NF-kappa B2 p100 is a pro-apoptotic protein with anti-oncogenic function

Pirin Inhibits FAS-Mediated Apoptosis to Support Colorectal Cancer Survival

Resistance to immunotherapy in colorectal cancer (CRC) is associated with obstruction of FAS (Apo-1 or CD95)-dependent apoptosis, a hallmark of cancer. Here it is demonstrated that the upregulation of pirin (PIR) protein in colon cancers promotes tumorigenesis. Knockout or inhibition of PIR dramatically increases FAS expression, FAS-dependent apoptosis and attenuates colorectal tumor formation in mice. Specifically, NFκB2 is a direct transcriptional activator of FAS and robustly suppressed by PIR in dual mechanisms. One is the disruption of NFκB2 complex (p52-RELB) association with FAS promoter, the other is the inhibition of NIK-mediated NFκB2 activation and nuclear translocation, leading to the inability of active NFκB2 complex toward the transcription of FAS. Furthermore, PIR interacts with FAS and recruits it in cytosol, preventing its membrane translocation and assembling. Importantly, knockdown or knockout of PIR dramatically sensitizes cells to FAS mAb- or active CD8+ T cells-triggered cell death. Taken together, a PIR-NIK-NFκB2-FAS survival pathway is established, which plays a key role in supporting CRC survival.

p52 signaling promotes cellular senescence

Background

Nuclear factor-κB is a multi-subunit transcription factor that plays a central role in cellular senescence. We previously reported that an increase in the p52 subunit is seen in senescent cells and aged tissue. In the current work, we examined the mechanism by which p52 is activated and whether the increase in p52 promotes senescence.

Results

Using both primary mouse embryonic fibroblasts (MEFs) and WI-38 human lung fibroblasts, we examined cells after serial passage and following prolonged culture. An increase in p52 was found in the nucleus relative to pre-senescent cells. The increase in p52 protein was not reflected by an increase in NFKB2 mRNA or by an increase in the abundance of upstream activating kinases, IKKα and NIK. To examine whether p52 promotes senescence, we over-expressed mature p52 in primary MEFs. Significantly more senescence was seen compared to control, a finding not seen with p52 mutated at critical DNA binding residues. In addition, blocking p52 nuclear translocation with the peptide inhibitor, SN52, decreased β-galactosidase (β-gal) formation. Subsequent filtration studies demonstrated that proteins in conditioned media (CM) were necessary for the increase in p52 and mass spectrometry identified S100A4 and cyclophilin A (CYPA) as potential factors in CM necessary for induction of p52. The requirement of these proteins in CM for induction of p52 was confirmed using depletion and supplementation studies. In addition, we found that activation of STAT3 signaling was required for the increase in p52. Finally, genome wide ChIP-sequencing analysis confirmed that there is an increase in p52 chromatin enrichment with senescence and identified several downstream factors whose expression is regulated by increased p52 binding.

Conclusions

These results demonstrate that p52 nuclear translocation is increased in senescent cells by factors in conditioned media and that mature p52 induces cellular senescence. The data are consistent with the prior observation that p52 is elevated in aged tissue and support the hypothesis that p52 contributes to organismal aging.

Supplementary information

The online version contains supplementary material available at 10.1186/s13578-022-00779-6.

Inflammatory bowel disease-associated Escherichia coli strain LF82 in the damage of gut and cognition of honeybees

Patients with inflammatory bowel disease (IBD) are often accompanied with some cognitive impairment, but the mechanism is unclear. By orally exposing honeybees (Apis mellifera) to IBD-associated Escherichia coli LF82 (LF82), and non-pathogenic Escherichia coli MG1655 (MG1655) as the normal strain, we investigated whether and how LF82 induces enteritis-like manifestations and cognitive behavioral modifications in honeybees using multiparametric analysis. LF82 significantly increased gut permeability, impaired learning and memory ability in olfactory proboscis extension response conditioning, and shortened the lifespan of honeybees. Compared to MG1655, LF82 reduced the levels of tryptophan metabolism pathway substances in the honeybee gut. LF82 also upregulated genes involved in immune and apoptosis-related pathways and downregulated genes involved in G protein-coupled receptors in the honeybee brain. In conclusion, LF82 can induce enteritis-like manifestations and cognition impairment through gut metabolites and brain transcriptome alteration in honeybees. Honeybees can serve as a novel potential model to study the microbiota-gut-brain interaction in IBD condition.

From Anti-EBV Immune Responses to the EBV Diseasome via Cross-reactivity

Sequence analyses highlight a massive peptide sharing between immunoreactive Epstein-Barr virus (EBV) epitopes and human proteins that—when mutated, deficient or improperly functioning—associate with tumorigenesis, diabetes, lupus, multiple sclerosis, rheumatoid arthritis, and immunodeficiencies, among others. Peptide commonality appears to be the molecular platform capable of linking EBV infection to the vast EBV-associated diseasome via cross-reactivity and questions the hypothesis of the “negative selection” of self-reactive lymphocytes. Of utmost importance, this study warns that using entire antigens in anti-EBV immunotherapies can associate with autoimmune manifestations and further supports the concept of peptide uniqueness for designing safe and effective anti-EBV immunotherapies.

NFκB2 p52 stabilizes rhogdiβ mRNA by inhibiting AUF1 protein degradation via a miR-145/Sp1/USP8-dependent axis

Although overexpression of the non-canonical NFκB subunit p52 has been observed in several tumors, the function and mechanism of p52 in bladder cancer (BC) are less well understood. Here, we aimed at understanding the role and mechanism underlying p52 regulation of BC invasion. Human p52 was stably knockdown with shRNA targeting p52 in two bladder cancer cell lines (T24 and UMUC3). Two constitutively expressing constructs, p52 and p100, were stably transfected in to T24 or UMUC3, respectively. The stable transfectants were used to determine function and mechanisms responsible for p52 regulation of BC invasion. We demonstrate that p52 mediates human BC invasion. Knockdown of p52 impaired bladder cancer invasion by reduction of rhogdiβ mRNA stability and expression. Positively regulation of rhogdiβ mRNA stability was mediated by p52 promoting AUF1 protein degradation, consequently resulting in reduction of AUF1 binding to rhogdiβ mRNA. Further studies indicated that AUF1 protein degradation was mediated by upregulating USP8 transcription, which was modulated by its negative regulatory transcription factor Sp1. Moreover, we found that p52 upregulated miR-145, which directly bound to the 3'-UTR of sp1 mRNA, leading to downregulation of Sp1 protein translation. Our results reveal a comprehensive pathway that p52 acts as a positive regulator of BC invasion by initiating a novel miR-145/Sp1/USP8/AUF1/RhoGDIβ axis. These findings provide insight into the understanding of p52 in the pathology of human BC invasion and progression, which may be useful information in the development of preventive and therapeutic approaches for using p52 as a potential target.

