The DNA binding subunit of NF-kappa B is identical to factor KBF1 and homologous to the rel oncogene product

Shared pathways of IkappaB kinase-induced SCF(betaTrCP)-mediated ubiquitination and degradation for the NF-kappaB precursor p105 and IkappaBalpha

p105 (NFKB1) acts in a dual way as a cytoplasmic IkappaB molecule and as the source of the NF-kappaB p50 subunit upon processing. p105 can form various heterodimers with other NF-kappaB subunits, including its own processing product, p50, and these complexes are signal responsive. Signaling through the IkappaB kinase (IKK) complex invokes p105 degradation and p50 homodimer formation, involving p105 phosphorylation at a C-terminal destruction box. We show here that IKKbeta phosphorylation of p105 is direct and does not require kinases downstream of IKK. p105 contains an IKK docking site located in a death domain, which is separate from the substrate site. The substrate residues were identified as serines 923 and 927, the latter of which was previously assumed to be a threonine. S927 is part of a conserved DSGPsi motif and is functionally most critical. The region containing both serines is homologous to the N-terminal destruction box of IkappaBalpha, -beta, and -epsilon. Upon phosphorylation by IKK, p105 attracts the SCF E3 ubiquitin ligase substrate recognition molecules betaTrCP1 and betaTrCP2, resulting in polyubiquitination and complete degradation by the proteasome. However, processing of p105 is independent of IKK signaling. In line with this and as a physiologically relevant model, lipopolysaccharide (LPS) induced degradation of endogenous p105 and p50 homodimer formation, but not processing in pre-B cells. In mutant pre-B cells lacking IKKgamma, processing was unaffected, but LPS-induced p105 degradation was abolished. Thus, a functional endogenous IKK complex is required for signal-induced p105 degradation but not for processing.

Cloning and characterization of a potential transcriptional activator of human gamma-globin genes

Hybrids produced by fusing human fetal erythroblasts (HFE) with mouse erythroleukemia (MEL) cells initially produce predominantly or exclusively human gamma-globin and switch to human beta globin expression as time in culture advances. One explanation for the initially predominant expression of gamma-globin gene in these hybrids is the presence of trans-acting factors that activate gamma-globin gene transcription. We used differential display of hybrids before and after the gamma to beta switch as well as fetal liver and adult erythroblasts to identify cDNAs that could be candidates for potential gamma gene activators. Identically sized amplicons which were present in fetal liver erythroblasts and in the hybrids expressing only gamma-globin but were absent in the adult erythroblasts and in the same hybrids after they had switched to beta globin expression were cloned and sequenced. Fifty pairs of cDNAs fitting these criteria were chosen for further analysis. The sequences of the two members of 48 pairs differed from each other, revealing the low efficiency of this experimental approach. One clone pair coded for human proteosome subunit X. The second pair coded for a protein containing an acidic domain in the N-terminus and three consecutive CDC10/SW16/ankyrin repeats in the C-terminus. Transactivation assays in the yeast hybrid system and transient transfection assays in COS cells showed that a potent trans-activating domain resides in the N-terminus of this protein. Northern blot and RT-PCR assays showed that this gene is expressed in several fetal tissues but not in adult tissues. Stable transfection assays provided evidence that the product of this gene may increase the level of gamma mRNA in HFE x MEL cell hybrids that undergo the gamma to beta switch, suggesting that this new gene encodes a protein that may function as gamma gene activator.

HTLV-I Tax related dysfunction of cell cycle regulators and oncogenesis of adult T cell leukemia

HTLV-I is causually related to the oncogenesis of adult T cell leukemia (ATL). However, the precise mechanism of HTLV-I oncogenesis is unclear. HTLV-I Tax protein functions as an activator of various cellular genes, including IL-2, IL-2 receptor-alpha, and c-fos through the activation of nuclear transfer factors such as NF-kappaB and SRF, and also potently activates trascription of viral genes through CREB/ATF sites in the viral LTR. However, Tax activation of HTLV-I infected T cells through the above pathways induces polyclonal proliferation of the cells in vitro; Tax however may function only transiently in the immediate post-infection period following infection in vivo. The long latent period of 60 years from infection to onset of disease suggests other mechanisms for ATL oncogenesis. Recent studies suggest that the malignant transformation of ATL is a multi-hit phenomena, suggesting that discrete genetic events are responsible for ATL oncogenesis. These genetic events could be responsible for the different stages of ATL: smoldering, chronic, lymphoma, and acute type, p16 and p53 genes are important negative regulators of the cell cycle and are often found to be mutated in neoplasms. Recent studies including ours demonstrated a high frequency of alteration of these two genes in primary ATL cells. Furthermore, alteration of the two genes is associated with acute but not chronic type ATL. In addition, p16 gene alteration is linked to the growth rate of ATL cells, suggesting that the alteration of these cell cycle regulatory genes may be related to progression from smoldering or chronic to acute or lymphoma type ATL. Tax may be involved in mutagenesis of these genes through suppression of DNA-beta polymerase gene expression during the process from latent period to acute/lymphoma type. Once transformation occurs, activation of the pathway between Tax and the three nuclear transfer factors, NF-kappaB, SRF, and CREB/ATF, contributes to establish the aggressive manifestations of acute/lymphoma type ATL cells.

TNF-alpha-dependent activation of NF-kappa B in human osteoblastic HOS-TE85 cells is repressed in vector-averaged gravity using clinostat rotation

Effects of vector-averaged gravity on tumor necrosis factor (TNF)-alpha-dependent activation of nuclear factor kappa B (NF-kappa B) in human osteoblastic HOS-TE85 cells were investigated by culturing the cells using clinostat rotation (clinorotation). Cell cultures were rotated for 72 h at 40 rpm in a clinostat. At the end of clinorotation, the cells were treated with TNF-alpha for 30 min under stationary conditions. Electrophoretic mobility shift assays revealed that TNF-alpha-dependent activation of NF-kappa B was markedly reduced in the clinorotated cells when compared with the cells in control stationary cultures or after horizontal rotation (motional controls). The NF-kappa B-dependent transactivation was also impaired in the clinorotated cells, as evidenced by a transient transfection assay with a reporter plasmid containing multimerized NF-kappa B sites. Consistent with these findings, the TNF-alpha-dependent induction of endogenous NF-kappa B-responsive genes p105, I kappa B-alpha, and IL-8, was significantly attenuate in clinorotated cells. These results demonstrate that vector-averaged gravity inhibits the responsiveness of osteoblasts to TNF-alpha by repressing NF-kappa B activation.

MHC class I gene expression and regulation

Major histocompatibility complex (MHC) is a conglomerate of genes that play an important role in recognition of self and nonself. These genes are under tight control. In this review we have discussed the transcription processes regulating MHC gene expression. Various biological or chemical modulators can modulate MHC gene expression. The promoter region of class I genes can be activated through several pathways. Hence, these genes are not typical "domestic" genes. Extensive studies on regulation of MHC class I expression, using transfection techniques and transgenic animal models, have resulted in identification of various cis-acting sequences involved in positive and negative regulation of class I genes. Work is in progress to identify the transacting proteins that bind to these sites and to delineate the mechanisms that regulate constitutive and inducible expression of class I genes in normal and diseased cells. It has been seen that various biological molecules (IFN, GM-CSF, IL-2) and other chemicals up-regulate the MHC expression. If the exact mechanisms are known by which the expression of class I genes is up regulated, the efforts can be made to balance the beneficial and toxic effects of biological molecules with one another, which may facilitate the use of combination of these molecules in subpharmacological doses (to eliminate toxicity) for early and better management of neoplastic diseases, as it is well-known that during malignancy MHC gene expression is down-regulated. In the future, the use of transgenic and knockout mice will be useful in acquiring a better understanding, which may further help in cancer therapy.

