Cytokine-inducible expression in endothelial cells of an I kappa B alpha-like gene is regulated by NF kappa B

Transcriptional basis for the differences in inducible nitric oxide synthase (iNOS) expression between nonmetastatic and metastatic murine melanoma cell lines

An inverse correlation exists between expression of the inducible nitric oxide synthase (iNOS) gene and the ability of cloned K1735 murine melanoma cell lines to metastasize. We have analyzed the basis for the difference in iNOS induction by interferon-gamma (IFN-gamma) and lipopolysaccharide (LPS) in metastatic and non-metastatic K1735 cells. Nuclear run-on (NRO) assays revealed an upregulation of iNOS transcription on treatment with IFN-gamma plus LPS in nonmetastatic cells but not in a metastatic line. Transcription factors IFN regulatory factor 1 (IRF-1) and NF-kappaB were induced and functional in both metastatic and nonmetastatic K1735 lines treated with IFN-gamma plus LPS. Furthermore, a reporter construct driven by the wild-type iNOS promoter was transcriptionally activated in both nonmetastatic and metastatic cells. The iNOS-inducible phenotype was dominant in somatic cell hybrids generated by the fusion of nonmetastatic and metastatic cells, suggesting that no inhibitors of iNOS expression are present in metastatic cells. We conclude that the selective block in iNOS transcription in metastatic K1735 cells is likely due to an alteration in iNOS gene regulatory sequences. However, no such alteration was detected within the 1.7 kb iNOS promoter region in metastatic cells.

Bcl-2 and Bcl-XL serve an anti-inflammatory function in endothelial cells through inhibition of NF-kappaB

To maintain the integrity of the vascular barrier, endothelial cells (EC) are resistant to cell death. The molecular basis of this resistance may be explained by the function of antiapoptotic genes such as bcl family members. Overexpression of Bcl-2 or Bcl-XL protects EC from tumor necrosis factor (TNF)-mediated apoptosis. In addition, Bcl-2 or Bcl-XL inhibits activation of NF-kappaB and thus upregulation of proinflammatory genes. Bcl-2-mediated inhibition of NF-kappaB in EC occurs upstream of IkappaBalpha degradation without affecting p65-mediated transactivation. Overexpression of bcl genes in EC does not affect other transcription factors. Using deletion mutants of Bcl-2, the NF-kappaB inhibitory function of Bcl-2 was mapped to bcl homology domains BH2 and BH4, whereas all BH domains were required for the antiapoptotic function. These data suggest that Bcl-2 and Bcl-XL belong to a cytoprotective response that counteracts proapoptotic and proinflammatory insults and restores the physiological anti-inflammatory phenotype to the EC. By inhibiting NF-kappaB without sensitizing the cells (as with IkappaBalpha) to TNF-mediated apoptosis, Bcl-2 and Bcl-XL are prime candidates for genetic engineering of EC in pathological conditions where EC loss and unfettered activation are undesirable.

NF-kappaB activity is induced by neural cell adhesion molecule binding to neurons and astrocytes

The neural cell adhesion molecule, N-CAM, is expressed on the surface of astrocytes and neurons, and N-CAM homophilic binding has been shown to alter gene expression in both of these cell types. To determine mechanisms by which N-CAM regulates gene expression, we have analyzed DNA binding of and transcriptional activation by NF-kappaB after N-CAM binding to the cell surface. Addition of purified N-CAM, the recombinant third immunoglobulin domain of N-CAM, or N-CAM antibodies either to neonatal rat forebrain astrocytes or to cerebellar granule neurons increased NF-kappaB/DNA binding activity in nuclear extracts as measured by electrophoretic mobility shift assays. Analysis using supershifting antibodies indicated that, in both cell types, p50 and p65 but not p52, c-Rel, or Rel B were contained in the NF-kappaB-binding complex. NF-kappaB-mediated transcription was increased after N-CAM binding to astrocytes and neurons as demonstrated by the activation of two different luciferase reporter constructs containing NF-kappaB-binding sites. N-CAM binding also resulted in degradation of IkappaB-alpha protein followed by an increase in the levels of IkappaB-alpha mRNA and protein. These results indicate that N-CAM homophilic binding at the cell membrane leads to increased NF-kappaB binding to DNA and transcriptional activation in both neurons and astrocytes. Activation of NF-kappaB, however, did not influence the previously reported ability of N-CAM to inhibit astrocyte proliferation. These observations together support the hypothesis that N-CAM binding activates multiple pathways leading to changes in gene expression in both astrocytes and neurons.

The role of oxidative stress and NF-kappaB activation in late diabetic complications

A common endpoint of hyperglycemia dependent cellular changes is the generation of reactive oxygen intermediates (ROIs) and the presence of elevated oxidative stress. Therefore, oxidative stress is supposed to play an important role in the development of late diabetic complications. Formation of advanced glycation end products (AGE's) due to elevated nonenzymatic glycation of proteins, lipids and nucleic acids is accompanied by oxidative, radical-generating reactions and thus represents a major source for oxygen free radicals under hyperglycemic conditions. Once formed, AGE's can influence cellular function by binding to several binding sites including the receptor for AGE's, RAGE. Binding of AGE's (and other ligands) to RAGE results in generation of intracellular oxidative stress and subsequent activation of the redox-sensitive transcription factor NF-kappaB in vitro and in vivo. Consistently, activation of NF-kappaB in diabetic patients correlates with the quality of glycemic control and can be reduced by treatment with the antioxidant alpha-lipoic acid. The development of techniques allowing for a tissue culture independent measurement of NF-kappaB activation in patients with diabetes mellitus gives insights into the molecular mechanisms linking diabetes mellitus and hyperglycemia with formation of advanced glycated endproducts and generation of oxidative stress finally resulting in oxidative stress mediated cellular activation.