Roles of NF-κB Signaling in the Regulation of miRNAs Impacting on Inflammation in Cancer

The NF-κB family of transcription factors regulate the expression of genes encoding proteins and microRNAs (miRNA, miR) precursors that may either positively or negatively regulate a variety of biological processes such as cell cycle progression, cell survival, and cell differentiation. The NF-κB-miRNA transcriptional regulatory network has been implicated in the regulation of proinflammatory, immune, and stress-like responses. Gene regulation by miRNAs has emerged as an additional epigenetic mechanism at the post-transcriptional level. The expression of miRNAs can be regulated by specific transcription factors (TFs), including the NF-κB TF family, and vice versa. The interplay between TFs and miRNAs creates positive or negative feedback loops and also regulatory networks, which can control cell fate. In the current review, we discuss the impact of NF-κB-miRNA interplay and feedback loops and networks impacting on inflammation in cancer. We provide several paradigms of specific NF-κB-miRNA networks that can regulate inflammation linked to cancer. For example, the NF-κB-miR-146 and NF-κB-miR-155 networks fine-tune the activity, intensity, and duration of inflammation, while the NF-κB-miR-21 and NF-κB-miR-181b-1 amplifying loops link inflammation to cancer; and p53- or NF-κB-regulated miRNAs interconnect these pathways and may shift the balance to cancer development or tumor suppression. The availability of genomic data may be useful to verify and find novel interactions, and provide a catalogue of 162 miRNAs targeting and 40 miRNAs possibly regulated by NF-κB. We propose that studying active TF-miRNA transcriptional regulatory networks such as NF-κB-miRNA networks in specific cancer types can contribute to our further understanding of the regulatory interplay between inflammation and cancer, and also perhaps lead to the development of pharmacologically novel therapeutic approaches to combat cancer.

CD147 regulates extrinsic apoptosis in spermatocytes by modulating NFκB signaling pathways

CD147 null mutant male mice are infertile with arrested spermatogenesis and increased apoptotic germ cells. Our previous studies have shown that CD147 prevents apoptosis in mouse spermatocytes but not spermatogonia. However, the underlying mechanism remains elusive. In the present study, we aim to determine the CD147-regulated apoptotic pathway in mouse spermatocytes. Our results showed that immunodepletion of CD147 triggered apoptosis through extrinsic apoptotic pathway in mouse testis and spermatocyte cell line (GC-2 cells), accompanied by activation of non-canonical NFκB signaling and suppression of canonical NFκB signaling. Furthermore, CD147 was found to interact with TRAF2, a factor known to regulate NFκB and extrinsic apoptotic signaling, and interfering CD147 led to the decrease of TRAF2. Consistently, depletion of CD147 by CRISPR/Cas9 technique in GC-2 cells down-regulated TRAF2 and resulted in cell death with suppressed canonical NFκB and activated non-canonical NFκB signaling. On the contrary, interfering of CD147 had no effect on NFκB signaling pathways as well as TRAF2 protein level in mouse spermatogonia cell line (GC-1 cells). Taken together, these results suggested that CD147 plays a key role in reducing extrinsic apoptosis in spermatocytes, but not spermatogonia, through modulating NFκB signaling pathway.

NF-κB functions as a molecular link between tumor cells and Th1/Tc1 T cells in the tumor microenvironment to exert radiation-mediated tumor suppression

Radiation modulates both tumor cells and immune cells in the tumor microenvironment to exert its anti-tumor activity; however, the molecular connection between tumor cells and immune cells that mediates radiation-exerted tumor suppression activity in the tumor microenvironment is largely unknown. We report here that radiation induces rapid activation of the p65/p50 and p50/p50 NF-κB complexes in human soft tissue sarcoma (STS) cells. Radiation-activated p65/p50 and p50/p50 bind to the TNFα promoter to activate its transcription in STS cells. Radiation-induced TNFα induces tumor cell death in an autocrine manner. A sublethal dose of Smac mimetic BV6 induces cIAP1 and cIAP2 degradation to increase tumor cell sensitivity to radiation-induced cell death in vitro and to enhance radiation-mediated suppression of STS xenografts in vivo. Inhibition of caspases, RIP1, or RIP3 blocks radiation/TNFα-induced cell death, whereas inhibition of RIP1 blocks TNFα-induced caspase activation, suggesting that caspases and RIP1 act sequentially to mediate the non-compensatory cell death pathways. Furthermore, we determined in a syngeneic sarcoma mouse model that radiation up-regulates IRF3, IFNβ, and the T cell chemokines CCL2 and CCL5 in the tumor microenvironment, which are associated with activation and increased infiltration of Th1/Tc1 T cells in the tumor microenvironment. Moreover, tumor-infiltrating T cells are in their active form since both the perforin and FasL pathways are activated in irradiated tumor tissues. Consequently, combined BV6 and radiation completely suppressed tumor growth in vivo. Therefore, radiation-induced NF-κB functions as a molecular link between tumor cells and immune cells in the tumor microenvironment for radiation-mediated tumor suppression.

Inhibition of PHLPP2/cyclin D1 protein translation contributes to the tumor suppressive effect of NFκB2 (p100)

Although the precursor protein of NFκB2 (p100) is thought to act as a tumor suppressor in mammalian cells, the molecular mechanism of its anti-tumor activity is far from clear. Here, we are, for the first time, to report that p100 protein expression was dramatically decreased in bladder cancers of N-butyl-N-(4-hydroxybutyl)-nitrosamine (BBN)-treated mice and human patients. Knockdown of p100 in cultured human bladder cancer cells promoted anchorage-independent growth accompanied with elevating abundance of cell-cycle-related proteins and accelerated cell-cycle progression. Above effects could be completely reversed by ectopically expression of p100, but not p52. Mechanistically, p100 inhibited Cyclin D1 protein translation by activating the transcription of LARP7 and its hosted miR-302d, which could directly bind to 3'-UTR of cyclin d1 mRNA and inhibited its protein translation. Furthermore, p100 suppressed the expression of PHLPP2 (PH domain and leucine-rich repeat protein phosphatases 2), thus promoting CREB phosphorylation at Ser133 and subsequently leading to miR-302d transcription. Taken together, our studies not only for the first time establish p100 as a key tumor suppressor of bladder cancer growth, but also identify a novel molecular cascade of PHLPP2/CREB/miR-302d that mediates the tumor suppressive function of p100.

Uncaria tomentosa (Willd. ex Schult.) DC (Rubiaceae) Sensitizes THP-1 Cells to Radiation-induced Cell Death

Background:

Uncaria tomentosa (Willd. ex Schult.) DC (Rubiaceae), known as Cat's Claw or Uña de gato, is a traditionally used medicinal plant native to Peru. Some studies have shown that U. tomentosa can act as an antiapoptotic agent and enhance DNA repair in chemotherapy-treated cells although others have shown that U. tomentosa enhanced apoptosis.

Objective:

To determine if treatment with U. tomentosa can significantly enhance cell death in THP-1 cells exposed to ionizing radiation.

Materials and Methods:

THP-1 monocyte-like cells were treated with ethanolic extracts of U. tomentosa in the presence or absence of bacterial lipopolysaccharide and then exposed to ionizing radiation. Cell proliferation was assessed by MTT and clonogenic assays and the effects on cell cycle measured by flow cytometry and immunoblotting. Changes in cell signaling were determined by immunoblotting and cytokine ELISA and activation of apoptosis measured by caspase activation and DNA fragmentation analysis.

