Signal transduction through NF-kappa B

NF-kappaB/Rel proteins are required for neuronal differentiation of SH-SY5Y neuroblastoma cells

The expression, cellular localization, and activation of the NF-kappaB/Rel transcription factors are altered during neuronal differentiation, but the significance is unclear. Here we investigate the requirement for NF-kappaB/Rel proteins in neuronal differentiation. SH-SY5Y neuroblastoma cells were induced to differentiate with retinoic acid (RA) or 12-O-tetradecanoylphorbol 13-acetate (TPA), and differentiation was demonstrated by morphological criteria and the enhanced expression of Bcl-2. NF-kappaB was transiently activated after the addition of the differentiation inducers before the morphological signs of differentiation and the enhanced Bcl-2 synthesis. The onset of NF-kappaB activation coincided with a significant reduction in the amount of only one of four NF-kappaB-inhibitory proteins examined (I-kappaBbeta). In contrast, NF-kappaB activation and the reduction in I-kappaBbeta failed to occur in SH-SY5Y cells transformed with I-kappaBalphaM, a dominant-negative inhibitor of NF-kappaB/Rel proteins. These I-kappaBalphaM-expressing cells failed to differentiate into neuronal cell types when treated with RA or TPA, and the increased Bcl-2 synthesis was blocked. Therefore, NF-kappaB/Rel proteins are required for neuronal differentiation of SH-SY5Y neuroblastoma cells.

Mechanisms of the antiinflammatory effects of alpha-MSH. Role of transcription factor NF-kappa B and adhesion molecule expression

The recruitment of leukocytes from the circulation to inflamed tissue is regulated by the expression of adhesion molecules on both leukocytes and endothelial cells. The proopiomelanocortin-derived peptide alpha-melanocyte stimulating hormone (alpha-MSH) is known to modulate inflammation. Thus, we investigated the influence of alpha-MSH on the LPS-induced expression of the adhesion molecules E-selectin and VCAM-1 on endothelial cells. Human microvascular endothelial cells (HMEC-1) were treated with LPS (100 ng/ml) alone or in the presence of alpha-MSH (10(-8) to 10(-16) M). RT-PCR analysis showed that alpha-MSH significantly reduced LPS-induced expression of VCAM-1 and E-selectin. Since many adhesion molecules contain regulatory NF-kappa B sites in their promoter region, the role of alpha-MSH in the activation of the transcription factor NF-alpha B was also investigated. alpha-MSH significantly downregulated the LPS-mediated activation of NF-kappa B, in a dose-dependent manner. These findings indicate that modulation of the transcription factor NF-kappa B is a crucial molecular event, one that seems to be responsible for the antiinflammatory effects of alpha-MSH.

beta-TrCP mediates the signal-induced ubiquitination of IkappaBbeta

We have examined the role of beta-TrCP (beta-transducin repeat-containing protein) in the ubiquitination and degradation of IkappaBbeta, one of the two major IkappaB isoforms in mammalian cells. We demonstrate that beta-TrCP interacts specifically with IkappaBbeta, and such interaction is dependent on prior phosphorylation of IkappaBbeta on serines 19 and 23. Interaction with beta-TrCP is also necessary for ubiquitination of IkappaBbeta upon stimulation of cells, and deletion of the F-box in beta-TrCP abolishes its ability to ubiquitinate IkappaBbeta. Therefore, these results indicate that beta-TrCP plays a critical role in the activation of NF-kappaB by assembling the ubiquitin ligase complex for both phosphorylated IkappaBalpha and IkappaBbeta.

The NF-κB Family Member RelB Is Required for Innate and Adaptive Immunity to Toxoplasma gondii

The NF-κB family of transcription factors are associated with the regulation of innate and adaptive immunity to infection. Infection of C57BL/6 mice with Toxoplasma gondii resulted in up-regulation of NF-κB activity that included the NF-κB family member RelB. To assess the role of RelB in the regulation of the immune response to this infection, we challenged RelB-deficient mice (RelB−/−) and wild-type (WT) littermate controls with T. gondii. Although WT controls were resistant to T. gondii, RelB−/− mice succumbed 10–15 days after infection. Examination of accessory cell functions associated with resistance to T. gondii revealed that RelB−/− macrophages stimulated with IFN-γ plus LPS or TNF-α produced IL-12 as well as reactive nitrogen intermediates and inhibited parasite replication similar to WT macrophages. Analysis of the systemic responses of RelB−/− and WT mice revealed that infected mice had similar serum levels of IL-12. However, RelB−/− mice challenged with T. gondii produced negligible levels of IFN-γ and had reduced NK cell activity compared with WT mice. Similarly, splenocytes from uninfected RelB−/− mice stimulated with polyclonal stimuli were deficient in their ability to produce IFN-γ. Together, our results demonstrate that RelB is essential for the development of innate NK and adaptive T cell responses that lead to the production of IFN-γ and resistance to T. gondii.

Molecular dissection of the interactions among IkappaBalpha, FWD1, and Skp1 required for ubiquitin-mediated proteolysis of IkappaBalpha

The SCF complex containing Skp1, Cul1, and the F-box protein FWD1 (the mouse homologue of Drosophila Slimb and Xenopus beta-TrCP) functions as the ubiquitin ligase for IkappaBalpha. FWD1 associates with Skp1 through the F-box domain and also recognizes the conserved DSGXXS motif of IkappaBalpha. The structural requirements for the interactions of FWD1 with IkappaBalpha and with Skp1 have now been investigated further. The D31A mutation (but not the G33A mutation) in the DSGXXS motif of IkappaBalpha abolished the binding of IkappaBalpha to FWD1 and its subsequent ubiquitination without affecting the phosphorylation of IkappaBalpha. The IkappaBalpha mutant D31E still exhibited binding to FWD1 and underwent ubiquitination. These results suggest that, in addition to site-specific phosphorylation at Ser(32) and Ser(36), an acidic amino acid at position 31 is required for FWD1-mediated ubiquitination of IkappaBalpha. Deletion analysis of Skp1 revealed that residues 61-143 of this protein are required for binding to FWD1. On the other hand, the highly conserved residues Pro(149), Ile(160), and Leu(164) in the F-box domain of FWD1 were dispensable for binding to Skp1. Together, these data delineate the structural requirements for the interactions among IkappaBalpha, FWD1, and Skp1 that underlie substrate recognition by the SCF ubiquitin ligase complex.

Sodium salicylate and 17beta-estradiol attenuate nuclear transcription factor NF-kappaB translocation in cultured rat astroglial cultures following exposure to amyloid A beta(1-40) and lipopolysaccharides

In recent years inflammatory mechanisms have become increasingly appreciated as important steps in the Alzheimer's pathogenic pathway. There is accumulating evidence that amyloid beta-peptide (A beta), the peptide product of the cleavage of amyloid precursor protein, may promote or exacerbate local inflammation by stimulating glial cells to release immune mediators. In addition, clinical studies using nonsteroidal antiinflammatory drugs have found a reduced risk for Alzheimer's disease with their use. Here we show that the neurotoxic A beta, a major plaque component, and lipopolysaccharides (LPS), an immune reaction-triggering portion of bacterial membranes, are both potent activators of the nuclear transcription factor NF-kappaB in primary rat astroglial cells. The activation was found to be concentration- and time-dependent and could be attenuated in the presence of NF-kappaB decoy nucleotides. The pretreatment by either 17beta-estradiol (1-10 microg) or sodium salicylate (3-30 mM) reduced the A beta (LPS)-induced activation of NF-kappaB by 48 (50%) and 60% (50%) of activated levels, respectively. In addition, 17beta-estradiol (10 microM) and sodium salicylate (10 mM) were able to attenuate the increase in interleukin-1beta levels following exposure to 25 microM A beta. Our data suggest that the aberrant gene expression is at least in part due to A beta-induced activation of NF-kappaB, a potent immediate-early transcriptional regulator of numerous proinflammatory genes; this event takes place in astroglial cells. The results of our experiments provide a further understanding of the effects of estrogen and aspirin on astroglial cells exposed to A beta and LPS.

