Antiapoptotic function of NF-kappaB in T lymphocytes is influenced by their differentiation status: roles of Fas, c-FLIP, and Bcl-xL

NF-κB and Extrinsic Cell Death Pathways - Entwined Do-or-Die Decisions for T cells

NF-κB signaling is required at multiple stages of T cell development and function. The NF-κB pathway integrates signals from many receptors and involves diverse adapters and kinases. Recent advances demonstrate that kinases controlling NF-κB activation, such as the IKK complex, serve dual independent functions because they also control cell death checkpoints. Survival functions previously attributed to NF-κB are in fact mediated by these upstream kinases by novel mechanisms. This new understanding has led to a refined view of how NF-κB and cell death signaling are interlinked and how they regulate cell fate. We discuss how NF-κB activation and control of cell death signaling by common upstream triggers cooperate to regulate different aspects of T cell development and function.

LncRNAs as Chromatin Regulators in Cancer: From Molecular Function to Clinical Potential

During the last decade, high-throughput sequencing efforts in the fields of transcriptomics and epigenomics have shed light on the noncoding part of the transcriptome and its potential role in human disease. Regulatory noncoding RNAs are broadly divided into short and long noncoding transcripts. The latter, also known as lncRNAs, are defined as transcripts longer than 200 nucleotides with low or no protein-coding potential. LncRNAs form a diverse group of transcripts that regulate vital cellular functions through interactions with proteins, chromatin, and even RNA itself. Notably, an important regulatory aspect of these RNA species is their association with the epigenetic machinery and the recruitment of its regulatory apparatus to specific loci, resulting in DNA methylation and/or post-translational modifications of histones. Such epigenetic modifications play a pivotal role in maintaining the active or inactive transcriptional state of chromatin and are crucial regulators of normal cellular development and tissue-specific gene expression. Evidently, aberrant expression of lncRNAs that interact with epigenetic modifiers can cause severe epigenetic disruption and is thus is closely associated with altered gene function, cellular dysregulation, and malignant transformation. Here, we survey the latest breakthroughs concerning the role of lncRNAs interacting with the epigenetic machinery in various forms of cancer.

LMP2 immunoproteasome promotes lymphocyte survival by degrading apoptotic BH3-only proteins

The role of the immunoproteasome is perceived as confined to adaptive immune responses given its ability to produce peptides ideal for MHC Class-I binding. Here, we demonstrate that the immunoproteasome subunit, LMP2, has functions beyond its immunomodulatory role. Using LMP2-deficient mice, we demonstrate that LMP2 is crucial for lymphocyte development and survival in the periphery. Moreover, LMP2-deficient lymphocytes show impaired degradation of key BH3-only proteins, resulting in elevated levels of pro-apoptotic BIM and increased cell death. Interestingly, LMP2 is the sole immunoproteasome subunit required for BIM degradation. Together, our results suggest LMP2 has important housekeeping functions and represents a viable therapeutic target for cancer.

Novel Noncompetitive IL-1 Receptor-Biased Ligand Prevents Infection- and Inflammation-Induced Preterm Birth

Preterm birth (PTB) is firmly linked to inflammation regardless of the presence of infection. Proinflammatory cytokines, including IL-1β, are produced in gestational tissues and can locally upregulate uterine activation proteins. Premature activation of the uterus by inflammation may lead to PTB, and IL-1 has been identified as a key inducer of this condition. However, all currently available IL-1 inhibitors are large molecules that exhibit competitive antagonism properties by inhibiting all IL-1R signaling, including transcription factor NF-κB, which conveys important physiological roles. We hereby demonstrate the efficacy of a small noncompetitive (all-d peptide) IL-1R-biased ligand, termed rytvela (labeled 101.10) in delaying IL-1β-, TLR2-, and TLR4-induced PTB in mice. The 101.10 acts without significant inhibition of NF-κB, and instead selectively inhibits IL-1R downstream stress-associated protein kinases/transcription factor c-jun and Rho GTPase/Rho-associated coiled-coil-containing protein kinase signaling pathways. The 101.10 is effective at decreasing proinflammatory and/or prolabor genes in myometrium tissue and circulating leukocytes in all PTB models independently of NF-κB, undermining NF-κB role in preterm labor. In this work, biased signaling modulation of IL-1R by 101.10 uncovers a novel strategy to prevent PTB without inhibiting NF-κB.

T cell-NF-κB activation is required for tumor control in vivo

BACKGROUND

T cells have the capacity to eliminate tumors but the signaling pathways by which they do so are incompletely understood. T cell priming requires activation of the transcription factors AP-1, NFAT and NF-κB downstream of the TCR, but whether activation of T cell-NF-κB in vivo is required for tumor control has not been addressed. In humans and mice with progressively growing tumors, the activity of T cell-intrinsic NF-κB is often reduced. However, it is not clear if this is causal for an inability to reject transformed cells, or if it is a consequence of tumor growth. T cell-NF-κB is important for T cell survival and effector differentiation and plays an important role in enabling T cells to reject cardiac and islet allografts, suggesting the possibility that it may also be required for tumor elimination. In this study, we tested whether normal T cell-NF-κB activation is necessary for the rejection of tumors whose growth is normally controlled by the immune system.

METHODS

Mice with genetically impaired T cell-NF-κB activity were subcutaneously injected with MC57-SIY tumor cells. Tumor growth was measured over time, and the anti-tumor immune response was evaluated using flow cytometry and cytokine detection assays.