The crystal structure of the IkappaBalpha/NF-kappaB complex reveals mechanisms of NF-kappaB inactivation

IkappaBalpha regulates the transcription factor NF-kappaB through the formation of stable IkappaBalpha/NF-kappaB complexes. Prior to induction, IkappaBalpha retains NF-kappaB in the cytoplasm until the NF-kappaB activation signal is received. After activation, NF-kappaB is removed from gene promoters through association with nuclear IkappaBalpha, restoring the preinduction state. The 2.3 A crystal structure of IkappaBalpha in complex with the NF-kappaB p50/p65 heterodimer reveals mechanisms of these inhibitory activities. The presence of IkappaBalpha allows large en bloc movement of the NF-kappaB p65 subunit amino-terminal domain. This conformational change induces allosteric inhibition of NF-kappaB DNA binding. Amino acid residues immediately preceding the nuclear localization signals of both NF-kappaB p50 and p65 subunits are tethered to the IkappaBalpha amino-terminal ankyrin repeats, impeding NF-kappaB from nuclear import machinery recognition.

Role of NF-kappaB in immune and inflammatory responses in the gut

NF-kappaB is a pleiotropic transcription factor with key functions in the intestinal immune system. NF-kappaB family members control transcriptional activity of various promoters of proinflammatory cytokines, cell surface receptors, transcription factors, and adhesion molecules that are involved in intestinal inflammation. The perpetuated activation of NF-kappaB in patients with active inflammatory bowel disease suggests that regulation of NF-kappaB activity is a very attractive target for therapeutic intervention. Such strategies include antioxidants, proteasome inhibitors, inhibition of NF-kappaB by adenoviral I kappaB alpha expression vectors, and antisense DNA targeting of NF-kappaB. These approaches will hopefully permit the design of new treatment strategies for chronic intestinal inflammation.

Impaired fungicide activity in plants blocked in disease resistance signal transduction

Fungicide action is generally assumed to be dependent on an antibiotic effect on a target pathogen, although a role for plant defense mechanisms as mediators of fungicide action has not been excluded. Here, we demonstrate that in Arabidopsis, the innate plant defense mechanism contributes to the effectiveness of fungicides. In NahG and nim1 (for noninducible immunity) Arabidopsis plants, which normally exhibit increased susceptibility to pathogens, the fungicides metalaxyl, fosetyl, and Cu(OH)2 are much less active and fail to control Peronospora parasitica. In contrast, the effectiveness of these fungicides is not altered in Arabidopsis mutants defective in the ethylene or jasmonic acid signal transduction pathways. Application of the systemic acquired resistance activator benzothiadiazole (BTH) in combination with these fungicides results in a synergistic effect on pathogen resistance in wild-type plants and an additive effect in NahG and BTH-unresponsive nim1 plants. Interestingly, BTH treatment normally induces long-lasting pathogen protection; however, in NahG plants, the protection is transient. These observations suggest that BTH treatment can compensate only partially for an impaired signal transduction pathway and support the idea that pathogen defense mechanisms are under positive feedback control. These observations are strikingly reminiscent of the reduced efficacy of antifungal agents in immunocompromised animals.

Induction of the stress response with prostaglandin A1 increases I-kappaBalpha gene expression

I-kappaBalpha is an intracellular protein that functions as a primary inhibitor of the proinflammatory transcription factor NF-kappaB. Induction of the stress response with heat shock was previously demonstrated to induce I-kappaBalpha gene expression. Because the stress response can also be induced by nonthermal stimuli, we determined whether induction of the stress response with prostaglandin A1 (PGA1) would induce I-kappaBalpha gene expression. Treatment of human bronchial epithelium (BEAS-2B cells) with PGA1 induced nuclear translocation of heat shock factor 1, thus confirming that PGA1 induces the stress response in BEAS-2B cells. Induction of the stress response with PGA1 increased I-kappaBalpha mRNA expression in a time-dependent manner and increased I-kappaBalpha peptide expression. Transient transfection assays involving a human I-kappaBalpha promoter-luciferase reporter construct demonstrated that induction of the stress response with PGA1 activated the I-kappaBalpha promoter. Induction of the stress response with PGA1 and concomitant induction of I-kappaBalpha were associated with inhibition of TNF-alpha-mediated secretion of interleukin 8 and with inhibition of TNF-alpha-mediated nuclear translocation and activation of NF-kappaB. These data demonstrate that induction of the stress response, by a nonthermal stimulus, increases I-kappaBalpha gene expression by a mechanism involving activation of the I-kappaBalpha promoter. Coupled with previous data demonstrating heat shock-mediated induction of I-kappaBalpha gene expression, these data suggest that I-kappaBalpha may be considered to be one of the stress proteins. The functional consequences of stress response-mediated I-kappaBalpha gene expression may involve attenuation of cellular proinflammatory responses.