IkappaBalpha and IkappaBalpha /NF-kappa B complexes are retained in the cytoplasm through interaction with a novel partner, RasGAP SH3-binding protein 2

IkappaBalpha inhibits the transcriptional activity of NF-kappaB both in the cytoplasm by preventing the nuclear translocation of NF-kappaB and in the nucleus where it dissociates NF-kappaB from DNA and transports it back to the cytoplasm. Cytoplasmic localization of inactive NF-kappaB/IkappaBalpha complexes is controlled by mutual masking of nuclear import sequences of NF-kappaB p65 and IkappaBalpha and active CRM1-mediated nuclear export. Here, we describe an additional mechanism accounting for the cytoplasmic anchoring of IkappaBalpha or NF-kappaB/IkappaBalpha complexes. The N-terminal domain of IkappaBalpha contains a sequence responsible for the cytoplasmic retention of IkappaBalpha that is specifically recognized by G3BP2, a cytoplasmic protein that interacts with both IkappaBalpha and IkappaBalpha/NF-kappaB complexes. G3BP2 is composed of an N-terminal domain homologous to the NTF2 protein, followed by an acidic domain sufficient for the interaction with the IkappaBalpha cytoplasmic retention sequence, a region containing five PXXP motifs and a C-terminal domain containing RNA-binding motifs. Overexpression of G3BP2 directly promotes retention of IkappaBalpha in the cytoplasm, indicating that subcellular distribution of IkappaBalpha and NF-kappaB/IkappaBalpha complexes likely results from a equilibrium between nuclear import, nuclear export, and cytoplasmic retention. The molecular organization of G3BP2 suggests that this putative scaffold protein might connect the NF-kappaB signal transduction cascade with cellular functions such as nuclear transport or RNA metabolism.

One path to cell death in the nervous system

Both acute and chronic insults to the nervous system can result in changes in homeostasis that result in cell death or recovery processes that alter function. The signaling mechanisms for this broad spectrum of events that impair neurological function span the gamut from abrupt injury to the slow onset of neurodegenerative diseases in extreme aging. A common element in all of these events is the triggering of signal cascades that determine cellular commitment to apoptosis as a ameliorative alternative to inflammatory necrosis. Key in these cascades is the activation of the caspase and Bcl-family of proteins by the NF-kappaB transcription factor. Here we consider aspects of specificity of activation as a result of the differential expression of NF-kappaB proteins and their regulation of selective genes as a result of binding to select DNA consensus sequences out of the 64 different combinations that constitute the NF-kappaB DNA binding consensus sequence.

Protein kinase C-zeta mediates TNF-alpha-induced ICAM-1 gene transcription in endothelial cells

We addressed the role of protein kinase C (PKC) isozymes in mediating tumor necrosis factor-alpha (TNF-alpha)-induced oxidant generation in endothelial cells, a requirement for nuclear factor-kappaB (NF-kappaB) activation and intercellular adhesion molecule-1 (ICAM-1) gene transcription. Depletion of the conventional (c) and novel (n) PKC isozymes following 24 h exposure of human pulmonary artery endothelial (HPAE) cells with the phorbol ester, phorbol 12-myristate 13-acetate (500 nM), failed to prevent TNF-alpha-induced oxidant generation. In contrast, inhibition of PKC-zeta synthesis by the antisense oligonucleotide prevented the oxidant generation following the TNF-alpha stimulation. We observed that PKC-zeta also induced the TNF-alpha-induced NF-kappaB binding to the ICAM-1 promoter and the resultant ICAM-1 gene transcription. We showed that expression of the dominant negative mutant of PKC-zeta prevented the TNF-alpha-induced ICAM-1 promoter activity, whereas overexpression of the wild-type PKC-zeta augmented the response. These data imply a critical role for the PKC-zeta isozyme in regulating TNF-alpha-induced oxidant generation and in signaling the activation of NF-kappaB and ICAM-1 transcription in endothelial cells.

Cotranslational dimerization of the Rel homology domain of NF-kappaB1 generates p50-p105 heterodimers and is required for effective p50 production

Generation of the NF-kappaB p50 transcription factor is mediated by the proteasome. We found previously that p50 is generated during translation of the NFKB1 gene and that this cotranslational processing allows the production of both p50 and p105 from a single mRNA. We now demonstrate that the Rel homology domain in p50 undergoes cotranslational dimerization and that this interaction is required for efficient production of p50. We further show that this coupling of dimerization and proteasome processing during translation uniquely generates p50-p105 heterodimers. Accordingly, after the primary cotranslational event, additional posttranslational steps regulate p50 homodimer formation and the intracellular ratio of p50 and p105. This cellular strategy places p50 under the control of the p105 inhibitor early in its biogenesis, thereby regulating the pool of p50 homodimers within the cell.

Inhibitory effect of NF-kappaB on 1,25-dihydroxyvitamin D(3) and retinoid X receptor function

Responsiveness to 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] may be diminished in osteoporosis and inflammatory arthritis. The inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) is produced in excess in these disorders and has been shown to decrease osteoblast transcriptional responsiveness to vitamin D and to inhibit the binding of the vitamin D receptor (VDR) and its nuclear partner the retinoid X receptor (RXR) to DNA. Previous studies have shown that a vitamin D (VDRE) or retinoid X DNA response element (RXRE) is sufficient to confer TNF-alpha inhibition of vitamin D or retinoid-stimulated transcription in the absence of known TNF-alpha-responsive DNA sequences. We tested the hypothesis that the TNF-alpha-stimulated transcription factor nuclear factor (NF)-kappaB could, in part, mediate TNF-alpha action by inhibiting the transcriptional potency of the VDR and RXR at their cognate cis regulatory sites. Osteoblastic ROS 17/2.8 cells transfected with a dose of NF-kappaB comparable to that stimulated by TNF-alpha decreased 1,25(OH)(2)D(3)-stimulated transcription. This inhibitory effect of NF-kappaB was not observed on basal transcription of a heterologous reporter in the absence of the VDRE. The effects of NF-kappaB and TNF-alpha were comparable but not additive. COS-7 cells were cotransfected with reporters under the regulation of VDRE or RXRE along with vectors expressing VDR, RXR, and NF-kappaB nuclear proteins. Reconstituted NF-kappaB and the NF-kappaB subunit p65 alone, but not p50, dose dependently suppressed basal and ligand-stimulated transcription. p65 overexpression completely abrogated enhanced VDRE-mediated transcriptional activity in response to 1,25(OH)(2)D(3). Electrophoretic mobility shift experiments did not reveal a direct effect of recombinant NF-kappaB or its individual subunits on the binding of heterodimeric VDR-RXR to DNA. These results suggest that TNF-alpha inhibition of hormone-stimulated transcriptional activation may be mediated by activation of NF-kappaB. In contrast, the inhibitory effect of TNF-alpha on binding of receptors to DNA is unlikely to be mediated by NF-kappaB and is not necessary for inhibition of transcription.

Identification of NF-kappaB in the marine fish Stenotomus chrysops and examination of its activation by aryl hydrocarbon receptor agonists

Members of the Rel family of proteins have been identified in Drosophila, an echinoderm, Xenopus, birds and mammals. Dimers of Rel proteins form the transcription factor nuclear factor kappaB (NF-kappaB) that rapidly activates genes encoding cytokines, cell surface receptors, cell adhesion molecules and acute phase proteins. Evidence suggests that xenobiotic compounds also may alter the activation of NF-kappaB. This study had a dual objective of identifying members of the Rel family and examining their activation by xenobiotic compounds in a marine fish model, scup (Stenotomus chrysops). A DNA-protein crosslinking technique demonstrated that liver, kidney and heart each had at least three nuclear proteins that showed specific binding to an NF-kappaB consensus sequence, with molecular weights suggesting that the proteins potentially corresponded to mouse p50, p65 (RelA) and c-rel. In addition, an approximately 35kD NF-kappaB binding protein was evident in liver and kidney. The 50 kD protein was immunoprecipitated by mammalian p50-specific antibodies. The presence of Rel members in fish implied by those results was confirmed by RT-PCR cloning of a Rel homology domain (an apparent c-rel) from scup liver. NF-kappaB activation occurred in vehicle-treated fish, but this appeared to decrease over time. In fish treated with 0.01 or 1 mg 3,3',4,4', 5-pentachlorobiphenyl per kg, NF-kappaB activation in liver did not decrease, and there was a 6-8-fold increase in activation 16-18 days following treatment. Treatment with 10 mg benzo[a]pyrene/kg had no effect on NF-kappaB-DNA binding, either at 3 or 6 days following treatment. The data show that the Rel family of proteins is present in fish, represented at least by a p50/105 homologue, and support a hypothesis that some aryl hydrocarbon receptor agonists can activate NF-kappaB in vivo.