RESULTS

Mice with impaired T cell-NF-κB activity were unable to reject tumors that were otherwise eliminated by wildtype mice, despite equal accumulation of tumor-reactive T cells. In addition, specific impairment of NF-κB signaling downstream of the TCR was sufficient to prevent tumor rejection. Tumor antigen-specific T cell-IFN-γ and TNF-α production, as well as cytotoxic ability, were all reduced in mice with impaired T cell-NF-κB, suggesting an important role for this transcription factor in the effector differentiation of tumor-specific effector T cells.

CONCLUSIONS

Our results have identified the NF-κB pathway as an important signaling axis in T cells, required for the elimination of growing tumors in vivo. Maintaining or enhancing T cell-NF-κB activity may be a promising avenue for anti-tumor immunotherapy.

Basal NF-κB controls IL-7 responsiveness of quiescent naïve T cells

T cells are essential for immune defenses against pathogens, such that viability of naïve T cells before antigen encounter is critical to preserve a polyclonal repertoire and prevent immunodeficiencies. The viability of naïve T cells before antigen recognition is ensured by IL-7, which drives expression of the prosurvival factor Bcl-2. Quiescent naïve T cells have low basal activity of the transcription factor NF-κB, which was assumed to have no functional consequences. In contrast to this postulate, our data show that basal nuclear NF-κB activity plays an important role in the transcription of IL-7 receptor α-subunit (CD127), enabling responsiveness of naïve T cells to the prosurvival effects of IL-7 and allowing T-cell persistence in vivo. Moreover, we show that this property of basal NF-κB activity is shared by mouse and human naïve T cells. Thus, NF-κB drives a distinct transcriptional program in T cells before antigen encounter by controlling susceptibility to IL-7. Our results reveal an evolutionarily conserved role of NF-κB in T cells before antigenic stimulation and identify a novel molecular pathway that controls T-cell homeostasis.

Gene-expression differences in peripheral blood between lithium responders and non-responders in the Lithium Treatment-Moderate dose Use Study (LiTMUS)

This study was designed to identify genes whose expression in peripheral blood may serve as early markers for treatment response to lithium (Li) in patients with bipolar disorder. Although changes in peripheral blood gene-expression may not relate directly to mood symptoms, differences in treatment response at the biochemical level may underlie some of the heterogeneity in clinical response to Li. Subjects were randomized to treatment with (n=28) or without (n=32) Li. Peripheral blood gene-expression was measured before and 1 month after treatment initiation, and treatment response was assessed after 6 months. In subjects treated with Li, 62 genes were differentially regulated in treatment responders and non-responders. Of these, BCL2L1 showed the greatest difference between Li responders and non-responders. These changes were specific to Li responders (n=9), and were not seen in Li non-responders or patients treated without Li, suggesting that they may have specific roles in treatment response to Li.

The JNk/NFkappaB pathway is required to activate murine lymphocytes induced by a sulfated polysaccharide from Ecklonia cava

BACKGROUND

The proven immunomodulatory and immune system activating properties of Ecklonia cava (E. cava) have been attributed to its plentiful polysaccharide content. Therefore, we investigated whether the sulfated polysaccharide (SP) of E. cava specifically activates the protein kinases (MAPKs) and nuclear factor-kappaB (NFkappaB) to incite immune responses.

METHODS

To assess immune responsiveness, lymphocytes were isolated from spleens of ICR mice and cultured with SP and its inhibitors. Assays included 3H-thymidine incorporation, flow cytometry, real time polymerase chain reaction (rtPCR), enzyme linked immunosorbent assay (ELISA), intracellular cytokine assay. Western blot, and electrophoretic mobility shift assay (EMSA).

RESULTS

SP dose-dependently increased the proliferation of lymphocytes without cytotoxicity. In particular, SP markedly enhanced the proliferation and differentiation of CD3+ mature T cells and CD45R/B220+ pan B cells. Additionally, SP increased the expression and/or production of IL-2, IgG(1a), and IgG(2b) compared to that in untreated cells. The subsequent application of JNK (SP600125), NFkappaB (PDTC), and serine protease (TPCK) inhibitors significantly inhibited the proliferation and IL-2 production of SP-treated lymphocytes as well as the phosphorylation of JNK and IkappaB, the activation of nuclear NFkappaB p65, and binding of NFkappaB p65 DNA. Moreover, co-application of both JNK and NFkappaB inhibitors completely blocked the proliferation of lymphocytes even in the presence of SP.

CONCLUSION

These results suggest that SP induced T and B cell responses via both JNK and NFkappaB pathways.

GENERAL SIGNIFICANCE

The effect of SP on splenic lymphocyte activation was assayed here for the first time and indicated the underlying functional mechanism.

Role of T-cell-specific nuclear factor κB in islet allograft rejection

BACKGROUND

Pancreatic islet transplantation has the potential to cure type 1 diabetes, a chronic lifelong disease, but its clinical applicability is limited by allograft rejection. Nuclear factor κB (NF-κB) is a transcription factor important for survival and differentiation of T cells. In this study, we tested whether NF-κB in T cells is required for the rejection of islet allografts.