Functional redundancy of the nuclear factor kappa B inhibitors I kappa B alpha and I kappa B beta

The transcription factor NF-kappaB is sequestered in the cytoplasm by the inhibitor proteins of the IkappaB family. Each member of the IkappaB exhibits structural and biochemical similarities as well as differences. In an effort to address the functional redundancy of two closely related IkappaB molecules, IkappaBalpha and IkappaBbeta, we generated knock-in mice by replacing the IkappaBalpha gene with the IkappaBbeta gene. The knock-in mice do not express IkappaBalpha, but express a T7-tagged IkappaBbeta under the promoter and regulatory sequence of ikba. Unlike the IkappaBalpha-deficient mice, which display severe postnatal developmental defects and die by postnatal day 8, homozygous knock-in mice survive to adulthood, are fertile, and exhibit no apparent abnormalities. Furthermore, thymocytes and embryonic fibroblasts from the knock-in animals exhibit an inducible NF-kappaB response similar to that of wild-type animals. These results indicate that IkappaBalpha and IkappaBbeta share significant similarities in their biochemical activity, and that they acquired their different functions from divergent expression patterns during evolution.

Increased levels of myocardial IkappaB-alpha protein promote tolerance to endotoxin

Endotoxin [lipopolysaccharide (LPS)] causes tumor necrosis factor-alpha (TNF-alpha)-mediated myocardial contractile depression. Tolerance to the cardiac toxicity of LPS can be induced by a prior exposure to LPS or by pretreatment with glucocorticoids. The mechanisms by which the myocardium acquires tolerance to LPS remain unknown. LPS causes phosphorylation and degradation of inhibitory kappaB-alpha (IkappaB-alpha), releasing nuclear factor-kappaB (NF-kappaB) to activate TNF-alpha gene transcription. We hypothesized that LPS induces supranormal synthesis of myocardial IkappaB-alpha protein and thus renders the myocardium tolerant to subsequent LPS. Rats were challenged with LPS after pretreatment with LPS, dexamethasone, or saline. In saline-pretreated rats, LPS caused a rapid decrease in myocardial IkappaB-alpha protein levels, activation of NF-kappaB, and increased TNF-alpha production. These events were followed by myocardial contractile depression. After the initial decrease in myocardial IkappaB-alpha, IkappaB-alpha protein levels rebounded to a level greater than control levels by 24 h. Dexamethasone pretreatment similarly increased myocardial IkappaB-alpha protein levels. In rats pretreated with either LPS or dexamethasone, myocardial IkappaB-alpha protein levels remained similar to control levels after LPS challenge. The preserved level of myocardial IkappaB-alpha protein was associated with diminished NF-kappaB activation, attenuated myocardial TNF-alpha production, and improved cardiac contractility. We conclude that LPS and dexamethasone upregulate myocardial IkappaB-alpha protein expression and that an increased level of myocardial IkappaB-alpha protein may promote cardiac tolerance to LPS by inhibition of NF-kappaB intranuclear translocation and myocardial TNF-alpha production.

NF-kappa B and Rel proteins: evolutionarily conserved mediators of immune responses

The transcription factor NF-kappa B, more than a decade after its discovery, remains an exciting and active area of study. The involvement of NF-kappa B in the expression of numerous cytokines and adhesion molecules has supported its role as an evolutionarily conserved coordinating element in the organism's response to situations of infection, stress, and injury. Recently, significant advances have been made in elucidating the details of the pathways through which signals are transmitted to the NF-kappa B:I kappa B complex in the cytosol. The field now awaits the discovery and characterization of the kinase responsible for the inducible phosphorylation of I kappa B proteins. Another exciting development has been the demonstration that in certain situations NF-kappa B acts as an anti-apoptotic protein; therefore, elucidation of the mechanism by which NF-kappa B protects against cell death is an important goal. Finally, the generation of knockouts of members of the NF-kappa B/I kappa B family has allowed the study of the roles of these proteins in normal development and physiology. In this review, we discuss some of these recent findings and their implications for the study of NF-kappa B.

Effect of linoleic acid on endothelial cell inflammatory mediators

Selected lipids may influence the inflammatory cascade within the vascular endothelium. To test this hypothesis, endothelial cells were treated with linoleic acid (18:2, n - 6) for 12 hours and/or tumor necrosis factor-alpha (TNF) for 4 hours. For a combined exposure to 18:2 and TNF (18:2 + TNF), cells were first preenriched with 18:2 for 8 hours before exposure to TNF for an additional 4 hours. Exposure to 18:2 increased cellular oxidative stress, activated nuclear factor-kappaB (NF-kappaB), increased interleukin-8 (IL-8) production, and elevated intercellular adhesion molecule-1 (ICAM-1) levels. A combined exposure to 18:2+ TNF resulted in decreased NF-kappaB activation compared with TNF treatment alone. In addition, preexposure to 18:2 altered TNF-mediated IkappaB-alpha signaling. Within the first 15 minutes of a 90-minute period, cytoplasmic levels of IkappaB-alpha decreased more rapidly in cells treated with 18:2 + TNF compared with TNF, suggesting translocation and activation of NF-kappaB in cultures that were pretreated with 18:2 before TNF exposure. A combined exposure to 18:2+TNF had various effects on IL-8 production and ICAM-1 levels depending on the time of exposure. For example, 18:2 + TNF treatment increased ICAM-1 levels at 12 hours but decreased ICAM-1 levels at 24 hours compared with treatment with TNF alone. These data suggest that selected fatty acids such as 18:2 can exert proinflammatory effects and, in addition, may markedly alter TNF-mediated inflammatory events.