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

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

Epstein-barr virus latent membrane protein (LMP1) induces specific NFkappaB complexes in human T-lymphoid cells

The Epstein-Barr virus (EBV) latent membrane protein (LMP1) is believed to play a crucial role in oncogenesis mediated by this virus. We and others previously showed that LMP1 can induce NFkappaB activity in several non-lymphoid cells and B-lymphoid cell lines. Here we show that LMP1 is also able to efficiently induce NFkappaB in human T-lymphoid and monocytic cells. Specific NFkappaB complexes were detected in the nuclei of transfected Jurkat cells using gel mobility shift assays and Western blot analyses. Using antibodies, we demonstrated that these complexes contain NFkappaB subunits NFkB1, NFkB2, RelA and c-Rel. Our results also showed that the NFkappaB complexes induced by LMP1 are able to bind to the NFkappaB consensus sequence in the promoter of the interleukin-2alpha receptor gene and induce expression from a minimal promoter linked to four tandem copies of this sequence. This suggests a possible mechanism by which LMP1 could induce T-cell activation and proliferation.

Essential role of human leukocyte antigen-encoded proteasome subunits in NF-kappaB activation and prevention of tumor necrosis factor-alpha-induced apoptosis

The multisubunit proteasome complex is the principal mediator of nonlysosomal protein degradation. The proteasome subunit varies minimally between cells with the exception of LMP2, LMP7, and LMP10 subunits in rodent and human cells. LMP2 and LMP7 subunits are encoded by the human lymphocyte antigen region, and they optimize proteolytic mediated antigen presentation. The proteasome is also important for the function of transcription factor nuclear factor-kappaB (NF-kappaB). It is required for NF-kappaB subunits p50 and p52 generation and catalyzes degradation of phosphorylated IkappaBalpha. These proteasome-mediated reactions have now been shown to be defective in T2 cells, a human lymphocyte cell line that lacks both LMP2 and LMP7. Although T2 cells contain normal expression of p100 and p105, the abundance of p50 and p52 was greatly reduced. Tumor necrosis factor-alpha (TNF-alpha) induced normal phosphorylation of IkappaBalpha but failed to induce degradation of phosphorylated IkappaBalpha. Both DNA binding assays and luciferase assays revealed that TNF-alpha-induced NF-kappaB activation is defective in T2 cells. Unlike parental cells, T2 cells were susceptible to TNF-alpha-induced apoptosis. These data indicate human leukocyte antigen-linked proteasome subunits are essential for NF-kappaB activation and protection of cells from TNF-alpha-induced apoptosis.

Oxidative stress and gene regulation

Reactive oxygen species are produced by all aerobic cells and are widely believed to play a pivotal role in aging as well as a number of degenerative diseases. The consequences of the generation of oxidants in cells does not appear to be limited to promotion of deleterious effects. Alterations in oxidative metabolism have long been known to occur during differentiation and development. Experimental perturbations in cellular redox state have been shown to exert a strong impact on these processes. The discovery of specific genes and pathways affected by oxidants led to the hypothesis that reactive oxygen species serve as subcellular messengers in gene regulatory and signal transduction pathways. Additionally, antioxidants can activate numerous genes and pathways. The burgeoning growth in the number of pathways shown to be dependent on oxidation or antioxidation has accelerated during the last decade. In the discussion presented here, we provide a tabular summary of many of the redox effects on gene expression and signaling pathways that are currently known to exist.

Casein kinase 2 as a potentially important enzyme in the nervous system

Protein kinase CK2 is a ubiquitous and pleiotropic seryl/threonyl protein kinase which is highly conserved in evolution indicating a vital cellular role for this kinase. The holoenzyme is generally composed of two catalytic (alpha and/or alpha') and two regulatory (beta) subunits, but the free alpha/alpha' subunits are catalytically active by themselves and can be present in cells under some circumstances. Special attention has been devoted to phosphorylation status and structure of these enzymic molecules, however, their regulation and roles remain intriguing. Until recently, CK2 was believed to represent a kinase especially required for cell cycle progression in non-neural cells. At present, with respect to recent findings, four essential features suggest potentially important roles for this enzyme in specific neural functions: (1) CK2 is much more abundant in brain than in any other tissue; (2) there appear to be a myriad of substrates for CK2 in both synaptic and nuclear compartments that have clear implications in development, neuritogenesis, synaptic transmission, synaptic plasticity, information storage and survival; (3) CK2 seems to be associated with mechanisms underlying long-term potentiation in hippocampus; and (4) neurotrophins stimulate activity of CK2 in hippocampus. In addition, some data are suggestive that CK2 might play a role in processes underlying progressive disorders due to Alzheimer's disease, ischemia, chronic alcohol exposure or immunodeficiency virus HIV. The present review focuses mainly on the latest data concerning the regulatory mechanisms and the possible neurophysiological functions of this enzyme.

Aging-dependent proteolysis of NF-kappaB in human fibroblasts

We investigated the NF-kappaB-like factor induced in the late-passage human oral mucosal fibroblasts stimulated with interleukin-1 (IL-1). Compared with the NF-kappaBs of HeLa cells and early-passage fibroblasts, the NF-kappaB-like factor of late-passage (passage 15) fibroblasts migrated faster in the electrophoretic mobility shift assay (EMSA) and behaved like a 70-80 kDa protein in the gel filtration chromatography. Both antibodies against p50 and p65 subunits of NF-kappaB could supershift the small NF-kappaB-like factor of late-passage cells in the EMSAs. A 47-kDa band was detected in late-passage fibroblasts by immunoblotting against p50. The mobility of the trypsin-degraded NF-kappaB of HeLa cells corresponded to that of the small NF-kappaB-like factor of late-passage fibroblasts in the EMSAs. Furthermore, when the nuclear extracts of the IL-1-stimulated HeLa cells were incubated with those of the IL-1-stimulated old fibroblasts, the p65-p50 NF-kappaB band disappeared, leaving behind a small NF-kappaB-like band. This reduction of NF-kappaB was prevented by the addition of a cysteine protease inhibitor leupeptin. These results suggest that the small NF-kappaB-like factor of late-passage fibroblasts is a part of the NF-kappaB truncated by aging-induced protease(s).

Angiotensin II induces nuclear factor (NF)-kappaB1 isoforms to bind the angiotensinogen gene acute-phase response element: a stimulus-specific pathway for NF-kappaB activation

The vasopressor angiotensin II (AII) activates transcriptional expression of its precursor, angiotensinogen. This biological "positive feedback loop" occurs through an angiotensin receptor-coupled pathway that activates a multihormone-responsive enhancer of the angiotensinogen promoter, termed the acute-phase response element (APRE). Previously, we showed that the APRE is a cytokine [tumor necrosis factor-alpha (TNFalpha)]- inducible enhancer by binding the heterodimeric nuclear factor-kappaB (NF-kappaB) complex Rel A x NF-kappaB1. Here, we compare the mechanism for NF-kappaB activation by the AII agonist, Sar1 AII, with TNFalpha in HepG2 hepatocytes. Although Sar1 AII and TNFalpha both rapidly activate APRE-driven transcription within 3 h of treatment, the pattern of inducible NF-kappaB binding activity in electrophoretic mobility shift assay is distinct. In contrast to the TNFalpha mechanism, which strongly induces Rel A x NF-kappaB1 binding, Sar1 AII selectively activates a heterogenous pattern of NF-kappaB1 binding. Using a two-step microaffinity DNA binding assay, we observe that Sar1 AII recruits 50-, 56-, and 96-kDa NF-kappaB1 isoforms to bind the APRE. Binding of all three NF-kappaB1 isoforms occurs independently of changes in their nuclear abundance or proteolysis of cytoplasmic IkappaB inhibitors. Phorbol ester-sensitive protein kinase C (PKC) isoforms are required because PKC down-regulation completely blocks AII-inducible transcription and inducible NF-kappaB1 binding. We conclude that AII stimulates the NF-kappaB transcription factor pathway by activating latent DNA-binding activity of NF-kappaB subunits through a phorbol ester-sensitive (PKC-dependent) mechanism.

