cancer

Selective cyclooxygenase-2 (COX-2) inhibitors are promising anti-inflammatory drugs with potential antitumor activities. The nuclear factor-kappa B (NF-kappaB) family of proteins is important transcriptional regulators of genes involved in immunity, inflammation, and carcinogenesis. In the present study, we investigated whether and by which molecular mechanism the selective COX-2 inhibitors inhibit NF-kappaB activation in gastric cancer. The effects of SC236 and its derivative, but devoid of COX-2 enzyme inhibition activity on NF-kappaB signaling, were evaluated using electromobility shift, transfection, and reporter gene assay. The translocation of RelA/p65 was investigated using Western blotting and immunocytochemistry. We showed that SC236 suppressed NF-kappaB-mediated gene transcription and binding activity in gastric cancer. This effect occurred through a mechanism independent of cyclooxygenase activity and prostaglandin synthesis. Furthermore, unlike aspirin, SC236 affected neither the phosphorylation, degradation, nor expression of IkappaB-alpha, suggesting that the effects of SC236 are independent of IKK activity and IkappaB-alpha gene transcription. Instead, SC236 worked directly through suppressing nuclear translocation of RelA/p65. It is possible that SC236 directly targets proteins that facilitate the nuclear translocation of NF-kappaB. Our study suggests an important molecular mechanism by which COX-2 inhibitors reduce inflammation and suppress carcinogenesis in gastrointestinal tract.

Non-apoptotic Fas signaling

Fas (Apo-1, CD95) and Fas-Ligand (FasL, CD95L) are typical members of the TNF receptor and TNF ligand family, respectively, with a pivotal role in the regulation of apoptotic processes, including activation-induced cell death, T-cell-induced cytotoxicity, immune privilege and tumor surveillance. Impairment of the FasL/Fas system has been implicated in liver failure, autoimmune diseases and immune deficiency. Thus, the FasL/Fas system was mainly appreciated with respect to its death-inducing capabilities. However, there is increasing evidence that activation of Fas can also result in non-apoptotic responses like cell proliferation or NF-kappaB activation. While the apoptotic features of the FasL/Fas system and the pathways involved are comparably well investigated, the pathways that are utilized by Fas to transduce proliferative and activating signals are poorly understood. This review is focused on the non-apoptotic functions of the FasL/Fas system. In particular, the similarities and differences of the molecular mechanisms of apoptotic and non-apoptotic Fas signaling are addressed.

Activation of the transcription factor NF-kappaB in Schwann cells is required for peripheral myelin formation

Peripheral myelin formation is initiated by axonal cues that trigger a differentiation program in associated Schwann cells. Here, we define one essential differentiation signal: activation of the transcription factor NF-kappaB. In rat sciatic nerves, NF-kappaB was highly upregulated in pre-myelinating Schwann cells, and then its expression progressively declined until it was nearly absent in adults. Similarly, in co-cultures of Schwann cells and sensory neurons, NF-kappaB activation paralleled myelination, and blocking its activity or using cells from mice lacking the NF-kappaB subunit p65 markedly attenuated myelination. Inhibiting NF-kappaB also prevented activation of Oct-6, a transcription factor induced by axonal contact and required for proper myelin formation. These results show that the activation of NF-kappaB is an essential signal for the progression of axon-associated Schwann cells into a myelinating phenotype.

Expression of the inhibitor of apoptosis (IAP) family members in human neutrophils: up-regulation of cIAP2 by granulocyte colony-stimulating factor and overexpression of cIAP2 in chronic neutrophilic leukemia

Human neutrophils were found to express members of the inhibitor of apoptosis (IAP) family, namely cellular IAP1 (cIAP1), cIAP2, and X-linked IAP. Among these members, cIAP2 expression was selectively up-regulated by stimulation with granulocyte colony-stimulating factor (G-CSF), but not with granulocyte-macrophage CSF. The increased expression of cIAP2 mRNA was detected as early as 30 minutes after in vitro stimulation with G-CSF, and the elevated level of cIAP2 protein was detected at 1 hour. The elevated level of cIAP2 protein was also detected in peripheral blood neutrophils obtained from healthy donors receiving G-CSF administration. G-CSF-induced up-regulation of cIAP2 mRNA and protein, phosphorylation of signal transducer and activator of transcription 3 (STAT3), and the antiapoptotic effects were inhibited by pretreatment of cells with AG490, a specific inhibitor of Janus kinase 2 (JAK2). Mature neutrophils from a patient with chronic neutrophilic leukemia exhibited remarkable overexpression of cIAP2 mRNA and prolongation of survival, whereas cIAP2 mRNA expression and survival in mature neutrophils from patients with chronic myelogenous leukemia were essentially similar to those in normal neutrophils. These findings suggest that cIAP2 expression is up-regulated by G-CSF through activation of the JAK2-STAT3 pathway, and increased expression of cIAP2 protein may contribute to G-CSF-mediated antiapoptosis. In addition, overexpression of cIAP2 may be partly responsible for sustained neutrophilia at least in some cases of chronic neutrophilic leukemia.

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.

Enhancement of TNF-alpha-mediated cell death in vascular smooth muscle cells through cytochrome c-independent pathway by the proteasome inhibitor

There is substantial evidence that cytokines induce apoptosis of vascular smooth muscle cells (VSMCs) in atherosclerosis. Its regulation, however, is not completely defined. The aim of this study is to investigate whether proteasome activity is related with apoptosis in VSMCs by tumor necrosis factor-alpha (TNF-alpha). Rat aorta smooth muscle cells were treated with TNF-alpha and proteasome inhibitor MG132 and then cell death was determined by morphology, viability, and DNA fragmentation. MG132 or TNF-alpha alone did not induce cell death. In contrast, co-treatment of TNF-alpha and proteasome inhibitor induced death and DNA degradation in VSMCs, suggesting proteasome inhibitor enhanced death activity of TNF-alpha. The death was not blocked by ascorbic acid but by nitric oxide synthase inhibitor N(G)-monomethyl-L-arginine. Both caspase-3 and -8 were activated during the death by the proteasome inhibitor and TNF-alpha. The death was effectively blocked by the caspase-3 inhibitor z-DEVD-fmk, suggesting a role of caspase-3 in the death. Nonetheless, there were no significant alterations in the level of Bcl-2, Bcl-X(L), Bax and Bak by the proteasome inhibitor, nor any evidence of cytochrome (cyt) c release into cytosol from dying cells, suggesting that cyt c is not involved. These results suggest that proteasome inhibition potentiates TNF-mediated death in VSMCs in a cyt c-independent pathway. The present study proposes a new mechanism by which VSMCs undergo death by cytokines.