In vivo regulation of the IkappaB homologue cactus during the immune response of Drosophila

The dorsoventral regulatory gene pathway (spätzle/Toll/cactus) controls the expression of several antimicrobial genes during the immune response of Drosophila. This regulatory cascade shows striking similarities with the cytokine-induced activation cascade of NF-kappaB during the inflammatory response in mammals. Here, we have studied the regulation of the IkappaB homologue Cactus in the fat body during the immune response. We observe that the cactus gene is up-regulated in response to immune challenge. Interestingly, the expression of the cactus gene is controlled by the spätzle/Toll/cactus gene pathway, indicating that the cactus gene is autoregulated. We also show that two Cactus isoforms are expressed in the cytoplasm of fat body cells and that they are rapidly degraded and resynthesized after immune challenge. This degradation is also dependent on the Toll signaling pathway. Altogether, our results underline the striking similarities between the regulation of IkappaB and cactus during the immune response.

Tumor necrosis factor-alpha- or lipopolysaccharide-induced expression of the murine P-selectin gene in endothelial cells involves novel kappaB sites and a variant activating transcription factor/cAMP response element

Tumor necrosis factor-alpha (TNF-alpha) or lipopolysaccharide (LPS) increases expression of the P-selectin gene in murine, but not in human, endothelial cells. These mediators augment expression of a reporter gene driven by the murine, but not the human, P-selectin promoter in transfected endothelial cells. The regions from -593 to -474 and from -229 to -13 in the murine P-selectin promoter are required for TNF-alpha or LPS to stimulate reporter gene expression. Within these regions, we identified two tandem kappaB elements, a reverse-oriented kappaB site and a variant activating transcription factor/cAMP response element (ATF/CRE), that participate in TNF-alpha- or LPS-induced expression. The tandem kappaB elements bound to NF-kappaB heterodimers and p65 homodimers, the reverse-oriented kappaB site bound to p65 homodimers, and the variant ATF/CRE bound to nuclear proteins that included activating transcription factor-2. Mutations in each individual element eliminated binding to nuclear proteins and decreased by 20-60% the TNF-alpha- or LPS-induced expression of a reporter gene driven by the murine P-selectin promoter in transfected endothelial cells. Simultaneous mutations of all elements further decreased, but did not abolish, induced expression. Co-overexpression of p50 and p65 enhanced murine P-selectin promoter activity in a kappaB site-dependent manner. These data indicate that the kappaB sites and the variant ATF/CRE are required for TNF-alpha or LPS to optimally induce expression of the murine P-selectin gene. The presence of these elements in the murine, but not the human, P-selectin gene may explain in part why TNF-alpha or LPS stimulates transcription of P-selectin in a species-specific manner.

A20 Inhibits NF-κB Activation in Endothelial Cells Without Sensitizing to Tumor Necrosis Factor–Mediated Apoptosis

Expression of the NF-κB–dependent gene A20 in endothelial cells (EC) inhibits tumor necrosis factor (TNF)–mediated apoptosis in the presence of cycloheximide and acts upstream of IκBα degradation to block activation of NF-κB. Although inhibition of NF-κB by IκBα renders cells susceptible to TNF-induced apoptosis, we show that when A20 and IκBα are coexpressed, the effect of A20 predominates in that EC are rescued from TNF-mediated apoptosis. These findings place A20 in the category of “protective” genes that are induced in response to inflammatory stimuli to protect EC from unfettered activation and from undergoing apoptosis even when NF-κB is blocked. From a therapeutic perspective, genetic engineering of EC to express an NF-κB inhibitor such as A20 offers the mean of achieving an anti-inflammatory effect without sensitizing the cells to TNF-mediated apoptosis.

A20 Inhibits NF-κB Activation in Endothelial Cells Without Sensitizing to Tumor Necrosis Factor–Mediated Apoptosis

Expression of the NF-κB–dependent gene A20 in endothelial cells (EC) inhibits tumor necrosis factor (TNF)–mediated apoptosis in the presence of cycloheximide and acts upstream of IκBα degradation to block activation of NF-κB. Although inhibition of NF-κB by IκBα renders cells susceptible to TNF-induced apoptosis, we show that when A20 and IκBα are coexpressed, the effect of A20 predominates in that EC are rescued from TNF-mediated apoptosis. These findings place A20 in the category of “protective” genes that are induced in response to inflammatory stimuli to protect EC from unfettered activation and from undergoing apoptosis even when NF-κB is blocked. From a therapeutic perspective, genetic engineering of EC to express an NF-κB inhibitor such as A20 offers the mean of achieving an anti-inflammatory effect without sensitizing the cells to TNF-mediated apoptosis.