Results:

Treatment of THP-1 cells with U. tomentosa had a small effect on cell proliferation. However, when the U. tomentosa-pretreated cells were also subjected to 5–9 Gy ionizing radiation, they showed a significant decrease in cell proliferation and increased cellular apoptosis as measured by DNA fragmentation and caspase activation. Treatment with U. tomentosa also decreased the expression of Cyclin E and Cyclin B, key regulators of normal cell cycle progression, and decreased the phosphorylation of various stress-activated, cell survival proteins including p38, ERK, and SAP/JNK kinase.

Conclusions:

These results suggest that U. tomentosa could be useful in enhancing cell death following anticancer therapies including ionizing radiation.

SUMMARY

Treatment of THP-1 cells with Uncaria tomentosa increases their susceptibility to X-rays. The combination of Uncaria tomentosa and X-ray exposure strongly inhibits cell signaling and promotes apoptosis.

Abbreviations Used: LPS: Lipopolysaccharide, TNF: Tumor necrosis factor: IL-1, Interleukin-1: SDS: Sodium dodecylsulphate, TBS: Tris-buffered saline.

Neuroprotective Effects of Exercise Treatments After Injury: The Dual Role of Neurotrophic Factors

BACKGROUND

Shared connections between physical activity and neuroprotection have been studied for decades, but the mechanisms underlying this effect of specific exercise were only recently brought to light. Several evidences suggest that physical activity may be a reasonable and beneficial method to improve functional recovery in both peripheral and central nerve injuries and to delay functional decay in neurodegenerative diseases. In addition to improving cardiac and immune functions, physical activity may represent a multifunctional approach not only to improve cardiocirculatory and immune functions, but potentially modulating trophic factors signaling and, in turn, neuronal function and structure at times that may be critical for neurodegeneration and regeneration.

METHODS

Research content related to the effects of physical activity and specific exercise programs in normal and injured nervous system have been reviewed.

RESULTS

Sustained exercise, particularly if applied at moderate intensity and early after injury, exerts anti-inflammatory and pro-regenerative effects, and may boost cognitive and motor functions in aging and neurological disorders. However, newest studies show that exercise modalities can differently affect the production and function of brain-derived neurotrophic factor and other neurotrophins involved in the generation of neuropathic conditions. These findings suggest the possibility that new exercise strategies can be directed to nerve injuries with therapeutical benefits.

CONCLUSION

Considering the growing burden of illness worldwide, understanding of how modulation of neurotrophic factors contributes to exercise-induced neuroprotection and regeneration after peripheral nerve and spinal cord injuries is a relevant topic for research, and represents the beginning of a new non-pharmacological therapeutic approach for better rehabilitation of neural disorders.

Tumor-suppressor NFκB2 p100 interacts with ERK2 and stabilizes PTEN mRNA via inhibition of miR-494

Emerging evidence from The Cancer Genome Atlas has revealed that nuclear factor κB2 (nfκb2) gene encoding p100 is genetically deleted or mutated in human cancers, implicating NFκB2 as a potential tumor suppressor. However, the molecular mechanism underlying the antitumorigenic action of p100 remains poorly understood. Here we report that p100 inhibits cancer cell anchorage-independent growth, a hallmark of cellular malignancy, by stabilizing the tumor-suppressor phosphatase and tensin homolog (PTEN) mRNA via a mechanism that is independent of p100's inhibitory role in NFκB activation. We further demonstrate that the regulatory effect of p100 on PTEN expression is mediated by its downregulation of miR-494 as a result of the inactivation of extracellular signal-regulated kinase 2 (ERK2), in turn leading to inhibition of c-Jun/activator protein-1-dependent transcriptional activity. Furthermore, we identify that p100 specifically interacts with non-phosphorylated ERK2 and prevents ERK2 phosphorylation and nuclear translocation. Moreover, the death domain at C-terminal of p100 is identified as being crucial and sufficient for its interaction with ERK2. Taken together, our findings provide novel mechanistic insights into the understanding of the tumor-suppressive role for NFκB2 p100.

A dominant-negative F-box deleted mutant of E3 ubiquitin ligase, β-TrCP1/FWD1, markedly reduces myeloma cell growth and survival in mice

Treatment of multiple myeloma with bortezomib can result in severe adverse effects, necessitating the development of targeted inhibitors of the proteasome. We show that stable expression of a dominant-negative F-box deleted (ΔF) mutant of the E3 ubiquitin ligase, SCF^β-TrCP/FWD1, in murine 5TGM1 myeloma cells dramatically attenuated their skeletal engraftment and survival when inoculated into immunocompetent C57BL/KaLwRij mice. Similar results were obtained in immunodeficient bg-nu-xid mice, suggesting that the observed effects were independent of host recipient immune status. Bone marrow stroma offered no protection for 5TGM1-ΔF cells in cocultures treated with tumor necrosis factor (TNF), indicating a cell-autonomous anti-myeloma effect. Levels of p100, IκBα, Mcl-1, ATF4, total and cleaved caspase-3, and phospho-β-catenin were elevated in 5TGM1-ΔF cells whereas cIAP was down-regulated. TNF also activated caspase-3 and downregulated Bcl-2, correlating with the enhanced susceptibility of 5TGM1-ΔF cells to apoptosis. Treatment of 5TGM1 tumor-bearing mice with a β-TrCP1/FWD1 inhibitor, pyrrolidine dithiocarbamate (PDTC), significantly reduced tumor burden in bone. PDTC also increased levels of cleaved Mcl-1 and caspase-3 in U266 human myeloma cells, correlating with our murine data and validating the development of specific β-TrCP inhibitors as an alternative therapy to nonspecific proteasome inhibitors for myeloma patients.

Targeting nuclear factor-kappa B to overcome resistance to chemotherapy

Intrinsic or acquired resistance to chemotherapeutic agents is a common phenomenon and a major challenge in the treatment of cancer patients. Chemoresistance is defined by a complex network of factors including multi-drug resistance proteins, reduced cellular uptake of the drug, enhanced DNA repair, intracellular drug inactivation, and evasion of apoptosis. Pre-clinical models have demonstrated that many chemotherapy drugs, such as platinum-based agents, antracyclines, and taxanes, promote the activation of the NF-κB pathway. NF-κB is a key transcription factor, playing a role in the development and progression of cancer and chemoresistance through the activation of a multitude of mediators including anti-apoptotic genes. Consequently, NF-κB has emerged as a promising anti-cancer target. Here, we describe the role of NF-κB in cancer and in the development of resistance, particularly cisplatin. Additionally, the potential benefits and disadvantages of targeting NF-κB signaling by pharmacological intervention will be addressed.

SCF(Fbw7) modulates the NFkB signaling pathway by targeting NFkB2 for ubiquitination and destruction

The NFkB/Rel family of proteins play critical roles in a variety of cellular processes. Thus, their physiological activation is tightly controlled. Recently, the NFkB2/p100 precursor has been characterized as the fourth IkB type of suppressor for NFkB. However, the molecular mechanism(s) underlying regulated destruction of NFkB2 remains largely unknown. Here, we report that, unlike other IkBs, ubiquitination and destruction of NFkB2 are governed by SCF(Fbw7) in a GSK3-dependent manner. In Fbw(7-/-) cells, elevated expression of NFkB2/p100 leads to a subsequent reduction in NFkB signaling pathways and elevated sensitivity to TNFa-induced cell death. Reintroducing wild-type Fbw7, but not disease-derived mutant forms of Fbw7, rescues NFkB activity. Furthermore, T cell-specific depletion of Fbw7 also leads to reduced NFkB activity and perturbed T cell differentiation. Therefore, our work identifies Fbw7 as a physiological E3 ligase controlling NFkB20s stability. It further implicates that Fbw7 might exert its tumor-suppressor function by regulating NFkB activity.

