Characterization of an immediate-early gene induced in adherent monocytes that encodes I kappa B-like activity

NF-κB, the first quarter-century: remarkable progress and outstanding questions

The ability to sense and adjust to the environment is crucial to life. For multicellular organisms, the ability to respond to external changes is essential not only for survival but also for normal development and physiology. Although signaling events can directly modify cellular function, typically signaling acts to alter transcriptional responses to generate both transient and sustained changes. Rapid, but transient, changes in gene expression are mediated by inducible transcription factors such as NF-κB. For the past 25 years, NF-κB has served as a paradigm for inducible transcription factors and has provided numerous insights into how signaling events influence gene expression and physiology. Since its discovery as a regulator of expression of the κ light chain gene in B cells, research on NF-κB continues to yield new insights into fundamental cellular processes. Advances in understanding the mechanisms that regulate NF-κB have been accompanied by progress in elucidating the biological significance of this transcription factor in various physiological processes. NF-κB likely plays the most prominent role in the development and function of the immune system and, not surprisingly, when dysregulated, contributes to the pathophysiology of inflammatory disease. As our appreciation of the fundamental role of inflammation in disease pathogenesis has increased, so too has the importance of NF-κB as a key regulatory molecule gained progressively greater significance. However, despite the tremendous progress that has been made in understanding the regulation of NF-κB, there is much that remains to be understood. In this review, we highlight both the progress that has been made and the fundamental questions that remain unanswered after 25 years of study.

Human immunodeficiency virus-1 Tat activates NF-κB via physical interaction with IκB-α and p65

Nuclear factor (NF)-κB is a master regulator of pro-inflammatory genes and is upregulated in human immunodeficiency virus 1 (HIV-1) infection. Mechanisms underlying the NF-κB deregulation by HIV-1 are relevant for immune dysfunction in AIDS. We report that in single round HIV-1 infection, or single-pulse PMA stimulation, the HIV-1 Tat transactivator activated NF-κB by hijacking the inhibitor IκB-α and by preventing the repressor binding to the NF-κB complex. Moreover, Tat associated with the p65 subunit of NF-κB and increased the p65 DNA-binding affinity and transcriptional activity. The arginine- and cysteine-rich domains of Tat were required for IκB-α and p65 association, respectively, and for sustaining the NF-κB activity. Among an array of NF-κB-responsive genes, Tat mostly activated the MIP-1α expression in a p65-dependent manner, and bound to the MIP-1α NF-κB enhancer thus promoting the recruitment of p65 with displacement of IκB-α; similar findings were obtained for the NF-κB-responsive genes CSF3, LTA, NFKBIA and TLR2. Our results support a novel mechanism of NF-κB activation via physical interaction of Tat with IκB-α and p65, and may contribute to further insights into the deregulation of the inflammatory response by HIV-1.

Differential gene expression in bovine cells infected with wild type and leaderless foot-and-mouth disease virus

The leader proteinase (L(pro)) of foot-and-mouth disease virus (FMDV) plays a critical role in viral pathogenesis. Molecular studies have demonstrated that L(pro) inhibits translation of host capped mRNAs and transcription of some genes involved in the innate immune response. We have used microarray technology to study the gene expression profile of bovine cells infected with wild type (WT) or leaderless FMDV. Thirty nine out of approximately 22,000 bovine genes were selectively up-regulated by 2 fold or more in leaderless versus WT virus infected cells. Most of the up-regulated genes corresponded to IFN-inducible genes, chemokines or transcription factors. Comparison of promoter sequences suggested that host factors NF-kappaB, ISGF3G and IRF1 specifically contributed to the differential expression, being NF-kappaB primarily responsible for the observed changes. Our results suggest that L(pro) plays a central role in the FMDV evasion of the innate immune response by inhibiting NF-kappaB dependent gene expression.

Regulation of IkappaBalpha function and NF-kappaB signaling: AEBP1 is a novel proinflammatory mediator in macrophages

NF-κB comprises a family of transcription factors that are critically involved in various inflammatory processes. In this paper, the role of NF-κB in inflammation and atherosclerosis and the regulation of the NF-κB signaling pathway are summarized. The structure, function, and regulation of the NF-κB inhibitors, IκBα and IκBβ, are reviewed. The regulation of NF-κB activity by glucocorticoid receptor (GR) signaling and IκBα sumoylation is also discussed. This paper focuses on the recently reported regulatory function that adipocyte enhancer-binding protein 1 (AEBP1) exerts on NF-κB transcriptional activity in macrophages, in which AEBP1 manifests itself as a potent modulator of NF-κB via physical interaction with IκBα and a critical mediator of inflammation. Finally, we summarize the regulatory roles that recently identified IκBα-interacting proteins play in NF-κB signaling. Based on its proinflammatory roles in macrophages, AEBP1 is anticipated to serve as a therapeutic target towards the treatment of various inflammatory conditions and disorders.

Zinc modulates the innate immune response in vivo to polymicrobial sepsis through regulation of NF-kappaB

Zinc is an essential element that facilitates coordination of immune activation during the host response to infection. We recently reported that zinc deficiency increases systemic inflammation, vital organ damage, and mortality in a small animal model of sepsis. To investigate potential mechanisms that cause these phenomena, we used the same animal model and observed that zinc deficiency increases bacterial burden and enhances NF-kappaB activity in vital organs including the lung. We conducted further studies in the lung to determine the overall impact of zinc deficiency. At the molecular level, NF-kappaB p65 DNA-binding activity was enhanced by zinc deficiency in response to polymicrobial sepsis. Furthermore, expression of the NF-kappaB-targeted genes IL-1beta, TNFalpha, ICAM-1, and the acute phase response gene SAA1/2 were elevated by zinc deficiency. Unexpectedly, the amount of NF-kappaB p65 mRNA and protein was increased in the lung including alveolar epithelia of zinc-deficient mice. These events occurred with a significant and concomitant increase in caspase-3 activity within 24 h of sepsis onset in zinc-deficient mice relative to control group. Short-term zinc supplementation reversed these effects. Reconstitution of zinc deficiency in lung epithelial cultures resulted in similar findings in response to TNFalpha. Taken together, zinc deficiency systemically enhances the spread of infection and NF-kappaB activation in vivo in response to polymicrobial sepsis, leading to enhanced inflammation, lung injury, and, as reported previously, mortality. Zinc supplementation immediately before initiation of sepsis reversed these effects thereby supporting the plausibility of future studies that explore zinc supplementation strategies to prevent sepsis-mediated morbidity and mortality.

Control of NF-κB activity by proteolysis

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

Dexamethasone enhances trichosanthin-induced apoptosis in the HepG2 hepatoma cell line

AIMS

Trichosanthin (TCS) is a type I ribosome-inactivating protein (RIP) with antitumor activities for various cancers. In this paper, we aimed to investigate whether dexamethasone, an important synthetic member of the glucocorticoid steroids, in combination with TCS can be a potential therapy in treating hepatoma.