Augmented expression of inducible NO synthase in vascular smooth muscle cells during aging is associated with enhanced NF-kappaB activation

Vascular smooth muscle cells (SMCs) are important targets for endothelium-derived nitric oxide (NO), but this production is attenuated in injured and diseased arteries and during aging. However, SMCs can produce NO themselves by expressing an inducible form of NO synthase (iNOS) under inflammatory conditions and in the repair process after arterial injury. We examined iNOS expression in SMCs derived from the aortic media of newborn, young adult, and old rats. Our results show that SMCs from newborn rats cannot produce significant amounts of NO on stimulation with interferon-gamma plus lipopolysaccharide or interleukin-1beta. In contrast, SMCs from old rats exhibit markedly enhanced iNOS activity. The difference in iNOS activity between the newborn and the old SMCs was closely correlated with levels of iNOS protein, mRNA, and gene promoter activity. Similarly, intercellular adhesion molecule-1 (ICAM-1) was also expressed more abundantly in the old than in the newborn SMCs in response to cytokines. Both iNOS and ICAM-1 are transcriptionally regulated by nuclear factor kappaB (NF-kappaB). Our data demonstrate an intense transactivation of NF-kappaB in old SMCs on tumor necrosis factor-alpha stimulation but only a weak one in newborn SMCs. The difference in the NF-kappaB activation could be explained by a much faster and more extensive IkappaBalpha degradation in old than in newborn SMCs. These data indicate that the capability to respond to proinflammatory stimuli by activating NF-kappaB differs between SMCs at different stages of development. This results in differential capability to express NF-kappaB-dependent genes such as iNOS and ICAM-1, which could have implications for host defense and the pathogenesis of vascular diseases.

Multiple mutations contribute to the oncogenicity of the retroviral oncoprotein v-Rel

The avian Rev-T retrovirus encodes the v-Rel oncoprotein, which is a member of the Rel/NF-kappaB transcription factor family. v-Rel induces a rapidly fatal lymphoma/leukemia in young birds, and v-Rel can transform and immortalize a variety of avian cell types in vitro. Although Rel/NF-kappaB transcription factors have been associated with oncogenesis in mammals, v-Rel is the only member of this family that is frankly oncogenic in animal model systems. The potent oncogenicity of v-Rel is the consequence of a number of mutations that have altered its activity and regulation: for example, certain mutations decrease its ability to be regulated by IkappaBalpha, change its DNA-binding site specificity, and endow it with new transactivation properties. The study of v-Rel will continue to increase our knowledge of how cellular Rel proteins contribute to oncogenesis by affecting cell growth, altering cell-cycle regulation, and blocking apoptosis. This review will discuss biological and molecular activities of v-Rel, with particular attention to how these activities relate to structure - function aspects of the Rel/NF-kappaB transcription factors.

The generation of nfkb2 p52: mechanism and efficiency

nfkb2 encodes two members of the NF-kappa B/Rel family of proteins: p52 and p100. The p100 polypeptide has been proposed to serve as a precursor of p52, which corresponds to the N-terminal half of p100. While p52 functions as a Rel transcription factor, the larger p100 protein acts as a cytoplasmic inhibitor of select NF-kappa B/Rel transcription factor complexes. Because of their distinct functions, we have studied the biochemical basis for the production of these two nfkb2-derived gene products. Like the p50 product of the nfkb1 gene, p52 is principally generated in a cotranslational manner involving proteolytic processing by the proteasome. The generation of p52 is dependent on a glycine-rich region (GRR) located upstream of the p52 C-terminus, and repositioning of this GRR alters the location of proteasome processing. In most cells, small amounts of p52 are produced relative to the levels of p100, unlike the usually balanced production of nfkb1-derived p50 and p105. Using p100/p105 chimeras containing different segments of the nfkb1 and nfkb2 genes, we have found that diminished p52 processing is a property conferred by peptide sequences located downstream of the GRR, flanking the site of p52 processing.

E2F-1 potentiates cell death by blocking antiapoptotic signaling pathways

The E2F family of transcription factors plays an essential role in promoting cell cycle progression, and one member of the family, E2F-1, is also capable of inducing apoptosis. We show here that E2F-1 can induce apoptosis by a death receptor-dependent mechanism, by downregulating TRAF2 protein levels and inhibiting activation of antiapoptotic signals including NF-kappa B. In this way, E2F-1 expression can lead to the sensitization of cells to apoptosis by a number of agents independently of p53. Deregulation of E2F-1 activity occurs in the majority of human tumors, and the ability of E2F-1 to inhibit antiapoptotic signaling may contribute to the enhanced sensitivity of transformed cells to chemotherapeutic agents.

Evidence for the presence of an NF-kappaB signal transduction system in Dictyostelium discoideum

The Rel/NF-kappaB family of transcription factors and regulators has so far only been described in vertebrates and arthropods, where they mediate responses to many extracellular signals. No counterparts of genes coding for such proteins have been identified in the Caenorhabditis elegans genome and no NF-kappaB activity was found in Saccharomyces cerevisiae. We describe here the presence of an NF-kappaB transduction pathway in the lower eukaryote Dictyostelium discoideum. Using antibodies raised against components of the mammalian NF-kappaB pathway, we demonstrate in Dictyostelium cells extracts the presence of proteins homologous to Rel/NF-kappaB, IkappaB and IKK components. Using gel-shift experiments in nuclear extracts of developing Dictyostelium cells, we demonstrate the presence of proteins binding to kappaB consensus oligonucleotides and to a GC-rich kappaB-like sequence, lying in the promoter of cbpA, a developmentally regulated Dictyostelium gene encoding the Ca(2+)-binding protein CBP1. Using immunofluorescence, we show specific nuclear translocation of the p65 and p50 homologues of the NF-kappaB transcription factors as vegetatively growing cells develop to the slug stage. Taken together, our results strongly indicate the presence of a complete NF-kappaB signal transduction system in Dictyostelium discoideum that could be involved in the developmental process.

Control of NF-kappa B transcriptional activation by signal induced proteolysis of I kappa B alpha

In unstimulated cells the transcription factor NF-kappa B is held in the cytoplasm in an inactive state by I kappa B inhibitor proteins. Ultimately activation of NF-kappa B is achieved by ubiquitination and proteasome-mediated degradation of I kappa B alpha and we have therefore investigated factors which control this proteolysis. Signal-induced degradation of I kappa B alpha exposes the nuclear localization signal of NF-kappa B, thus allowing it to translocate into the nucleus and activate transcription from responsive genes. An autoregulatory loop is established when NF-kappa B induces expression of the I kappa B alpha gene and newly synthesized I kappa B alpha accumulates in the nucleus where it negatively regulates NF-kappa B-dependent transcription. As part of this post-induction repression, the nuclear export signal on I kappa B alpha mediates transport of NF-kappa B-I kappa B alpha complexes from the nucleus to the cytoplasm. As nuclear export of I kappa B alpha is blocked by leptomycin B this drug was used to examine the effect of cellular location on susceptibility of I kappa B alpha to signal-induced degradation. In the presence of leptomycin B, I kappa B alpha is accumulated in the nucleus and in this compartment is resistant to signal-induced degradation. Thus signal-induced degradation of I kappa B alpha is mainly, if not exclusively a cytoplasmic process. An efficient nuclear export of I kappa B alpha is therefore essential for maintaining a low level of I kappa B alpha in the nucleus and allowing NF-kappa B to be transcriptionally active upon cell stimulation. We have detected a modified form of I kappa B alpha, conjugated to the small ubiquitin-like protein SUMO-1, which is resistant to signal-induced degradation. SUMO-1 modified I kappa B alpha remains associated with NF-kappa B and thus overexpression of SUMO-1 inhibits the signal-induced activation of NF-kappa B-dependent transcription. Reconstitution of the conjugation reaction with highly purified proteins demonstrated that in the presence of a novel E1 SUMO-1 activating enzyme, Ubch9 directly conjugated SUMO-1 to I kappa B alpha on residues K21 and K22, which are also used for ubiquitin modification. Thus, while ubiquitination targets proteins for rapid degradation, SUMO-1 modification acts antagonistically to generate proteins resistant to degradation.