Increased nuclear factor-kappaB activation in colitis of interleukin-2-deficient mice

Recent studies support nuclear factor-kappaB (NF-kappaB) as a critical transcription factor in inflammatory bowel disease. We examined NF-kappaB and its inhibitors, IkappaB-alpha and IkappaB-beta, in the colitis of interleukin-2 deficient (IL-2-/-) mice at the ages of 5, 10, and 15 weeks and compared them with those of age-matched wild-type mice. Colon levels of nuclear NF-kappaB and mRNA for NF-kappaB responsive cytokines interleukin-1beta and tumor necrosis factor-alpha were markedly increased in interleukin-2-/-mice. Colon interleukin-1beta protein levels were significantly elevated, consistent with increased interleukin-1beta mRNA, whereas tumor necrosis factor-alpha protein levels were either lower than those of the control group or did not differ. Protein levels of the immunomodulatory cytokine interleukin-10 were diminished. The NF-kappaB responsive IkappaB-alpha was also increased, mirroring NF-kappaB activation. In contrast, IkappaB-beta levels did not differ from those of wild-type mice in the 5- and 10-week groups and were only mildly increased in the 15-week group. Serum amyloid A, an acute phase protein that also is NF-kappaB-responsive, was dramatically elevated in the serum of interleukin-2-/- mice and correlated with the severity of the colitis. These data support a role for NF-kappaB in the pathogenesis of intestinal inflammation in interleukin-2-/- mice. The measurement of NF-kappaB in colon tissue samples may provide a sensitive means of assessing the state of activation of the mucosal immune response, and serum amyloid A appears to be a reliable biochemical marker of disease activity.

The Inhibitory Action of Mycobacterium ulcerans Soluble Factor on Monocyte/T Cell Cytokine Production and NF-κB Function

Buruli ulcer is a chronic and progressive necrotizing ulcer for which there is no medical treatment. Historically, a soluble toxin (factor) derived from the causative Mycobacterium ulcerans was found to induce the massive necrosis of skin and s.c. tissue seen in this condition. However, the persistence of the disease is thought to be caused by a lack of any immune response. We therefore investigated whether the factor was related to immunosuppression. A protocol to partially purify the factor was developed, and its effects on immune competent cells were tested. The factor produced >95% inhibition of LPS-induced release of TNF and IL-10 from human monocytes and caused a loss of adherence of these cells without cell death. The factor also blocked the production of IL-2 from activated T lymphocytes. The factor had no effect on TNF-induced cytotoxicity, but abrogated TNF-induced NF-κB activation. Surprisingly, a synergy was observed between the factor and phorbol ester-directed NF-κB activation. The factor had no effect on IL-1- or LPS-induced NF-κB activity, indicating selective activity of the factor. The factor did not inhibit the degradation of IκBα induced by TNF, indicating that the target for its activity lies within an undefined part of the TNF signaling mechanism. The data indicate that the localized immunosuppression associated with Buruli ulcer relates to the activity of the released factor, and this may provide a target for future therapeutic strategies for this intractable disease.

Mouse receptor interacting protein 3 does not contain a caspase-recruiting or a death domain but induces apoptosis and activates NF-kappaB

The death domain-containing receptor superfamily and their respective downstream mediators control whether or not cells initiate apoptosis or activate NF-kappaB, events critical for proper immune system function. A screen for upstream activators of NF-kappaB identified a novel serine-threonine kinase capable of activating NF-kappaB and inducing apoptosis. Based upon domain organization and sequence similarity, this novel kinase, named mRIP3 (mouse receptor interacting protein 3), appears to be a new RIP family member. RIP, RIP2, and mRIP3 contain an N-terminal kinase domain that share 30 to 40% homology. In contrast to the C-terminal death domain found in RIP or the C-terminal caspase-recruiting domain found in RIP2, the C-terminal tail of mRIP3 contains neither motif and is unique. Despite this feature, overexpression of the mRIP3 C terminus is sufficient to induce apoptosis, suggesting that mRIP3 uses a novel mechanism to induce death. mRIP3 also induced NF-kappaB activity which was inhibited by overexpression of either dominant-negative NIK or dominant-negative TRAF2. In vitro kinase assays demonstrate that mRIP3 is catalytically active and has autophosphorylation site(s) in the C-terminal domain, but the mRIP3 catalytic activity is not required for mRIP3 induced apoptosis and NF-kappaB activation. Unlike RIP and RIP2, mRIP3 mRNA is expressed in a subset of adult tissues and is thus likely to be a tissue-specific regulator of apoptosis and NF-kappaB activity. While the lack of a dominant-negative mutant precludes linking mRIP3 to a known upstream regulator, characterizing the expression pattern and the in vitro functions of mRIP3 provides insight into the mechanism(s) by which cells modulate the balance between survival and death in a cell-type-specific manner.

New insights into the roles of ReL/NF-kappa B transcription factors in immune function, hemopoiesis and human disease

In mammals, Rel/NF-kappa B proteins are a small family of transcription factors which serve as pivotal regulators of immune, inflammatory and acute phase responses. Pathways leading to the activation of Rel/NF-kappa B have recently been dissected in some detail and shown to converge on a unique high molecular weight cytoplasmic complex that includes several kinases and regulatory molecules. Moreover, gene targeting experiments have identified novel roles for Rel/NF-kappa B proteins in the development and maturation of hemopoietic precursors as well as in the function of mature cells in the immune system. These include regulating the cell cycle, controlling cell survival and providing a link between the innate and adaptive immune systems. Since the dysregulation of Rel/NF-kappa B function is associated with various pathologies including inflammatory and neoplastic disease, new insights into the role of Rel/NF-kappa B in human disease may provide a basis for therapeutic strategies in the treatment of chronic inflammatory diseases and certain malignancies.

The net repressor is regulated by nuclear export in response to anisomycin, UV, and heat shock

The ternary complex factors (TCFs) are targets for Ras/mitogen-activated protein kinase signalling pathways. They integrate the transcriptional response at the level of serum response elements in early-response genes, such as the c-fos proto-oncogene. An important aim is to understand the individual roles played by the three TCFs, Net, Elk1, and Sap1a. Net, in contrast to Elk1 and Sap1a, is a strong repressor of transcription. We now show that Net is regulated by nuclear-cytoplasmic shuttling in response to specific signalling pathways. Net is mainly nuclear under both normal and basal serum conditions. Net contains two nuclear localization signals (NLSs); one is located in the Ets domain, and the other corresponds to the D box. Net also has a nuclear export signal (NES) in the conserved Ets DNA binding domain. Net is apparently unique among Ets proteins in that a particular leucine in helix 1, a structural element, generates a NES. Anisomycin, UV, and heat shock induce active nuclear exclusion of Net through a pathway that involves c-Jun N-terminal kinase kinase and is inhibited by leptomycin B. Nuclear exclusion relieves transcriptional repression by Net. The specific induction of nuclear exclusion of Net by particular signalling pathways shows that nuclear-cytoplasmic transport of transcription factors can add to the specificity of the response to signalling cascades.