Biphasic regulation of transcription factor nuclear factor-kappaB activity in human endothelial cells by lysophosphatidylcholine through protein kinase C-mediated pathway

Lysophosphatidylcholine (lysoPC), which is generated in oxidized LDL (Ox-LDL) and abundantly exists in atherosclerotic arterial walls, has been shown to alter various endothelial functions and induces several endothelial genes expressed in atherosclerotic arterial walls. Nuclear factor-kappa B (NF-kappaB), a pleiotropic transcription factor, plays an important role in regulation of expression of various genes implicated in atherosclerosis. We have previously reported that lysoPC transferred from Ox-LDL to endothelial surface membrane activates endothelial protein kinase C (PKC), leading to modulated endothelial functions. This study was aimed at determining whether lysoPC could modulate activity of transcription factors in cultured human umbilical vein endothelial cells (HUVECs) by using electrophoretic mobility shift assay. LysoPC was found to increase DNA-binding activity of NF-kappaB in HUVECs within 15 minutes, which peaked at 1 to 2 hours and subsequently declined to the baseline level at 6 hours. Lower concentrations (5 to 15 micromol/L) of lysoPC markedly increased NF-kappaB activity, but higher concentration (50 micromol/L) of lysoPC inhibited the activity. Phorbol 12-myristate 13-acetate, a potent activator of PKC, also augmented NF-kappaB activity in HUVECs, mimicking the effects of lysoPC; furthermore, calphostin C and chelerythrine chloride, specific PKC inhibitors, and alpha-tocopherol, a clinically potent PKC inhibitor, suppressed the lysoPC-induced NF-kappaB activation. These results indicate that lysoPC regulates NF-kappaB activity in a biphasic manner dependent on its concentrations and incubation time in human endothelial cells and the endothelial PKC activation may in part be involved in the lysoPC-induced NF-kappaB activation. Thus, the time course and the positive and negative biphasic regulatory actions of lysoPC on NF-kappaB activity in endothelial cells might exhibit a unique effect of lysoPC in arterial walls on the different stages of atherosclerosis.

Inhibition of nuclear factor kappaB activation by a virus-encoded IkappaB-like protein

Certain viruses have evolved mechanisms to counteract innate immunity, a host response in which nuclear factor kappaB (NF-kappaB) transcription factors play a central role. African swine fever virus encodes a protein of 28.2 kDa containing ankyrin repeats similar to those of cellular IkappaB proteins, which are inhibitors of NF-kappaB. Transfection of the African swine fever virus IkappaB gene inhibited tumor necrosis factor- or phorbol ester-induced activation of kappaB- but not AP-1-driven reporter genes. Moreover, African swine fever virus IkappaB co-immunoprecipitated with p65 NF-kappaB, and the purified recombinant protein prevented the binding of p65-p50 NF-kappaB proteins to their target sequences in the DNA. NF-kappaB activation induced by tumor necrosis factor, as detected by mobility shift assays or by transfection of kappaB-driven reporter genes, is impaired in African swine fever virus-infected cells. These results indicate that the African swine fever virus IkappaB gene homologue interferes with NF-kappaB activation, likely representing a new mechanism to evade the immune response during viral infection.

Nuclear Targeted Suppression of NF-κB Activity by the Novel Quinone Derivative E3330

The activation of NF-κB consists of at least three steps: degradation of IκBα, translocation of NF-κB into the nucleus, and post-translational modification of NF-κB (e.g., phosphorylation of p65). In the present study, we found that a novel quinone derivative E3330 selectively inhibited NF-κB-mediated gene expression without affecting any of these steps. E3330, when included in the culture medium, suppressed NF-κB DNA-binding activity in PMA-induced Jurkat cell nuclear extracts, suggesting that the inhibition by E3330 of NF-κB-mediated gene expression was due to its ability to suppress NF-κB DNA-binding activity. Fractionation of the nuclear extracts by column chromatography revealed that a nuclear factor enhanced NF-κB DNA-binding activity and that this enhancing activity was interrupted after treatment with E3330. Moreover, a major polypeptide with a molecular mass of 40 kDa was found to be in the highly purified fraction containing the NF-κB-enhancing activity and predominantly bind E3330. Taken together, these results suggest that the NF-κB activity, after dissociation from IκB, is enhanced by a nuclear factor that is active irrespective of PMA treatment, and the nuclear factor-mediated enhancement is selectively inhibited by E3330. Thus, we conclude that E3330 may belong to a novel class of anti-NF-κB drugs.

A newly established porcine aortic endothelial cell line: characterization and application to the study of human-to-swine graft rejection

The establishment of cell lines allows reproductible in vitro studies that would be far more difficult to perform using primary cells that rapidly undergo phenotypical alterations in culture. The purpose of this work was to establish an endothelial cell line appropriate for in vitro study of endothelial cell activation during xenograft rejection. Porcine aortic endothelial cells were transfected with the early region of SV40 and selected on the basis of morphological, phenotypical, and functional features. By light and electron microscopy, the porcine aortic endothelial cell line (PAEC11) and primary cells were similar except that PAEC11 was slightly smaller. PAEC11 displayed endothelial cell characteristics since it endocytosed acetylated low density lipoproteins, produced von Willebrand factor, and expressed E-selectin. Human natural antibodies bound to the same xenoantigens on PAEC11 and primary cells. That binding was followed by human complement activation and cell lysis. In addition, PAEC11 was found appropriate for genetic engineering since it could be transfected with a plasmid encoding a foreign gene. Therefore, this cell line should be a useful model for in vitro study of endothelial cell function in general and human-to-swine xenograft rejection in particular.