NF-kappaB is constitutively activated in high-grade squamous intraepithelial lesions and squamous cell carcinomas of the human uterine cervix

We demonstrate, for the first time, that the transcription factor NF-kappaB is constitutively activated during human cervical cancer progression. Immunohistochemical analysis was done using 106 paraffin-embedded cervical tissue specimens of different histological grades. In normal cervical tissue and low-grade squamous intraepithelial lesions, p50, RelA and IkappaB-alpha were mainly localized in the cytosol, whereas in high-grade lesions and squamous cell carcinomas, p50-RelA heterodimers translocated into the nucleus with a concurrent decrease in IkappaB-alpha protein. By Western blot analysis, p50 and RelA were detectable mainly in the cytosolic and nuclear extracts in normal and cancer tissues, respectively, and cytosolic IkappaB-alpha expression was detectable in normal but not in cancer cervical tissues. NF-kappaB DNA-binding activity increased during cervical cancer progression and the binding complex was mainly composed of the p50-RelA heterodimers as revealed by electrophoretic mobility shift assays. Semiquantitative RT-PCR analysis, however, showed increased levels of IkappaB-alpha mRNA in cancer samples presumably because of feedback regulation as a result of enhanced NF-kappaB DNA-binding activity and a consequent functional activation of NF-kappaB. Further immunohistochemical analysis with an antibody to phospho IkappaB-alpha revealed that phosphorylation occurs mainly in squamous intraepithelial lesions, suggesting that the IkappaB-alpha gets phosphorylated initially and degraded as the tumor progressed.

Characterization of p21Ras-mediated apoptosis induced by protein kinase C inhibition and application to human tumor cell lines

Suppression of PKC activity can selectively induce apoptosis in cells expressing a constitutively activated p21Ras protein. We demonstrate that continued expression of p21Ras activity is required in PKC-mediated apoptosis because farnesyltransferase inhibitors abrogated the loss of viability in p21Ras-transformed cells occurring following PKC inhibition. Studies utilizing gene transfer or viral vectors demonstrate that transient expression of oncogenic p21Ras activity is sufficient for induction of apoptosis by PKC inhibition, whereas physiologic activation of p21Ras by growth factor is not sufficient to induce apoptosis. Mechanistically, the p21Ras-mediated apoptosis induced by PKC inhibition is dependent upon mitochondrial dysregulation, with a concurrent loss of mitochondrial membrane potential (psim). Cyclosporine A, which prevented the loss of psim, also inhibited HMG-induced DNA fragmentation in cells expressing an activated p21Ras. Induction of apoptosis by PKC inhibition in human tumors with oncogenic p21Ras mutations was demonstrated. Inhibition of PKC caused increased apoptosis in MIA-PaCa-2, a human pancreatic tumor line containing a mutated Ki-ras allele, when compared to HS766T, a human pancreatic tumor line with normal Ki-ras alleles. Furthermore, PKC inhibition induced apoptosis in HCT116, a human colorectal tumor line containing an oncogenic Ki-ras allele but not in a subline (Hke3) in which the mutated Ki-ras allele had been disrupted. The PKC inhibitor 1-O-hexadecyl-2-O-methyl-rac-glycerol (HMG), significantly reduced p21Ras-mediated tumor growth in vivo in a nude mouse MIA-PaCa-2 xenograft model. Collectively these studies suggest the therapeutic feasibility of targeting PKC activity in tumors expressing an activated p21Ras oncoprotein.

Molecular basis of rifampicin-induced inhibition of anti-CD95-induced apoptosis of peripheral blood T lymphocytes: the role of CD95 ligand and FLIPs

Rifampicin modulates immune response; however, mechanisms by which it exerts these effects are incompletely understood. Recently, rifampicin has been shown to bind to and activate glucocorticoid receptors. Because of the evidence for a role of glucocorticoids in lymphocyte apoptosis, we hypothesized that rifampicin may exert its influence on the immune system by regulating apoptosis. Therefore, we examined the effect of rifampicin on signaling pathway of anti-CD95-induced apoptosis in peripheral blood lymphocytes. Rifampicin, in a concentration-dependent manner, inhibited anti-CD95-induced apoptosis in both CD4+ and CD8+ T cells, which was associated with the inhibition of activation of both caspase-3 and caspase-8. In addition, rifampicin down-regulated the expression of CD95L and Bax. The inhibitory effects of rifampicin on apoptosis and caspase activation as well as its effect on the expression of CD95L and FLIPs were reversed by RU486, an antagonist of glucocorticoid receptor. These data suggest that rifampicin inhibits anti-CD95-mediated apoptosis in lymphocytes by modulating the expression of certain proteins that regulate apoptosis, at least in part, via glucocorticoid receptors.

The adenovirus e3 promoter is sensitive to activation signals in human T cells

The group C adenoviruses typically cause acute respiratory disease in young children. In addition, a persistent phase of infection has been observed in which virus may be shed for years without producing overt pathology. Our laboratory recently reported that group C adenovirus DNA can be found in tonsil and adenoid T lymphocytes from the majority of pediatric donors (C. T. Garnett, D. Erdman, W. Xu, and L. R. Gooding, J. Virol. 76:10608-10616, 2002). This finding suggests that immune evasion strategies of human adenoviruses may be directed, in part, toward protection of persistently or latently infected T lymphocytes. Many of the adenoviral gene products implicated in prevention of immune destruction of virus-infected cells are encoded within the E3 transcription unit. In this study, the E3 promoter was evaluated for sensitivity to T-cell activation signals by using a promoter reporter plasmid. Indeed, this promoter is extremely sensitive to T-cell activation, with phorbol myristate acetate (PMA) plus ionomycin increasing E3-directed transcription 100-fold. By comparison, in the same cells E1A expression leads to a 5.5-fold increase in transcription from the E3 promoter. In contrast to induction by E1A, activation by PMA plus ionomycin requires the two E3 NF-kappaB binding sites. Interestingly, expression of E1A inhibits induction of the E3 promoter in response to T-cell activation while increasing E3 promoter activity in unactivated cells. Collectively, these data suggest that the E3 promoter may have evolved the capacity to respond to T-cell activation in the absence of E1A expression and may act to upregulate antiapoptotic gene expression in order to promote survival of persistently infected T lymphocytes.

Tumor necrosis factor signaling

A single mouse click on the topic tumor necrosis factor (TNF) in PubMed reveals about 50,000 articles providing one or the other information about this pleiotropic cytokine or its relatives. This demonstrates the enormous scientific and clinical interest in elucidating the biology of a molecule (or rather a large family of molecules), which began now almost 30 years ago with the description of a cytokine able to exert antitumoral effects in mouse models. Although our understanding of the multiple functions of TNF in vivo and of the respective underlying mechanisms at a cellular and molecular level has made enormous progress since then, new aspects are steadily uncovered and it appears that still much needs to be learned before we can conclude that we have a full comprehension of TNF biology. This review shortly covers some general aspects of this fascinating molecule and then concentrates on the molecular mechanisms of TNF signal transduction. In particular, the multiple facets of crosstalk between the various signalling pathways engaged by TNF will be addressed.