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.

Bradykinin induces interleukin-6 expression in astrocytes through activation of nuclear factor-kappaB

Bradykinin, a mediator of inflammation, is produced in the brain during trauma and stroke. It is thought to open the blood-brain barrier, although the mechanism is unclear. We have investigated, therefore, the effect of bradykinin on the expression of interleukin-6 (IL-6), a putative modulator of the blood-brain barrier, in astrocytes. IL-6 gene transcription was evaluated by transient transfection of the human IL-6 promoter linked to the luciferase gene. In murine astrocytes, bradykinin stimulated IL-6 secretion and gene transcription. The effect of bradykinin was blocked by KN-93, an inhibitor of Ca2+/calmodulin-dependent protein kinases, and by bisindolylmaleimide I, an inhibitor of protein kinase C, suggesting the involvement of these protein kinases. Mutations in the multiple response element and the binding site for nuclear factor-kappaB (NF-kappaB), but not in other known elements of the IL-6 promoter, interfered with induction of IL-6 transcription. The involvement of NF-kappaB was supported further by the finding that overexpression of nmIkappaB alpha, a stable inhibitor of NF-kappaB, inhibited the induction of IL-6 by bradykinin. Bradykinin activated NF-kappaB in primary astrocytes as shown by increased DNA binding of NF-kappaB. These data demonstrate that bradykinin stimulates IL-6 expression through activation of NF-kappaB, which may explain several inflammatory effects of bradykinin.

Ubiquitin-mediated proteolysis in learning and memory

Sensitization of defensive reflexes in Aplysia is a simple behavioral paradigm for studying both short- and long-term memory. In the marine mollusk, as in other animals, memory has at least two phases: a short-term phase lasting minutes and a long-term phase lasting several days or longer. Short-term memory is produced by covalent modification of pre-existing proteins. In contrast, long-term memory needs gene induction, synthesis of new protein, and the growth of new synapses. The switch from short-term (STF) to long-term facilitation (LTF) in Aplysia sensory neurons requires not only positive regulation through gene induction, but also the specific removal of several inhibitory proteins. One important inhibitory protein is the regulatory (R) subunit of the cAMP-dependent protein kinase (PKA). Degradation of R subunits, which is essential for initiating long-term stable memory, occurs through the ubiquitin-proteasome pathway.

Regulation of inducible gene expression by the transcription factor NF-kappaB

The transcription factor NF-kappaB plays a critical role in regulating inducible gene expression in immune responses. The activation of NF-kappaB is regulated at multiple levels, probably reflecting a need to maintain a tight control of its activity. We have recently discovered that direct phosphorylation of NF-kappaB itself is essential for its transcriptional activity and that phosphorylation acts as a switch to determine association of nuclear NF-kappaB with histone acetylases vs deacetylases.

Renal cell carcinoma-derived gangliosides suppress nuclear factor-kappaB activation in T cells

Activation of the transcription factor nuclear factor-kappaB (NFkappaB) is impaired in T cells from patients with renal cell carcinomas (RCCs). In circulating T cells from a subset of patients with RCCs, the suppression of NFkappaB binding activity is downstream from the stimulus-induced degradation of the cytoplasmic factor IkappaBalpha. Tumor-derived soluble products from cultured RCC explants inhibit NFkappaB activity in T cells from healthy volunteers, despite a normal level of stimulus-induced IkappaBalpha degradation in these cells. The inhibitory agent has several features characteristic of a ganglioside, including sensitivity to neuraminidase but not protease treatment; hydrophobicity; and molecular weight less than 3 kDa. Indeed, we detected gangliosides in supernatants from RCC explants and not from adjacent normal kidney tissue. Gangliosides prepared from RCC supernatants, as well as the purified bovine gangliosides G(m1) and G(d1a), suppressed NFkappaB binding activity in T cells and reduced expression of the cytokines IL-2 and IFN-gamma. Taken together, our findings suggest that tumor-derived gangliosides may blunt antitumor immune responses in patients with RCCs.

Inhibition of interleukin-1-stimulated NF-kappaB RelA/p65 phosphorylation by mesalamine is accompanied by decreased transcriptional activity

Nuclear factor kappaB (NF-kappaB) is an inducible transcription factor that regulates genes important in immunity and inflammation. The activity of NF-kappaB is highly regulated: transcriptionally active NF-kappaB proteins are sequestered in the cytoplasm by inhibitory proteins, IkappaB. A variety of extracellular signals, including interleukin-1 (IL-1), activate NF-kappaB by inducing phosphorylation and degradation of IkappaB, allowing nuclear translocation and DNA binding of NF-kappaB. Many of the stimuli that activate NF-kappaB by inducing IkappaB degradation also cause phosphorylation of the NF-kappaB RelA (p65) polypeptide. The transactivating capacity of RelA is positively regulated by phosphorylation, suggesting that in addition to cytosolic sequestration by IkappaB, phosphorylation represents another mechanism for control of NF-kappaB activity. In this report, we demonstrate that mesalamine, an anti-inflammatory aminosalicylate, dose-dependently inhibits IL-1-stimulated NF-kappaB-dependent transcription without preventing IkappaB degradation or nuclear translocation and DNA binding of the transcriptionally active NF-kappaB proteins, RelA, c-Rel, or RelB. Mesalamine was found to inhibit IL-1-stimulated RelA phosphorylation. These data suggest that pharmacologic modulation of the phosphorylation status of RelA regulates the transcriptional activity of NF-kappaB, independent of nuclear translocation and DNA binding. These findings highlight the importance of inducible phosphorylation of RelA in the control of NF-kappaB activity.

Persistent activation of nuclear factor-kappaB in cultured rat hepatic stellate cells involves the induction of potentially novel Rel-like factors and prolonged changes in the expression of IkappaB family proteins

Rat hepatic stellate cells (HSC) cultured in serum-containing medium underwent a rapid (3-hour) classical induction of p50:p65 and p65:p65 nuclear factor-kappaB (NF-kappaB) dimers. Subsequent culturing was associated with prolonged expression of active p50:p65 and persistent induction of a high-mobility NF-kappaB DNA binding complex consisting of potentially novel Rel-like protein(s). Formation of the latter complex was competed for by specific double-stranded oligonucleotides, was up-regulated by treatment of HSCs with tumor necrosis factor alpha (TNF-alpha), and was maintained at basal levels of expression by a soluble HSC-derived factor. An NF-kappaB-responsive CAT reporter gene was highly active in early cultured HSCs but was also trans-activated at a lower but significant level in longer-term cultured cells and could be completely suppressed by expression of dominant negative IkappaB-alpha. Physiological significance of the lower persistent NF-kappaB activities was also demonstrated by the ability of long-term cultured HSCs to support the activity of the NF-kappaB-dependent human intercellular adhesion molecule-1 (ICAM-1) promoter. Freshly isolated HSCs expressed high levels of IkappaB-alpha and IkappaB-beta. Culture activation was accompanied by a long-term reduction in levels of IkappaB-alpha with no detectable expression in the nuclear fraction of cells, under these conditions p50:p65 was detected in the nucleus. IkappaB-beta expression was transiently reduced and, upon replenishment, was associated with appearance of a lower-mobility IkappaB-beta antibody-reactive species. Bcl3 expression was absent in freshly isolated HSC but was induced during culturing and became a persistent feature of the activated HSC. Inhibition of NF-kappaB DNA binding activity by gliotoxin was associated with increased numbers of apoptotic cells. We suggest that activation of NF-kappaB in cultured HSC is required for expression of specific genes associated with the activated phenotype such as ICAM-1 and may be antiapoptotic for rat HSCs.