MAIN METHODS

Cell viability was investigated using MTT assay, and apoptosis was evaluated with Hoechst 33258 staining. Western blot analysis was used to examine the changes in the expression levels of IkappaB-alpha, NF-kappaB p65 subunit and Cox-2. Additionally, we took advantage of dominant-negative IkappaB (IkappaB-DM) over-expression and chemical inhibitor PDTC to inhibit NF-kappaB activation.

KEY FINDINGS

Our results demonstrated that dexamethasone could enhance TCS-induced apoptosis in the hepatoma cell line HepG2, decreasing IC50 values from in excess of 200microg/ml to 50microg/ml. In addition, our results demonstrated that TCS could induce rapid degradation of IkappaB-alpha, nuclear translocation of NF-kappaB and decrease of COX-2 expression in HepG2 cells. Inhibition of NF-kappaB by biological (IkappaB-DM) or chemical inhibitor (PDTC) increased HepG2 cells' sensitivity to TCS, resulting in cell viability rate decreasing and apoptotic rate increasing. Simultaneously, dexamethasone increased the level of IkappaB-alpha protein and effectively inhibited TCS-induced degradation of IkappaB-alpha.

SIGNIFICANCE

These results suggest that dexamethasone could enhance trichosanthin-induced apoptosis in the HepG2, at least in part, by inhibiting the NF-kappaB signaling pathway and thus strengthening the antitumor effects of TCS, which highlights the possibility of combined drug application of TCS and dexamethasone in the clinical treatment of hepatoma.

Effect of curcumin on nuclear factor kappaB signaling pathways in human chronic myelogenous K562 leukemia cells

Curcumin, a natural product isolated from the plant Curcuma longa, has a diverse range of molecular targets that influence numerous biochemical and molecular cascades. Curcumin has been shown to inhibit nuclear factor kappaB (NF-kappaB) activation at several steps in the NF-kappaB signaling pathways and thereby controls numerous NF-kappaB-regulated genes involved in various diseases. In the present study, we investigated the effect of curcumin pretreatment on 84 tumor necrosis factor-alpha (TNF-alpha)-activated genes of NF-kappaB pathways in K562 cells, using a real-time PCR array. Our results show that transcription of 29 NF-kappaB-related mRNAs was significantly downregulated (CARD4, CCL2, CD40, CSF2, F2R, ICAM1, IKBKB, IKBKE, IL1A, IL1B, IL6, IL8, IRAK2, MALT1, MAP3K1, MYD88, NFKB1, NFKB2, NFKBIA, PPM1A, RAF1, RELB, STAT1, TLR3, TNF, TNFalphaIP3, TNFSF10, and TICAM1), whereas 10 mRNAs were induced (AGT, CASP1, CSF3, FOS, IFNG, IL10, TICAM2, TLR2, TLR9, and TNFRSF7). Western blot analysis of CD40, NFKB1 (p50), RELB, NFKBIA (IkappaBalpha), and IL10 as well as an IL8 secretion assay confirmed our results. Taken together, we show that curcumin regulates an impressive number of NF-kappaB genes within the different NF-kappaB signaling pathways.

Selective regulation of growth factor expression in cultured cortical astrocytes by neuro-pathological toxins

Astrocytes are integrated in the complex regulation of neurodegeneration and neuronal damage in the CNS. It is well-known that astroglia produces a plethora of growth factors which might be protective for neurons. Growth factors prevent neurons from cell death and promote proliferation and differentiation of precursor cells. Previous data suggest that astrocytes may respond to toxic stimuli by a selective mobilization of guarding molecules. In the present study, we have investigated the potency of different pathological stimuli such as lipopolysaccharides, tumor necrosis factor alpha, glutamate, and hydrogen peroxide to activate cultured cortical astroglia and stimulate growth factor expression. Astroglial cultures were exposed to the above factors for 24h at non-toxic concentrations for astrocytes. Growth factor expression was analyzed by real-time PCR, oligo-microarray technique, and ELISA. Insulin-like growth factor-1 was selectively down-regulated by lipopolysaccharides and tumor necrosis factor alpha, bone morphogenetic protein 6 by all stimuli. In contrast, lipopolysaccharides, tumor necrosis factor alpha, and glutamate increased leukemia inhibitory factor. Fibroblast growth factor 2 was up-regulated by lipopolysaccharides and tumor necrosis factor alpha and down-regulated by hydrogen peroxide. Besides hydrogen peroxide, all other stimuli promoted vascular epithelial growth factor A mRNA and protein expression. It appears that lipopolysaccharides but not tumor necrosis factor alpha effects on vascular epithelial growth factor A depend on the classic NFkappaB pathway. Our data clearly demonstrate that astroglia actively responses to diverse pathological compounds by a selective expression pattern of growth factors. These findings make astrocytes likely candidates to participate in disease-specific characteristics of neuronal support or damage.

Rosiglitazone, a peroxisome proliferator-activated receptor-gamma agonist, attenuates acrolein-induced airway mucus hypersecretion in rats

BACKGROUND

Peroxisome proliferator-activated receptor-gamma (PPAR-gamma), a member of the ligand-activated nuclear receptor superfamily, has been shown to be implicated in anti-inflammatory and immunomodulatory responses, but its role in airway mucus hypersecretion remains not clear.

OBJECTIVE

To investigate the role of PPAR-gamma in airway mucus hypersecretion, we used an acrolein-exposed rat model treated with rosiglitazone, a peroxisome proliferator-activated receptor-gamma agonist.

METHODS

Rats were exposed to acrolein (3.0 ppm, 6h/day, 7 days/week) and orally administered with rosiglitazone (2, 4, 8 mg/kg) once daily for up to 2 weeks. The expressions of Muc5ac protein and mRNA, and infiltration of inflammatory cells and levels of inflammatory cytokines (interleukin (IL)-1beta, IL-8 and tumor necrosis factor (TNF)-alpha) in bronchoalveolar lavage fluid (BALF) were detected with real-time PCR, Western blot, cell counting and ELISA. In addition, the role of nuclear factor (NF)-kappaB pathway in this process was also explored.

RESULTS

Acrolein exposure significantly induced goblet cell hyperplasia in bronchial epithelium and Muc5ac mRNA and protein expressions in rat lungs, as well as the associated airway inflammation evidenced by the increased numbers of inflammatory cells and levels of inflammatory cytokines in BALF, which were attenuated with rosiglitazone treatment in a dose-dependent manner (P<0.05). Simultaneously, the increased expression of NF-kappaB and decreased expression of cytoplasmic IkappaB in acrolein-exposed lungs were reversed by rosiglitazone treatment.