Inhibition of endothelial vascular cell adhesion molecule-1 expression by nitric oxide involves the induction and nuclear translocation of IkappaBalpha

The induction of vascular cell adhesion molecule-1 (VCAM-1) expression by tumor necrosis factor (TNF)-alpha requires the activation of nuclear factor-kappaB (NF-kappaB) via a process involving the phosphorylation and degradation of its cytoplasmic inhibitor, IkappaBalpha. We have shown that nitric oxide (NO) decreases VCAM-1 expression via inhibition of NF-kappaB activation. To determine how NO inhibits NF-kappaB, we studied the fate of IkappaBalpha following TNF-alpha stimulation in the presence of NO donors S-nitrosoglutathione and sodium nitroprusside. Activation of NF-kappaB by TNF-alpha occurred within 15 min and coincided with rapid degradation of IkappaBalpha. Co-treatment with NO donors did not prevent IkappaBalpha phosphorylation or degradation. However, after 2 h of TNF-alpha stimulation, NO donors inhibited NF-kappaB activation and augmented IkappaBalpha resynthesis and nuclear translocation by 2.5- and 3-fold, respectively. This correlated with a 75% reduction in TNF-alpha-induced VCAM-1 expression. In a time-dependent manner, NO donors alone caused the nuclear translocation of IkappaBalpha. To confirm that NO donors have similar effects as endogenously derived NO, murine macrophage-like cells, RAW264.7, were co-cultured with endothelial cells. Induction of RAW264.7-derived NO inhibited lipopolysaccharide-induced endothelial VCAM-1 expression, which was reversed by the NO synthase inhibitor Nomega-monomethyl-L-arginine. These findings indicate that NO inhibits NF-kappaB activation and VCAM-1 expression by increasing the expression and nuclear translocation of IkappaBalpha.

Parasite-mediated nuclear factor kappaB regulation in lymphoproliferation caused by Theileria parva infection

Infection of cattle with the protozoan Theileria parva results in uncontrolled T lymphocyte proliferation resulting in lesions resembling multicentric lymphoma. Parasitized cells exhibit autocrine growth characterized by persistent translocation of the transcriptional regulatory factor nuclear factor kappaB (NFkappaB) to the nucleus and consequent enhanced expression of interleukin 2 and the interleukin 2 receptor. How T. parva induces persistent NFkappaB activation, required for T cell activation and proliferation, is unknown. We hypothesized that the parasite induces degradation of the IkappaB molecules which normally sequester NFkappaB in the cytoplasm and that continuous degradation requires viable parasites. Using T. parva-infected T cells, we showed that the parasite mediates continuous phosphorylation and proteolysis of IkappaBalpha. However, IkappaBalpha reaccumulated to high levels in parasitized cells, which indicated that T. parva did not alter the normal NFkappaB-mediated positive feedback loop which restores cytoplasmic IkappaBalpha. In contrast, T. parva mediated continuous degradation of IkappaBbeta resulting in persistently low cytoplasmic IkappaBbeta levels. Normal IkappaBbeta levels were only restored following T. parva killing, indicating that viable parasites are required for IkappaBbeta degradation. Treatment of T. parva-infected cells with pyrrolidine dithiocarbamate, a metal chelator, blocked both IkappaB degradation and consequent enhanced expression of NFkappaB dependent genes. However treatment using the antioxidant N-acetylcysteine had no effect on either IkappaB levels or NFkappaB activation, indicating that the parasite subverts the normal IkappaB regulatory pathway downstream of the requirement for reactive oxygen intermediates. Identification of the critical points regulated by T. parva may provide new approaches for disease control as well as increase our understanding of normal T cell function.

Activation of nuclear factor-kappaB in cultured endothelial cells by increased glucose concentration: prevention by calphostin C

Nuclear factor kappaB (NFkappaB) plays a pivotal role in early gene responses by promoting messenger RNA (mRNA) synthesis for various cell-adhesion molecules and inducible nitric oxide synthase. In this study, we examined whether increases in glucose concentration enhance NFkappaB expression in nuclear fractions of endothelial cells by using electrophoretic mobility shift assay. Bovine aortic endothelial cells (BAECs) were incubated in media containing 5.5-35 mM glucose. NFkappaB activity was increased as early as 1 h (peak activation at 2-4 h) after incubation with 35 mM glucose compared with 5.5 mM. Similar increases at 2 h of incubation were observed by using 25 but not 15 mM glucose. Glucose-induced NFkappaB activation was blocked by inhibiting nuclear translocation by using a peptide (SN-50) containing the nuclear-localization sequence of NFkappaB p50 linked to a membrane-permeable motif of the sequence for Kaposi fibroblast growth factor. Co-incubation with a selective protein kinase C (PKC) inhibitor, calphostin C, produced a concentration-dependent inhibition of glucose-induced NFkappaB activation. Thus NFkappaB activation is an early event in response to elevations in glucose, which may elicit multiple pathways contributing to the origin of hyperglycemia- or diabetes-induced endothelial cell injury.