Protein kinase C and calcineurin synergize to activate IkappaB kinase and NF-kappaB in T lymphocytes

The nuclear factor of kappaB (NF-kappaB) is a ubiquitous transcription factor that is key in the regulation of the immune response and inflammation. T cell receptor (TCR) cross-linking is in part required for activation of NF-kappaB, which is dependent on the phosphorylation and degradation of IkappaBalpha. By using Jurkat and primary human T lymphocytes, we demonstrate that the simultaneous activation of two second messengers of the TCR-initiated signal transduction, protein kinase C (PKC) and calcineurin, results in the synergistic activation of the IkappaBalpha kinase (IKK) complex but not of another putative IkappaBalpha kinase, p90(rsk). We also demonstrate that the IKK complex, but not p90(rsk), is responsible for the in vivo phosphorylation of IkappaBalpha mediated by the co-activation of PKC and calcineurin. Each second messenger is necessary, as inhibition of either one reverses the activation of the IKK complex and IkappaBalpha phosphorylation in vivo. Overexpression of dominant negative forms of IKKalpha and -beta demonstrates that only IKKbeta is the target for PKC and calcineurin. These results indicate that within the TCR/CD3 signal transduction pathway both PKC and calcineurin are required for the effective activation of the IKK complex and NF-kappaB in T lymphocytes.

Serine 32 and serine 36 of IkappaBalpha are directly phosphorylated by protein kinase CKII in vitro

IkappaBalpha is an inherently unstable protein which binds to and retains the ubiquitous transcription factor NFkappaB in the cytoplasm of resting cells. A continuous low level translocation of NFkappaB to the nucleus, secondary to the basal turnover of IkappaBalpha, is hypothesized to be necessary for cellular maturation, survival and, potentially, transformation. In response to cellular stimulation by inflammatory cytokines or mitogens, IkappaBalpha is rapidly degraded allowing larger pools of NFkappaB to translocate to the nucleus. Phosphorylation of IkappaBalpha at serine 32 (S32) and serine 36 (S36) is necessary for this stimuli-induced degradation. IKKalpha/beta kinases and p90(rsk1)are involved in stimuli-induced targeting of one or both of these IkappaBalpha sites. Whether other kinases phosphorylate S32 and S36 directly, and if so, what function they serve in NFkappaB activation remains unknown. Here we present evidence of a direct phosphorylation of IkappaBalpha at both S32 and S36 by purified or immunoprecipitated protein kinase CKII (PK-CKII) and a specific in vivo association between IkappaBalpha and PK-CKII. This PK-CKII-specific kinase activity is not found within the IKKalpha/beta-containing signalsome complex and is biochemically distinct from that of the IKKalpha/beta kinases. The identification of an additional N-terminal IkappaBalpha kinase which is constitutively active and not significantly inducible raises numerous possibilities as to its role in cellular function.

NF-kappaB involvement in the activation of primary adult T-cell leukemia cells and its clinical implications

The HTLV-I provirus-encoded Tax protein induces NF-kappaB in Tax-transfected Jurkat T cells or HTLVL-I- infected T cells in vitro. Tax induction of NF-kappaB is presumed to be involved in proliferation and activation of primary leukemia cells in vivo. Recent studies have demonstrated that NF-kappaB activities in human T cells are mediated by at least four c-Rel-related DNA binding proteins - p50, p55, p75 and p85. We examined the significance of NF-kappaB induction in primary adult T cell leukemia cells and the induction kinetics of each of the four NF-kappaB species. Marked NF-kappaB activity was detected using an electrophoretic mobility shift assay (EMSA) in the primary cells of patients with acute disease, but little activity was noted in the cells of chronic patients. NF-kappaB activity was enhanced in a time-dependent manner in acute type cells cultured with mitogen-free medium; there was no induction of activity in chronic type cells. UV crosslinking demonstrated all four species of NFkappaB complex - high levels of p50 and lower levels of p55 and p75, in acute type cells; chronic type cells showed only the p50. As a control, normal resting T cells similarly showed only p50; control cells showed little change in activity when cultured without mitogenic stimulation, analogous to chronic type ATL. Northern blotting revealed enhancement of c-rel (encoding p85) and KBFI (encoding p50 and p55) expression in acute type cells during culture, while there was no significant enhancement of mRNAs in chronic type ATL cells or unstimulated normal T cells. Northern blotting also revealed that Tax is upregulated at the mRNA level in acute- but not chronic-type cells during culture. Expression of c-rel and KBF1 mRNAs in acute type cells appeared to be related to Tax mRNA expression. These results suggest that Tax is capable of inducing nuclear expression of all four NF-kappaB species in primary ATL cells of acute type patients, with marked effects on p55, p75, and p85. Tax induction of NF-kappaB species is regulated, at least in part, at a pretranslational level involving increases in c-rel and KBF1 mRNA.

CLAP, a novel caspase recruitment domain-containing protein in the tumor necrosis factor receptor pathway, regulates NF-kappaB activation and apoptosis

Molecules that regulate NF-kappaB activation play critical roles in apoptosis and inflammation. We describe the cloning of the cellular homolog of the equine herpesvirus-2 protein E10 and show that both proteins regulate apoptosis and NF-kappaB activation. These proteins were found to contain N-terminal caspase-recruitment domains (CARDs) and novel C-terminal domains (CTDs) and were therefore named CLAPs (CARD-like apoptotic proteins). The cellular and viral CLAPs induce apoptosis downstream of caspase-8 by activating the Apaf-1-caspase-9 pathway and activate NF-kappaB by acting upstream of the NF-kappaB-inducing kinase, NIK, and the IkB kinase, IKKalpha. Deletion of either the CARD or the CTD domain inhibits both activities. The CARD domain was found to be important for homo- and heterodimerization of CLAPs. Substitution of the CARD domain with an inducible FKBP12 oligomerization domain produced a molecule that can induce NF-kappaB activation, suggesting that the CARD domain functions as an oligomerization domain, whereas the CTD domain functions as the effector domain in the NF-kappaB activation pathway. Expression of the CARD domain of human CLAP abrogates tumor necrosis factor-alpha-induced NF-kappaB activation, suggesting that cellular CLAP plays an essential role in this pathway of NF-kappaB activation.

The roles of Sarcophaga defense molecules in immunity and metamorphosis

This article summarizes recent progress (1996 1998) in our studies on self-defense molecules in Sarcophaga peregrina. A new antibacterial substance was purified and its unique structure and function revealed a novel aspect of the Sarcophaga defense system. We found a novel lectin and cysteine protease in hemocytes which will assist in the understanding of immune response of hemocytes. There have been two major advances in research on the regulation of defense gene induction: (i) cDNA cloning of a new transcriptional factor binding to the kappaB-like promoter sequence of the Sarcophaga lectin gene, (ii) methylation of cytosolic factors essential for induction of immune genes in the fatbody. Metamorphosis is an interesting event from an immunological point of view: (i) a novel protease with antibacterial activity was discovered from metamorphosing gut, and (ii) a pupal hemocyte-specific surface antigen was purified and characterized in terms of its structure and possible function for larval tissue recognition and elimination.

Regulation of NF-kappaB activity by I kappaB-related proteins in adenocarcinoma cells

Constitutive NF-kappaB activity varies widely among cancer cell lines. In this report, we studied the expression and the role of different I kappaB inhibitors in adenocarcinoma cell lines. High constitutive NF-kappaB activity and low I kappaB-alpha expression was found in a number of these cell lines. Moreover, some of these cells showed a high p100 expression, responsible for the cytoplasmic sequestration of most of p65 complexes. Treatment of these cells with TNF-alpha or other NF-kappaB activating agents induced only weakly nuclear NF-kappaB activity without significant p100 processing and led to a very weak transcription of NF-kappaB-dependent reporter gene. Induction of NF-kappaB activity can be restored by expression of the Tax protein or by treatment with antisense p100 oligonucleotides. In MCF7 A/Z cells stably transfected with a p100 expression vector, p65 complexes were sequestered in the cytoplasm by p100. These cells showed a reduced nuclear NF-kappaB induction and NF-kappaB-dependent gene transcription following TNF-alpha stimulation. As a consequence of a competition between I kappaB-alpha and p100, cells expressing high levels of p100 respond poorly to NF-kappaB activating stimuli as TNF-alpha.