METHODS

Mice expressing a superrepressor form of NF-κB selectively in T cells (IκBαΔN-Tg mice) with or without the antiapoptotic factor Bcl-xL, or mice with impaired T-cell receptor (TCR)- and B cell receptor-driven NF-κB activity (CARMA1-KO mice) were rendered diabetic and transplanted with islet allografts. Secondary skin transplantation in long-term acceptors of islet allografts was used to test for the development of donor-specific tolerance. Immune infiltration of the transplanted islets was examined by immunofluorescence. TCR-transgenic CD4 T cells were used to follow T-cell priming and differentiation.

RESULTS

Islet allograft survival was prolonged in IκBαΔN-Tg mice, although the animals did not develop donor-specific tolerance. Reduced NF-κB activity did not prevent T-cell priming or differentiation but reduced survival of activated T cells, as transgenic expression of Bcl-xL restored islet allograft rejection in IκBαΔN-Tg mice. Abolishing TCR- and B cell receptor-driven activation of NF-κB selectively by CARMA1 deficiency prevented T-cell priming and islet allograft rejection.

CONCLUSIONS

Our data suggest that T cell-NF-κB plays an important role in the rejection of islet allografts. Targeting NF-κB selectively in lymphocytes seems a promising approach to facilitate acceptance of transplanted islets.

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

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

Transcriptional activation of microRNA-34a by NF-kappa B in human esophageal cancer cells

Background

miR-34a functions as an important tumor suppressor during the process of carcinogenesis. However, the mechanism of miR-34a dysregulation in human malignancies has not been well elucidated. Our study aimed to further investigate the regulation mechanism of miR-34a.

Results

We found that overexpression of NF-kappa B p65 subunit could increase miR-34a levels in EC109, an esophageal squamous cancer cell line, while ectopic expression of DN IkappaB leaded to a significant reduction of miR-34a expression. Bioinformatics analysis suggested three putative KB sites in promoter region of miR-34a gene. Mutation two of these KB sites impaired p65 induced miR-34a transcriptional activity. Chromatin immunoprecipitation and electrophoretic mobility shift assays both showed that NF-kappaB could specifically bind to the third KB site located in miR-34a promoter. In addition, we found that overexpression of NF-kappaB p65 could not successfully induce miR-34a expression in esophageal cancer cell lines with mutant p53 or decreased p53. Reporter assay further showed that NF-kappaB-induced miR-34a transcriptional activity was reduced by p53 impairment. Nevertheless, CHIP analysis suggested binding of NF-kappaB to miR-34a promoter was not affected in cells with mutant p53.

Conclusions

Our work indicates a novel mechanism of miR-34a regulation that NF-kappaB could elevate miR-34a expression levels through directly binding to its promoter. And wildtype p53 is responsible for NF-kappaB-mediated miR-34a transcriptional activity but not for NF-kappaB binding. These findings might be helpful in understanding miR-34a abnormality in human malignancies and open new perspectives for the roles of miR-34a and NF-kappaB in tumor progression.

Enzymatic extract from Ecklonia cava induces the activation of lymphocytes by IL-2 production through the classical NF-κB pathway

Activated nuclear factor-kappa B (NF-κB), a well-known transcription factor, leads to the development, differentiation, and proliferation of T and B lymphocytes and the secretion of cytokines by the classical pathway. We have examined here whether an enzymatic extract (ECK) from the brown seaweed, Alariaceae Laminariales Ecklonia cava may contribute to activating lymphocytes through the NF-κB pathway for participation in immune responses. In our study, ECK dose-dependently enhanced the proliferation of lymphocytes. ECK significantly increased the phosphorylation of inhibitors of κB at 0.25 and 0.5 h of exposure, followed by its gradual decrease. In addition, NF-κB p65 was gradually activated, and its binding to nuclear deoxyribonucleic acid was observed from 0.25 h after stimulation (up to 0.5 h). Further experiments showed that the application of N-p-tosyl-L: -phenylalanine chloromethyl ketone, an NF-κB inhibitor, significantly blocked ECK-induced lymphocyte's proliferation and the interleukin (IL)-2 productions. Accordingly, our results suggest that ECK increases the production of IL-2 through the activation of NF-κB then induces the proliferation of lymphocytes with the coordinated stimulation of IL-2.

Inhibition of NF-κB induces a switch from CD95L-dependent to CD95L-independent and JNK-mediated apoptosis in T cells

NF-κB is a crucial transcription factor regulating apoptosis sensitivity and resistance. It has been shown that inhibition of NF-κB in T lymphocytes leads to sensitization towards apoptosis. The underlying molecular mechanism is not entirely understood. Therefore, we investigated T cell receptor (TCR) stimulated apoptosis in T cells in which NF-κB activity is blocked by an inhibitor or IκBα overexpression. We show that enhanced apoptosis upon TCR stimulation is caspase- and JNK-dependent, but independent of the CD95/CD95L system. Generation of reactive oxygen species (ROS) induced sustained JNK phosphorylation by inactivation of MAP kinase phosphatase 7 (MKP7). Sustained JNK activation causes upregulation of the pro-apototic protein BIM. Thus, inhibition of NF-κB causes a switch from classical activation-induced cell death (AICD) to CD95L-independent apoptosis.