Direct association and nuclear import of the hepatitis B virus X protein with the NF-kappaB inhibitor IkappaBalpha

The X protein of hepatitis B virus (HBV) is a transcriptional activator which is required for infection and may play an important role in HBV-associated hepatocarcinogenesis. It has been suggested that X acts as a nuclear coactivator or stimulates several signal transduction pathways by acting in the cytoplasm. One of these pathways leads to the nuclear translocation of NF-kappaB. A recent report indicates that X activates NF-kappaB by acting on two cytoplasmic inhibitors of this family of transcription factors: IkappaBalpha and the precursor/inhibitor p105. We demonstrate here that X directly interacts with IkappaBalpha, which is able to transport it to the nucleus by a piggyback mechanism. This transport requires a region of IkappaBalpha (the second ankyrin repeat) which has been demonstrated to be involved in its nuclear import following NF-kappaB activation. Using deletion mutants, we showed that amino acids 249 to 253 of IkappaBalpha (located in the C-terminal part of the sixth ankyrin repeat) play a critical role in the interaction with X. This small region overlaps one of the domains of IkappaBalpha mediating the interaction with the p50 and p65 subunits of NF-kappaB and is also close to the nuclear export sequence of IkappaBalpha, therefore providing a potential explanation for the nuclear accumulation of IkappaBalpha with X. This association can also be observed upon the induction of endogenous IkappaBalpha by tumor necrosis factor alpha (TNF-alpha) treatment of Chang cells expressing X. In accordance with this observation, band shift analysis indicates that X induces a sustained NF-kappaB activation following TNF-alpha treatment, probably by preventing the reassociation of newly synthesized nuclear IkappaBalpha with DNA-bound NF-kappaB complexes.

Differential effects of lipopolysaccharide and tumor necrosis factor on monocytic IkappaB kinase signalsome activation and IkappaB proteolysis

The inflammatory mediators lipopolysaccharide (LPS) and tumor necrosis factor (TNF) are potent activators of NF-kappaB. This study compared the effect of these stimuli on endogenous IkappaB kinase (IKK) signalsome activation and IkappaB phosphorylation/proteolysis in human monocytic cells and investigated the role of the signalsome proteins IKK-alpha, IKK-beta, NF-kappaB-inducing kinase (NIK), IKK-gamma (NF-kappaB essential modulator), and IKK complex-associated protein. Kinase assays showed that TNF elicited a rapid but short-lived induction of IKK activity with a 3-fold greater effect on IKK-alpha than on IKK-beta, peaking at 5 min. In contrast, LPS predominantly stimulated IKK-beta activity, which slowly increased, peaking at 30 min. A second peak was observed at a later time point following LPS stimulation, which consisted of both IKK-alpha and -beta activity. The endogenous levels of the signalsome components were unaffected by stimulation. Furthermore, our studies showed association of the IKK-alpha/beta heterodimer with NIK, IkappaB-alpha and -epsilon in unstimulated cells. Exposure to LPS or TNF led to differential patterns of IkappaB-alpha and IkappaB-epsilon disappearance from and reassembly with the signalsome, whereas IKK-alpha, IKK-beta, and NIK remained complex-associated. NIK cannot phosphorylate IkappaB-alpha directly, but it appears to be a functionally important subunit, because mutated NIK inhibited stimulus-induced kappaB-dependent transcription more effectively than mutated IKK-alpha or -beta. Overexpression of IKK complex-associated protein inhibited stimulus-mediated transcription, whereas NF-kappaB essential modulator enhanced it. The understanding of LPS- and TNF-induced signaling may allow the development of specific strategies to treat sepsis-associated disease.

Interleukin-18 induces interferon-gamma production through NF-kappaB and NFAT activation in murine T helper type 1 cells

Interleukin-18 (IL-18) combined with anti-CD3 monoclonal antibody (mAb) induced interferon-gamma (IFN-gamma) production by T helper type 1 (Th1) cells. Neither IL-18 nor anti-CD3 mAb alone induced production of IFN-gamma. Although treatment with IL-18 alone induced full activation of NF-kappaB in Th1 cells, it was not sufficient for the production of IFN-gamma. To examine the importance of NF-kappaB activation in IFN-gamma production, we established Th1 cells which expressed a transdominant IkappaBalpha mutant. In these cells, activation of NF-kappaB and production of IFN-gamma by IL-18 were suppressed. On the other hand, we examined the T cell receptor (TCR)/CD3-mediated signaling pathway. FK506, an inhibitor of NFAT activation, inhibited IFN-gamma production by IL-18 without any effect on the NF-kappaB activation. We conclude that dual signaling consisting of IL-18-induced NF-kappaB activation and TCR/CD3-mediated NFAT activation is crucial for IFN-gamma production by IL-18 in murine Th1 cells.

Up-Regulation of ICAM-1 by Cytokines in Human Tracheal Smooth Muscle Cells Involves an NF-κB-Dependent Signaling Pathway That Is Only Partially Sensitive to Dexamethasone

Although the precise mechanisms by which steroids mediate their therapeutic effects remain unknown, steroids have been reported to abrogate cytokine-induced activation of the transcription factor NF-κB. In some cell types, NF-κB activation is necessary to regulate cytokine-mediated cellular functions. However, compelling evidence suggests that the steroid inhibition of NF-κB is complex and cell specific. Using EMSA, we show that stimulation with TNF-α or IL-1β induces NF-κB DNA-binding activity in human airway smooth muscle cells. TNF-α and IL-1β also increased luciferase activity in airway smooth muscle cells transfected with a reporter plasmid containing κB enhancer elements. Cytokines activated NF-κB by rapidly degrading its cytosolic inhibitor IκBα, which was then regenerated after 60 min. Cytokine-mediated IκBα reappearance was completely blocked by the protein synthesis inhibitor cycloheximide. Inhibition of cytokine-mediated IκBα proteolysis using the protease inhibitors N-tosyl-l-phenylalanine chloromethyl ketone and N-acetyl-l-leucinyl-l-leucinyl-norleucinal also inhibited cytokine-mediated early expression of ICAM-1. Although dexamethasone partially inhibited IL-1β- and TNF-α-induced up-regulation of ICAM-1 at 4 h, dexamethasone had no effect on cytokine-induced ICAM-1 expression at 18–24 h. In addition, neither cytokine-induced degradation or resynthesis of IκBα nor NF-κB DNA-binding activity were affected by dexamethasone. In cells transfected with the luciferase reporter, dexamethasone did not affect TNF-α-induced NF-κB-dependent transcription. Interestingly, cytokine-mediated expression of cyclooxygenase-2 was completely abrogated by dexamethasone at 6 h. Together, these data demonstrate that cytokine-mediated NF-κB activation and ICAM-1 expression involve activation of a steroid-insensitive pathway.

ECSIT is an evolutionarily conserved intermediate in the Toll/IL-1 signal transduction pathway

Activation of NF-kappaB as a consequence of signaling through the Toll and IL-1 receptors is a major element of innate immune responses. We report the identification and characterization of a novel intermediate in these signaling pathways that bridges TRAF6 to MEKK-1. This adapter protein, which we have named ECSIT (evolutionarily conserved signaling intermediate in Toll pathways), is specific for the Toll/IL-1 pathways and is a regulator of MEKK-1 processing. Expression of wild-type ECSIT accelerates processing of MEKK-1, whereas a dominant-negative fragment of ECSIT blocks MEKK-1 processing and activation of NF-kappaB. These results indicate an important role for ECSIT in signaling to NF-kappaB and suggest that processing of MEKK-1 is required for its function in the Toll/IL-1 pathway.