Human Cytomegalovirus Binding to Human Monocytes Induces Immunoregulatory Gene Expression

To continue our investigation of the cellular events that occur following human CMV (HCMV) infection, we focused on the regulation of cellular activation following viral binding to human monocytes. First, we showed that viral binding induced a number of immunoregulatory genes (IL-1β, A20, NF-κB-p105/p50, and IκBα) in unactivated monocytes and that neutralizing Abs to the major HCMV glycoproteins, gB (UL55) and gH (UL75), inhibited the induction of these genes. Next, we demonstrated that these viral ligands directly up-regulated monocyte gene expression upon their binding to their appropriate cellular receptors. We then investigated if HCMV binding also resulted in the translation and secretion of cytokines. Our results showed that HCMV binding to monocytes resulted in the production and release of IL-1β protein. Because these induced gene products have NF-κB sites in their promoter regions, we next examined whether there was an up-regulation of nuclear NF-κB levels. These experiments showed that, in fact, NF-κB was translocated to the nucleus following viral binding or purified viral ligand binding. Changes in IκBα levels correlated with the changes in NF-κB translocation. Lastly, we demonstrated that p38 kinase activity played a central role in IL-1β production and that it was rapidly up-regulated following infection. These results support our hypothesis that HCMV initiates a signal transduction pathway that leads to monocyte activation and pinpoints a potential mechanism whereby HCMV infection of monocytes can result in profound pathogenesis, especially in chronic inflammatory-type conditions.

A 3'-flanking NF-kappaB site mediates developmental silencing of the human zeta-globin gene

The central developmental event in the human (h)alpha-globin gene cluster is selective silencing of the zeta-globin gene as erythropoiesis shifts from primitive erythroblasts in the embryonic yolk sac to definitive erythroblasts in the fetal liver. Previous studies have demonstrated that full developmental silencing of the hzeta-globin gene in transgenic mice requires the proximal 2.1 kb of its 3'-flanking region. In the current report, we localize this silencing activity to a 108 bp segment located 1.2 kb 3' to the zeta-globin gene. Protein(s) in nuclear extracts from cell lines representing the fetal/adult erythroid stage bind specifically to an NF-kappaB motif located at this site. In contrast, this binding activity is lacking in the nuclear extract of an embryonic-stage erythroid line expressing zeta-globin. This complex is quantitatively recognized by antisera to the NF-kappaB p50 and to a lesser extent to p65 subunits. A two-base substitution that disrupts NF-kappaB site protein binding in vitro also results in the loss of the developmental silencing activity in vivo. The data suggest that NF-kappaB complex formation is a crucial component of hzeta-globin gene silencing. This finding expands the roles of this widely distributed transcriptional complex to include negative regulation in mammalian development.

Regulation of DNA binding activity and nuclear transport of B-Myb in Xenopus oocytes

DNA binding activity and nuclear transport of B-Myb in Xenopus oocytes are negatively regulated. Two distinct sequence elements in the C-terminal portion of the protein are responsible for these different inhibitory activities. A C-terminal Xenopus B-Myb protein fragment inhibits the DNA binding activity of the N-terminal repeats in trans, indicating that intramolecular folding may result in masking of the DNA binding function. Xenopus B-Myb contains two separate nuclear localization signals (NLSs), which, in Xenopus oocytes, function only outside the context of the full-length protein. Fusion of an additional NLS to the full-length protein overcomes the inhibition of nuclear import, suggesting that masking of the NLS function rather than cytoplasmic anchoring is responsible for the negative regulation of Xenopus B-Myb nuclear transfer. During Xenopus embryogenesis, when inhibition of nuclear import is relieved, Xenopus B-myb is preferentially expressed in the developing nervous system and neural crest cells. Within the developing neural tube, Xenopus B-myb gene transcription occurs preferentially in proliferating, non-differentiated cells.

Angiotensin II induces interleukin-6 transcription in vascular smooth muscle cells through pleiotropic activation of nuclear factor-kappa B transcription factors

Interleukin-6 (IL-6) is a multifunctional cytokine expressed by angiotensin II (Ang II)-stimulated vascular smooth muscle cells (VSMCs) that functions as an autocrine growth factor. In this study, we analyze the mechanism for Ang II-inducible IL-6 expression in quiescent rat VSMCs. Stimulation with the Ang II agonist Sar1 Ang II (100 nmol/L) induced transcriptional expression of IL-6 mRNA transcripts of 1.8 and 2.4 kb. In transient transfection assays of IL-6 promoter/luciferase reporter plasmids, Sar1 Ang II treatment induced IL-6 transcription in a manner completely dependent on the nuclear factor-kappaB (NF-kappaB) motif. Sar1 Ang II induced cytoplasmic-to-nuclear translocation of the NF-kappaB subunits Rel A and NF-kappaB1 with parallel changes in DNA-binding activity in a biphasic manner, which produced an early peak at 15 minutes followed by a nadir 1 to 6 hours later and a later peak at 24 hours. The early phase of NF-kappaB translocation was dependent on weak simultaneous proteolysis of the IkappaBalpha and beta inhibitors, whereas later translocation was associated with enhanced processing of the p105 precursor into the mature 50-kDa NF-kappaB1 form. Pretreatment with a potent inhibitor of IkappaBalpha proteolysis, TPCK, completely blocked Sar1 Ang IIAng II-induced NF-kappaB activation and induction of endogenous IL-6 gene expression, which indicated the essential role of NF-kappaB in mediating IL-6 expression. We conclude that Ang II is a pleiotropic regulator of the NF-kappaB transcription factor family and may be responsible for activating the expression of cytokine gene networks in VSMCs.

Nuclear retention of IkappaBalpha protects it from signal-induced degradation and inhibits nuclear factor kappaB transcriptional activation

Transcriptional activation of nuclear factor kappaB (NF-kappaB) is mediated by signal-induced phosphorylation and degradation of its inhibitor, IkappaBalpha. However, NF-kappaB activation induces rapid resynthesis of IkappaBalpha, which is responsible for post-induction repression of transcription. Newly synthesized IkappaBalpha translocates to the nucleus, where it dissociates NF-kappaB from DNA and transports NF-kappaB from the nucleus to the cytoplasm in a nuclear export sequence-dependent process that is sensitive to leptomycin B (LMB). In the present study, LMB was used as a tool to inhibit nuclear export sequence-mediated nuclear protein export and evaluate the consequences for regulation of NF-kappaB-dependent transcriptional activity. Pretreatment of cells with LMB inhibits NF-kappaB-dependent transcriptional activation mediated by interleukin 1beta or tumor necrosis factor alpha. This is a consequence of the inhibition of signal-induced degradation of IkappaBalpha. Although LMB treatment does not affect the signal transduction pathway leading to IkappaBalpha degradation, it blocks IkappaBalpha nuclear export. IkappaBalpha is thus accumulated in the nucleus, and in this compartment it is resistant to signal-induced degradation. These results indicate that the signal-induced degradation of IkappaBalpha is mainly, if not exclusively, a cytoplasmic process. An efficient nuclear export of IkappaBalpha is therefore essential for maintaining a low level of IkappaBalpha in the nucleus and allowing NF-kappaB to be transcriptionally active upon cell stimulation.

A critical role for the RelA subunit of nuclear factor kappaB in regulation of multiple immune-response genes and in Fas-induced cell death

Binding sites for the nuclear factor (NF)-kappaB transcription factor have been identified within control regions of many genes involved in inflammatory and immune responses. Such kappaB sites are often found adjacent to those of interferon (IFN)-gamma-inducible transcription factors, suggesting a requirement for multiple signaling pathways for gene regulation. Using fibroblasts from RelA (p65)-deficient mice generated by gene targeting, we have investigated the role of this subunit of NF-kappaB in gene activation by microbial lipopolysaccharide, tumor necrosis factor alpha, and in possible synergism with the IFN-gamma-signaling pathway. Our results indicate not only that RelA is required for activation of key genes involved in adaptive (acquired) immune responses, including major histocompatibility complex class I, CD40, and the Fas death receptor, but also that both NF-kappaB-inducing signals and IFN-gamma are necessary for maximal activation. In contrast, neutrophil-specific chemokine genes KC and MIP-2, which can function as nonspecific mediators in innate immune responses, were strongly induced by RelA in the absence of IFN-gamma. Our results show that RelA plays a critical role in activation of immune system genes in response to nonspecific stimuli and demonstrate a novel proapoptotic function for this protein in Fas-induced cell death.