The significance of OX40 and OX40L to T-cell biology and immune disease

SUMMARY

OX40 (CD134) and its binding partner, OX40L (CD252), are members of the tumor necrosis factor receptor/tumor necrosis factor superfamily and are expressed on activated CD4(+) and CD8(+) T cells as well as on a number of other lymphoid and non-lymphoid cells. Costimulatory signals from OX40 to a conventional T cell promote division and survival, augmenting the clonal expansion of effector and memory populations as they are being generated to antigen. OX40 additionally suppresses the differentiation and activity of T-regulatory cells, further amplifying this process. OX40 and OX40L also regulate cytokine production from T cells, antigen-presenting cells, natural killer cells, and natural killer T cells, and modulate cytokine receptor signaling. In line with these important modulatory functions, OX40-OX40L interactions have been found to play a central role in the development of multiple inflammatory and autoimmune diseases, making them attractive candidates for intervention in the clinic. Conversely, stimulating OX40 has shown it to be a candidate for therapeutic immunization strategies for cancer and infectious disease. This review provides a broad overview of the biology of OX40 including the intracellular signals from OX40 that impact many aspects of immune function and have promoted OX40 as one of the most prominent costimulatory molecules known to control T cells.

Fas mediates cardiac allograft acceptance in mice with impaired T-cell-intrinsic NF-kappaB signaling

The transcription factor NF-kappaB is critical for T-cell activation and survival. We have shown that mice expressing a T-cell-restricted NF-kappaB superrepressor (IkappaBalphaDeltaN-Tg) permanently accept heart but not skin allografts. Overexpression of the prosurvival factor Bcl-x(L) in T cells restored heart rejection, suggesting that graft acceptance in IkappaBalphaDeltaN-Tg mice was attributable to deletion of alloreactive T cells.In vitro, the increased death of IkappaBalphaDeltaN-Tg T cells upon TCR stimulation when compared with wildtype T cells was mostly because of Fas/FasL interaction. Similarly, Fas played a key role in cardiac allograft acceptance by IkappaBalphaDeltaN-Tg mice as both genetic and antibody-mediated inhibition of Fas-signaling restored cardiac allograft rejection. Rejection correlated with graft infiltration by T cells and splenic production of IFN-gamma upon allostimulation. These results indicate that T-cell inhibition of NF-kappaB results in cardiac allograft acceptance because of increased susceptibility to Fas-mediated cell death.

Apigenin, a dietary flavonoid, sensitizes human T cells for activation-induced cell death by inhibiting PKB/Akt and NF-kappaB activation pathway

Resistance of T cells to activation-induced cell death (AICD) is associated with autoimmunity and lymphoproliferation. We found that apigenin (4',5,7-trihydroxyflavone), a non-mutagenic dietary flavonoid, augmented both extrinsic and intrinsic pathways of apoptosis in recurrently activated, but not in primarily stimulated, human blood CD4+ T cells. Apigenin potentiated AICD by inhibiting NF-kappaB activation and suppressing NF-kappaB-regulated anti-apoptotic molecules, cFLIP, Bcl-x(L), Mcl-1, XIAP and IAP, but not Bcl-2. Apigenin suppressed NF-kappaB translocation to nucleus and inhibited IkappaBalpha phosphorylation and degradation in response to TCR stimulation in reactivated peripheral blood CD4 T cells, as well as in leukemic Jurkat T cell lines. Among the pathways that lead to NF-kappaB activation upon TCR stimulation, apigenin selectively inhibited PI3K-PKB/Akt, but not PKC-theta activation in the human T cells, and synergized with a PI3K inhibitor to markedly augment AICD. Apigenin also suppressed expression of anti-apoptotic cyclooxygenase 2 (COX-2) protein in activated human T cells, but it did not affect activation of Erk MAPKinase. Thus, in chronically activated human T cells, relatively non-toxic apigenin can suppress anti-apoptotic pathways involving NF-kappaB activation, and especially cFLIP and COX-2 expression that are important for functioning and maintenance of immune cells in inflammation, autoimmunity and lymphoproliferation.

Activation of NF-kappaB1 by OX40 contributes to antigen-driven T cell expansion and survival

The costimulatory molecule OX40 (CD134) is required in many instances for effective T cell-mediated immunity, controlling proliferation, and survival of T cells after encountering specific Ag. We previously found that the functional targets of OX40 are survivin and aurora B that regulate proliferation and Bcl-2 antiapoptotic family members that regulate survival. However, the intracellular pathways from OX40 that mediate these effects are unclear. In this study, we show that OX40 signaling can target the canonical NF-kappaB (NF-kappaB1) pathway in peripheral Ag-responding CD4 T cells. Phosphorylation of IkappaBalpha, nuclear translocation of NF-kappaB1/p50 and RelA, and NF-kappaB1 activity, are impaired in OX40-deficient T cells. Retroviral transduction of active IkappaB kinase that constitutively activates NF-kappaB1 rescues the poor expansion and survival of OX40-deficient T cells, directly correlating with increased expression and activity of survivin, aurora B, and Bcl-2 family members. Moreover, active IkappaB kinase expression alone is sufficient to restore the defective expansion and survival of OX40-deficient T cells in vivo when responding to Ag. Thus, OX40 signals regulate T cell number and viability through the NF-kappaB1 pathway that controls expression and activity of intracellular targets for proliferation and survival.