Chlamydia pneumoniae induces the expression of inhibitor of apoptosis 2 (c-IAP2) in a human monocytic cell line by an NF-kappaB-dependent pathway

Members of the inhibitor of apoptosis protein family are important factors that regulate apoptotic cell death. As demonstrated both by RT-PCR and Western Blot analysis C. pneumoniae infection of the human monocytic cell line Mono Mac 6 induces the expression of mRNA and protein of the cellular inhibitor of apoptosis 2 (c-IAP2). Blocking NF-kappaB DNA-binding activity by the proteasome inhibitor MG-132 results in decrease of C. pneumoniae-induced c-IAP2 expression. Therefore, C. pneumoniae may exploit the NF-kappaB pathway to induce expression of an antiapoptotic host cell protein that may contribute to intracellular survival of the pathogen.

The PAAD/PYRIN-family protein ASC is a dual regulator of a conserved step in nuclear factor kappaB activation pathways

Apoptosis-associated speck-like protein containing a Caspase recruitment domain (ASC) belongs to a large family of proteins that contain a Pyrin, AIM, ASC, and death domain-like (PAAD) domain (also known as PYRIN, DAPIN, Pyk). Recent data have suggested that ASC functions as an adaptor protein linking various PAAD-family proteins to pathways involved in nuclear factor (NF)-kappaB and pro-Caspase-1 activation. We present evidence here that the role of ASC in modulating NF-kappaB activation pathways is much broader than previously suspected, as it can either inhibit or activate NF-kappaB, depending on cellular context. While coexpression of ASC with certain PAAD-family proteins such as Pyrin and Cryopyrin increases NF-kappaB activity, ASC has an inhibitory influence on NF-kappaB activation by various proinflammatory stimuli, including tumor necrosis factor (TNF)alpha, interleukin 1beta, and lipopolysaccharide (LPS). Elevations in ASC protein levels or of the PAAD domain of ASC suppressed activation of IkappaB kinases in cells exposed to pro-inflammatory stimuli. Conversely, reducing endogenous levels of ASC using siRNA enhanced TNF- and LPS-induced degradation of the IKK substrate, IkappaBalpha. Our findings suggest that ASC modulates diverse NF-kappaB induction pathways by acting upon the IKK complex, implying a broad role for this and similar proteins containing PAAD domains in regulation of inflammatory responses.

Reactive oxygen intermediates in TNF signaling

Tumor necrosis factor (TNF) is arguably the most potent inducer of several intracellular signals, including apoptosis, cell differentiation, and gene transcription. It does so through the activation of caspases, specific kinases including mitogen-activated protein kinase (MAPK) and c-Jun N-terminal kinase (JNK), transcription factors Activated protein 1 (AP-1), and nuclear factor kappa-B (NF-kappaB). By activating these signals, TNF mediates pro-apoptotic and pro-survival mechanisms in the cell. It has also been suggested that TNF mediates its intracellular signaling by adjusting the redox potential of the cell, specifically through reactive oxygen intermediates (also known as reactive oxygen species). Here we review the evidence linking ROI to TNF-induced signaling and propose that ROI mediate both pro-apoptotic and pro-survival signals. How these antagonistic signals are balanced to maintain homeostasis is still not clear.

The absence of NF-kappaB-mediated inhibition of c-Jun N-terminal kinase activation contributes to tumor necrosis factor alpha-induced apoptosis

The proinflammatory cytokine tumor necrosis factor alpha (TNF-alpha) regulates immune responses, inflammation, and programmed cell death (apoptosis). TNF-alpha exerts its biological activities by activating multiple signaling pathways, including IkappaB kinase (IKK), c-Jun N-terminal protein kinase (JNK), and caspases. IKK activation inhibits apoptosis through the transcription factor NF-kappaB, whose target genes include those that encode inhibitors of both caspases and JNK. Despite activation of the antiapoptotic IKK/NF-kappaB pathway, TNF-alpha is able to induce apoptosis in cells sensitive to it, such as human breast carcinoma MCF-7 and mouse fibroblast LM cells. The molecular mechanism underlying TNF-alpha-induced apoptosis is incompletely understood. Here we report that in TNF-alpha-sensitive cells activation of the IKK/NF-kappaB pathway fails to block TNF-alpha-induced apoptosis, although its inactivation still promotes TNF-alpha-induced apoptosis. Interestingly, TNF-alpha-induced apoptosis is suppressed by inhibition of the JNK pathway but promoted by its activation. Furthermore, activation of JNK by TNF-alpha was transient in TNF-alpha-insensitive cells but prolonged in sensitive cells. Conversion of JNK activation from prolonged to transient suppressed TNF-alpha-induced apoptosis. Thus, absence of NF-kappaB-mediated inhibition of JNK activation contributes to TNF-alpha-induced apoptosis.

The true face of JNK activation in apoptosis

Age-associated changes in apoptotic rates have been observed in a number of different tissues. While the implications of these findings remain unclear, a better understanding of how apoptosis is regulated may further our understanding of the aging process. The role of the JNK pathway in apoptosis has been highly controversial with studies suggesting that it plays a pro-apoptotic, anti-apoptotic or no role in this process. Here we discuss what is currently known about JNK's role in apoptosis, highlighting recent findings regarding NF-kappaB-mediated inhibition of JNK activation and its impact on TNF-alpha induced apoptosis.

Oxidative modulation of nuclear factor-kappaB in human cells expressing mutant fALS-typical superoxide dismutases

Previous evidence supports the notion of a redox regulation of protein phosphatase calcineurin that might be relevant for neurodegenerative processes where an imbalance between generation and removal of reactive oxygen species occurs. We have recently observed that calcineurin activity is depressed in human neuroblastoma cells expressing Cu,Zn superoxide dismutase (SOD1) mutant G93A and in brain areas from G93A transgenic mice, and that mutant G93A-SOD1 oxidatively inactivates calcineurin in vitro. We have studied the possibility that, by interfering directly with calcineurin activity, mutant SOD1 can modulate pathways of signal transduction mediated by redox-sensitive transcription factors. In this paper, we report a calcineurin-dependent activation of nuclear factor-kappaB (NF-kappaB) induced by the expression of familial amyotrophic lateral sclerosis (fALS)-SOD1s in human neuroblastoma cell lines. Alteration of the phosphorylation state of IkappaBalpha (the inhibitor of NF-kappaB translocation into the nucleus) and induction of cyclooxygenase 2 are consistent with the up-regulation of this transcription factor in this system. All of these modifications might be relevant to signaling pathways involved in the pathogenesis of fALS.

Constitutive nuclear factor-kappaB activity is crucial for human retinoblastoma cell viability

Retinoblastoma (Rb) is the most common intraocular malignancy of childhood. Although systemic and intrathecal chemotherapy with local and cranial radiotherapy have improved overall survival, the prognosis for patients with central nervous system involvement is still poor. We investigated the role of the transcription factor nuclear factor (NF)-kappaB, which promotes cell survival in several other models, in the pathophysiology of Rb. The human Rb cell lines Y79 and WERI-Rb1 were treated with the cell permeable peptide SN50, that specifically inhibits the transcriptional activity of NF-kappaB by blocking its translocation into the nucleus. We found that NF-kappaB inhibition up-regulated Bax; down-regulated the anti-apoptotic proteins Bcl-2, A1, and cIAP-2; and induced loss of the mitochondrial transmembrane potential and caspase-independent, calpain-dependent apoptosis in Rb cells. Inhibition of the p38 kinase sensitized cells to SN50-induced cell death, whereas insulin-like growth factor-1 activated NF-kappaB and attenuated the proapoptotic effect of SN50. Finally, NF-kappaB inhibition sensitized Rb cells to doxorubicin. In conclusion, inhibition of NF-kappaB activity in Rb cells leads to loss of mitochondrial transmembrane potential and caspase-independent, calpain-dependent apoptosis. Therapeutic strategies targeting NF-kappaB could be beneficial in the clinical management of Rb, either alone or in combination with conventional chemotherapy.