CONCLUSIONS

These findings suggest that PPAR-gamma activation by its ligands can attenuate acrolein-induced airway mucus hypersecretion in rats, which may be involved in inhibition of NF-kappaB pathway.

Tumor necrosis factor alpha induces gamma-glutamyltransferase expression via nuclear factor-kappaB in cooperation with Sp1

Gamma-glutamyltransferase (GGT) cleaves the gamma-glutamyl moiety of glutathione (GSH), an endogenous antioxidant, and is involved in mercapturic acid metabolism and in cancer drug resistance when overexpressed. Moreover, GGT converts leukotriene (LT) C4 into LTD4 implicated in various inflammatory pathologies. So far the effect of inflammatory stimuli on regulation of GGT expression and activity remained to be addressed. We found that the proinflammatory cytokine tumor necrosis factor alpha (TNFalpha) induced GGT promoter transactivation, mRNA and protein synthesis, as well as enzymatic activity. Remicade, a clinically used anti-TNFalpha antibody, small interfering RNA (siRNA) against p50 and p65 nuclear factor-kappaB (NF-kappaB) isoforms, curcumin, a well characterized natural NF-kappaB inhibitor, as well as a dominant negative inhibitor of kappaB alpha (IkappaBalpha), prevented GGT activation at various levels, illustrating the involvement of this signaling pathway in TNFalpha-induced stimulation. Over-expression of receptor of TNFalpha-1 (TNFR1), TNFR-associated factor-2 (TRAF2), TNFR-1 associated death domain (TRADD), dominant negative (DN) IkappaBalpha or NF-kappaB p65 further confirmed GGT promoter activation via NF-kappaB. Linker insertion mutagenesis of 536 bp of the proximal GGT promoter revealed NF-kappaB and Sp1 binding sites at -110 and -78 relative to the transcription start site, responsible for basal GGT transcription. Mutation of the NF-kappaB site located at -110 additionally inhibited TNFalpha-induced promoter induction. Chromatin immunoprecipitation (ChIP) assays confirmed mutagenesis results and further demonstrated that TNFalpha treatment induced in vivo binding of both NF-kappaB and Sp1, explaining increased GGT expression, and led to RNA polymerase II recruitment under inflammatory conditions.

Tumor-derived variants of Epstein-Barr virus latent membrane protein 1 induce sustained Erk activation and c-Fos

Latent membrane protein 1 (LMP1) of Epstein-Barr virus (EBV) is a proven oncogene that is essential for transformation of human B cells by the virus. LMP1 induces constitutive activation of several signal transduction pathways involving nuclear factor kappaB, phosphatidylinositol 3-kinase/Akt, and the mitogen-activated protein kinases (MAPK) p38, c-Jun N-terminal kinase (JNK), and extracellular signal-regulated kinase (Erk). Sequencing of LMP1 isolated from a panel of EBV+ B cell lymphomas identified three different variants of LMP1, each distinct from the B95.8 prototype isoform. All tumor variants of LMP1 as well as the B95.8 LMP1 isoform were able to induce rapid p38 phosphorylation as well as Akt and JNK activation. Additionally all variants showed similar ability to activate nuclear factor kappaB. In contrast, only tumor-derived LMP1 variants induced prolonged Erk activation and c-Fos expression. Sequence analysis revealed only two amino acids, 212 and 366, shared by the tumor variants but distinct from B95.8. Point mutation of either amino acids 212 (glycine to serine) or 366 (serine to threonine) from the B95.8 isoform to the tumor variant version of LMP1 was sufficient for gain of function characterized by sustained activation of Erk and subsequent c-Fos induction and binding to the AP1 site. Our results indicate that the enhanced ability of tumor-derived LMP1 to induce and stabilize the c-Fos oncogene can be localized to two amino acids in the C terminus of LMP1.

The 22.5 kDa spectrin-binding domain of ankyrinR binds spectrin with high affinity and changes the spectrin distribution in cells in vivo

It was previously shown that ankyrins play a crucial role in the membrane skeleton arrangement. Purifying ankyrinR obtained from erythrocytes is a time-consuming process. Therefore, cloned and bacterially expressed ankyrinR-spectrin-binding domain (AnkSBD) is a demanded tool for studying spectrin-ankyrin interactions. In this communication, we report on the cloning and purification of AnkSBD and describe the results of binding experiments, in which we showed high-affinity interactions between the AnkSBD construct and isolated erythrocyte or non-erythroid spectrins. pEGFP-AnkSBD-transfected cells co-localised with non-erythroid spectrin in HeLa cells. The functional interactions of the AnkSBD construct in vivo and in vitro open many possibilities to study the structure and function of this domain, which has not yet been as extensively studied when compared to the aminoterminal domain of this protein.

IL-21 is expressed in Hodgkin lymphoma and activates STAT5: evidence that activated STAT5 is required for Hodgkin lymphomagenesis

Classical Hodgkin lymphoma (HL) is a malignant disorder characterized by the presence of neoplastic mononucleated Hodgkin and multinucleated Reed-Sternberg cells. Here, we show that both the interleukin (IL)-21 receptor as well as IL-21 are expressed by HL cells. IL-21 activates signal transducer of activation and transcription 3 (STAT3) and STAT5 in HL cell lines and activated human B cells. Ectopic expression of constitutively active STAT5 in primary human B cells resulted in immortalized B cells that have lost the B-cell phenotype and strongly resembled HL cells, which could partially be rescued by ectopic expression of the B cell-determining transcription factor E47. Data from experiments using reporter assays and overexpression of constitutively active IKK2 support the hypothesis that the STAT5 and nuclear factor-kappaB (NF-kappaB) pathways collaborate in HL genesis.

Flavonoids protect against cytokine-induced pancreatic beta-cell damage through suppression of nuclear factor kappaB activation

OBJECTIVES

In the past few decades, the use of natural compounds, such as flavonoids, as anti-inflammatory agents has gained much attention. Our current study focuses on the preventive effects of quercetin, apigenin, and luteolin on cytokine-induced beta-cell damage.

METHODS

Pancreatic beta-cells or islets were treated with cytokine mixtures in the presence or absence of flavonoids and the inhibitory effect of flavonoids against cytokine toxicity was determined.

RESULTS

Treatment of RINm5F (RIN) rat insulinoma cells with interleukin 1beta (IL-1beta) and interferon gamma (IFN-gamma) induced cell damage. Quercetin, apigenin, and luteolin completely protected against IL-1beta- and IFN-gamma-mediated cytotoxicity in RIN cells. Incubation with quercetin, apigenin, and luteolin resulted in a significant reduction in IL-1beta- and IFN-gamma-induced nitric oxide production, a finding that correlated well with reduced levels of the inducible form of NO synthase messenger RNA and protein. The molecular mechanism by which quercetin, apigenin, and luteolin inhibited inducible NO synthase gene expression appeared to involve the inhibition of nuclear factor kappaB (NF-kappaB) activation. The IL-1beta- and IFN-gamma-stimulated RIN cells showed increases in NF-kappaB binding activity, p50 and p65 subunit levels in nucleus, and IkappaB alpha degradation in cytosol compared with unstimulated cells. Quercetin, apigenin, and luteolin also prevented IL-1beta- and IFN-gamma-mediated inhibition of insulin secretion.