Inhibition of host cell signal transduction by Leishmania: observations relevant to the selective impairment of IL-12 responses

Leishmania parasites are able to delay the onset of cell-mediated immunity by selectively impairing the ability of infected macrophages to produce interleukin (IL)-12. Leishmania infection arrests the JAK/STAT-mediated signal transduction involved in activation of the IL-12 p40 promoter; the phosphorylation defects may be initiated by ligation of the phagocyte receptors used by these organisms to gain entry into the host cell.

IKK-i, a novel lipopolysaccharide-inducible kinase that is related to IkappaB kinases

Using the suppression subtractive hybridization technique, we isolated a novel kinase, IKK-i, whose message is drastically induced by lipopolysaccharide (LPS) in the mouse macrophage cell line RAW264. 7. The predicted protein contains the kinase domain in its N-terminus, which shares 30% identity to that of IKK-alpha or IKK-beta. The C-terminal portion contains a leucine zipper and a potential helix-loop-helix domain, as in the case of IKK-alpha and IKK-beta. IKK-i is expressed mainly in immune cells, and is induced in response to proinflammatory cytokines such as tumor necrosis factor-alpha, IL-1 and IL-6, in addition to LPS. Overexpression of wild-type IKK-i phosphorylated serine residues Ser32 and Ser36 of IkappaB-alpha (preferentially Ser36), and significantly stimulated NF-kappaB activation. These results suggest that IKK-i is an inducible IkappaB kinase which may play a special role in the immune response.

NF-κB Is a Central Regulator of the Intestinal Epithelial Cell Innate Immune Response Induced by Infection with Enteroinvasive Bacteria

Human intestinal epithelial cells up-regulate the expression of an inflammatory gene program in response to infection with a spectrum of different strains of enteroinvasive bacteria. The conserved nature of this program suggested that diverse signals, which are activated by enteroinvasive bacteria, can be integrated into a common signaling pathway that activates a set of proinflammatory genes in infected host cells. Human intestinal epithelial cell lines, HT-29, Caco-2, and T84, were infected with invasive bacteria that use different strategies to induce their uptake and have different intracellular localizations (i.e., Salmonella dublin, enteroinvasive Escherichia coli, or Yersinia enterocolitica). Infection with each of these bacteria resulted in the activation of TNF receptor associated factors, two recently described serine kinases, IκB kinase (IKK) α and IKKβ, and increased NF-κB DNA binding activity. This was paralleled by partial degradation of IκBα and IκBε in bacteria-infected Caco-2 cells. Mutant proteins that act as superrepressors of IKKβ and IκBα inhibited the up-regulated transcription and expression of downstream targets genes of NF-κB that are key components of the epithelial inflammatory gene program (i.e., IL-8, growth-related oncogene-α, monocyte chemoattractant protein-1, TNF-α, cyclooxygenase-2, nitric oxide synthase-2, ICAM-1) activated by those enteroinvasive bacteria. These studies position NF-κB as a central regulator of the epithelial cell innate immune response to infection with enteroinvasive bacteria.

Genistein inhibits constitutive and inducible NFkappaB activation and decreases IL-8 production by human cystic fibrosis bronchial gland cells

The inflammatory pathogenesis in airways of patients with cystic fibrosis (CF) is still unresolved. We demonstrate here that in in situ human DeltaF508 homozygous CF bronchial tissues, submucosal gland cells exhibit an absence of inhibitor factor kappaBalpha (IkappaBalpha) and high levels of chemokine interleukin-8 (IL-8) expression. These results were confirmed by cultured human CF bronchial gland cells in which a lack of cytosolic IkappaBalpha and high levels of constitutively activated nuclear factor kappaB (NFkappaB) associated with an up-regulation of IL-8 production (13-fold increase) were found when compared to non-CF (control) disease bronchial gland cells. We also demonstrated that the isoflavone genistein, a well known CFTR mutant Cl(-) channel stimulator, significantly reduces the endogenous and Pseudomonas aeruginosa lipopolysaccharide-induced IL-8 production in cultured CF bronchial gland cells by increasing cytosolic IkappaBalpha protein levels. Overall, results show that genistein is a potent inhibitor of the activated NFkappaB identified in CF gland cells. This strong inhibition of constitutively activated NFkappaB and the resulting down-regulation of IL-8 production by genistein in the CF gland cells highlights the key role played by cytosolic IkappaBalpha in the regulation of inflammatory processes in CF human airway cells.

Selective sensitization to tumor necrosis factor-alpha-induced apoptosis by blockade of NF-kappaB in primary glomerular mesangial cells

Recent data have implicated nuclear factor kappaB (NF-kappaB) in the prevention of apoptosis in transformed cell lines exposed to tumor necrosis factor alpha (TNF-alpha). However, it is obscure whether NF-kappaB plays an anti-apoptotic role in nontransformed cells, and it is not clear whether NF-kappaB inhibits apoptosis triggered by other mediators. We investigated the effect of specific inhibition of NF-kappaB on cytokine-induced apoptosis of glomerular mesangial cells, which is important in determining the outcome of glomerulonephritis. Cultured rat mesangial cells were stably transfected with the dominant negative mutant inhibitor of NF-kappaB (IkappaBalphaM). IkappaBalphaM was resistant to stimulus-dependent degradation and suppressed NF-kappaB activation induced by TNF-alpha (10 ng/ml) or IL-1beta (10 ng/ml). IkappaBalphaM significantly sensitized mesangial cells to TNF-alpha-induced apoptosis in a dose- and time-dependent manner but had no significant effects on the level of apoptosis in the presence of proinflammatory or apoptosis-inducing stimuli including Fas ligand, IL-1alpha, IL-1beta, hydrogen peroxide, lipopolysaccharide, cycloheximide, or serum deprivation. Moreover, IkappaBalphaM-mediated sensitization to TNF-alpha overcame the protective effect of mesangial cell survival factors present in serum, which usually inhibit killing of mesangial cells by the proapoptotic stimuli used. These data show that inhibition of NF-kappaB selectively sensitizes primary adult glomerular mesangial cells to TNF-induced apoptosis but not to other mediators of cell death including the Fas ligand.

Constitutive Nuclear Translocation of NF-κB in B Cells in the Absence of IκB Degradation

Members of the NF-κB/Rel family of transcription factors are involved in many aspects of B lymphocyte development and function. NF-κB is constitutively active in these cells, in contrast with most other cell types. In the inactive form, NF-κB/Rel proteins are sequestered in the cytoplasm by members of the IκB family of NF-κB inhibitors. When activated, NF-κB is translocated to the nucleus, a process that involves the phosphorylation and proteasomal degradation of IκB proteins. Thus, NF-κB activation is accompanied by the rapid turnover of IκB proteins. We show that while this “classical” mode of NF-κB activation is a uniform feature of IgM+ B cell lines, all IgG+ B cells analyzed contain nuclear NF-κB yet have stable IκBα, IκBβ, and IκBε. Furthermore, Iκβε levels are at least 10 times lower in IgG+ B cells than in IgM+ B cells, an additional indication that the regulation of constitutive NF-κB activity in these two types of B cells is fundamentally different. These data imply the existence of a novel mechanism of NF-κB activation in IgG+ B cells that operates independently of IκB degradation. They further suggest that different isoforms of the B cell receptor may have distinct roles in regulating NF-κB activity.