Rapid Up-regulation of IkappaBbeta and abrogation of NF-kappaB activity in peritoneal macrophages stimulated with lipopolysaccharide

Lipopolysaccharide (LPS) administration to mice elicited the activation of nuclear factor kappaB (NF-kappaB) in several tissues including liver and macrophages. Maximal activation was observed 1 h after treatment but declined at 3 and 6 h. The levels of IkappaBalpha and IkappaBbeta were analyzed during this period in an attempt to correlate NF-kappaB activity with IkappaB resynthesis. Degradation of IkappaBalpha was very rapid and was followed by recovery 1 h after LPS administration. IkappaBbeta degradation, which has been associated with persistent NF-kappaB activation, was complete at 1 h. However, a rapid recovery of IkappaBbeta in these tissues was observed at 3 h in parallel with the abrogation of NF-kappaB activity. Immunolocalization of newly synthesized IkappaBbeta by confocal microscopy revealed its preferential accumulation in the cytosol. Analysis of IkappaBbeta by Western blot using high resolution polyacrylamide gel electrophoresis showed the presence of two bands in cytosolic extracts of LPS-treated macrophages at 3 h, but only one band with the same mobility as the control was detected at 6 h. Moreover, treatment of extracts of resynthesized IkappaBbeta with alkaline phosphatase resulted in the accumulation of the protein of slightly higher electrophoretic mobility, indicating the prevalence of a rapid phosphorylation of the newly synthesized IkappaBbeta. At the mRNA level, up-regulation of IkappaBbeta was observed in macrophages stimulated for 1 h with LPS. When the effect of pro-inflammatory cytokines was investigated, tumor necrosis factor alpha, but not interleukin-1 or interferon-gamma, promoted an important degradation of IkappaBbeta followed by an increase in the mRNA at 1 h. These results suggest the existence of LPS- and tumor necrosis factor alpha- specific pathways involved in a rapid IkappaBbeta degradation and resynthesis and might explain the transient period of activation of NF-kappaB in these tissues upon stimulation with these factors. This rapid control of NF-kappaB function may contribute to the attenuation of the inflammatory response of these cells.

The immediate-early gene product MAD-3/EDG-3/IkappaB alpha is an endogenous modulator of fibroblast growth factor-1 (FGF-1) dependent human endothelial cell growth

The tumor promoter phorbol 12-myristic 13-acetate inhibits the growth of human endothelial cells and induces the formation of capillary-like, tubular structures. We report the novel growth regulatory function of the immediate-early gene, edg-3, which is identical to the IkappaB alpha/MAD-3 gene. We employed phosphothioate oligonucleotides (PTO) directed against the translation initiation site of IkappaB alpha to inhibit its expression. The antisense IkappaB alpha PTO-treated cells exhibited an exaggerated growth response to fibroblast growth factor-1 (FGF-1). In contrast, IL-1-induced growth arrest response was not modulated. These data suggest that the early response gene IkappaB alpha is an endogenous regulator of endothelial cell growth in vitro.

A conserved African swine fever virus IkappaB homolog, 5EL, is nonessential for growth in vitro and virulence in domestic swine

An African swine fever virus (ASFV) gene with similarity to the cellular inhibitor of NFkappaB (IkappaB) was described in the pathogenic African isolate Malawi Lil-20/1 (ORF 5EL) and a cell-culture-adapted European virus, BA71V (ORF A238L). Recently, this gene was shown to be a functional IkappaB homolog capable of downregulating NFkappaB-regulated gene expression. This observation suggests the gene may be of significance to aspects of ASFV pathogenesis and virulence in domestic swine by interfering with a normal antiviral host response. Here we show, using nucleotide sequence analysis, that 5EL is highly conserved among various African and European pathogenic field isolates and that in all cases its similarity to IkappaB genes is limited to the presence of four low complexity ankyrin repeats in the ASFV gene. The 5EL gene of Malawi Lil-20/1 encodes a 28-kDa protein which was expressed early in virus-infected macrophage cell cultures with maximum levels observed at 3 to 5 hr postinfection. To study gene function, a Malawi Lil-20/1 5EL gene deletion mutant (Delta5EL) was constructed. Growth characteristics of Delta5EL in porcine macrophage cell cultures were indistinguishable from those of the parental virus. And, Delta5EL exhibited an unaltered parental Malawi Lil-20/1 disease and virulence phenotype in domestic swine. Thus, although highly conserved among ASFV isolates, 5EL is nonessential for growth in porcine macrophages in vitro and for viral virulence in domestic swine. A possible role for this gene in transmission of ASFV in nature, a setting which involves the cycling of ASFV between two highly adapted hosts, Ornithodoros ticks and warthogs or bush pigs, in sub-Saharan Africa is discussed.

The nuclear factor kappa-B signaling pathway participates in dysregulation of vascular smooth muscle cells in vitro and in human atherosclerosis

In the lesions of atherosclerosis, vascular smooth muscle cells (SMC) display many functions characteristic of cytokine activation that likely contribute importantly to ongoing inflammation during human atherogenesis. The transcription factor nuclear factor kappa-B (NFkappaB) often mediates the effects of cytokines on target cells, but the identity of Rel family members important in human SMC activation remains uncertain. In vitro, human SMC express multiple Rel family members. Of these, dimers of p65 and p50, but not a putative SMC-Rel, comprise basal and inducible NFkappaB binding activities. SMC express two inhibitor proteins IkappaBbeta and IkappaBalpha. Interleukin-1beta stimulation caused transient loss of IkappaBalpha and a sustained decrease of IkappaBbeta that correlated with increased and persistent levels of p65/p50 protein and binding activity in the nucleus. SMC cultured under serum-free conditions displayed little NFkappaB activity, but addition of serum or platelet-derived growth factor did activate NFkappaB. In situ analyses showed no evidence for basal NFkappaB activity in SMC in vivo as nonatherosclerotic arteries did not contain nuclear p65 or p50 protein. However, the nuclei of intimal SMC within human atheroma did contain both Rel proteins. We conclude that (i) dimers of p65 and p50, but not SMC-Rel, comprise NFkappaB complexes in human SMC; (ii) stimulatory components in serum activate NFkappaB and likely account for previously reported "constitutive" NFkappaB activity in cultured SMC; and (iii) exposure to inflammatory cytokines may produce prolonged NFkappaB activation in SMC because of sustained decreases in the inhibitory subunit IkappaB-beta.