CONCLUSION

Quercetin, apigenin, and luteolin inhibited cytotoxicity in RIN cells and attenuated the decrease of glucose-stimulated insulin secretion in islets by IL-1beta and IFN-gamma.

Functional genomic delineation of TLR-induced transcriptional networks

Background

The innate immune system is the first line of defense mechanisms protecting the host from invading pathogens such as bacteria and viruses. The innate immunity responses are triggered by recognition of prototypical pathogen components by cellular receptors. Prominent among these pathogen sensors are Toll-like receptors (TLRs). We sought global delineation of transcriptional networks induced by TLRs, analyzing four genome-wide expression datasets in mouse and human macrophages stimulated with pathogen-mimetic agents that engage various TLRs.

Results

Combining computational analysis of expression profiles and cis-regulatory promoter sequences, we dissected the TLR-induced transcriptional program into two major components: the first is universally activated by all examined TLRs, and the second is specific to activated TLR3 and TLR4. Our results point to NF-κB and ISRE-binding transcription factors as the key regulators of the universal and the TLR3/4-specific responses, respectively, and identify novel putative positive and negative feedback loops in these transcriptional programs. Analysis of the kinetics of the induced network showed that while NF-κB regulates mainly an early-induced and sustained response, the ISRE element functions primarily in the induction of a delayed wave. We further demonstrate that co-occurrence of the NF-κB and ISRE elements in the same promoter endows its targets with enhanced responsiveness.

Conclusion

Our results enhance system-level understanding of the networks induced by TLRs and demonstrate the power of genomics approaches to delineate intricate transcriptional webs in mammalian systems. Such systems-level knowledge of the TLR network can be useful for designing ways to pharmacologically manipulate the activity of the innate immunity in pathological conditions in which either enhancement or repression of this branch of the immune system is desired.

Gene expression pattern in apoptotic QGY-7703 cells induced by homoharringtonine

AIM

To classify the genes responsible for apoptosis in QGY-7703 cells induced by homoharringtonine (HHT).

METHODS

Apoptosis in QGY-7703 cells induced by HHT was demonstrated by DNA fragmentation and morphological observation. cDNA microarray technology was used to detect gene transcription, and the result of microarrays for genes was confirmed by RT-PCR.

RESULTS

Seventy-eight individual mRNA were identified and their transcription levels changed significantly. Those genes, of which 68% were upregulated and 32% were downregulated, were partially related to apoptosis. They were mostly oncogenes, tumor suppressors, enzymes, and kinases.

CONCLUSION

HHT is a potential drug in the treatment of liver cancer. TGF-beta, TNF, FAS, p38MAPK, and p53 apoptosis signaling pathways were activated during apoptosis in QGY-7703 cells. Such inducible genes may play important roles in apoptosis and deserve to be further studied.

Dendritic cells from lupus-prone mice are defective in repressing immunoglobulin secretion

Autoimmunity results from a breakdown in tolerance mechanisms that regulate autoreactive lymphocytes. We recently showed that during innate immune responses, secretion of IL-6 by dendritic cells (DCs) maintained autoreactive B cells in an unresponsive state. In this study, we describe that TLR4-activated DCs from lupus-prone mice are defective in repressing autoantibody secretion, coincident with diminished IL-6 secretion. Reduced secretion of IL-6 by MRL/lpr DCs reflected diminished synthesis and failure to sustain IL-6 mRNA production. This occurred coincident with lack of NF-kappaB and AP-1 DNA binding and failure to sustain IkappaBalpha phosphorylation. Analysis of individual mice showed that some animals partially repressed Ig secretion despite reduced levels of IL-6. This suggests that in addition to IL-6, DCs secrete other soluble factor(s) that regulate autoreactive B cells. Collectively, the data show that MRL/lpr mice are defective in DC/IL-6-mediated tolerance, but that some individuals maintain the ability to repress autoantibody secretion by an alternative mechanism.

Effect of a cyclooxygenase-2 inhibitor on interleukin-1beta-stimulated activation of the transcription factor nuclear factor-kappa B in human gingival fibroblasts

BACKGROUND

In previous work, the cyclooxygenase-2 inhibitor NS-398 inhibited interleukin (IL)-1beta-stimulated prostaglandin E(2) (PGE(2)) production almost completely while partially inhibiting IL-6 production in aggressive periodontitis (AgP) human gingival fibroblasts. PGE(2) and the transcription factor nuclear factor-kappa B (NF-kappaB) regulate IL-1beta-stimulated IL-6 production. Cytoplasmic NF-kappaB is bound to inhibitors (IkappaB proteins). IL-1beta initiates a cascade resulting in phosphorylation and degradation of IkappaB, allowing nuclear translocation of NF-kappaB and target gene activation. The purpose of this study was to determine whether NS-398 inhibited phosphorylation of IkappaB and NF-kappaB activation.

METHODS

AgP fibroblasts (1 to 2 x 10(6)) were exposed to IL-1beta (1 x 10(11)M) with or without NS-398 (10 nM) in serum-free medium. The NF-kappaB subunit p65 and phospho-IkappaBalpha were measured in whole cell, cytoplasmic, or nuclear extracts, using colorimetric assays. Enzyme-linked immunosorbent assays were used to measure PGE(2) and IL-6 production by 2.5 x 10(4) cells after exposure to IL-1beta with or without NS-398 in serum-free medium.

RESULTS

Consistent with previous results, NS-398 reduced IL-1beta-stimulated PGE(2) by approximately 98% (P <0.001) and IL-6 by approximately 65% (P <0.001). IL-1beta increased nuclear and cytoplasmic p65 ( approximately 8-fold [P <0.001] and approximately 2.5-fold [P <0.03], respectively) over control levels. NS-398 reduced IL-1beta-stimulated nuclear and cytoplasmic p65 to control levels. IL-1beta increased phospho-IkappaBalpha in whole cell extracts by a maximum of approximately 9.5 times (P = 0.0001), and this was inhibited significantly by NS-398 (P <or=0.008).

CONCLUSIONS

NS-398 inhibited NF-kappaB activation and nuclear p65 levels in human gingival fibroblasts. This seemed to be due to inhibition of the phosphorylation cascade resulting in formation of phospho-IkappaBalpha and free p65. NF-kappaB inhibition may be useful in treating inflammatory diseases such as AgP.