Required and nonessential functions of nuclear factor-kappa B in bone cells

Nuclear factor-kappa B (NF-kappaB) is a set of five polypeptide transcription factors, called p50, p52, p65 (also called Rel A), Rel B, and c-Rel, which regulate the expression of a variety of genes involved in immune and inflammatory responses. They were originally named because they were considered essential regulators of B cell kappa light chain expression. More recent studies indicate that NF-kappaB proteins are involved in the regulation of a variety of other cell functions, including cell proliferation, responses to stress, and apoptosis. NF-kappaB heterodimers reside in the cytoplasm of cells bound to inhibitory proteins, the two commonest of which are IkappaBalpha and IkappaBbeta, which prevent NF-kappaB from entering the nucleus. When cells are stimulated, IkappaB is phosphorylated by specific IkappaB kinases and subsequently is ubiquitinated and degraded in proteosomes. This allows NF-kappaB to translocate to the nucleus to regulate the expression of a growing list of genes, including the proinflammatory cytokines, interleukin-1 (IL-1), IL-6, and tumor necrosis factor. IL-1 and tumor necrosis factor in turn also regulate the expression of NF-kappaB. Thus, once activated, NF-kappaB may be involved in upregulatory loops, which can amplify the effects of the initiating stimulus. Because these proinflammatory cytokines have been implicated in the pathogenesis of estrogen deficiency and inflammation-related bone loss, it is likely that NF-kappaB has a significant role in the increased generation and function of osteoclasts in these circumstances. However, an unexpected and essential role of NF-kappaB in the formation of osteoclasts during development was discovered recently after the generation of knockout mice, which lack the expression of the p50 and p52 subunits. This paper will describe recent studies that reveal an essential role for NF-kappaB signaling in the generation of osteoclasts and that suggest that NF-kappaB may also play a key central role in the activation and survival of osteoclasts in conditions in which osteoclastogenesis is upregulated.

Immunopharmacology: anti-inflammatory therapy targeting transcription factors

Immunopharmacology is one of the most dynamic areas in pharmacology encompassing classical immunosuppressive drugs which reveal completely new clues concerning their mode of action as well as novel molecular biology approaches for treating inflammatory and autoimmune diseases, infections and cancer. This article focuses on transcription factors that regulate cell activities involved in immune and inflammatory cell responses and how traditional anti-inflammatory compounds such as glucocorticoids, cyclosporins, tacrolismus and salicylates interfere with the activation cascades triggering the transcription factors. Moreover, promising new initiatives for selective therapeutics including recombinant anti-inflammatory cytokines and proinflammatory cytokine antagonists, and gene therapy will be presented.

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.

Role of tyrosine kinase activity in 2,2',2''-tripyridine-induced nitricoxide generation in macrophages

In this paper, we demonstrated that 2,2',2"-tripyridine (TP, 1-20 microM) is a potent inducer of nitric oxide (NO) synthase in the cultured murine macrophage RAW 264.7 cell line. TP increased not only nitrite but also inducible NO synthase (iNOS) protein and mRNA production. Co-treatment with either NOS inhibitors (N(G)-monomethyl-L-arginine and aminoguanidine) or cycloheximide and actinomycin D all inhibited TP-induced nitrite production, indicating the requirement of protein and mRNA synthesis. The signaling pathway of TP-induced iNOS expression was explored, and the results obtained suggested that increased tyrosine kinase activity followed by inhibitor of nuclear factor for immunoglobulin kappa chain in B cells (IkappaB) degradation and then nuclear factor kappaB (NFkappaB) activation was involved in TP-induced iNOS expression. Tyrosine kinase inhibitors (e.g. genistein and tyrphostin AG126) inhibited both TP-induced nitrite and iNOS protein production. Whether the metalochelating property of TP was involved in these effects was explored by saturating TP with FeCl3. Although the ferrated TP became inactive, the specific iron chelator desferrioxamine, at a very high concentration of 400 microM, induced only a weak enhancement of nitrite production in this RAW cell line. It was thereby concluded that TP induces NO production through an increase in iNOS expression, which is initiated by a signaling pathway via tyrosine kinases leading to an activation of NFkappaB. Since TP is much more potent than desferrioxamine in increasing nitrite production, it is suspected that the primary event induced by TP was possibly mediated by TP's interacting with certain macromolecules in addition to its metal-chelating property.

New Immunosuppressive Drug PNU156804 Blocks IL-2-Dependent Proliferation and NF-κB and AP-1 Activation

We had previously shown that the drug undecylprodigiosin (UP) blocks human lymphocyte proliferation in vitro. We have now investigated the mechanism of action of a new analogue of UP, PNU156804, which shows a more favorable activity profile than UP in mice. We demonstrate here that the biological effect of PNU156804 in vitro is indistinguishable from UP: PNU156804 blocks human T cell proliferation in mid-late G1, as determined by cell cycle analysis, expression of cyclins, and cyclin-dependent kinases and retinoblastoma phosphorylation. In addition, we show that PNU156804 does not block significantly the induction of either IL-2 or IL-2R α- and γ-chains but inhibits IL-2-dependent T cell proliferation. We have investigated several molecular pathways that are known to be activated by IL-2 in T cells. We show that PNU156804 does not inhibit c-myc and bcl-2 mRNA induction. On the other hand, PNU156804 efficiently inhibits the activation of the NF-κB and AP-1 transcription factors. PNU156804 inhibition of NF-κB activation is due to the inhibition of the degradation of IκB-α and IκB-β. PNU156804 action is restricted to some signaling pathways; it does not affect NF-κB activation by PMA in T cells but blocks that induced by CD40 cross-linking in B lymphocytes. We conclude that the prodigiosin family of immunosuppressants is a new family of molecules that show a novel target specificity clearly distinct from that of other immunosuppressive drugs such as cyclosporin A, FK506, and rapamycin.

Interleukin-9 Regulates NF-κB Activity Through BCL3 Gene Induction

BCL3 encodes a protein with close homology to IκB proteins and interacts with p50 NF-κB homodimers. However, the regulation and transcriptional activity of BCL3 remain ill-defined. We observed here that interleukin-9 (IL-9) and IL-4, but not IL-2 or IL-3, transcriptionally upregulated BCL3 expression in T cells and mast cells. BCL3 induction by IL-9 was detected as soon as 4 hours after stimulation and appeared to be dependent on the Jak/STAT pathway. IL-9 stimulation was associated with an increase in p50 homodimers DNA binding activity, which was mimicked by stableBCL3 expression. This contrasts with tumor necrosis factor (TNF)-dependent NF-κB activation, which occurs earlier, involves p65/p50 dimers, and is dependent on IκB degradation. Moreover, IL-9 stimulation or BCL3 transient transfection similarly inhibited NF-κB–mediated transcription in response to TNF. Taken together, our observations show a new regulatory pathway for the NF-κB transcription factors through STAT-dependent upregulation ofBCL3 gene expression.

Interleukin-9 Regulates NF-κB Activity Through BCL3 Gene Induction

BCL3 encodes a protein with close homology to IκB proteins and interacts with p50 NF-κB homodimers. However, the regulation and transcriptional activity of BCL3 remain ill-defined. We observed here that interleukin-9 (IL-9) and IL-4, but not IL-2 or IL-3, transcriptionally upregulated BCL3 expression in T cells and mast cells. BCL3 induction by IL-9 was detected as soon as 4 hours after stimulation and appeared to be dependent on the Jak/STAT pathway. IL-9 stimulation was associated with an increase in p50 homodimers DNA binding activity, which was mimicked by stableBCL3 expression. This contrasts with tumor necrosis factor (TNF)-dependent NF-κB activation, which occurs earlier, involves p65/p50 dimers, and is dependent on IκB degradation. Moreover, IL-9 stimulation or BCL3 transient transfection similarly inhibited NF-κB–mediated transcription in response to TNF. Taken together, our observations show a new regulatory pathway for the NF-κB transcription factors through STAT-dependent upregulation ofBCL3 gene expression.