Up-regulation of c-FLIP short by NFAT contributes to apoptosis resistance of short-term activated T cells

Upon encounter with pathogens, T cells activate several defense mechanisms, one of which is the up-regulation of CD95 ligand (CD95L/FasL) which induces apoptosis in sensitive target cells. Despite expression of the CD95 receptor, however, recently activated T cells are resistant to CD95L, presumably due to an increased expression of antiapoptotic molecules. We show here that, in contrast to naive or long-term activated T cells, short-term activated T cells strongly up-regulate the caspase-8 inhibitor, cellular FLICE-inhibitory protein (c-FLIP). Intriguingly, upon activation, T cells highly induced the short splice variant c-FLIP(short), whereas expression of c-FLIP(long) was only marginally modulated. In contrast to the general view that c-FLIP transcription is controlled predominantly by nuclear factor-kappaB (NF-kappaB), induction of c-FLIP(short) in T cells was primarily mediated by the calcineurin-nuclear factor of activated T cells (NFAT) pathway. Importantly, blockage of NFAT-mediated c-FLIP expression by RNA interference or inhibition of calcineurin rendered T cells sensitive toward CD95L, as well as activation-induced apoptosis. Thus, the resistance of recently activated T cells depends crucially on induction of c-FLIP expression by the calcineurin/NFAT pathway. Our findings imply that preventing autocrine CD95L signaling by c-FLIP facilitates T-cell effector function and an efficient immune response.

CD4+ and CD8+ T cell survival is regulated differentially by protein kinase Ctheta, c-Rel, and protein kinase B

An effective immune response requires the expansion and survival of a large number of activated T cells. This study compared the role of protein kinase C (PKC)theta and associated signaling molecules in the survival of activated primary CD4+ vs CD8+ murine T cells. We demonstrate that the absence of PKCtheta resulted in a moderate survival defect in CD4+ T cells and a striking survival defect of CD8+ T lymphocytes. CD8+ T cells lacking the c-Rel, but not the NF-kappaB1/p50, member of the NF-kappaB family of transcription factors displayed a similar impairment in cell survival as PKCtheta(-/-) CD8(+) T lymphocytes. This implicates c-Rel as a key target of PKCtheta-mediated survival signals in CD8+ T cells. In addition, both c-Rel(-/-) and PKCtheta(-/-) T cells also displayed impaired expression of the antiapoptotic Bcl-x(L) protein upon activation. Changes in Bcl-x(L) expression, however, did not correlate with the survival of CD4+ or CD8+ lymphocytes. The addition of protein kinase B-mediated survival signals could restore partially CD4+ T cell viability, but did not dramatically influence CD8+ survival. Active protein kinase B was also unable to restore proliferative responses in CD8+ PKCtheta(-/-) T cells. The survival of CD4+ and CD8+ T cells deficient in either PKCtheta or c-Rel, however, was promoted by the addition of IL-2. Collectively, these data demonstrate that CD4+ and CD8+ T cell survival signals are differentially programmed.

Unravelling the complexities of the NF-κB signalling pathway using mouse knockout and transgenic models

The nuclear factor-kappaB (NF-kappaB) signalling pathway serves a crucial role in regulating the transcriptional responses of physiological processes that include cell division, cell survival, differentiation, immunity and inflammation. Here we outline studies using mouse models in which the core components of the NF-kappaB pathway, namely the IkappaB kinase subunits (IKKalpha, IKKbeta and NEMO), the IkappaB proteins (IkappaBalpha, IkappaBbeta, IkappaBvarepsilon and Bcl-3) and the five NF-kappaB transcription factors (NF-kappaB1, NF-kappaB2, c-Rel, RelA and RelB), have been genetically manipulated using transgenic and knockout technology.

Differential sensitivity of naïve and memory subsets of human CD8+ T cells to TNF-alpha-induced apoptosis

In this investigation, we have examined the relative sensitivity of human naïve, central memory (T(CM)), and two types of effector memory CD8+ T cells (T(EM) and T(EMRA)) to TNF-alpha-induced apoptosis. Our data show that naïve and T(CM) CD8+ T cells were sensitive, whereas T(EM) and T(EMRA) CD8+ T cells were relatively resistant to TNF-alpha-induced apoptosis. The apoptosis profile correlated with the activation of caspase-8 and caspase-3. However, no correlation was observed between relative sensitivity of four CD8+ T cell subsets to apoptosis and the expression of TNFR-I or TNFR-II. T(EM) and T(EMRA) CD8+ T cells displayed increased phosphorylation of IKKalpha/beta and IkappaB and increased NF-kappaB activity as compared to naïve and T(CM) CD8+ T cells. Bcl-2, Bcl-x(L) and FLIP(L) expression was higher and Bax expression was lower in T(EM) and T(EMRA) CD8+ T cells as compared to naïve and T(CM) CD8+ T cells. These data suggest that signaling molecules downstream of TNFRs may be responsible for differential sensitivity among subsets of CD8+ T cells to TNF-alpha-induced apoptosis.