NFkappaB and caspase-3 activity in apoptotic hepatocytes of galactosamine-sensitized mice treated with TNFalpha

Tumor necrosis factor-alpha (TNFalpha) induces apoptosis in hepatocytes only under transcriptional arrest induced by galactosamine (GalN). In this study we demonstrated the shuttle of the transcription factor NFkappaB (nuclear factor-kappa B) in the liver tissue of mice within 30 min-4.5 hr hours after GalN/TNFalpha treatment. NFkappaB translocation from cytoplasm to the nucleus is initiated by its separation from the inhibitory IkappaB proteins which include IkappaBalpha, IkappaBbeta, and IkappaB. Thirty minutes after GalN/TNFalpha administration, NFkappaBp65 in hepatocellular nuclei becomes increasingly detectable and reaches its highest level after 2.5 hr. Then export back into cytoplasm begins but, surprisingly, approximately 30% of NFkappaB remains in the nuclear fraction and appears as an immunoprecipitate in the nuclei of apoptotic hepatocytes. Non-apoptotic hepatocytes do not show any reaction product in the nuclei 4.5 hr after treatment. Correspondingly, the amount of dissociated IkappaBbeta decreases in the cytoplasm up to 2.5 hr and increases again afterwards, although it does not reach the level of the control samples. No evidence of IkappaBbeta in the nuclei was found either immunocytochemically or biochemically. Caspase-3 activity, which is responsible for apoptosis, increases significantly after 3.5 hr. At that time, apoptotic hepatocytes can occasionally be observed and, 4.5 hr after GalN/TNFalpha treatment, constitute approximately 30% of the hepatocytes.

Rocaglamide derivatives are potent inhibitors of NF-kappa B activation in T-cells

Crude extracts from different Aglaia species are used as anti-inflammatory remedies in the traditional medicine of several countries from Southeast Asia. Because NF-kappaB transcription factors represent key regulators of genes involved in immune and inflammatory responses, we supposed that the anti-inflammatory effects of Aglaia extracts are mediated by the inhibition of NF-kappaB activity. Purified compounds of Aglaia species, namely 1H-cyclopenta[b]benzofuran lignans of the rocaglamide type as well as one aglain congener were tested for their ability to inhibit NF-kappaB activity. We show that a group of rocaglamides represent highly potent and specific inhibitors of tumor necrosis factor-alpha (TNFalpha) and phorbol 12-myristate 13-acetate (PMA)-induced NF-kappaB-dependent reporter gene activity in Jurkat T cells with IC(50) values in the nanomolar range. Some derivatives are less effective, and others are completely inactive. Rocaglamides are able to suppress the PMA-induced expression of NF-kappaB target genes and sensitize leukemic T cells to apoptosis induced by TNFalpha, cisplatin, and gamma-irradiation. The suppression of NF-kappaB activation correlated with the inhibition of induced IkappaB(alpha) degradation and IkappaB(alpha) kinase activation. The level of interference was determined and found to be localized upstream of the IkappaB kinase complex but downstream of the TNF receptor-associated protein 2. Our data suggest that rocaglamide derivatives could serve as lead structures in the development of anti-inflammatory and tumoricidal drugs.

IKK beta is required for Bcl-2-mediated NF-kappa B activation in ventricular myocytes

The transcription factor nuclear factor kappa B (NF-kappa B) is regulated by cytoplasmic inhibitor I kappa B alpha. An integral step in the activation of NF-kappa B involves the phosphorylation and degradation of I kappa B alpha. We have previously reported that I kappa B alpha activity is diminished in ventricular myocytes expressing Bcl-2 (de Moissac, D., Zheng, H., and Kirshenbaum, L. A. (1999) J. Biol. Chem. 274, 29505-29509). The underlying mechanism by which Bcl-2 activates NF-kappa B is undefined. In view of growing evidence that the I kappa B kinases (IKKs), notably IKK beta, are involved in signal induced phosphorylation of I kappa B alpha, we ascertained whether IKK beta is necessary and sufficient for Bcl-2 mediated NF-kappa B activation. Here we demonstrate that expression of Bcl-2 in ventricular myocytes resulted in an increase in NF-kappa B-dependent DNA binding, NF-kappa B gene transcription and reduced I kappa B alpha levels. An increase in the IKK beta kinase activity was observed in cells expressing full-length Bcl-2 but not in cells expressing the BH4 deletion mutant of Bcl-2 (Delta BH4; residues 10-30). Catalytically inactive mutants of IKK beta, but not IKK alpha, suppressed Bcl-2-mediated I kappa B alpha phosphorylation and NF-kappa B activation. Transfection of human embryonic 293 cells with a kinase-defective Raf-1 or a kinase-defective mitogen-activated protein kinase/extracellular signal-regulated kinase kinase-1 (MEKK-1) suppressed Bcl-2-mediated IKK beta activity and NF-kappa B activation. Further, Bcl-2-mediated NF-kappa B activity was impaired in nullizygous mouse embryonic fibroblasts deficient for IKK beta. In this report, we provide the first direct evidence that Bcl-2 activates NF-kappa B by a signaling mechanism that involves Raf-1/MEKK-1 mediated activation of IKK beta.

Osmotic stress sensitizes naturally resistant cells to TNF-alpha-induced apoptosis

Most cells are naturally resistant to TNF-alpha-induced cell death and become sensitized when NF-kappaB transactivation is blocked or in the presence of protein synthesis inhibitors that prevent the expression of anti-apoptotic genes. In this report we analyzed the role of osmotic stress on TNF-alpha-induced cell death. We found that it sensitizes the naturally resistant HeLa cells to TNF-alpha-induced apoptosis, with the involvement of an increase in the activity of several kinases, the inhibition of Bcl-2 expression, and a late increase on NF-kappaB activation. Cell death occurs regardless of the enhanced NF-kappaB activity, whose inhibition produces an increase in apoptosis. The inhibition of p38 kinase, also involved in NF-kappaB activation, significantly increases the effect of osmotic stress on TNF-alpha-induced cell death.