Listeriolysin O-dependent activation of endothelial cells during infection with Listeria monocytogenes: activation of NF-kappa B and upregulation of adhesion molecules and chemokines

The facultative intracellular bacterium Listeria monocytogenes is an invasive pathogen that crosses the vascular endothelium and disseminates to the placenta and the central nervous system. Its interaction with endothelial cells is crucial for the pathogenesis of listeriosis. By infecting in vitro human umbilical vein endothelial cells (HUVEC) with L. monocytogenes, we found that wild-type bacteria induced the expression of the adhesion molecules (ICAM-1 and E-selectin), chemokine secretion (IL-8 and monocyte chemotactic protein-1) and NF-kappa B nuclear translocation. The activation of HUVEC required viable bacteria and was abolished in prfA-deficient mutants of L. monocytogenes, suggesting that virulence genes are associated with endothelial cell activation. Using a genetic approach with mutants of virulence genes, we found that listeriolysin O (LLO)-deficient mutants inactivated in the hly gene did not induce HUVEC activation, as opposed to mutants inactivated in the other virulence genes. Adhesion molecule expression, chemokine secretion and NF-kappa B activation were fully restored by a strain of Listeria innocua transformed with the hly gene encoding LLO. The relevance in vivo of endothelial cell activation for listerial pathogenesis was investigated in transgenic mice carrying an NF-kappa B-responsive lacZ reporter gene. NF-kappa B activation was visualized by a strong lacZ expression in endothelial cells of capillaries of mice infected with a virulent haemolytic strain, but was not seen in those infected with a non-haemolytic isogenic mutant. Direct evidence that LLO is involved in NF-kappa B activation in transgenic mice was provided by injecting intravenously purified LLO, thus inducing stimulation of NF-kappa B in endothelial cells of blood capillaries. Our results demonstrate that functional listeriolysin O secreted by bacteria contributes as a potent inflammatory stimulus to inducing endothelial cell activation during the infectious process.

Characterization of Chlamydomonas reinhardtii zygote-specific cDNAs that encode novel proteins containing ankyrin repeats and WW domains

Genes that are expressed only in the young zygote are considered to be of great importance in the development of an isogamous green alga, Chlamydomonas reinhardtii. Clones representing the Zys3 gene were isolated from a cDNA library prepared using zygotes at 10 min after fertilization. Sequencing of Zys3 cDNA clones resulted in the isolation of two related molecular species. One of them encoded a protein that contained two kinds of protein-to-protein interaction motifs known as ankyrin repeats and WW domains. The other clone lacked the ankyrin repeats but was otherwise identical. These mRNA species began to accumulate simultaneously in cells beginning 10 min after fertilization, and reached maximum levels at about 4 h, after which time levels decreased markedly. Genomic DNA gel-blot analysis indicated that Zys3 was a single-copy gene. The Zys3 proteins exhibited parallel expression to the Zys3 mRNAs at first, appearing 2 h after mating, and reached maximum levels at more than 6 h, but persisted to at least 1 d. Immunocytochemical analysis revealed their localization in the endoplasmic reticulum, which suggests a role in the morphological changes of the endoplasmic reticulum or in the synthesis and transport of proteins to the Golgi apparatus or related vesicles.

Reduced phosphorylation of p50 is responsible for diminished NF-kappaB binding to the major histocompatibility complex class I enhancer in adenovirus type 12-transformed cells

Reduced cell surface levels of major histocompatibility complex class I antigens enable adenovirus type 12 (Ad12)-transformed cells to escape immunosurveillance by cytotoxic T lymphocytes (CTL), contributing to their tumorigenic potential. In contrast, nontumorigenic Ad5-transformed cells harbor significant cell surface levels of class I antigens and are susceptible to CTL lysis. Ad12 E1A mediates down-regulation of class I transcription by increasing COUP-TF repressor binding and decreasing NF-kappaB activator binding to the class I enhancer. The mechanism underlying the decreased binding of nuclear NF-kappaB in Ad12-transformed cells was investigated. Electrophoretic mobility shift assay analysis of hybrid NF-kappaB dimers reconstituted from denatured and renatured p50 and p65 subunits from Ad12- and Ad5-transformed cell nuclear extracts demonstrated that p50, and not p65, is responsible for the decreased ability of NF-kappaB to bind to DNA in Ad12-transformed cells. Hypophosphorylation of p50 was found to correlate with restricted binding of NF-kappaB to DNA in Ad12-transformed cells. The importance of phosphorylation of p50 for NF-kappaB binding was further demonstrated by showing that an NF-kappaB dimer composed of p65 and alkaline phosphatase-treated p50 from Ad5-transformed cell nuclear extracts could not bind to DNA. These results suggest that phosphorylation of p50 is a key step in the nuclear regulation of NF-kappaB in adenovirus-transformed cells.

Expression of IkappaBalpha in the nucleus of human peripheral blood T lymphocytes

According to current models the inhibitory capacity of I(kappa)B(alpha) would be mediated through the retention of Rel/NF-kappaB proteins in the cytosol. However, I(kappa)B(alpha) has also been detected in the nucleus of cell lines and when overexpressed by transient transfection. To gain better insight into the potential role of nuclear I(kappa)B(alpha) in a physiological context we have analysed its presence in the nucleus of human peripheral blood T lymphocytes (PBL). We demonstrate the nuclear localization of I(kappa)B(alpha) in PBL by different techniques: Western blot, indirect immunofluorescence and electron microscopy. Low levels of nuclear I(kappa)B(alpha) were detected in resting cells whereas a superinduction was obtained after PMA activation. The nuclear pool of I(kappa)B(alpha) showed a higher stability than cytosolic I(kappa)B(alpha) and was partially independent of the resynthesis of the protein. Unexpectedly, the presence of nuclear I(kappa)B(alpha) did not inhibit NF-kappaB binding to DNA and this phenomenon was not due to the presence of IkappaBbeta at the nuclear level. Immunoprecipitation experiments failed to demonstrate an association between nuclear I(kappa)B(alpha) and NF-kappaB proteins. Our results demonstrate that in resting and PMA-activated human PBL, I(kappa)B(alpha) is present in the nucleus in an apparently inactive form unable to disrupt NF-kappaB binding from DNA.

The p65 Subunit of NF-κB Is Redundant with p50 During B Cell Proliferative Responses, and Is Required for Germline CH Transcription and Class Switching to IgG3

B cells lacking individual NF-κB/Rel family members exhibit defects in activation programs. We generated small resting B cells lacking p65 or p50 alone, or lacking both p50 and p65, then evaluated the ability of these cells to proliferate, secrete Ig, and undergo Ig class switching. B cells lacking p65 proliferated well in response to all stimuli tested. However, these cells demonstrated an isolated defect in switching to IgG3, which was associated with a decrease in γ3 germline CH gene expression. Whereas, previously reported, B cells lacking p50 alone had a severe proliferative defect in response to LPS, a moderate defect in response to CD40 ligand (CD40L), and normal proliferation to Ag receptor cross-linking using dextran-conjugated anti-IgD Abs (αδ-dex), B cells lacking both p50 and p65 exhibited severely impaired proliferation in response to LPS, αδ-dex, and CD40L. This defect could be overcome by simultaneous administration of αδ-dex and CD40L. In response to this latter combination of stimuli, B cells lacking both p50 and p65 secreted Ig and underwent isotype switching to IgG1 as efficiently as B cells lacking p50 alone. These data demonstrate a role for the p65 subunit of NF-κB in germline CH gene expression as well as functional redundancy between p50 and p65 during proliferative responses.