Proteomic screen reveals Fbw7 as a modulator of the NF-κB pathway

Fbw7 is a ubiquitin-ligase that targets several oncoproteins for proteolysis, but the full range of Fbw7 substrates is not known. Here we show that by performing quantitative proteomics combined with degron motif searches, we effectively screened for a more complete set of Fbw7 targets. We identify 89 putative Fbw7 substrates, including several disease-associated proteins. The transcription factor NF-κB2 (p100/p52) is one of the candidate Fbw7 substrates. We show that Fbw7 interacts with p100 via a conserved degron and that it promotes degradation of p100 in a GSK3β phosphorylation-dependent manner. Fbw7 inactivation increases p100 levels, which in the presence of NF-κB pathway stimuli, leads to increased p52 levels and activity. Accordingly, the apoptotic threshold can be increased by loss of Fbw7 in a p100-dependent manner. In conclusion, Fbw7-mediated destruction of p100 is a regulatory component restricting the response to NF-κB2 pathway stimulation.

Fbw7 is a ubiquitin-ligase, which targets several oncoproteins for proteolysis, and is therefore important for the control and prevention of tumorigenesis. In this study, Arabi and colleagues carry out a proteomic screen of the targets of Fbw7, and identify Nuclear Factor of κ-B2 as a substrate.

LY294002 potentiates the anti-cancer effect of oxaliplatin for gastric cancer via death receptor pathway

AIM: To examine the effects of combined treatment of oxaliplatin and phosphatidylinositol 3’-kinase inhibitor, 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002) for gastric cancer.

METHODS: Cell viability was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Apoptotic cells were detected by flow cytometric analysis and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assay. Western blotting and immuno-precipitation were used to examine protein expression and recruitment, respectively. Nuclear factor κB (NFκB) binding activities were investigated using electrophoretic mobility shift assay. Nude mice were used to investigate tumor growth.

RESULTS: Treatment with combined oxaliplatin and LY294002 resulted in increased cell growth inhibition and cell apoptosis in vitro, and increased tumor growth inhibition and cell death in the tumor mass in vivo. In MKN45 and AGS cells, oxaliplatin treatment promoted both protein kinase B (Akt) and NFκB activation, while pretreatment with LY294002 significantly attenuated oxaliplatin-induced Akt activity and NFκB binding. LY294002 promoted oxaliplatin-induced Fas ligand (FasL) expression, Fas-associated death domain protein recruitment, caspase-8, Bid, and caspase-3 activation, and the short form of cellular caspase-8/FLICE-inhibitory protein (c-FLIP_S) inhibition. In vivo, LY294002 inhibited oxaliplatin-induced activation of Akt and NFκB, and increased oxaliplatin-induced expression of FasL, inhibition of c-FLIP_S, and activation of caspase-8, Bid, and caspase-3.

CONCLUSION: Combination of oxaliplatin and LY294002 was therapeutically promising for gastric cancer treatment. The enhanced sensitivity of the combined treatment was associated with the activation of the death receptor pathway.

The unexpected role of lymphotoxin beta receptor signaling in carcinogenesis: from lymphoid tissue formation to liver and prostate cancer development

The cytokines lymphotoxin (LT) alpha, beta and their receptor (LTbetaR) belong to the tumor necrosis factor (TNF) superfamily, whose founder-TNFalpha-was initially discovered due to its tumor necrotizing activity. LTbetaR signaling serves pleiotropic functions including the control of lymphoid organ development, support of efficient immune responses against pathogens due to maintenance of intact lymphoid structures, induction of tertiary lymphoid organs, liver regeneration or control of lipid homeostasis. Signaling through LTbetaR comprises the noncanonical/canonical nuclear factor-kappaB (NF-kappaB) pathways thus inducing chemokine, cytokine or adhesion molecule expression, cell proliferation and cell survival. Blocking LTbetaR signaling or Fcgamma-receptor mediated immunoablation of LT-expressing cells was demonstrated to be beneficial in various infectious or noninfectious inflammatory or autoimmune disorders. Only recently, LTbetaR signaling was shown to initiate inflammation-induced carcinogenesis, to influence primary tumorigenesis and to control reemergence of carcinoma in various cancer models through distinct mechanisms. Indeed, LTbetaR signaling inhibition has already been used as efficient anti-inflammatory, anti-cancer therapy in some experimental models. Here, we review the pleiotropic functions attributed to LT, the effects of its deregulation and extensively discuss the recent literature on LT's link to carcinogenesis.

Loss of negative feedback control of nuclear factor-kappaB2 activity in lymphocytes leads to fatal lung inflammation

Proteolytic processing of the nuclear factor (NF)-kappaB2 precursor protein p100 generates the active NF-kappaB2 subunit p52, which in turn transcriptionally up-regulates p100 expression. p100 also functions as an IkappaB molecule capable of repressing p52 activity. The biological significance of this negative feedback control loop has yet to be demonstrated in vivo. Here we show that mice deficient in p100 but with constitutive expression of p52 in lymphocytes developed fatal lung inflammation characterized by diffuse alveolar damage with marked peribronchial fibrosis. In contrast, their littermates with only p100 deficiency or constitutive expression of p52 in lymphocytes developed mild lung inflammation with perivascular lymphocyte infiltration and had a normal life span. The fatal lung inflammation is associated with high-level induction of interferon-gamma and its inducible inflammatory chemokines, suggesting the involvement of a T-helper-1 immune response. These findings demonstrate the physiological relevance of the NF-kappaB2 p100 precursor protein in limiting the potentially detrimental effects of constitutive NF-kappaB2 signaling in lymphocytes.

Mechanisms of parenchymal injury and signaling pathways in ectatic ducts of chronic pancreatitis: implications for pancreatic carcinogenesis

The pathobiology of chronic pancreatitis (CP) remains enigmatic despite remarkable progress made recently in uncovering key mechanisms involved in the initiation and progression of the disease. CP is increasingly thought of as a multifactorial disorder. Apoptosis plays a role in parenchymal destruction, the pathological hallmark of CP. The apoptotic mechanisms preferentially target the exocrine compartment, leaving endocrine islets relatively intact for a prolonged period. Exocrine cells shed their 'immunoprivileged' status, express death receptors, and are rendered susceptible to apoptosis induced by death ligands on infiltrating lymphocytes, and released locally by activated pancreatic stellate cells. Islet cells retain their 'immunoprivileged' status and activate anti-apoptotic programs through NF-kappaB. Ductal changes, including distortion, dilatation, and pancreatic ductal hypertension in the setting of CP, induce genomic damage and increased cell turnover. In addition, signaling mechanisms that play a role in the development of embryonic pancreas are reinstated, thus, playing a role in repair, regeneration, and transformation. This, in turn, leads to acino-ductal metaplasia (ADM) and pancreatic intraepithelial neoplasia (PanIN). Some of these pathways are activated in pancreatic cancer. We attempt to integrate the current knowledge and major concepts in the pathogenesis of CP and to explain the mechanism of differential cell loss. We also discuss the possible implications of signaling pathway activation in pancreatic inflammation, relevant to the cellular transformation that leads to pancreatic neoplasia.