IL-12 Provides Proliferation and Survival Signals to Murine CD4+T Cells Through Phosphatidylinositol 3-Kinase/Akt Signaling Pathway

IL-12 is a pleiotropic cytokine that plays an important role in innate and adaptive immunity. IL-12 induces T cell proliferation and IFN-gamma secretion from activated T cells. It was also reported that IL-12 prevents apoptosis of CD4(+) T cells. However, the signaling mechanism that regulates these IL-12-induced responses is poorly understood yet. In this study, we demonstrated that IL-12 activates phosphatidylinositol 3-kinase (PI3K)/Akt pathway in murine CD4(+) T cells, and that this signaling pathway is required for IL-12-induced T cell proliferation and antiapoptotic function, but not for IFN-gamma induction. Through PI3K/Akt pathway, IL-12 up-regulates the expression of cell cycle-related molecule such as cyclin D3, and antiapoptotic molecules such as Bcl-2 and cellular inhibitors of apoptosis proteins-2, followed by down-regulation of active caspase-3. These results suggest that PI3K/Akt pathway is critical for mediating IL-12-induced CD4(+) T cell responses such as T cell proliferation and survival.

Tumor escape from killing: role of killer inhibitory receptors and acquisition of tumor resistance to cell death

Immunotherapy of cancer has always been a very attractive fourth-modality therapeutic approach. Over the past few years, advances in the identification of tumor antigens have offered new perspectives and provided new opportunities for more accurate immunotherapy for cancer. However, when applied to patients with established tumors, it rarely leads to an objective response. This is partly due to the fact that tumors evade host immunity at both the induction and effector phases. Thus, understanding tumor escape mechanisms may be the key to successful immunotherapy for cancer. In the present review, we will focus on how the expression of killer Ig receptors (KIR) on tumor infiltrating lymphocytes can compromise their function and how tumors evade apoptotic death - two additional mechanisms of tumor escape.

ATM gene regulates oxygen-glucose deprivation-induced nuclear factor-kappaB DNA-binding activity and downstream apoptotic cascade in mouse cerebrovascular endothelial cells

BACKGROUND AND PURPOSE

Cells lacking the ATM (ataxia telangectasia mutated) gene are hypersensitive to DNA damage caused by a variety of insults. ATM may regulate oxidative stress-induced signaling cascades involving nuclear factor-kappaB (NF-kappaB), a transcription factor that is upstream of a wide variety of stress-responsive genes. We investigated the potential interaction of ATM and NF-kappaB after oxygen-glucose deprivation (OGD) in cerebral endothelial cells (CECs).

METHODS

Primary cultures of mouse CECs were subjected to OGD in the absence or presence of ATM antisense oligonucleotides or the NF-kappaB inhibitor SN50. ATM expression was determined with the use of reverse transcription-polymerase chain reaction and Western blot, and NF-kappaB activity was assessed by electrophoretic mobility shift assay. Cells were assessed for mitochondrial DNA damage with the use of long polymerase chain reaction and were assessed for caspase-3 and caspase-8 activity with the use of fluorogenic substrates. Cell death was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide and LDH release.

RESULTS

OGD stimulated ATM gene expression at the mRNA and protein level in CECs as early as 1 hour after OGD initiation. ATM gene knockdown with the use of an antisense oligonucleotide suppressed OGD-induced ATM protein expression, which was accompanied by an attenuation of NF-kappaB activation and the subsequent expression of downstream genes, including the antiapoptotic gene c-IAP2. ATM knockdown also accentuated OGD-induced mitochondrial DNA damage and the activation of caspase-3 and caspase-8, leading to enhanced CEC death. The specific NF-kappaB inhibitor SN50 mimicked the effects of ATM knockdown.

CONCLUSIONS

We conclude that ATM may play a cytoprotective role in OGD-induced CEC death via a NF-kappaB-dependent signaling pathway.

c-Myc sensitizes cells to tumor necrosis factor-mediated apoptosis by inhibiting nuclear factor kappa B transactivation

Nuclear factor kappaB (NF-kappaB) plays a key role in suppression of tumor necrosis factor (TNF)-mediated apoptosis by inducing a variety of anti-apoptotic genes. Expression of c-Myc has been shown to sensitize cells to TNF-mediated apoptosis by inhibiting NF-kappaB activation. However, the precise step in the NF-kappaB signaling pathway and apoptosis modified by c-Myc has not been identified. Using the inducible c-MycER system and c-Myc null fibroblasts, we found that expression of c-Myc inhibited NF-kappaB activation by interfering with RelA/p65 transactivation but not nuclear translocation of NF-kappaB. Activation of c-Myc promoted TNF-induced release of cytochrome c from mitochondria to the cytosol because of the inhibition of NF-kappaB. Furthermore, we found that NF-kappaB-inducible gene A1 was attenuated by expression of c-Myc and that the restoration of A1 expression suppressed c-Myc-induced TNF sensitization. Our results elucidate the molecular mechanisms by which c-Myc increases cell susceptibility to TNF-mediated apoptosis, indicating that c-Myc may exhibit its pro-apoptotic activities by repression of cell survival genes.

Endogenous membrane tumor necrosis factor (TNF) is a potent amplifier of TNF receptor 1-mediated apoptosis

The heat shock protein 90 (Hsp-90) inhibitor, geldanamycin, and the proteasome inhibitor, MG-132, both inhibited tumor necrosis factor receptor 1 (TNF-R1)- but not TRAIL-induced apoptosis in Kym-1 cells, suggesting that TNF-R1-induced cell death is dependent on NF-kappaB activation in this model. Triggering of TNF-R1 by agonistic antibodies led to cell-type specific induction of endogenous TNF and apoptosis, the latter of which was abrogated by neutralizing TNF specific antibodies. TNF-R1-stimulated cells expressed TNF mainly in a cell-associated form, suggesting that the endogenously produced TNF act in its membrane-bound form. Geldanamycin failed to inhibit apoptosis induction by a combination of agonistic TNF-R1- and TNF-R2-specific antibodies, indicating that both TNF receptors co-operate in TNF-R1-triggered apoptosis in Kym-1 cells. Thus, TNF-R1 stimulation can elicit a strong and rapid apoptotic response via induction of membrane TNF and subsequent cooperation of TNF-R1 and TNF-R2. Moreover, we give evidence that this mechanism circumvents the need of the prolonged presence of exogenous soluble TNF for TNF-R1-mediated apoptosis induction.

Nitrosative stress-induced apoptosis through inhibition of NF-kappa B

Nitrosative stress produced by cytokines predisposes to apoptotic cell death. However, the molecular mechanism by which this occurs is not well understood. We have shown previously that nitric oxide (NO) regulates the activity of the anti-apoptotic transcription factor NF-kappaB. Here we demonstrate that the inhibition of NF-kappaB by NO sensitizes A549 and Jurkat T cells to tumor necrosis factor-alpha (TNFalpha)-induced apoptosis. The molecular basis of NF-kappaB inhibition is different in the two cell types. In A549 cells, NO functions at the nuclear level to inhibit NF-kappaB by S-nitrosylation. In Jurkat cells, NO inhibits the NF-kappaB activating pathway in the cytoplasm at a step proximal to the degradation of IkappaBalpha. The inhibition of NF-kappaB is reflected in the level of intracellular S-nitrosothiols, which are constitutively metabolized. These data suggest that NO can influence cell death by modulating NF-kappaB activity with the sites of inhibition being cell type-specific. The data also show that NO bioactivity regulates tumor necrosis factor-alpha signaling.