A role for STAT5A/B in protection of peripheral T-lymphocytes from postactivation apoptosis: Insights from gene expression profiling

Activation of the transcription factors STAT5A and STAT5B by JAK1 and JAK3 tyrosine kinases is a key event in downstream signaling of gammac (common gamma chain)-family cytokine receptors in lymphoid cells. STAT5A/B-deficiency in mice causes, among other consequences, a reduced size and altered composition of the peripheral T-cell pool with predominance of an activated or memory-like population (CD4(+)/CD44(high)/CD62L(low)) and a proliferative deficiency following antigenic stimulation and subsequent IL-2 treatment. To further elucidate the critical function of STAT5A/B in homeostasis and activation of murine naïve peripheral T-lymphocytes, we have analyzed global gene expression of STAT5A/B-deficient versus wild-type splenic T-cells by profiling with high-density oligonucleotide arrays (Affymetrix). Comparison of (1) basal gene expression of untreated peripheral STAT5A/B-deficient and control T-cells and (2) immediate early gene induction upon in vitro stimulation of either population with IL-2 has revealed differential expression of a broad range of genes potentially contributing to the defects of STAT5A/B deficient T-cells. In the context of enhanced apoptotic rates of STAT5A/B(-/-)-T-cells in vivo and upon TCR-stimulation in culture our data suggest a role for STAT5 in post-activation survival beyond regulation of antiapoptotic Bcl-2 proteins and hence provide new insights into the nature of the late proliferative block in the T-cell compartment caused by STAT5-deficiency.

Pyridine N-oxide derivatives inhibit viral transactivation by interfering with NF-κB binding

Pyridine N-oxide derivatives represent a new class of anti-HIV compounds for which some members exclusively inhibit HIV-1 RT, whereas other members act, additionally or alternatively, at a post-integrational event in the replicative cycle of HIV. A prototype pyridine N-oxide derivative, JPL-32, inhibited tumor necrosis factor alpha (TNF-alpha)-induced HIV-1 expression in latently HIV-1-infected OM-10.1 and U1 cells, which could be reversed by the addition of N-acetyl-L-cysteine (NAC). The reversal of the antiviral activity of JPL-32 by NAC suggested the possible role of a redox-sensitive factor as target of inhibition. Indeed, when nuclear extracts of TNF-alpha-stimulated OM-10.1 and U1 cells cultured in the presence of JPL-32 were analyzed by an electrophoretic mobility shift assay (EMSA), a dose-dependent inhibition of DNA binding of nuclear NF-kappaB was observed, which could be reversed by the addition of NAC. JPL-32 did not inhibit the release and subsequent degradation of IkappaBalpha, nor did JPL-32 affect the nuclear translocation of NF-kappaB. EMSA revealed that the inhibition of the NF-kappaB DNA binding activity by JPL-32 could be reversed by the addition of reducing agents such as dithiothreitol or beta-mercaptoethanol. Moreover, JPL-32 was able to directly oxidize the thiol groups on the purified p50 subunit of recombinant NF-kappaB. The oxidative modification of the thiol groups on NF-kappaB by JPL-32 could be ascribed to the intracellular pro-oxidant effect of JPL-32. Consequently, JPL-32 was able to increase the intracellular glutathione (GSH) levels and to induce apoptosis in a dose-dependent way.

NF-kappaB-dependent regulation of the timing of activation-induced cell death of T lymphocytes

One of the mechanisms by which activated T cells die is activation-induced cell death (AICD). This pathway requires persistent stimulation via the TCR and engagement of death receptors. We found that TCR stimulation led to transient nuclear accumulation of the NF-kappaB component p65/RelA. In contrast, nuclear c-Rel levels remained high even after extended periods of activation. Loss of nuclear p65/RelA correlated with the onset of AICD, suggesting that p65/RelA target genes may maintain cell viability. Quantitative RNA analyses showed that three of several putative NF-kappaB-dependent antiapoptotic genes were expressed with kinetics that paralleled nuclear expression of p65/RelA. Of these three, ectopic expression only of Gadd45beta protected significantly against AICD, whereas IEX-1 and Bcl-x(L) were much less effective. We propose that the timing of AICD, and thus the length of the effector phase, are regulated by transient expression of a subset of p65/RelA-dependent antiapoptotic genes.

Enhancement of sensitivity to tumor necrosis factor alpha in non-small cell lung cancer cells with acquired resistance to gefitinib

Tumor cells that have acquired resistance to gefitinib through continuous drug administration may complicate future treatment. To investigate the mechanisms of acquired resistance, we established PC-9/ZD2001, a non-small-cell lung cancer cell line resistant to gefitinib, by continuous exposure of the parental cell line PC-9 to gefitinib. After 6 months of culture in gefitinib-free conditions, PC-9/ZD2001 cells reacquired sensitivity to gefitinib and were established as a revertant cell line, PC-9/ZD2001R. PC-9/ZD2001 cells showed collateral sensitivity to several anticancer drugs (vinorelbine, paclitaxel, camptothecin, and 5-fluorouracil) and to tumor necrosis factor alpha (TNF-alpha). Compared with PC-9 cells, PC-9/ZD2001 cells were 67-fold more sensitive to TNF-alpha and PC-9/ZD2001R cells were 1.3-fold more sensitive. Therefore, collateral sensitivity to TNF-alpha was correlated with gefitinib resistance. PC-9/ZD2001 cells expressed a lower level of epidermal growth factor receptor (EGFR) than did PC-9 cells; this down-regulation was partially reversed in PC-9/ZD2001R cells. TNF-alpha-induced autophosphorylation of EGFR (cross-talk signaling) was detected in all three cell lines. However, TNF-alpha-induced Akt phosphorylation and IkappaB degradation were observed much less often in PC-9/ZD2001 cells than in PC-9 cells or PC-9/ZD2001R cells. Expression of the inhibitor of apoptosis proteins c-IAP1 and c-IAP2 was induced by TNF-alpha in PC-9 and PC-9/ZD2001R cells but not in PC-9/ZD2001 cells. This weak effect of EGFR on Akt pathway might contribute to the TNF-alpha sensitivity of PC-9/ZD2001 cells. These results suggest that therapy with TNF-alpha would be effective in some cases of non-small-cell lung cancer that have acquired resistance to gefitinib.