HDACi--targets beyond chromatin

Histone deacetylases (HDACs) play an important role in gene regulation. Inhibitors of HDACs (HDACi) are novel anti-cancer drugs, which induce histone (hyper-) acetylation and counteract aberrant gene repression. On the other hand, HDACi treatment can also result in decreased gene expression, and targeting HDACs affects more than chromatin. Recently, HDACi were shown to evoke non-histone protein acetylation, which can alter signaling networks relevant for tumorgenesis. Furthermore, HDACi can promote the degradation of (proto-) oncoproteins. Here, we summarize these findings and discuss how these substances could be beneficial for the treatment and prevention of human ailments, such as cancer and unbalanced immune functions.

Therapeutic targeting of TWEAK/Fnl4 in cancer: exploiting the intrinsic tumor cell killing capacity of the pathway

TNF-like weak inducer of apoptosis (TWEAK) and FGF-inducible molecule 14 (Fn14) are a TNF superfamily ligand-receptor pair. Initially identified as an inducer of tumor cell killing, TWEAK has pleiotropic effects, mediating proinflammatory and pro-angiogenic activity as well as stimulation of invasion, migration, and survival through its widely recognized receptor, Fn14. Fn14 is expressed at relatively low levels in normal tissues, but is dramatically elevated locally in injured and diseased tissues, where it plays a role in tissue remodeling. Herein we review the link between the TWEAK/Fn14 pathway and cancer as well as discuss potential therapeutic strategies targeting this pathway for cancer treatment. Many of the activities associated with the TWEAK/Fn14 pathway are linked with tumorigenesis and could thereby provide a growth advantage to tumors, suggesting that inhibition of the pathway may be beneficial in the treatment of cancer. At the same time, the elevated expression of Fn14 by tumor cells as well as the intrinsic tumor cell killing capacity of this receptor represents a promising alternative of harnessing the intrinsic tumor cell killing capacity of Fn14 to treat cancer.

NF-kappaB2/p52 enhances androgen-independent growth of human LNCaP cells via protection from apoptotic cell death and cell cycle arrest induced by androgen-deprivation

PURPOSE

Androgen-deprivation therapy only causes a temporary regression of prostate cancer, as all tumors will eventually progress to refractory to hormonal therapy after 1-3 years of treatment. The underlying mechanisms of prostate cancer androgen refractory progression are incompletely understood. In this study, we employed in vitro as well as in vivo models to examine the role of NF-kappaB2/p52 in prostate cancer growth and androgen independent progression.

EXPERIMENTAL DESIGN

The effects of NF-kappaB2/p52 on cell growth, androgen responsiveness, cell cycle and apoptosis were examined in androgen sensitive LNCaP cells. The effect of NF-kappaB2/p52 on tumor growth was examined in intact and castrated male mice.

RESULTS

Overexpression of NF-kappaB2/p52 enhances androgen-sensitive LNCaP human prostate cancer cell growth and clonogenic ability in androgen-deprived condition in vitro. NF-kappaB2/p52 induced androgen-independent growth is through protecting LNCaP cells from apoptotic cell death and cell cycle arrest induced by androgen-deprivation. In addition, NF-kappaB2/p52 stimulates Cyclin D1 expression and knock down of Cyclin D1 expression by siRNA abolished NF-kappaB2/p52-induced cell growth in vitro. Adenoviral mediated NF-kappaB2/p52 expression in LNCaP cells enhances tumor growth in intact male nude mice and induces tumor growth in castrated male nude mice, suggesting that overexpression of NF-kappaB2/p52 induces androgen-independent growth of androgen-sensitive LNCaP cells.

CONCLUSIONS

Overexpression of NF-kappaB2/p52 protects androgen sensitive LNCaP cells from apoptotic cell death and cell cycle arrest induced by androgen-deprivation. NF-kappaB2/p52 activation induces androgen-independent growth in vitro and in vivo.

Constitutive production of NF-kappaB2 p52 is not tumorigenic but predisposes mice to inflammatory autoimmune disease by repressing Bim expression

Normal development of the immune system requires regulated processing of NF-kappaB2 p100 to p52, which activates NF-kappaB2 signaling. Constitutive production of p52 has been suggested as a major mechanism underlying lymphomagenesis induced by NF-kappaB2 mutations, which occur recurrently in a variety of human lymphoid malignancies. To test the hypothesis, we generated transgenic mice with targeted expression of p52 in lymphocytes. In contrast to their counterparts expressing the tumor-derived NF-kappaB2 mutant p80HT, which develop predominantly B cell tumors, p52 transgenic mice are not prone to lymphomagenesis. However, they are predisposed to inflammatory autoimmune disease characterized by multiorgan infiltration of activated lymphocytes, high levels of autoantibodies in the serum, and immune complex glomerulonephritis. p52, but not p80HT, represses Bim expression, leading to defects in apoptotic processes critical for elimination of autoreactive lymphocytes and control of immune response. These findings reveal distinct signaling pathways for actions of NF-kappaB2 mutants and p52 and suggest a causal role for sustained NF-kappaB2 activation in the pathogenesis of autoimmunity.

Targeting the lymphotoxin-beta receptor with agonist antibodies as a potential cancer therapy

The lymphotoxin-beta receptor (LT beta R) is a tumor necrosis factor receptor family member critical for the development and maintenance of various lymphoid microenvironments. Herein, we show that agonistic anti-LT beta R monoclonal antibody (mAb) CBE11 inhibited tumor growth in xenograft models and potentiated tumor responses to chemotherapeutic agents. In a syngeneic colon carcinoma tumor model, treatment of the tumor-bearing mice with an agonistic antibody against murine LT beta R caused increased lymphocyte infiltration and necrosis of the tumor. A pattern of differential gene expression predictive of cellular and xenograft response to LT beta R activation was identified in a panel of colon carcinoma cell lines and when applied to a panel of clinical colorectal tumor samples indicated 35% likelihood a tumor response to CBE11. Consistent with this estimate, CBE11 decreased tumor size and/or improved long-term animal survival with two of six independent orthotopic xenografts prepared from surgical colorectal carcinoma samples. Targeting of LT beta R with agonistic mAbs offers a novel approach to the treatment of colorectal and potentially other types of cancers.