Activation of peroxisome proliferator-activated receptor-γ protects pancreatic β-cells from cytokine-induced cytotoxicity via NFκB pathway

Diabetes mellitus is characterized by cytokine-induced insulitis and a deficit in beta-cell mass. Ligands for peroxisome proliferator-activated receptor-gamma (PPAR-gamma) have been shown to have anti-inflammatory effects in various experimental models. We questioned whether activation of endogenous PPAR-gamma by either PPAR-gamma ligands or adenoviral-directed overexpression of PPAR-gamma (Ad-PPAR-gamma) could inhibit cytokine-induced beta-cell death in RINm5F (RIN) cells, a rat insulinoma cell line. Treatment of RIN cells with interleukin-1 beta (IL-1 beta) and interferon-gamma (IFN-gamma) induced beta-cell damage through NF kappaB-dependent signaling pathways. Activation of PPAR-gamma by PPAR-gamma ligands or Ad-PPAR-gamma inhibited IL-1 beta and IFN-gamma-stimulated nuclear translocation of the p65 subunit and DNA binding activity. NF kappaB target gene expression and their product formation, namely inducible nitric oxide synthase and cyclooxygenase-2 were decreased by PPAR-gamma activation, as established by real-time PCR, Western blots and measurements of NO and PGE(2). The mechanism by which PPAR-gamma activation inhibited NF kappaB-dependent cell death signals appeared to involve the inhibition of I kappa B alpha degradation, evidenced by inhibition of cytokine-induced NF kappaB-dependent signaling events by Ad-I kappaB alpha (S32A, S36A), non-degradable I kappaB alpha mutant. I kappaB beta mutant, Ad-I kappaB beta (S19A, S23A) was not effective in preventing cytokine toxicity. Furthermore, a protective effect of PPAR-gamma ligands was proved by assaying for normal insulin secreting capacity in response to glucose in isolated rat pancreatic islets. The beta-cell protective function of PPAR-gamma ligands might serve to counteract cytokine-induced beta-cell destruction.

MKK3/6-p38 MAPK signaling is required for IL-1beta and TNF-alpha-induced RANKL expression in bone marrow stromal cells

Coupled bone turnover is directed by the expression of receptor-activated NF-kappaB ligand (RANKL) and its decoy receptor, osteoprotegerin (OPG). Proinflammatory cytokines, such as interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) induce RANKL expression in bone marrow stromal cells. Here, we report that IL-1beta and TNF-alpha-induced RANKL requires p38 mitogen-activating protein kinase (MAPK) pathway activation for maximal expression. Real-time PCR was used to assess the p38 contribution toward IL-1beta and TNF-alpha-induced RANKL mRNA expression. Steady-state RANKL RNA levels were increased approximately 17-fold by IL-1beta treatment and subsequently reduced approximately 70%-90% when p38 MAPK was inhibited with SB203580. RANKL mRNA stability data indicated that p38 MAPK did not alter the rate of mRNA decay in IL-1beta-induced cells. Using a RANKL-luciferase cell line receptor containing a 120-kB segment of the 5' flanking region of the RANKL gene, reporter expression was stimulated 4-5-fold by IL-1beta or TNF-alpha treatment. IL-1beta-induced RANKL reporter expression was completely blocked with specific p38 inhibitors as well as dominant negative mutant constructs of MAPK kinase-3 and -6. In addition, blocking p38 signaling in bone marrow stromal cells partially inhibited IL-1beta and TNF-alpha-induced osteoclastogenesis in vitro. Results from these studies indicate that p38 MAPK is a major signaling pathway involved in IL-1beta and TNF-alpha-induced RANKL expression in bone marrow stromal cells.

Upregulated expression of kappa light chain by Epstein-Barr virus encoded latent membrane protein 1 in nasopharyngeal carcinoma cells via NF-kappaB and AP-1 pathways

B lymphocytes are generally considered to be the only source of immunoglobulins. However, increasing evidence revealed that some human epithelial cancer cell lines, including nasopharyngeal carcinoma (NPC) cell lines, expressed immunoglobulins. Moreover, we previously found that expression of kappa light chain in NPC cells could be upregulated by EBV-encoded latent membrane protein 1 (LMP1). Here, Western blot and flow cytometric analysis of intracellular kappa staining indicated that upregulation of the expression of kappa was inhibited by using LMP1-targeted DNAzyme and that Bay11-7082 and SP600125, inhibitors of JNK and NF-kappaB, respectively, inhibited LMP1-augmented kappa light chain expression in NPC cells. LMP1-positive NPC cells expressing the dominant-negative mutant of IkappaBalpha (DNMIkappaBalpha) or of c-Jun (TAM67) exhibited significantly decreasing kappa production compared with their parental cells. These results suggest that LMP1 elevated kappa light chain through activation of the NF-kappaB and AP-1 signaling pathways. The present study provided some hints of possible mechanisms by which human cancer cells of epithelial origin produced immunoglobulins.

Role of scavenger receptor MARCO in macrophage responses to CpG oligodeoxynucleotides

The macrophage Class A scavenger receptor MARCO (macrophage receptor with a collagenous structure) functions as a pattern-recognition receptor for bacterial components, but its role in responses to CpG oligonucleotide sequences (CpG-ODN) in microbial DNA has not been characterized. Phosphorothioate (PS)-linked CpG-ODN stimulated IL-12 and NO production in wild-type but not in MARCO-deficient, thioglycollate-elicited peritoneal macrophages. MARCO and the related class A receptor SR-A belong to a redundant system of receptors for PS ODNs. The ability of MARCO to bind CpG-ODNs and conversely, to costimulate IL-12 and NO production upon specific ligation with immobilized mAb is consistent with MARCO being a signaling receptor for CpG-ODNs, costimulating TLR9-mediated NO and IL-12 production in macrophages. In contrast to MARCO, SR-A is likely to mediate negative regulation of macrophage responses to CpG-ODNs. In particular, increased affinity toward SR-A may contribute to decreased potency of oligo G-modified CpG-ODNs in stimulating IL-12 production. The results suggest that differential involvement of activating and inhibitory membrane receptors, such as SR-A and MARCO, may underlie profound differences observed in biological activities of different ODN sequences.