RelA regulates the survival of activated effector CD8 T cells

Nuclear factor of kappa B (NF-kappaB) transcription factors are critical regulators of T-cell activation and survival. The relative contribution of individual NF-kappaB members to these processes remains elusive. We investigated the role of RelA in the regulation of CD8 T-cell activation. We overexpressed, in mature CD8 T cells, a transactivation domain-deficient RelA molecule (p65TAD). We show that p65TAD forms homo- and heterodimers with p50 that bind kappaB sites and selectively inhibit RelA-dependent transactivation. Expression of p65TAD does not affect initial activation or cell cycle progression but induces the death of activated CD8 T cells in vitro and in vivo. However, the long-term survival of resting effector CD8 T cells seems not to be affected by p65TAD expression. Collectively, our results indicate that RelA is a critical regulator of survival of proliferating CD8 T cells but may be dispensable for the survival of resting effector T cells.

NF-kappaB couples protein kinase B/Akt signaling to distinct survival pathways and the regulation of lymphocyte homeostasis in vivo

Protein kinase B (PKBalpha/Akt1) a PI3K-dependent serine-threonine kinase, promotes T cell viability in response to many stimuli and regulates homeostasis and autoimmune disease in vivo. To dissect the mechanisms by which PKB inhibits apoptosis, we have examined the pathways downstream of PKB that promote survival after cytokine withdrawal vs Fas-mediated death. Our studies show that PKB-mediated survival after cytokine withdrawal is independent of protein synthesis and the induction of NF-kappaB. In contrast, PKB requires de novo gene transcription by NF-kappaB to block apoptosis triggered by the Fas death receptor. Using gene-deficient and transgenic mouse models, we establish that NF-kappaB1, and not c-Rel, is the critical signaling molecule downstream of the PI3K-PTEN-PKB signaling axis that regulates lymphocyte homeostasis.

Caspase-8 activity prevents type 2 cytokine responses and is required for protective T cell-mediated immunity against Trypanosoma cruzi infection

During Trypanosoma cruzi infection, T cells up-regulate caspase-8 activity. To assess the role of caspase-8 in T cell-mediated immunity, we investigated the effects of caspase-8 inhibition on T cells in viral FLIP (v-FLIP) transgenic mice. Compared with wild-type controls, increased parasitemia was observed in v-FLIP mice infected with T. cruzi. There was a profound decrease in expansion of both CD4 and CD8 T cell subsets in the spleens of infected v-FLIP mice. We did not find differences in activation ratios of T cells from transgenic or wild-type infected mice. However, the numbers of memory/activated CD4 and CD8 T cells were markedly reduced in v-FLIP mice, possibly due to defective survival. We also found decreased production of IL-2 and increased secretion of type 2 cytokines, IL-4 and IL-10, which could enhance susceptibility to infection. Similar, but less pronounced, alterations were observed in mice treated with the caspase-8 inhibitor, zIETD. Furthermore, blockade of caspase-8 by zIETD in vitro mimicked the effects observed on T. cruzi infection in vivo, affecting the generation of activated/memory T cells and T cell cytokine production. Caspase-8 is also required for NF-kappaB signaling upon T cell activation. Blockade of caspase-8 by either v-FLIP expression or treatment with zIETD peptide decreased NF-kappaB responses to TCR:CD3 engagement in T cell cultures. These results suggest a critical role for caspase-8 in the establishment of T cell memory, cell signaling, and regulation of cytokine responses during protozoan infection.

Prevention of NF-kappaB activation in vivo by a cell-permeable NF-kappaB inhibitor peptide

The NF-kappaB/Rel transcription factor family plays a central role in coordinating the expression of a variety of genes that regulate stress responses, immune cell activation, apoptosis, proliferation, differentiation, and oncogenic transformation. Interventions that target the NF-kappaB pathway may be therapeutic for a variety of pathologies, especially immune/inflammatory diseases. Using membrane translocating sequence (MTS) technology, we developed a cell-permeable dominant inhibitor of NF-kappaB activation, termed IkappaBalpha-(DeltaN)-MTS. This molecule contains a 12-amino acid MTS motif attached to the COOH-terminal region of a nondegradable inhibitor protein [IkappaBalpha-(DeltaN)]. The recombinant protein enters cells and localizes in the cytoplasm. Delivery of the IkappaBalpha-(DeltaN)-MTS to cell lines and primary cells inhibited nuclear translocation of NF-kappaB proteins induced by cell activation. The protein also effectively inhibited NF-kappaB activation in vivo in two different animal models: NF-kappaB activation in response to skin wounding in mice and NF-kappaB activation in lungs after endotoxin treatment in sheep. Inhibition of NF-kappaB by the IkappaBalpha-(DeltaN)-MTS in the endotoxin model attenuated physiological responses to endotoxemia. These data demonstrate that activation of NF-kappaB can be inhibited using a recombinant protein designed to penetrate into cells. This technology may provide a new approach to NF-kappaB pathway-targeted therapies.