The IKKbeta subunit of IkappaB kinase (IKK) is essential for nuclear factor kappaB activation and prevention of apoptosis

The IkappaB kinase (IKK) complex is composed of three subunits, IKKalpha, IKKbeta, and IKKgamma (NEMO). While IKKalpha and IKKbeta are highly similar catalytic subunits, both capable of IkappaB phosphorylation in vitro, IKKgamma is a regulatory subunit. Previous biochemical and genetic analyses have indicated that despite their similar structures and in vitro kinase activities, IKKalpha and IKKbeta have distinct functions. Surprisingly, disruption of the Ikkalpha locus did not abolish activation of IKK by proinflammatory stimuli and resulted in only a small decrease in nuclear factor (NF)-kappaB activation. Now we describe the pathophysiological consequence of disruption of the Ikkbeta locus. IKKbeta-deficient mice die at mid-gestation from uncontrolled liver apoptosis, a phenotype that is remarkably similar to that of mice deficient in both the RelA (p65) and NF-kappaB1 (p50/p105) subunits of NF-kappaB. Accordingly, IKKbeta-deficient cells are defective in activation of IKK and NF-kappaB in response to either tumor necrosis factor alpha or interleukin 1. Thus IKKbeta, but not IKKalpha, plays the major role in IKK activation and induction of NF-kappaB activity. In the absence of IKKbeta, IKKalpha is unresponsive to IKK activators.

NF-kappaB to the rescue: RELs, apoptosis and cellular transformation

The REL/NF-kappaB/IkappaB superfamily of signal transducers and transcription factors are paradigmatic of molecular mechanisms by which rapid responses in the immune system can be achieved. NF-kappaB proteins have been implicated in diverse processes such as the ontogeny of the immune system, immune responses to pathogens and, importantly, in contributions to the multistage processes of oncogenesis, as described in this review. NF-kappaB and its regulators, the IkappaBs, are linked to pro- and anti-apoptotic events as well as signaling systems contributing to cellular transformation. How are these disparate events controlled to effect normal and abnormal processes in cells? Here we explore a few of the many events in which NF-kappaB appears to participate and processes that integrate signals to control important stages of oncogenesis.

Hepatitis C virus core protein inhibits Fas- and tumor necrosis factor alpha-mediated apoptosis via NF-kappaB activation

The effects of hepatitis C virus (HCV) proteins on anti-Fas (CD95/APO-1) antibody- and tumor necrosis factor alpha (TNF-alpha)-mediated apoptosis in different human cell lines were investigated by magnetic concentration of cells which transiently produced the exogenous protein. HepG2 cells, which produced whole HCV proteins, became resistant to anti-Fas-induced apoptotic cell death. Furthermore, the core protein among HCV proteins had a key role in protecting the various cells from apoptosis mediated by not only anti-Fas but also TNF-alpha. We also found that the core functioned in the activation of nuclear factor kappaB (NF-kappaB) in all cells examined. Deletion analysis of the core revealed that the region required for NF-kappaB activation was closely correlated with that for its antiapoptotic function. In addition, we revealed in some cases that the antiapoptotic effect of the core was restrained by coproduction of the inhibitor of NF-kappaB, IkappaB-alpha protein. These results demonstrated that the core inhibits Fas- and TNF-alpha-mediated apoptotic cell death via a mechanism dependent on the activation of NF-kappaB in particular cell lines.

Pyrrolidine dithiocarbamate protects mice from lethal shock induced by LPS or TNF-alpha

Although important advances have been made in the development of antibiotics and medical intensive care technology in recent years, systemic response to infection remains a major health problem, with growing incidence and high mortality rates. Here we demonstrate the ability of the antioxidant agent pyrrolidine dithiocarbamate (PDTC) to inhibit the in vivo activation of NF-kappaB in lung and liver tissues, as well as the systemic release of TNF-alpha in lipopolysaccharide (LPS)-treated mice. The in vivo effect of PDTC on NF-kappaB activation in liver tissues involved the inhibition of both LPS-induced I kappaB-alpha degradation and the translocation of the p50 and p65 NF-kappaB subunits to the nucleus. In addition to protecting mice against lethal LPS doses, PDTC curtailed TNF-alpha-induced lethal shock. This effect was observed even after LPS injection, and when PDTC was administered at a time when TNF-alpha was already at maximum levels in serum. PDTC-treated mice survived despite high IL-1beta and IL-6 levels, induction of VCAM-1 and ICAM-1 expression or leukocyte infiltration in tissues known to be associated with LPS-induced shock, indicating that PDTC does not act by modifying these responses. Taken together, these results indicate that PDTC interferes with the production as well as the action of TNF-alpha, and points to a possible approach toward the treatment of septic shock.

IKKgamma mediates the interaction of cellular IkappaB kinases with the tax transforming protein of human T cell leukemia virus type 1

The Tax oncoprotein of human T cell leukemia virus type 1 constitutively activates transcription factor NF-kappaB by a mechanism involving Tax-induced phosphorylation of IkappaBalpha, a labile cytoplasmic inhibitor of NF-kappaB. To trigger this signaling cascade, Tax associates stably with and persistently activates a cellular IkappaB kinase (IKK) containing both catalytic (IKKalpha and IKKbeta) and noncatalytic (IKKgamma) subunits. We now demonstrate that IKKgamma enables Tax to dock with the IKKbeta catalytic subunit, resulting in chronic IkappaB kinase activation. Mutations in either IKKgamma or Tax that prevent formation of these higher order Tax.IKK complexes also interfere with the ability of Tax to induce IKKbeta catalytic function in vivo. Deletion mapping studies indicate that amino acids 1-100 of IKKgamma are required for this Tax targeting function. Together, these findings identify IKKgamma as an adaptor protein that directs the stable formation of pathologic Tax.IKK complexes in virally infected T cells.

Repression of NF-kappaB impairs HeLa cell proliferation by functional interference with cell cycle checkpoint regulators

NF-kappaB is an inducible transcription factor, which is regulated by interaction with inhibitory IkappaB proteins. Previous studies linked the activity of NF-kappaB to the proliferative state of the cell. Here we have analysed the function of NF-kappaB in the cell cycle. Inhibition of NF-kappaB in HeLa cells by stable overexpression of a transdominant negative IkappaB-alpha protein reduced cell growth. A kinetic analysis of the cell cycle revealed a retarded G1/S transition. The IkappaB-alpha overexpressing cell clones showed a decreased percentage of cells in the S phase and an impaired incorporation of bromodeoxyuridine (BrdU). The amounts of cyclins A, B1, D1, D3, and E were unchanged, but the G1-specific proteins cyclin D2 and cdk2 were strongly elevated in the IkappaB-alpha overexpressing cell clones. These cell clones also displayed an increase in cyclin D1-dependent kinase activity, pointing to a cell cycle arrest at the late G1 phase. IkappaB-alpha overexpression crosstalked to cell cycle checkpoints via a reduction of transcription factor p53 and elevation of p21WAF. Surprisingly, the IkappaB-alpha overexpressing cells showed an enrichment of c-Myc in the nucleoli, although the total amount of c-Myc protein was unchanged. These experiments identify an important contribution of the NF-kappaB/IkappaB system for the growth of HeLa cells.