NF-kappaB2 mutation targets TRAF1 to induce lymphomagenesis

The NF-kappaB2 gene is recurrently mutated in human lymphoid malignancies. However, a causal relationship between NF-kappaB2 mutation and lymphomagenesis has not been established. It is also unclear how the mutation may lead to lymphoid malignancies. We report the generation of transgenic mice with targeted expression of p80HT, a lymphoma-associated NF-kappaB2 mutant, in lymphocytes. The transgenic mice display a marked expansion of peripheral B cell populations and develop predominantly small B cell lymphomas. p80HT expression has no apparent effect on the proliferation of B cells, but renders them specifically resistant to apoptosis induced by cytokine deprivation and mitogenic stimulation. Lymphocytes and lymphoma cells from p80HT mice express high levels of TRAF1, an antiapoptotic protein also implicated in lymphoid malignancies. p80HT binds the TRAF1 promoter in vivo and activates TRAF1 transcription. Moreover, TRAF1 knockdown abrogates the antiapoptotic activity of p80HT and TRAF1 deficiency reestablishes B cell homeostasis in p80HT mice. These findings demonstrate NF-kappaB2 mutation as an oncogenic event in vivo and suggest a molecular pathway for TRAF1 activation in the pathogenesis of lymphomas.

NF-kappaB as a potential molecular target for cancer therapy

Nuclear factor kappaB (NF-kappaB), a transcription factor, plays an important role in carcinogenesis as well as in the regulation of immune and inflammatory responses. NF-kappaB induces the expression of diverse target genes that promote cell proliferation, regulate apoptosis, facilitate angiogenesis and stimulate invasion and metastasis. Furthermore, many cancer cells show aberrant or constitutive NF-kappaB activation which mediates resistance to chemo- and radio-therapy. Therefore, the inhibition of NF-kappaB activation and its signaling pathway offers a potential cancer therapy strategy. In addition, recent studies have shown that NF-kappaB can also play a tumor suppressor role in certain settings. In this review, we focus on the role of NF-kappaB in carcinogenesis and the therapeutic potential of targeting NF-kappaB in cancer therapy.

NF-kappaB2 is required for the control of autoimmunity by regulating the development of medullary thymic epithelial cells

Medullary thymic epithelial cells function as antigen-presenting cells in negative selection of self-reactive T cell clones, a process essential for the establishment of central self-tolerance. These cells mirror peripheral tissues through promiscuous expression of a diverse set of tissue-restricted self-antigens. The genes and signaling pathways that regulate the development of medullary thymic epithelial cells are not fully understood. Here we show that mice deficient in NF-kappaB2, a member of the NF-kappaB family, display a marked reduction in the number of mature medullary thymic epithelial cells that express CD80 and bind the lectin Ulex europaeus agglutinin-1, leading to a significant decrease in the extent of promiscuous gene expression in the thymus of NF-kappaB2(-/-) mice. Moreover, NF-kappaB2(-/-) mice manifest autoimmunity characterized by multiorgan infiltration of activated T cells and high levels of autoantibodies to multiple organs. A subpopulation of the mice also develops immune complex glomerulonephritis. These findings identify a physiological function of NF-kappaB2 in the development of medullary thymic epithelial cells and, thus, the control of self-tolerance induction.

Mutations in the NF-kappaB signaling pathway: implications for human disease

The nuclear factor-kappa B (NF-kappaB) signaling pathway is a multi-component pathway that regulates the expression of hundreds of genes that are involved in diverse and key cellular and organismal processes, including cell proliferation, cell survival, the cellular stress response, innate immunity and inflammation. Not surprisingly, mis-regulation of the NF-kappaB pathway, either by mutation or epigenetic mechanisms, is involved in many human and animal diseases, especially ones associated with chronic inflammation, immunodeficiency or cancer. This review describes human diseases in which mutations in the components of the core NF-kappaB signaling pathway have been implicated and discusses the molecular mechanisms by which these alterations in NF-kappaB signaling are likely to contribute to the disease pathology. These mutations can be germline or somatic and include gene amplification (e.g., REL), point mutations and deletions (REL, NFKB2, IKBA, CYLD, NEMO) and chromosomal translocations (BCL-3). In addition, human genetic diseases are briefly described wherein mutations affect protein modifiers or transducers of NF-kappaB signaling or disrupt NF-kappaB-binding sites in promoters/enhancers.

Activation of non-canonical NF-kappaB pathway mediated by STP-A11, an oncoprotein of Herpesvirus saimiri

Although Saimiri Transforming Protein (STP)-A11, an oncoprotein of Herpesvirus saimiri, has been known to activate NF-kappaB signaling pathway, the detailed mechanism has not been reported yet. We herein report that STP-A11 activates non-canonical NF-kappaB pathway, resulting in p100 processing to p52. In addition, translocation of p52 protein (NF-kappaB2) into the nucleus is observed by the expression of STP-A11. STP-A11-mediated processing of p100 to p52 protein requires proteosome-mediated proteolysis because MG132 treatment clearly blocked p52 production in spite of the expression of STP-A11. Analysis of STP-A11 mutants to activate NF-kappaB2 pathway discloses the requirement of TRAF6-binding site not Src-binding site for STP-A11-mediated NF-kappaB2 pathway. Blockage of STP-A11-mediated p52 production using siRNA against p52 enhanced a chemotherapeutic drug-mediated cell death, suggesting that p52 production induced by the expression of STP-A11 would contribute to cellular transformation, which results from a resistance to cell death.

RIP death domain structural interactions implicated in TNF-mediated proliferation and survival

Death domain (DD)-containing proteins are involved in both apoptosis and survival/proliferation signaling induced by activated death receptors. Here, a phylogenetic and structural analysis was performed to highlight differences in DD domains and their key regulatory interaction sites. The phylogenetic analysis shows that receptor DDs are more conserved than DDs in adaptors. Adaptor DDs can be subdivided into those that activate or inhibit apoptosis. Modeling of six homotypic DD interactions involved in the TNF signaling pathway implicates that the DD of RIP (Receptor interacting protein kinase 1) is capable of interacting with the DD of TRADD (TNFR1-associated death domain protein) in two different, exclusive ways: one that subsequently recruits CRADD (apoptosis/inflammation) and another that recruits NFkappaB (survival/proliferation).

Dichotomy of fates of pancreatic epithelia in chronic pancreatitis: apoptosis versus survival

Chronic pancreatitis is now thought to have a multifactorial etiology. New concepts integrating cellular, molecular and genetic knowledge of the disease have been proposed to explain its pathogenesis. However, the mechanisms responsible for early exocrine parenchymal destruction and preservation of endocrine islets were unexplored until recently. In the course of chronic inflammation, pancreatic acini lose their "immunoprotective" status by neo-expressing death receptors. Therefore, they become susceptible to apoptosis that is triggered by their respective ligands expressed on lymphocytes and released by pancreatic stellate cells. By contrast, islets retain their immunoprotective status and activate nuclear factor-kappaB (NF-kappaB)-induced anti-apoptotic factors, thus enabling survival. This knowledge might be exploited for devising therapeutic approaches to retard acinar loss and to prolong islet survival.