Peripheral survival of naïve CD8+ T cells

Maintenance of a sufficient population of naive CD8+ T cells in the peripheral lymphoid compartment is critical for immunocompetence. Peripheral T cell number is a function of T cell generation, survival, and death. Homeostasis, a critical balance between survival and death, must exist to prevent either lymphopenia or lymphocytosis. In the current review, we discuss known requirements for the survival of naive peripheral CD8+ T cells as well as mechanisms of death when survival signals are lost. We also discuss associations between survival and homeostasis-driven proliferation, and highlight the gaps in our knowledge of these critical processes.

Transplantation Tolerance in NF-κB-Impaired Mice Is Not Due to Regulation but Is Prevented by Transgenic Expression of Bcl-xL

NF-kappaB is a key regulator of transcription after TCR and costimulatory receptor ligation. To determine the role of T cell-intrinsic NF-kappaB activation in acute allograft rejection, we used IkappaBalphaDeltaN-Tg mice (H-2b) that express an inhibitor of NF-kappaB restricted to the T cell compartment. We have previously shown that these mice permanently accept fully allogeneic (H-2d) cardiac grafts and secondary donor skin grafts, and that splenocytes from these tolerant mice have reduced alloreactivity when restimulated in vitro. These results were compatible with either deletion or suppression of allospecific T cells as possible mechanisms of tolerance. The aim of this study was to investigate the mechanism of transplant tolerance in these mice. IkappaBalphaDeltaN-Tg mice did not have increased numbers or function of CD4+ CD25+ regulatory T cells either before or after cardiac transplantation. In addition, tolerance could not be transferred to fresh NF-kappaB-competent T cells and was not permissive for linked suppression to skin grafts sharing donor and third-party alloantigens, suggesting that dominant suppression is not the mechanism by which IkappaBalphaDeltaN-Tg mice achieve tolerance. In contrast, overexpression of the antiapoptotic protein Bcl-xL in T cells from IkappaBalphaDeltaN-Tg mice resulted in effective rejection of cardiac allografts and correlated with an increased frequency of splenocytes producing IFN-gamma in response to alloantigen. Together, these results suggest that the death of alloreactive T cells may be partly responsible for the transplantation tolerance observed in mice with defective T cell-intrinsic NF-kappaB activation.

Role of NF-κB signaling pathway in increased tumor necrosis factor-α-induced apoptosis of lymphocytes in aged humans

In human aging, lymphocytes display increased sensitivity to tumor necrosis factor-alpha (TNF-alpha)-induced apoptosis. TNF-alpha induces both survival and apoptotic signals. The survival signal is mediated by the activation of NF-kappaB. Although a role of certain proapoptotic molecules in aging has been reported, a role of altered NF-kappaB signaling pathway has not been explored in detail. In this study, we have compared TNF-alpha-induced activation of NF-kappaB, phosphorylation of IkappaBalpha, and the expression of IKKbeta between lymphocytes from young and aged humans. Furthermore, we have explored a role of IKKbeta in increased susceptibility of lymphocytes from aged humans to TNF-alpha-induced apoptosis. Lymphocytes from aged humans displayed decreased activation of NF-kappaB, reduced phosphorylation of IkappaBalpha, and decreased expression of IKKbeta. In addition, overexpression of IKKbeta in lymphocytes from aged humans normalized TNF-alpha-induced apoptosis to the level of young subjects. These data suggest a deficiency of NF-kappaB signaling pathway and a role of IKKbeta, at least in part, for increased sensitivity of lymphocytes from aged humans to TNF-alpha-induced apoptosis.

Involvement of p53, nuclear factor kappaB and Fas/Fas ligand in induction of apoptosis and cell cycle arrest by saikosaponin d in human hepatoma cell lines

In this study, we report the proapoptotic effect of saikosaponin d in two liver cancer cell lines, Hep G2 and Hep 3B cells. Treatment with saikosaponin d decreased the cell proliferation of Hep G2 and Hep 3B cells in a dose dependent manner. In Hep G2, saikosaponin d blocked the progression of cell cycle at G1 phase by inducing p53 expression and further up-regulating p21/WAF1 expression. In addition, an enhancement in Fas/APO-1 and its two form ligands, membrane-bound Fas ligand (mFasL) and soluble Fas ligand (sFasL), as well as Bax protein, was responsible for the apoptotic effect induced by saikosaponin d. Furthermore, saikosaponin d also inhibited the cell survival signaling by enhancing the amount of IkappaBalpha in cytoplasm and reducing the level and activity of NF-kappaB in the nucleus, and subsequently attenuated the expression of Bcl-XL in Hep G2 and Hep 3B cells. Saikosaponin d therefore decreased the cell proliferation and inducted apoptosis both in p53-positive Hep G2 and p53-negative Hep 3B cells.

Serine protease inhibitor 2A is a protective factor for memory T cell development

An essential event in the development of memory CD8(+) T lymphocytes is the escape of progenitors from programmed cell death, but how this is mediated is unclear. Here we report that the gene encoding serine protease inhibitor 2A (Spi2A), an inhibitor of lysosomal executioner proteases dependent on transcription factor NF-kappaB, is upregulated in memory cell precursors. Spi2A upregulation protected lymphocytic choriomeningitis virus-specific memory progenitors from programmed cell death. Thus, Spi2A promotes the survival of cytotoxic T lymphocytes, allowing them to differentiate into memory CD8 T cells. These findings suggest a model in which commitment to the memory lineage is facilitated by the upregulation of protective genes.