4-Hydroxynonenal prevents NF-kappaB activation and tumor necrosis factor expression by inhibiting IkappaB phosphorylation and subsequent proteolysis

Extensively oxidized low density lipoprotein (ox-LDL), a modulator of atherogenesis, down-regulates the lipopolysaccharide (LPS)-induced activation of transcription factor NF-kappaB. We investigated whether 4-hydroxynonenal (HNE), a prominent aldehyde component of ox-LDL, represents one of the inhibitory substances. NF-kappaB activation by stimuli such as LPS, interleukin (IL)-1beta, and phorbol ester, but not tumor necrosis factor (TNF), was reversibly inhibited by HNE in a dose-dependent manner in human monocytic cells, whereas AP-1 binding was unaffected. Using similar HNE concentrations, LPS-induced kappaB- and TNF or IL-8 promoter-dependent transcription was prevented. Furthermore, pretreatment with HNE suppressed TNF production but not lactate dehydrogenase levels. Under these conditions the binding of LPS to monocytic cells was not significantly affected. However, induced proteolysis of the inhibitory proteins IkappaB-alpha, IkappaB-beta, and, at a later time point, IkappaB-epsilon was prevented. This is not due to inhibition of the proteasome, the major proteolytic activities of which remain unaffected, but rather to a specific prevention of the activation-dependent phosphorylation of IkappaB-alpha. This is the first report which demonstrates that HNE specifically inhibits the NF-kappaB/Rel system. Down-modulation of NF-kappaB-regulated gene expression may contribute at certain stages of atherosclerosis to low levels of chronic inflammation and may also be involved in other inflammatory/degenerative diseases.

NF-kappaB and apoptosis in mammary epithelial cells

A number of transcription factors have been identified as regulators of mammary development, including Stat5 and C/EBPbeta (1-3). In this review we summarize evidence which suggests that the NF-kappaB family of transcription factors also has a role in mammary gland development. NF-kappaB was originally described as a mediator of inflammatory reactions and cellular responses to viral pathogens. More recently it has been shown to possess an anti-apoptotic effect in a variety of cell types by regulating apoptosis-related genes. In the light of this function in other tissues, and the observation that aberrant activation of NF-kappaB can be associated with mammary tumors, we discuss the potential role of this transcription factor in modulating mammary epithelial apoptosis and involution of the mammary gland.

IkappaB-mediated inhibition of virus-induced beta interferon transcription

We have examined the consequences of overexpression of the IkappaBalpha and IkappaBbeta inhibitory proteins on the regulation of NF-kappaB-dependent beta interferon (IFN-beta) gene transcription in human cells after Sendai virus infection. In transient coexpression studies or in cell lines engineered to express different forms of IkappaB under tetracycline-inducible control, the IFN-beta promoter (-281 to +19) linked to the chloramphenicol acetyltransferase reporter gene was differentially inhibited in response to virus infection. IkappaBalpha exhibited a strong inhibitory effect on virus-induced IFN-beta expression, whereas IkappaBbeta exerted an inhibitory effect only at a high concentration. Despite activation of the IkappaB kinase complex by Sendai virus infection, overexpression of the double-point-mutated (S32A/S36A) dominant repressors of IkappaBalpha (TD-IkappaBalpha) completely blocked IFN-beta gene activation by Sendai virus. Endogenous IFN-beta RNA production was also inhibited in Tet-inducible TD-IkappaBalpha-expressing cells. Inhibition of IFN-beta expression directly correlated with a reduction in the binding of NF-kappaB (p50-RelA) complex to PRDII after Sendai virus infection in IkappaBalpha-expressing cells, whereas IFN-beta expression and NF-kappaB binding were only slightly reduced in IkappaBbeta-expressing cells. These experiments demonstrate a major role for IkappaBalpha in the regulation of NF-kappaB-induced IFN-beta gene activation and a minor role for IkappaBbeta in the activation process.

Proteolysis of monocyte CD14 by human leukocyte elastase inhibits lipopolysaccharide-mediated cell activation

Human leukocyte elastase (HLE), a polymorphonuclear neutrophil (PMN) serine proteinase, is proteolytically active on some membrane receptors at the surface of immune cells. The present study focused on the effect of HLE on the expression of CD14, the main bacterial lipopolysaccharide (LPS) receptor at the surface of monocytes. HLE exhibited a time- and concentration-dependent downregulatory effect on CD14 surface expression. A 30-minute incubation of 3 microM HLE was required to display 95% disappearance of the receptor. This downregulation resulted from a direct proteolytic process, not from a shedding consecutive to monocyte activation as observed upon challenge with phorbol myristate acetate (PMA). To confirm that CD14 is a substrate for HLE, this enzyme was incubated with recombinant human CD14 (Mr approximately 57,000), and proteolysis was further analyzed by immunoblot analysis. Cleavage of the CD14 molecule was directly evidenced by the generation of short-lived fragments (Mr approximately 47,000 and 30,000). As a consequence of the CD14 proteolysis, a decrease in the responsiveness of monocytes to LPS was observed, as assessed by measuring tumor necrosis factor-alpha (TNF-alpha) formation. This inhibition was only observed with 1 ng/ml of LPS, i.e., when only the CD14-dependent pathway was involved. At a higher LPS concentration, such as 10 microgram/ml, when CD14-independent pathways were operative, this inhibition was overcome. The direct proteolysis by HLE of the membrane CD14 expressed on monocytes illustrates a potential anti-inflammatory effect of HLE through inhibition of LPS-mediated cell activation.

The role of protein phosphatases in the expression of inducible nitric oxide synthase in the rat hepatocyte

Previously, we demonstrated that nuclear factor-kappaB (NF-kappaB) mediates cytokine-induced hepatic inducible nitric oxide synthase (iNOS) expression. NF-kappaB activation is regulated by kinases and phosphatases whose function is only beginning to be understood. Therefore, experiments were performed to determine the role of protein phosphatases (PPase) in cytokine-induced iNOS expression. Hepatocytes were stimulated with cytokines in the presence or absence of tyrosine phosphatase inhibitors (pervanadate [PV], phenylarsine oxide [PAO]) and a serine-threonine phosphatase inhibitor (okadaic acid [OA]). Cytokines induced hepatocyte iNOS mRNA, protein, and NO2- production that was substantially decreased by the addition of the tyrosine phosphatase inhibitors (PAO and PV). The serine-threonine phosphatase inhibitor (OA) decreased NO release and protein levels in a concentration-dependent fashion; however, iNOS mRNA levels were not significantly reduced. Nuclear run-on experiments demonstrated that protein tyrosine phosphatases (PTPases) are required for iNOS transcription, while the serine-threonine phosphatase inhibitor (OA) had no effect on iNOS transcription. Electromobility shift assays (EMSAs) revealed that the tyrosine-phosphatase inhibitors blocked cytokine-induced NF-kappaB activation, while OA did not have a significant effect on NF-kappaB DNA binding activity. Therefore, tyrosine phosphatases are involved in the regulation of cytokine-induced activation of NF-kappaB, while serine-threonine phosphatases posttranscriptionally regulate iNOS translation. These results identify the regulatory role of specific protein phosphatases (PPases) in hepatic iNOS expression.

Multiple signals converging on NF-kappaB

The recent identification of molecular components of the signal transduction pathway regulating activation of nuclear factor-kappaB (NF-kappaB) in response to cytokines such as tumor necrosis factor alpha and interleukin-1beta allows the evaluation of how other diverse stimuli impinge on the NF-kappaB activation pathway. These studies suggest a basis for specificity in activation of specific Rel-related family members and the genetic responses they promote.