Glycogen synthase kinase 3beta functions to specify gene-specific, NF-kappaB-dependent transcription

Loss of glycogen synthase kinase 3beta (GSK-3beta) in mice results in embryonic lethality via hepatocyte apoptosis. Consistent with this result, cells from these mice have diminished nuclear factor kappaB (NF-kappaB) activity, implying a functional role for GSK-3beta in regulating NF-kappaB. Here, we have explored mechanisms by which GSK-3beta may control NF-kappaB function. We show that cytokine-induced IkappaB kinase activity and subsequent phosphorylation of IkappaBalpha, p105, and p65 are not affected by the absence of GSK-3beta activity. Furthermore, nuclear accumulation of p65 following tumor necrosis factor treatment is unaffected by the loss of GSK-3beta. However, NF-kappaB DNA binding activity is reduced in GSK-3beta null cells and in cells treated with a pharmacological inhibitor of GSK-3. Expression of certain NF-kappaB-regulated genes, such as IkappaBalpha and macrophage inflammatory protein 2, is minimally affected by the absence of GSK-3beta. Conversely, we have identified a subset of NF-kappaB-regulated genes, including those for interleukin-6 and monocyte chemoattractant protein 1, that require GSK-3beta for efficient expression. We show that efficient localization of p65 to the promoter regions of the interleukin-6 and monocyte chemoattractant protein 1 genes following tumor necrosis factor alpha treatment requires GSK-3beta. Therefore, GSK-3beta has profound effects on transcription in a gene-specific manner through a mechanism involving control of promoter-specific recruitment of NF-kappaB.

HDAC inhibition prevents NF-kappa B activation by suppressing proteasome activity: down-regulation of proteasome subunit expression stabilizes I kappa B alpha

The short chain fatty acid (SCFA) butyrate (BA) and other histone deacetylase (HDAC) inhibitors can rapidly induce cell cycle arrest and differentation of colon cancer cell lines. We found that butyrate and the specific HDAC inhibitor trichostatin A (TSA) can reprogram the NF-(kappa)B response in colon cancer cells. Specifically, TNF-alpha activation is suppressed in butyrate-differentiated cells, whereas IL-1beta activation is largely unaffected. To gain insight into the relationship between butyrate-induced differentiation and NF-(kappa)B regulation, we determined the impact of butyrate on proteasome activity and subunit expression. Interestingly, butyrate and TSA reduced the cellular proteasome activity in colon cancer cell lines. The drop in proteasome activity results from the reduced expression of the catalytic beta-type subunits of the proteasome at both the protein and mRNA level. The selective impact of HDAC inhibitors on TNF-alpha-induced NF-(kappa)B activation appears to relate to the fact that the TNF-alpha-induced activation of NF-(kappa)B is mediated by the proteasome, whereas NF-kappaB activation by IL-1beta is largely proteasome-independent. These findings indicate that cellular differentation status and/or proliferative capacity can significantly impact proteasome activity and selectively alter NF-(kappa)B responses in colon cancer cells. This information may be useful for the further development and targeting of HDAC inhibitors as anti-neoplastic and anti-inflammatory agents.

Distinct transcriptional profiles characterize oral epithelium-microbiota interactions

Transcriptional profiling, bioinformatics, statistical and ontology tools were used to uncover and dissect genes and pathways of human gingival epithelial cells that are modulated upon interaction with the periodontal pathogens Actinobacillus actinomycetemcomitans and Porphyromonas gingivalis. Consistent with their biological and clinical differences, the common core transcriptional response of epithelial cells to both organisms was very limited, and organism-specific responses predominated. A large number of differentially regulated genes linked to the P53 apoptotic network were found with both organisms, which was consistent with the pro-apoptotic phenotype observed with A. actinomycetemcomitans and anti-apoptotic phenotype of P. gingivalis. Furthermore, with A. actinomycetemcomitans, the induction of apoptosis did not appear to be Fas- or TNF(alpha)-mediated. Linkage of specific bacterial components to host pathways and networks provided additional insight into the pathogenic process. Comparison of the transcriptional responses of epithelial cells challenged with parental P. gingivalis or with a mutant of P. gingivalis deficient in production of major fimbriae, which are required for optimal invasion, showed major expression differences that reverberated throughout the host cell transcriptome. In contrast, gene ORF859 in A. actinomycetemcomitans, which may play a role in intracellular homeostasis, had a more subtle effect on the transcriptome. These studies help unravel the complex and dynamic interactions between host epithelial cells and endogenous bacteria that can cause opportunistic infections.

Degradation of Chlamydia pneumoniae by peripheral blood monocytic cells

Chlamydia pneumoniae is a common human respiratory pathogen that has been associated with a variety of chronic diseases, including atherosclerosis. The role of this organism in the pathogenesis of atherosclerosis remains unknown. A key question is how C. pneumoniae is transferred from the site of primary infection to a developing atherosclerotic plaque. It has been suggested that circulating monocytes could be vehicles for dissemination of C. pneumoniae since the organism has been detected in peripheral blood monocytic cells (PBMCs). In this study we focused on survival of C. pneumoniae within PBMCs isolated from the blood of healthy human donors. We found that C. pneumoniae does not grow and multiply in cultured primary monocytes. In C. pneumoniae-infected monocyte-derived macrophages, growth of the organism was very limited, and the majority of the bacteria were eradicated. We also found that the destruction of C. pneumoniae within infected macrophages resulted in a gradual diminution of chlamydial antigens, although some of these antigens could be detected for days after the initial infection. The detected antigens present in infected monocytes and monocyte-derived macrophages represented neither chlamydial inclusions nor intact organisms. The use of {N-[7-(4-nitrobenzo-2-oxa-1,3-diazole)]}-6-aminocaproyl-d-erythro-sphingosine as a vital stain for chlamydiae proved to be a sensitive method for identifying rare C. pneumoniae inclusions and was useful in the detection of even aberrant developmental forms.

Constitutive Nuclear Expression of the IκB Kinase Complex and Its Activation in Human Neutrophils

A singular feature of human neutrophils is that they constitutively express substantial amounts of NF-kappaB/Rel proteins and IkappaB-alpha in the nucleus. In this study, we show that in these cells, IkappaB kinase alpha (IKKalpha), IKKbeta, and IKKgamma also partially localize to the nucleus, whereas IKK-related kinases (IKKepsilon, TANK-binding kinase-1) are strictly cytoplasmic, and the NF-kappaB-inducing kinase is strictly nuclear. Following neutrophil activation, IKKbeta and IKKgamma become transiently phosphorylated in both the cytoplasm and nucleus, whereas IKKalpha transiently vanishes from both compartments in what appears to be an IKKbeta-dependent process. These responses are paralleled by the degradation of IkappaB-alpha, and by the phosphorylation of RelA on serine 536, in both compartments. Although both proteins can be IKK substrates, inhibition of IKK prevented IkappaB-alpha phosphorylation, while that of RelA was mostly unaffected. Finally, we provide evidence that the nuclear IKK isoforms (alpha, beta, gamma) associate with chromatin following neutrophil activation, which suggests a potential role in gene regulation. This is the first study to document IKK activation and the phosphorylation of NF-kappaB/Rel proteins in primary neutrophils. More importantly, our findings unveil a hitherto unsuspected mode of activation for the IKK/IkappaB signaling cascade within the cell nucleus.