The role of NF-{kappa}B-1 and NF-{kappa}B-2-mediated resistance to apoptosis in lymphomas

The NF-kappaB pathways have been implicated in tumorigenesis in several lymphoid malignancies, including non-Hodgkin's and Hodgkin's lymphomas. However, the antiapoptotic functions and the mechanism responsible for signaling through each NF-kappaB pathway remain to be elucidated. In the current study, lymphoma cell lines with constitutively active NF-kappaB were found to be resistant to inducers of the extrinsic and intrinsic apoptosis pathways. Resistance to cell death resulted from blocks early and late in the apoptosis cascade. Several NF-kappaB target genes were overexpressed in these cell lines, including Bcl-xL, Fas-associated death domain-like IL-1beta-converting enzyme inhibitor protein, cellular inhibitor of apoptosis, and X inhibitor of apoptosis. Inhibition of the canonical or noncanonical NF-kappaB pathways with small interfering RNAs or adenovirus expressing a stable form of inhibitor of NF-kappaB (IkappaB) enhanced sensitivity to apoptosis inducers and resulted in lower levels of Bcl-xL or Fas-associated death domain-like IL-1beta-converting enzyme inhibitor protein, cellular inhibitor of apoptosis, and X inhibitor of apoptosis. These findings demonstrate an important role of both NF-kappaB pathways in mediating resistance to apoptosis and distinctive antiapoptotic downstream target gene profiles responsible for this effect.

Stat3 activation of NF-{kappa}B p100 processing involves CBP/p300-mediated acetylation

Activation of the noncanonical NF-kappaB signaling pathway involved in the proteolytic processing of NF-kappaB p100 to p52 is tightly regulated, and overproduction of p52 leads to lymphocyte hyperplasia and transformation. We have demonstrated that active but not latent Stat3, expressed in many types of human cancers involved in cell proliferation and survival, induces p100 processing to p52 by activation of IKKalpha and subsequent phosphorylation of p100. The Stat3-mediated p100 processing to p52 requires activation of Stat3 by the acetyltransferase activity of cAMP-response element-binding protein (CREB)-binding protein (CBP)/p300. A mutant of Stat3 defective in acetylation blocked Stat3-mediated p100 processing to p52 and acted as a dominant negative in blocking the production of p52. Furthermore, overexpression of p52 protected cells from apoptotic cell death. Thus, activation of the processing of p100 to p52 by Stat3 may represent one of the common pathways used by cancer cells to survive and escape therapy.

RelB regulates manganese superoxide dismutase gene and resistance to ionizing radiation of prostate cancer cells

The relationship between NF-kappaB and resistance to radiation treatment in many tumor cell types has been generally well recognized. However, which members of the NF-kappaB family contribute to radiation resistance is unclear. In the present study, we demonstrate that RelB plays an important radioprotective role in aggressive prostate cancer cells, in part by the induction of antioxidant and antiapoptotic manganese superoxide dismutase (MnSOD) gene. RelB is both constitutively present and is inducible by radiation in aggressive prostate cancer cells. Using ectopically expressed dominant negative inhibitor, p100 mutant, and the siRNA approach, we demonstrate that selective inhibition of RelB significantly decreases the levels of MnSOD resulting in a significant increase in the sensitivity of prostate cancer cells to radiation treatment. These results demonstrate that RelB plays an important role in redox regulation of the cell and protects aggressive prostate cancer cells against radiation-induced cell death. Thus, inhibition of RelB could be a novel mechanism to radiosensitize prostate cancer.

Notch3 and pre-TCR interaction unveils distinct NF-kappaB pathways in T-cell development and leukemia

Notch signaling plays a critical role in T-cell differentiation and leukemogenesis. We previously demonstrated that, while pre-TCR is required for thymocytes proliferation and leukemogenesis, it is dispensable for thymocyte differentiation in Notch3-transgenic mice. Notch3-transgenic premalignant thymocytes and T lymphoma cells overexpress pTalpha/pre-TCR and display constitutive activation of NF-kappaB, providing survival signals for immature thymocytes. We provide genetic and biochemical evidence that Notch3 triggers multiple NF-kappaB activation pathways. A pre-TCR-dependent pathway preferentially activates NF-kappaB via IKKbeta/IKKalpha/NIK complex, resulting in p50/p65 heterodimer nuclear entry and recruitment onto promoters of Cyclin D1, Bcl2-A1 and IL7-receptor-alpha genes. In contrast, upon pTalpha deletion, Notch3 binds IKKalpha and maintains NF-kappaB activation through an alternative pathway, depending on an NIK-independent IKKalpha homodimer activity. The consequent NF-kappaB2/p100 processing allows nuclear translocation of p52/RelB heterodimers, which only trigger transcription from Bcl2-A1 and IL7-receptor-alpha genes. Our data suggest that a finely tuned interplay between Notch3 and pre-TCR pathways converges on regulation of NF-kappaB activity, leading to differential NF-kappaB subunit dimerization that regulates distinct gene clusters involved in either cell differentiation or proliferation/leukemogenesis.

Pro-apoptotic role of NF-kappaB: implications for cancer therapy

Nuclear factor-kappaB (NF-kappaB) is generally viewed as anti-apoptotic and oncogenic, leading to a quest for its inhibitors. However, recent evidence suggests that in some situations NF-kappaB may promote apoptosis. Depending on the specific cell type and the stimulus involved, NF-kappaB activation may lead to either anti- or pro-apoptotic response. Both these effects can be mediated by NF-kappaB in a context-dependent manner by selectively regulating its target genes. In this review, we discuss the evidence for NF-kappaB's pro-apoptotic role and explore the possible mechanisms behind it. We emphasize that rather than trying to inhibit NF-kappaB in cancer therapy, agents should be developed to unleash its pro-apoptotic ability.

Parenchymal regression in chronic pancreatitis spares islets reprogrammed for the expression of NFkappaB and IAPs

In advanced chronic pancreatitis (CP), islets are preserved even in the midst of scarring. We recently showed in CP local production of interferon (IFN)gamma, transforming growth factor (TGF)beta and death receptor ligand TRAIL (tumor necrosis factor-related apoptosis-inducing ligand), along with functional death receptor neoexpression and apoptosis in exocrine but not in endocrine cells. However, islets are strongly induced for TRAIL-receptor (R)-4 lacking the functional death domain. TRAIL-R4 signaling in T cells induces NFkappaB, which activates antiapoptotic programs. Here, we demonstrate that in insulinoma cells CM, TGFbeta/IFNgamma/TRAIL in combination induced TRAIL-R4 surface expression. TRAIL/IFNgamma upregulated NFkappaB subunits and its target gene survivin while downmodulating IkappaB alpha mRNA. RelA transcriptional activity increased upon stimulation with IFNgamma and IFNgamma/TRAIL. In situ, normal pancreatic epithelia had low mRNA levels of NFkappaB subunits. These were higher in parenchymal areas of CP with severe fibrosis and highest in islets. NFkappaB-regulated proteins IkappaB alpha, survivin and another apoptosis inhibitor, cIAP1, were found in corresponding sites, again at highest levels in islets surrounded by fibrosis. In conclusion, islets in CP not only evade immune attack by nonexposure of functional death receptors in the presence of TRAIL-R4 but also additionally neoexpress NFkappaB and its target genes, survivin and cIAP1, to protect themselves from apoptosis.

Receptor-specific signaling for both the alternative and the canonical NF-kappaB activation pathways by NF-kappaB-inducing kinase

The NF-kappaB-inducing kinase (NIK) induces proteolytic processing of NF-kappaB2/p100 and, hence, the generation of NF-kappaB dimers such as p52:RelB but was suggested not to signal for the processing of IkappaB. Here, we show that although the induction of IkappaB degradation in lymphocytes by TNF is independent of NIK, its induction by CD70, CD40 ligand, and BLyS/BAFF, which all also induce NF-kappaB2/p100 processing, does depend on NIK function. Both CD70 and TNF induce recruitment of the IKK kinase complex to their receptors. In the case of CD70, but not TNF, this process is associated with NIK recruitment and is followed by prolonged receptor association of just IKK1 and NIK. Recruitment of the IKK complex to CD27, but not that of NIK, depends on NIK kinase function. Our findings indicate that NIK participates in a unique set of proximal signaling events initiated by specific inducers, which activate both canonical and noncanonical NF-kappaB dimers.