Role of TNF-alpha receptors in mice intoxicated with the parkinsonian toxin MPTP

The loss of dopaminergic neurons in Parkinson's disease is associated with a glial reaction and the overproduction of proinflammatory cytokines such as tumor necrosis factor alpha (TNF-alpha). TNF-alpha acts via two different receptors, TNFR1 and TNFR2, and is believed to have both a neuroprotective and a deleterious role for neurons. In order to analyze the putative role of TNF-alpha in parkinsonism, we compared the effect of the parkinsonian drug 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in mice lacking TNFR1, TNFR2, or both receptors and in wild-type littermates. We show that MPTP does not affect spontaneous activity or anxiety in any of the groups and that it reduces motor activity on a rotarod in double knock out mice but not in mice lacking only one receptor. Postmortem analysis revealed no differences in the number of nigral dopaminergic neurons whatever the group. In contrast, striatal dopamine level was slightly decreased in double knock-out mice and more reduced by MPTP in this group than in the other groups of mice. In addition, dopamine turnover was significantly more increased in double knock out mice after MPTP injection. These data suggest that TNF-alpha does not participate in the death of dopaminergic neurons in parkinsonism but that it slightly alters dopamine metabolism or the survival of dopaminergic terminals by a mechanism involving both receptors.

Novel therapies for multiple myeloma

Multiple myeloma (MM) continues to evade cure by conventional therapies, increasing the urgency for new, biologically based treatments. Reviewed in this discussion are novel chemotherapies under clinical trial that capitalize upon greater comprehension of tumor pathophysiology. In targeting tumor biology, these therapies serve as a model of treatment with great potential for improving outcomes in patients with MM.

Regulation of Fas (CD95)-induced apoptosis by nuclear factor-kappaB and tumor necrosis factor-alpha in macrophages

The APO-1/Fas ligand (FasL) and tumor necrosis factor-alpha (TNF-alpha) are two functionally related molecules that induce apoptosis of susceptible cells. Although the two molecules have been reported to induce apoptosis via distinct signaling pathways, we have shown that FasL can also upregulate the expression of TNF-alpha, raising the possibility that TNF-alpha may be involved in FasL-induced apoptosis. Because TNF-alpha gene expression is under the control of nuclear factor-kappaB (NF-kappaB), we investigated whether FasL can induce NF-kappaB activation and whether such activation plays a role in FasL-mediated cell death in macrophages. Gene transfection studies using NF-kappaB-dependent reporter plasmid showed that FasL did activate NF-kappaB promoter activity. Gel shift studies also revealed that FasL mobilized the p50/p65 heterodimeric form of NF-kappaB. Inhibition of NF-kappaB by a specific NF-kappaB inhibitor, caffeic acid phenylethyl ester, or by dominant expression of the NF-kappaB inhibitory subunit IkappaB caused an increase in FasL-induced apoptosis and a reduction in TNF-alpha expression. However, neutralization of TNF-alpha by specific anti-TNF-alpha antibody had no effect on FasL-induced apoptosis. These results indicate that FasL-mediated cell death in macrophages is regulated through NF-kappaB and is independent of TNF-alpha activation, suggesting the antiapoptotic role of NF-kappaB and a separate death signaling pathway mediated by FasL.

Activation of NF-kappaB and upregulation of intracellular anti-apoptotic proteins via the IGF-1/Akt signaling in human multiple myeloma cells: therapeutic implications

Interleukin-6 (IL-6) and insulin-like growth factor-1 (IGF-1) promote the proliferation of multiple myeloma (MM) cells and protect them against dexamethasone (Dex)-induced apoptosis. We have previously shown that Apo2 ligand/TNF-Related apoptosis inducing ligand (Apo2L/TRAIL) induces apoptosis of MM cells, including cells either sensitive or resistant to Dex and cytotoxic drugs, and overcomes the growth and survival effect of IL-6; conversely, NF-kappaB transcriptional activity attenuates their Apo2L/TRAIL-sensitivity. In the current study, we demonstrate that IGF-1 stimulates sustained activation of NF-kappaB and Akt; induces phosphorylation of the FKHRL-1 Forkhead transcription factor; upregulates a series of intracellular anti-apoptotic proteins including FLIP, survivin, cIAP-2, A1/Bfl-1, and XIAP; and decreases Apo2L/TRAIL-sensitivity of MM cells. In contrast, IL-6 does not cause sustained NF-kappaB activation, induces less pronounced Akt activation and FKHRL-1 phosphorylation than IGF-1, and increases the expression of only survivin. Forced overexpression of constitutively active Akt in MM-1S cells reduced their sensitivity to Apo2L/TRAIL and to doxorubicin (Doxo). In contrast, the Akt inhibitor IL-6-Hydroxymethyl-chiro-inositol 2-(R)-2-O-methyl-3-O-octadecylcarbonate induced cell death of both Dex- and Doxo-sensitive and -resistant cells; opposed the protective effect of constitutive Akt activity against Apo2L/TRAIL; and abrogated the NF-kappaB activation, increase of anti-apoptotic proteins and protection against Apo2L/TRAIL induced by IGF-1. These findings therefore define an important role of the Akt pathway in modulating tumor cell responsiveness to Apo2L/TRAIL, delineate molecular mechanisms for the survival effects of IGF-1, and characterize differential pathophysiologic sequelae of IGF-1 vs IL-6 on MM cells. Importantly, they provide the basis for future clinical trials in MM combining conventional or novel agents with strategies designed to neutralize IGF-1.

Biochemical and molecular basis of thimerosal-induced apoptosis in T cells: a major role of mitochondrial pathway

The major source of thimerosal (ethyl mercury thiosalicylate) exposure is childhood vaccines. It is believed that the children are exposed to significant accumulative dosage of thimerosal during the first 2 years of life via immunization. Because of health-related concerns for exposure to mercury, we examined the effects of thimerosal on the biochemical and molecular steps of mitochondrial pathway of apoptosis in Jurkat T cells. Thimerosal and not thiosalcylic acid (non-mercury component of thimerosal), in a concentration-dependent manner, induced apoptosis in T cells as determined by TUNEL and propidium iodide assays, suggesting a role of mercury in T cell apoptosis. Apoptosis was associated with depolarization of mitochondrial membrane, release of cytochrome c and apoptosis inducing factor (AIF) from the mitochondria, and activation of caspase-9 and caspase-3, but not of caspase-8. In addition, thimerosal in a concentration-dependent manner inhibited the expression of XIAP, cIAP-1 but did not influence cIAP-2 expression. Furthermore, thimerosal enhanced intracellular reactive oxygen species and reduced intracellular glutathione (GSH). Finally, exogenous glutathione protected T cells from thimerosal-induced apoptosis by upregulation of XIAP and cIAP1 and by inhibiting activation of both caspase-9 and caspase-3. These data suggest that thimerosal induces apoptosis in T cells via mitochondrial pathway by inducing oxidative stress and depletion of GSH.