Ikappabeta-related vankyrin genes in the Campoletis sonorensis ichnovirus: temporal and tissue-specific patterns of expression in parasitized Heliothis virescens lepidopteran hosts

Polydnaviruses (PDVs) are unusual insect viruses that occur in obligate symbiotic associations with parasitic ichneumonid (ichnoviruses, or IVs) and braconid (bracoviruses, or BVs) wasps. PDVs are injected with eggs, ovarian proteins, and venom during parasitization. Following infection of cells in host tissues, viral genes are expressed and their products function to alter lepidopteran host physiology, enabling endoparasitoid development. Here we describe the Campoletis sonorensis IV viral ankyrin (vankyrin) gene family and its transcription. The seven members of this gene family possess ankyrin repeat domains that resemble the inhibitory domains of the Drosophila melanogaster NF-kappabeta transcription factor inhibitor (Ikappabeta) cactus. vankyrin gene expression is detected within 2 to 4 h postparasitization (p.p.) in Heliothis virescens hosts and reaches peak levels by 3 days p.p. Our data indicate that vankyrin genes from the C. sonorensis IV genome are differentially expressed in the tissues of parasitized hosts and can be divided into two subclasses: those that target the host fat body and those that target host hemocytes. Polyclonal antibodies raised against a fat-body targeting vankyrin detected a 19-kDa protein in crude extracts prepared from the 3 days p.p. fat body. Vankyrin-specific Abs localized to 3-day p.p. fat-body and hemocyte nuclei, suggesting a role for vankyrin proteins in the nuclei of C. sonorensis IV-infected cells. These data are evidence for divergent tissue specificities and targeting of multigene families in IVs. We hypothesize that PDV vankyrin genes may suppress NF-kappabeta activity during immune responses and developmental cascades in parasitized lepidopteran hosts of C. sonorensis.

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.

High levels of p105 (NFKB1) and p100 (NFKB2) proteins in HPV16-transformed keratinocytes: role of E6 and E7 oncoproteins

We have previously shown that functional components of the NF-kappaB signaling pathway are up-regulated and sequestered in the cytoplasm of human papillomavirus 16 (HPV16)-transformed cell lines leading to a reduced activity of NF-kappaB. In this study, we examined the expression of the NF-kappaB precursors p100 and p105 in keratinocytes transformed or not by HPV16. Western immunoblotting experiments demonstrated high levels of p100 and p105 proteins not only in HPV16+ cervical carcinoma-derived keratinocytes but also in keratinocytes stably transfected by HPV16 E6 or E7 oncogenes. Moreover, p100 and p105 proteins were predominantly cytoplasmic and nuclear in keratinocytes expressing E7 and E6, respectively. A predominantly cytoplasmic localization of E7 protein was also detected in all keratinocytes expressing E7. Our results suggest that HPV16 E6 and E7 proteins modulate the expression and the subcellular localization of p100 and p105 NF-kappaB precursors.

Stroma-Mediated Dysregulation of Myelopoiesis in Mice Lacking IκBα

Hematopoiesis occurs in the liver and the bone marrow (BM) during murine development. Newborn mice with a ubiquitous deletion of I kappa B alpha develop a severe hematological disorder characterized by an increase of granulocyte/erythroid/monocyte/macrophage colony-forming units (CFU-GEMM) and hypergranulopoiesis. Here, we report that this particular myeloproliferative disturbance is mediated by continuously deregulated perinatal expression of Jagged1 in I kappa B alpha-deficient hepatocytes. The result is a permanent activation of Notch1 in neutrophils. In contrast, in mice with a conditional deletion of I kappa B alpha only in the myeloid lineage (ikba(flox/flox) x LysM-Cre) and in fetal liver cell chimeras (ikba(FL delta/FL delta)), a cell-autonomous induction of the myeloproliferative disease was not observed. Coculture of I kappa B alpha-deficient hepatocytes with wild-type (wt) BM cells induced a Jagged1-dependent increase in CFUs. In summary, we show that cell-fate decisions leading to a premalignant hematopoietic disorder can be initiated by nonhematopoietic cells with inactive I kappa B alpha.

Cycloprodigiosin up-regulates inducible nitric oxide synthase gene expression in hepatocytes stimulated by interleukin-1beta

The proinflammatory cytokine interleukin-1beta stimulates inducible nitric oxide synthase (iNOS) gene expression in hepatocytes via activation of a transcription factor, nuclear factor-kappaB (NF-kappaB). Nitric oxide has diverse cytoprotective and toxic effects. Cycloprodigiosin is an anticancer drug that induces apoptosis through NF-kappaB-dependent mechanisms. This study investigated whether cycloprodigiosin influenced NF-kappaB activation and induction of iNOS by interleukin-1beta. Cycloprodigiosin alone had no effect on NO production by primary cultured rat hepatocytes. Simultaneous addition of cycloprodigiosin and interleukin-1beta markedly stimulated the induction of iNOS mRNA and protein compared with addition of interleukin-1beta alone, resulting in overproduction of NO. Cycloprodigiosin had no effect on degradation of the inhibitory subunit of NF-kappaB (IkappaBalpha), but lessened the recovery of IkappaBalpha levels. The electrophoretic mobility shift assay revealed that cycloprodigiosin caused an increase of NF-kappaB activation. Consistent with this observation, cycloprodigiosin promoted the translocation of p65 (a subunit of NF-kappaB) to the nucleus. Furthermore, this drug enhanced expression of the type 1 interleukin-1 receptor, and this action showed similar concentration-dependence to its induction of iNOS. These results indicate that cycloprodigiosin up-regulates the induction of iNOS by increasing NF-kappaB activation, at least partly through enhancement of type 1 interleukin-1 receptor expression. By regulating the expression of NF-kappaB-dependent genes, such as iNOS, cycloprodigiosin administration may increase NO production during hepatic injury.

Mechanisms of glucocorticoid-induced apoptosis in hematologic malignancies: updates

PURPOSE OF REVIEW

Glucocorticoids remain a central component of the therapeutic armamentarium for a broad spectrum of hematologic malignancies. There is an extensive body of evidence suggesting that the efficacy of glucocorticoids stems from their ability to mediate apoptosis in leukemia, lymphoma, and myeloma cells.

RECENT FINDINGS

Traditionally, glucocorticoid-induced apoptosis is divided into three stages: an initiation stage, which involves glucocorticoid receptor activation and glucocorticoid receptor-mediated gene regulation; a decision stage, which engages the prosurvival and proapoptotic factors at the mitochondrial level; and an execution stage, which implicates caspases and endonuclease activation. Recent discoveries have clarified many aspects of the apoptotic pathway, including activation of the caspases cascade and multicatalytic proteasome, suppression of prosurvival transcription factors such as AP-1, c-myc, nuclear factor-kappaB, as well as cross-talk between the T-cell receptor and cytokine signaling pathways.