TPL-2 kinase regulates the proteolysis of the NF-kappaB-inhibitory protein NF-kappaB1 p105

The transcription factor NF-kappaB is composed of homodimeric and heterodimeric complexes of Rel/NF-kappaB-family polypeptides, which include Rel-A, c-Rel, Rel-B, NF-kappaB/p50 and NF-kappaB2/p52 . The NF-kappaB1 gene encodes a larger precursor protein, p105, from which p50 is produced constitutively by proteasome-mediated removal of the p105 carboxy terminus. The p105 precursor also acts as an NFkappaB-inhibitory protein, retaining associated p50, c-Rel and Rel-A proteins in the cytoplasm through its carboxy terminus. Following cell stimulation by agonists, p105 is proteolysed more rapidly and released Rel subunits translocate into the nucleus. Here we show that TPL-2 , which is homologous to MAP-kinase-kinase kinases in its catalytic domain, forms a complex with the carboxy terminus of p105. TPL-2 was originally identified, in a carboxy-terminal-deleted form, as an oncoprotein in rats and is more than 90% identical to the human oncoprotein COT. Expression of TPL-2 results in phosphorylation and increased degradation of p105 while maintaining p50 production. This releases associated Rel subunits or p50-Rel heterodimers to generate active nuclear NF-kappaB. Furthermore, kinase-inactive TPL-2 blocks the degradation of p105 induced by tumour-necrosis factor-alpha. TPL-2 is therefore a component of a new signalling pathway that controls proteolysis of NF-kappaB1 p105.

Involvement of regulatory and catalytic subunits of phosphoinositide 3-kinase in NF-kappaB activation

Hypoxia, reoxygenation, and the tyrosine phosphatase inhibitor pervanadate activate the transcription factor NF-kappaB, involving phosphorylation of its inhibitor IkappaB-alpha on tyrosine 42. This modification does not lead to degradation of IkappaB by the proteasome/ubiquitin pathway, as is seen on stimulation of cells with proinflammatory cytokines. It is currently unknown how tyrosine-phosphorylated IkappaB is removed from NF-kappaB. Here we show that p85alpha, the regulatory subunit of PI3-kinase, specifically associates through its Src homology 2 domains with tyrosine-phosphorylated IkappaB-alpha in vitro and in vivo after stimulation of T cells with pervanadate. This association could provide a mechanism by which newly tyrosine-phosphorylated IkappaB is sequestered from NF-kappaB. Another mechanism by which PI3-kinase contributed to NF-kappaB activation in response to pervanadate appeared to involve its catalytic p110 subunit. This was evident from the inhibition of pervanadate-induced NF-kappaB activation and reporter gene induction by treatment of cells with nanomolar amounts of the PI3-kinase inhibitor wortmannin. The compound had virtually no effect on tumor necrosis factor- and interleukin-1-induced NF-kappaB activities. Wortmannin did not inhibit tyrosine phosphorylation of IkappaB-alpha or alter the stability of the PI3-kinase complex but inhibited Akt kinase activation in response to pervanadate. Our data suggest that both the regulatory and the catalytic subunit of PI3-kinase play a role in NF-kappaB activation by the tyrosine phosphorylation-dependent pathway.

Role of the conserved lysine 80 in stabilisation of NF-kappaB p50 DNA binding

The transcriptional rate of a variety of genes involved in acute-phase response, inflammation, lymphocytic activation, and cell growth or differentiation, is regulated by the DNA binding activity of the inducible transcription factor NF-kappaB. NF-kappaB p50 homodimers bind specifically to DNA, via base and backbone contacts mediated by residues in the flexible loops which link secondary structure elements in both of its two distinct domains. However, it has been suggested that additional contacts which stabilise DNA binding are made by lysine residues located in the C-terminus of the flexible loop which connects A and B beta-sheets of the N-terminal domain of p50. To determine the importance of each of the lysine residues in this region (K77, K79, K80), a series of mutated p50 proteins were generated in which the lysines were changed to alanines. The DNA binding properties of these mutants were analysed by gel electrophoresis DNA binding assays and surface plasmon resonance. This study revealed that the C-terminus of AB loop interacts with DNA through an additional lysine-phosphate backbone ionic bond which makes a significant contribution to the binding energy, thus stabilising the complex. The lysine residue responsible for this interaction is K80 which is conserved in all NF-kappaB/Rel/Dorsal molecules.

Nuclear factor-kappa B activity in T cells from patients with rheumatic diseases: a preliminary report

OBJECTIVE

The NF-kappa B/Rel family of transcription factors regulates the expression of many genes involved in the immune or inflammatory response at the transcriptional level. The aim of this study was to determine whether distinctive patterns of NF-kappa B activation are seen in different forms of joint disease.

METHODS

The DNA binding activity of these nucleoproteins was examined in purified synovial and peripheral T cells from patients with various chronic rheumatic diseases (12: four with rheumatoid arthritis; five with spondyloarthropathies; and three with osteoarthritis).

RESULTS

Electrophoretic mobility shift assays disclosed two specific complexes bound to a NF-kappa B specific 32P-labelled oligonucleotide in nucleoproteins extracted from purified T cells isolated from synovial fluid and peripheral blood of patients with rheumatoid arthritis. The complexes consisted of p50/p50 homodimers and p50/p65 heterodimers. Increased NF-kappa B binding to DNA in synovial T cells was observed relative to peripheral T cells. In non-rheumatoid arthritis, binding of NF-kappa B in synovial T cells was exclusively mediated by p50/p50 homodimers.

CONCLUSION

Overall, the results suggest that NF-kappa B may play a central part in the activation of infiltrating T cells in chronic rheumatoid arthritis. The activation of this nuclear factor is qualitatively different in rheumatoid synovial T cells to that in other forms of non-rheumatoid arthritis (for example, osteoarthritis, spondyloarthropathies).

The hepatitis B virus X protein activates nuclear factor of activated T cells (NF-AT) by a cyclosporin A-sensitive pathway

The X gene product of the human hepatitis B virus (HBx) is a transcriptional activator of various viral and cellular genes. We recently have determined that the production of tumor necrosis factor-alpha (TNF-alpha) by HBV-infected hepatocytes is transcriptionally up-regulated by HBx, involving nuclear factor of activated T cells (NF-AT)-dependent activation of the TNF-alpha gene promoter. Here we show that HBx activates NF-AT by a cyclosporin A-sensitive mechanism involving dephosphorylation and nuclear translocation of the transcription factor. Luciferase gene expression assays demonstrated that HBx transactivates transcription through NF-AT-binding sites and activates a Gal4-NF-AT chimeric protein. DNA-protein interaction assays revealed that HBx induces the formation of NF-AT-containing DNA-binding complexes. Immunofluorescence analysis demonstrated that HBx induces the nuclear translocation of NF-AT, which can be blocked by the immunosuppressive drug cyclosporin A. Furthermore, immunoblot analysis showed that the HBx-induced activation and translocation of NF-AT are associated with its dephosphorylation. Thus, HBx may play a relevant role in the intrahepatic inflammatory processes by inducing locally the expression of cytokines that are regulated by NF-AT.

Activation of NF-kappaB mediates the PMA-induced differentiation of K562 cells

The role of NF-kappaB during the PMA-induced megakaryocytic differentiation of K562 cells was investigated using K562 cells transfected with each or both subunits of NF-kappaB. The NF-kappaB subunit-transfected cells have shown much higher sensitivity to PMA-induced differentiation than their parental cells. This result was consistent with the findings that PMA-stimulated activities of NF-kappaB were markedly increased in the NF-kappaB subunit-transfected cells in comparison with their parental cells and PMA-induced differentiation was enhanced by pretreatment with IkappaB-alpha antisense oligonucleotide in the NF-kappaB subunit-transfected cells. Meanwhile, there were basically no difference in the basal and PMA-stimulated MAP kinase activities among the parental and NF-kappaB subunit-transfected cells, respectively. However, PMA-induced differentiation was blocked by pretreatment with PD98059, a specific inhibitor of MEK, in both parental and NF-kappaB-transfected cells. Therefore, these results suggest that during the PMA-induced megakaryocytic differentiation of K562 cells, NF-kappaB works downstream of MAP kinase, or that activation of both NF-kappaB and MAP kinase pathways is involved.