Reduced expression of the inhibitor of apoptosis proteins in T cells from patients with multiple sclerosis following interferon-beta therapy

Treatment with interferon-beta reduces clinical exacerbations in multiple sclerosis (MS) through several immunomodulatory mechanisms that involve the augmentation of programmed cell death (apoptosis) of peripheral T lymphocytes. The recently identified family of inhibitor of apoptosis (IAP) proteins is a potent regulator of cell death. The expression of IAP-1, IAP-2, and X-linked IAP (XIAP) is upregulated in mitogen stimulated T lymphocytes from MS patients, and this expression correlates with MS disease activity. In this study, we sought to evaluate the effect of interferon-beta on cellular expression of IAP proteins and other apoptosis regulatory molecules. In a prospective study, we evaluated the expression of IAP proteins, the anti-apoptosis Bcl-2 protein, and the death receptor Fas in in vitro stimulated T lymphocytes from MS patients, before and serially after treatment with interferon-beta. We also investigated the long-term effects of interferon-beta on cellular expression of these proteins and T lymphocyte apoptosis in a cross-sectional study of MS patients receiving drug therapy for a mean of 4.8 years. Treatment with interferon-beta reduced the expression of IAP-1, IAP-2 and XIAP in stimulated T lymphocytes. This reduced expression correlated with increased T cell susceptibility to apoptosis and with clinical response to treatment. In contrast, interferon-beta therapy did not alter cellular expression of Bcl-2 protein or the death receptor Fas. This downregulatory effect of interferon-beta on cellular expression of IAP proteins was maintained following long-term therapy. Our findings suggest that interferon-beta therapy exerts a regulatory effect on peripheral T lymphocytes through an anti-apoptosis mechanism that involves the downregulation of cellular IAP proteins expression.

Regulation of Apo2L/tumor necrosis factor-related apoptosis-inducing ligand-induced apoptosis in thyroid carcinoma cells

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL)/Apo2 ligand selectively kills neoplastic cells, including thyroid carcinoma cells (Mitsiades et al: Thyroid carcinoma cells are resistant to FAS-mediated apoptosis but sensitive to tumor necrosis factor-related apoptosis-inducing ligand. Cancer Res 2000, 60:4122-41299). We investigated the mechanisms regulating Apo2L/TRAIL-induced apoptosis in thyroid carcinoma cells, as well as the impact of insulin-like growth factor (IGF)-1, interferon-gamma, and TNF-alpha. We found that the emergence of resistance to Apo2L/TRAIL, after prolonged incubation with this cytokine, was associated with increased levels of FLICE inhibitory protein (FLIP), and was overcome by cycloheximide and bisindolylmaleimide, that specifically down-regulated FLIP expression, as well as by transfection of a FLIP anti-sense oligonucleotide. IGF-1 activated Akt; up-regulated the caspase inhibitors FLIP, cIAP-2, XIAP, and survivin; and attenuated Apo2L/TRAIL-induced apoptosis. This effect was inhibited by the IGF-1 receptor neutralizing antibody aIR3, the PI-3K inhibitor wortmannin, and the heat shock protein-90 chaperone inhibitor geldanamycin. Transfection of constitutively active Akt protected from TRAIL. Conversely, interferon-gamma and TNF-alpha had a sensitizing effect. We conclude that FLIP may negatively regulate Apo2L/TRAIL-induced apoptosis in thyroid carcinomas. Microenvironmental paracrine survival factors, such as IGF-1, up-regulate caspase inhibitors, including FLIP, and protect from Apo2L/TRAIL in a PI-3K/Akt-dependent manner. T helper-1 cytokines and compounds that selectively abrogate the IGF-1 signaling pathway may be helpful adjunct agents in Apo2L/TRAIL-based anti-cancer therapeutic regimens.

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.

Hepatocyte growth factor inhibits anoikis in head and neck squamous cell carcinoma cells by activation of ERK and Akt signaling independent of NFkappa B

Hepatocyte growth factor (HGF), also known as a scatter factor, regulates a variety of biological activities including cell proliferation, survival, migration, and angiogenesis. Importantly, HGF and its receptor c-Met have been found to be associated with metastasis of human head and neck squamous cell carcinoma (HNSCC). Because anoikis resistance plays an important role in tumor progression and metastasis, here we examined whether HGF suppressed suspension-induced apoptosis (anoikis) in HNSCC cells, and if so, we assessed downstream signaling pathways mediated by HGF. We found that HNSCC cells underwent anoikis upon loss of matrix contact, whereas HGF provided protection against it. HGF-induced anoikis resistance was found to be dependent on both ERK and Akt signaling pathways. The inhibition of either ERK or Akt activation abolished HGF-mediated survival. Furthermore, we found that HGF did not activate NFkappaB transcription in HNSCC cells and that HGF-mediated anoikis resistance was independent of NFkappaB. Taken together, our results suggest that anoikis resistance induced by HGF may also play an important role in the progression and metastasis of HNSCC.

Influence of the nitric oxide donor glyceryl trinitrate on apoptotic pathways in human colon cancer cells

BACKGROUND & AIMS

We have previously reported the role of nitric oxide in colon tumor regression in vivo. The present study was designed to explore the influence of an endogenous nitric oxide donor, glyceryl trinitrate (GTN), on cell death pathways in colon cancer cells.

METHODS

Human colon cancer cell lines were treated with the NO donor GTN. Apoptosis was identified by morphological criteria and the terminal deoxynucleotidyl transferase-mediated deoxyuridine (TUNEL) method. The mitochondrial transmembrane potential was studied by flow cytometry, cytochrome c release by Western blot, and caspase activation by combining fluorogenic peptide substrates, peptide inhibitors, and immunoblotting. Expression of death receptors was studied by flow cytometry and confocal microscopy.

RESULTS

GTN induces a dose- and time-dependent cell death by apoptosis in colon cancer cells. This cell death pathway involves the mitochondria and caspases, mainly caspase-1 and caspase-10. In contrast, caspase-3 activation is a late and limited event. Death receptors are not involved in GTN-mediated cell death, while GTN sensitizes tumor cells to Fas-ligand-induced apoptosis. This permissive effect correlates with an increased expression of Fas receptor and a decreased expression of several endogenous inhibitors of apoptosis (IAPs).

CONCLUSIONS

Our results indicate that GTN (1) activates an unusual caspase cascade to induce apoptosis in colon cancer cells and (2) sensitizes these cells to Fas-mediated cell death by increasing the expression of Fas and decreasing the expression of several IAPs.

Regulation of the gadd45beta promoter by NF-kappaB

In addition to coordinating immune and inflammatory responses, NF-kappaB/Rel transcription factors control cell survival. The NF-kappaB antiapoptotic function is crucial to oncogenesis, cancer chemoresistance, and to antagonize tumor necrosis factor (TNF) receptor-induced killing. Recently, we have shown that the suppression of the c-Jun-N-terminal kinase (JNK) cascade is a pivotal protective mechanism by NF-kappaB, and that this suppression involves the upregulation of gadd45beta/myd118. Induction of gadd45beta by stress and cytokines requires NF-kappaB; however, the regulatory mechanisms underlying this induction are not known. Here, we report that, in HeLa cells, the NF-kappaB subunit RelA is sufficient to activate gadd45beta expression, whereas Rel and p50 are not. Activation of gadd45beta by RelA depends on three kappaB elements at positions -447/-438 (kappaB-1), -426/-417 (kappaB-2), and -377/-368 (kappaB-3) of the gadd45beta promoter. Each of these sites binds to NF-kappaB complexes in vitro, and is required for optimal promoter transactivation. The data establish the direct participation of NF-kappaB in the regulation of Gadd45beta, thereby providing important mechanistic insights into the control of apoptosis by the transcription factor.