SUMMARY

This review focuses primarily on insights gained during recent years into the mechanism of the signaling pathways responsible for mediating glucocorticoid-induced apoptosis in hematologic malignancies. This information provides a scientific basis to explore synergistic approaches that may enhance glucocorticoid-induced apoptosis and may bypass mechanism of resistance.

Cloning and characterization of a homologue of the alpha inhibitor of NF-κB in Rainbow trout (Oncorhynchus mykiss)

A homologue of IkappaBalpha, the alpha member of the IkappaB family of NF-kappaB inhibitors, was identified in a Rainbow trout suppression subtractive hybridization library enriched in sequences up-regulated in cultured leukocytes after lipopolysaccharide (LPS) and tumor necrosis factor alpha (TNFalpha) stimulation. The full-length cDNA was isolated and sequenced. The predicted amino acid sequence is 61.5% similar and 54% identical to human IkappaBalpha, while only 42% similar and 35% identical to IkappaBbeta, and 38% similar and 32% identical to IkappaBvarepsilon. Rainbow trout IkappaBalpha contains a central ankyrin repeat domain required for its interaction with NF-kappaB and a putative PEST-like sequence in the C-terminus. Expression of IkappaBalpha is up-regulated by LPS and TNFalpha treatment, two known activators of NF-kappaB, suggesting the existence of an autoregulatory loop in fish, as is the case for mammals. These results confirm the existence of the NF-kappaB signalling pathway in fish and suggest a similar functional interaction between IkappaBalpha and NF-kappaB.

Positive and negative regulation of nuclear factor-kappaB-mediated transcription by IkappaB-zeta, an inducible nuclear protein

IkappaB-zeta is an inducible nuclear protein that interacts with nuclear factor-kappaB (NF-kappaB) via its carboxyl-terminal ankyrin-repeats. Previous studies using an NF-kappaB reporter have shown that IkappaB-zeta inhibits the activity of NF-kappaB. In the present study, we dissected the amino-terminal region of IkappaB-zeta, which shows no homology to any other proteins. Indirect immunofluorescence studies demonstrated the presence of a bipartite nuclear localization signal spanning amino acids 163-178. Using GAL4 fusion proteins, we found that internal fragments containing amino acids 329-402 possessed intrinsic transcriptional activation activity. Interestingly, the activity was not detected in GAL4 fusion proteins of the full-length IkappaB-zeta. On the other hand, the GAL4-dependent transcriptional activity was generated by co-expression of the GAL4-NF-kappaB p50 subunit fusion protein and the full-length IkappaB-zeta, neither of which exhibited the activity on their own. A new splicing variant, IkappaB-zeta(D), with a deletion of amino acids 236-429, was found to lack transactivation activity. Forced expression of IkappaB-zeta, but not IkappaB-zeta(D), augmented interleukin-6 production, indicating the functional significance of the transactivation activity. In contrast, tumor necrosis factor-alpha production was inhibited by expression of IkappaB-zeta, highlighting the dual functions of this molecule. These results indicate that IkappaB-zeta harbors latent transcriptional activation activity, and that the activity is expressed upon interaction with the NF-kappaB p50 subunit. In addition to the inhibitory activity on NF-kappaB-mediated transcription, the transcriptional activation activity of IkappaB-zeta should be crucial for the regulation of inflammation.

How adhesion, migration, and cytoplasmic calcium transients influence interleukin-1beta mRNA stabilization in human monocytes

We investigated the mechanisms by which primary human monocyte migration and the production of important cytokines are co-regulated. Motile monocytes underwent cyclic morphologic and adhesive changes that were associated with intracellular free calcium changes; in such cells, cytokine transcripts were unstable and translationally repressed. Agents that activate monocytes, including lipopolysacharrides (LPS), cytomegalovirus (CMV), and tumor necrosis factor (TNFalpha), have been shown to de-repress translation and these agents stabilize adhesion-induced transcripts for IL-lbeta and IL-8 and markedly diminish cell migration in the presence of autologous serum. LPS suppressed Rho A activity and either this agent or C3 transferase elevated intracellular free calcium, stabilized transcripts, and, in tandem, inhibited cell migration by preventing tail retraction, a prerequisite for cell translocation. These results, therefore, suggest that monocyte activating agents inhibit the RhoA pathway and continuously elevate intracellular calcium leading to a concomitant decrease in monocyte migration and stabilization of cytokine transcripts prior to translation.

The effects of calpain inhibition on IkB alpha degradation after activation of PBMCs: identification of the calpain cleavage sites

Human peripheral blood mononuclear cells (PBMCs) were activated using anti-CD3/CD28 (HIT3A/CD28.2) resulting in degradation of IkB alpha, an inhibitor of NFkB, relative to unactivated cells. Degradation of IkB alpha began by 30 min and proceeded for at least 5 h. Calpeptin, a calpain inhibitor, inhibited IkB alpha degradation in a time- and dose-dependent manner. Furthermore, calpain inhibition increased IkB alpha levels compared to nonactivated controls. Recombinant IkB alpha was incubated with purified porcine m-calpain in the presence of 0.1% Triton X-100, and the degradation products were monitored by SDS-PAGE and sequenced. Most of the degradation products were peptides derived from calpain, but one was derived from IkB alpha cleaved between amino acids 50 and 51 (glutamine and glutamic acid). The liberated fragment included the entire signal response domain (SRD), a region containing key serine and threonine residues necessary for phosphorylation by the IKKinase complex and sites required for ubiquitination. The results suggest that calpain plays an important role in IkB alpha degradation, a crucial event in T cell activation.

Ultraviolet A Radiation-Induced Immediate Iron Release Is a Key Modulator of the Activation of NF-κB in Human Skin Fibroblasts

Ultraviolet A (UVA, 320-400 nm) radiation, an oxidizing component of sunlight, leads to an immediate increase in the labile iron in human skin fibroblasts. Exposure of skin fibroblasts to UVA radiation is also known to induce nuclear factor-kappaB (NF-kappaB) DNA-binding activity, although the underlying mechanism is unclear. We report here that in skin fibroblasts, the extent of NF-kappaB activation by UVA tightly correlates with the level of "UVA-induced" labile iron release as shown by both iron chelation and iron loading treatments. Furthermore, our data indicate that the slow kinetics of induction of NF-kappaB by UVA relative to other oxidants previously studied is due to a transient increase in permeability of nuclear membrane to proteins and occurs as a result of labile iron-mediated damage to nuclear membrane. Since in addition to iron chelators, lipid peroxidation inhibitors also decrease the UVA-mediated induction of NF-kappaB, we propose that the rapid release of labile iron by UVA might act as a catalyst to exacerbate the generation of lipid secondary messengers in skin cell membranes that are responsible for induction of NF-kappaB. This novel role for iron in amplifying NF-kappaB mobilization in response to UVA-induced oxidative stress aids understanding of its involvement in UV-induced skin inflammation.