Functions of NF-kappaB1 and NF-kappaB2 in immune cell biology

Two members of the NF-kappaB (nuclear factor kappaB)/Rel transcription factor family, NF-kappaB1 and NF-kappaB2, are produced as precursor proteins, NF-kappaB1 p105 and NF-kappaB2 p100 respectively. These are proteolytically processed by the proteasome to produce the mature transcription factors NF-kappaB1 p50 and NF-kappaB2 p52. p105 and p100 are known to function additionally as IkappaBs (inhibitors of NF-kappaB), which retain associated NF-kappaB subunits in the cytoplasm of unstimulated cells. The present review focuses on the latest advances in research on the function of NF-kappaB1 and NF-kappaB2 in immune cells. NF-kappaB2 p100 processing has recently been shown to be stimulated by a subset of NF-kappaB inducers, including lymphotoxin-beta, B-cell activating factor and CD40 ligand, via a novel signalling pathway. This promotes the nuclear translocation of p52-containing NF-kappaB dimers, which regulate peripheral lymphoid organogenesis and B-lymphocyte differentiation. Increased p100 processing also contributes to the malignant phenotype of certain T- and B-cell lymphomas. NF-kappaB1 has a distinct function from NF-kappaB2, and is important in controlling lymphocyte and macrophage function in immune and inflammatory responses. In contrast with p100, p105 is constitutively processed to p50. However, after stimulation with agonists, such as tumour necrosis factor-alpha and lipopolysaccharide, p105 is completely degraded by the proteasome. This releases associated p50, which translocates into the nucleus to modulate target gene expression. p105 degradation also liberates the p105-associated MAP kinase (mitogen-activated protein kinase) kinase kinase TPL-2 (tumour progression locus-2), which can then activate the ERK (extracellular-signal-regulated kinase)/MAP kinase cascade. Thus, in addition to its role in NF-kappaB activation, p105 functions as a regulator of MAP kinase signalling.

Gene expression profiling in fetal, aged, and Alzheimer hippocampus: a continuum of stress-related signaling

While specific components of normal brain aging and Alzheimer's disease (AD) appear to be genetically determined, it is not well understood whether AD is due to accelerated aging or if AD represents an independent disease entity superimposed upon senescence. Using gene expression profiling, significant alterations in brain-specific transcription patterns have been observed between AD and age-matched controls. In AD, although a general depression in brain genetic output has been reported, there are robust increases in the expression of potentially neuropathological genes. The data in this study show increases in the RNA abundance patterns for a stress-response, proinflammatory, apoptotic, and angiogenic gene family that occur during the transition from fetal to aged, and again during the transformation from aged to AD brain. Significantly up-regulated RNAs include those encoding stress-induced factors (HSP70), transcriptional repressors (DAXX), pentraxins (SAP), proapoptosis factors (FAS and DAXX), and several inflammatory markers (betaAPP, CEX1, NF-IL6, NF-kappaBp100, cyclooxygenase-2, IL-1alpha and IL-1beta precursors and cPLA2). These findings support the hypothesis that there is a continuum of stress-related gene expression as the brain ages and an advancement of inflammatory, apoptotic, and angiogenic gene signaling that correlates with the transition to AD.

Apoptosis defects and chemotherapy resistance: molecular interaction maps and networks

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

Identification of a ZU5 and Death Domain-containing Inhibitor of NF-κB

The transcription factor NF-kappaB plays important roles in inflammation and cell survival. NF-kappaB is composed of homodimeric and heterodimeric complexes of Rel/NF-kappaB family members, including p65 (RelA), c-Rel (Rel), RelB, NF-kappaB1/p50, and NF-kappaB2/p52. Here we report the identification and characterization of a novel ZU5 and death domain-containing protein designated ZUD. In reporter gene assays, overexpression of ZUD inhibited NF-kappaB-dependent transcription induced by both tumor necrosis factor (TNF) and interleukin-1 and their downstream signaling proteins. Gel shift assays indicated that the overexpression of ZUD inhibited binding of NF-kappaB to its target sequence. ZUD is a cytoplasmic protein, and coimmunoprecipitation assays indicated that ZUD interacted with the NF-kappaB subunit p105 and transactivator p65. Consistent with its role in inhibition of NF-kappaB-dependent transcription, ZUD sensitized cells to apoptosis induced by TNF and the TNF-related apoptosis-inducing ligand (TRAIL). Our findings suggest that ZUD is an inhibitor of NF-kappaB activation and that this protein may provide an alternative regulatory mechanism for NF-kappaB-mediated transcription.

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

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

Cutting Edge: NF-κB2 Is a Negative Regulator of Dendritic Cell Function

RelB, a member of the NF-kappaB family of transcription factors, is essential for dendritic cell (DC) maturation. Recent findings indicate that RelB is exclusively regulated through its interaction with cytoplasmic NF-kappaB2/p100. The studies presented in this report show that DCs lacking NF-kappaB2 have dramatically enhanced RelB activity, associated with increased MHC class II and costimulatory molecule expression and an enhanced ability to induce CD4(+) T cell responses. These studies identify a novel role for NF-kappaB2 in the negative regulation of RelB-induced DC maturation, with critical consequences for the regulation of adaptive immune responses.

Epstein-Barr virus-encoded latent infection membrane protein 1 regulates the processing of p100 NF-kappaB2 to p52 via an IKKgamma/NEMO-independent signalling pathway

The oncogenic Epstein-Barr virus (EBV)-encoded latent infection membrane protein 1 (LMP1) constitutively activates the 'canonical' NF-kappaB pathway that involves the phosphorylation and degradation of IkappaBalpha downstream of the IkappaB kinases (IKKs). In this study, we show that LMP1 also promotes the proteasome-mediated proteolysis of p100 NF-kappaB2 resulting in the generation of active p52, which translocates to the nucleus in complex with the p65 and RelB NF-kappaB subunits. LMP1-induced NF-kappaB transactivation is reduced in nf-kb2(-/-) mouse embryo fibroblasts, suggesting that p100 processing contributes to LMP1-mediated NF-kappaB transcriptional effects. This pathway is likely to operate in vivo, as the expression of LMP1 in primary EBV-positive Hodgkin's lymphoma and nasopharyngeal carcinoma biopsies correlates with the nuclear accumulation of p52. Interestingly, while the ability of LMP1 to activate the canonical NF-kappaB pathway is impaired in cells lacking IKKgamma/NEMO, the regulatory subunit of the IKK complex, p100 processing remains unaffected. As a result, nuclear translocation of p52, but not p65, occurs in the absence of IKKgamma. These data point to the existence of a novel signalling pathway that regulates NF-kappaB in LMP1-expressing cells, and may thereby play a role in both oncogenic transformation and the establishment of persistent EBV infection.