Apoptotic crosstalk of TNF receptors: TNF-R2-induces depletion of TRAF2 and IAP proteins and accelerates TNF-R1-dependent activation of caspase-8

We have recently shown that stimulation of TNF-R2 selectively enhances apoptosis induction by the death receptor TNF-R1. Here, we demonstrate that stimulation of CD30 or CD40 also leads to selective enhancement of TNF-R1-induced cell death. Enhancement of apoptosis was correlated with the depletion of endogenous TRAF2 within 1 to 6 hours. Selective prestimulation of TNF-R2 for several hours inhibited TNF-R2-induced activation of the anti-apoptotic NF-κB pathway up to 90% and dramatically enhanced apoptosis induction by this receptor. When both TNF-receptors were stimulated simultaneously, TNF-R1-induced NF-κB activation remained unaffected but TNF-R1-induced apoptosis was still significantly enhanced. Compared with FasL-induced cell death TNF-R1-induced activation of caspase-8 was significantly weaker and delayed. Costimulation or prestimulation of TNF-R2 enhanced caspase-8 processing. Life cell imaging and confocal microscopy revealed that both TNF-R1 and TNF-R2 recruited the anti-apoptotic factor cIAP1 in a TRAF2-dependent manner. Thus, TNF-R2 may compete with TNF-R1 for the recruitment of newly synthesized TRAF2-bound anti-apoptotic factors, thereby promoting the formation of a caspase-8-activating TNF-R1 complex. Hence,TNF-R2 triggering can interfere with TNF-R1-induced apoptosis by inhibition of NF-κB-dependent production of anti-apoptotic factors and by blocking the action of anti-apoptotic factors at the post-transcriptional level.

A small molecule ubiquitination inhibitor blocks NF-kappa B-dependent cytokine expression in cells and rats

A small molecule inhibitor of NF-kappaB-dependent cytokine expression was discovered that blocked tumor necrosis factor (TNF) alpha-induced IkappaB(alpha) degradation in MM6 cells but not the degradation of beta-catenin in Jurkat cells. Ro106-9920 blocked lipopolysaccharide (LPS)-dependent expression of TNFalpha, interleukin-1beta, and interleukin-6 in fresh human peripheral blood mononuclear cells with IC(50) values below 1 microm. Ro106-9920 also blocked TNFalpha production in a dose-dependent manner following oral administration in two acute models of inflammation (air pouch and LPS challenge). Ro106-9920 was observed to inhibit an ubiquitination activity that does not require betaTRCP but associates with IkappaB(alpha) and will ubiquitinate IkappaB(alpha) S32E,S36E (IkappaB(alpha)(ee)) specifically at lysine 21 or 22. Ro106-9920 was identified in a cell-free system as a time-dependent inhibitor of IkappaB(alpha)(ee) ubiquitination with an IC(50) value of 2.3 +/- 0.09 microm. The ubiquitin E3 ligase activity is inhibited by cysteine-alkylating reagents, supported by E2UBCH7, and requires cIAP2 or a cIAP2-associated protein for activity. These activities are inconsistent with what has been reported for SCF(betaTRCP), the putative E3 for IkappaB(alpha) ubiquitination. Ro106-9920 was observed to be selective for IkappaB(alpha)(ee) ubiquitination over the ubiquitin-activating enzyme (E1), E2UBCH7, nonspecific ubiquitination of cellular proteins, and 97 other molecular targets. We propose that Ro106-9920 selectively inhibits an uncharacterized but essential ubiquitination activity associated with LPS- and TNFalpha-induced IkappaB(alpha) degradation and NF-kappaB activation.

An inducible pathway for degradation of FLIP protein sensitizes tumor cells to TRAIL-induced apoptosis

TRAIL (Apo2 ligand) is a member of the tumor necrosis factor (TNF) family of cytokines that induces apoptosis. Because TRAIL preferentially kills tumor cells, sparing normal tissues, interest has emerged in applying this biological factor for cancer therapy in humans. However, not all tumors respond to TRAIL, raising questions about resistance mechanisms. We demonstrate here that a variety of natural and synthetic ligands of peroxisome proliferator-activated receptor-gamma (PPAR gamma) sensitize tumor but not normal cells to apoptosis induction by TRAIL. PPAR gamma ligands selectively reduce levels of FLIP, an apoptosis-suppressing protein that blocks early events in TRAIL/TNF family death receptor signaling. Both PPAR gamma agonists and antagonists displayed these effects, regardless of the levels of PPAR gamma expression and even in the presence of a PPAR gamma dominant-negative mutant, indicating a PPAR gamma-independent mechanism. Reductions in FLIP and sensitization to TRAIL-induced apoptosis were also not correlated with NF-kappa B, further suggesting a novel mechanism. PPAR gamma modulators induced ubiquitination and proteasome-dependent degradation of FLIP, without concomitant reductions in FLIP mRNA. The findings suggest the existence of a pharmacologically regulated novel target of this class of drugs that controls FLIP protein turnover, and raise the possibility of combining PPAR gamma modulators with TRAIL for more efficacious elimination of tumor cells through apoptosis.

Apoptotic signaling induced by immunomodulatory thalidomide analogs in human multiple myeloma cells: therapeutic implications

Thalidomide (Thal) achieves responses even in the setting of refractory multiple myeloma (MM). Although increased angiogenesis in MM bone marrow and the antiangiogenic effect of Thal formed the empiric basis for its use in MM, we have shown that Thal and its immunomodulatory analogs (IMiDs) directly induce apoptosis or growth arrest of MM cells, alter adhesion of MM cells to bone marrow stromal cells, inhibit the production of cytokines (interleukin-6 and vascular endothelial growth factor) in bone marrow, and stimulate natural killer cell anti-MM immunity. In the present study, we demonstrate that the IMiDs trigger activation of caspase-8, enhance MM cell sensitivity to Fas-induced apoptosis, and down-regulate nuclear factor (NF)-kappa B activity as well as expression of cellular inhibitor of apoptosis protein-2 and FLICE inhibitory protein. IMiDs also block the stimulatory effect of insulinlike growth factor-1 on NF-kappa B activity and potentiate the activity of TNF-related apoptosis-inducing ligand (TRAIL/Apo2L), dexamethasone, and proteasome inhibitor (PS-341) therapy. These studies both delineate the mechanism of action of IMiDs against MM cells in vitro and form the basis for clinical trials of these agents, alone and coupled with conventional and other novel therapies, to improve outcome in MM.