Activation of the NF-κB Pathway by Inflammatory Stimuli in Human Neutrophils

Activated neutrophils have the ability to upregulate the expression of many genes, in particular those encoding cytokines and chemokines, and to subsequently release the corresponding proteins. Although little is known to date concerning the regulation of gene transcription in neutrophils, it is noteworthy that many of these genes depend on the activation of transcription factors, such as NF-κB, for inducible expression. We therefore investigated whether NF-κB/Rel proteins are expressed in human neutrophils, as well as their fate on cell activation. We now report that dimers consisting of p50 NFκB1, p65 RelA, and/or c-Rel are present in neutrophils and that the greater part of these protein complexes is physically associated with cytoplasmic IκB-α in resting cells. Following neutrophil stimulation with proinflammatory agonists (such as lipopolysaccharide [LPS], tumor necrosis factor-α [TNF-α], and fMet-Leu-Phe) that induce the production of cytokines and chemokines in these cells, NF-κB/Rel proteins translocated to nuclear fractions, resulting in a transient induction of NF-κB DNA binding activity, as determined in gel mobility shift assays. The onset of both processes was found to be closely paralleled by, and dependent on, IκB-α degradation. Proinflammatory neutrophil stimuli also promoted the accumulation of IκB-α mRNA transcripts, resulting in the reexpression of the IκB-α protein. To our knowledge, this constitutes the first indication that NF-κB activation may underlie the action of proinflammatory stimuli towards human neutrophil gene expression and, as such, adds a new facet to our understanding of neutrophil biology.

Tumor necrosis factor alpha activates NF-kappaB in acid sphingomyelinase-deficient mouse embryonic fibroblasts

Tumor necrosis factor alpha (TNF-alpha) is one of the most potent inducer of the nuclear transcription factor kappaB (NF-kappaB). Activation of NF-kappaB is initiated by phosphorylation of the inhibitory subunit of the IkappaB-alpha-NF-kappaB complex. This leads to the dissociation of the complex and degradation of IkappaB-alpha. NF-kappaB is translocated into the nucleus. The sphingomyelin pathway is thought to mediate the TNF-alpha-induced activation of NF-kappaB by its second messenger ceramide. We have used the recently established acid sphingomyelinase-deficient mouse line (asmase-/- mice) to evaluate the role of acid sphingomyelinase in the TNF-alpha-induced signal transduction pathway. Here we present experimental evidence that acid sphingomyelinase is not involved in the TNF-alpha-induced activation of NF-kappaB. TNF-alpha treatment induced the dissociation and degradation of IkappaB-alpha and the nuclear translocation of NF-kappaB in embryonic fibroblasts derived from asmase-/- and wild type mice indiscriminately.

Regulation of IkappaBbeta degradation. Similarities to and differences from IkappaBalpha

The transcription factor NF-kappaB (nuclear factor-kappaB) is neutralized in nonstimulated cells through cytoplasmic retention by IkappaB inhibitors. In mammalian cells, two major forms of IkappaB proteins, IkappaBalpha and IkappaBbeta, have been identified. Upon treatment with a large variety of inducers, IkappaBalpha and IkappaBbeta are proteolytically degraded, resulting in NF-kappaB translocation into the nucleus. Recent observations suggest that phosphorylation of serines 32 and 36 and subsequent ubiquitination of lysines 21 and 22 of IkappaBalpha control its signal-induced degradation. In this study we provide evidence that critical residues in the NH2-terminal region of IkappaBbeta (serines 19 and 23) as well as its COOH-terminal PEST region control IkappaBbeta proteolysis. However Lys-9, the unique lysine residue in the NH2-terminal region of IkappaBbeta, is not absolutely required for its degradation. We also demonstrate that following stimulation, an underphosphorylated nondegradable form of IkappaBbeta accumulates. Surprisingly, our data suggest that unlike IkappaBalpha, IkappaBbeta is constitutively phosphorylated on one or two of the critical NH2-terminal serine residues. Thus, phosphorylation of these sites is necessary for degradation but does not necessarily constitute the signal-induced event that targets the molecule for proteolysis.

The Arabidopsis NIM1 protein shows homology to the mammalian transcription factor inhibitor I kappa B

The NIM1 (for noninducible immunity) gene product is involved in the signal transduction cascade leading to both systemic acquired resistance (SAR) and gene-for-gene disease resistance in Arabidopsis. We have isolated and characterized five new alleles of nim1 that show a range of phenotypes from weakly impaired in chemically induced pathogenesis-related protein-1 gene expression and fungal resistance to very strongly blocked. We have isolated the NIM1 gene by using a map-based cloning procedure. Interestingly, the NIM1 protein shows sequence homology to the mammalian signal transduction factor I kappa B subclass alpha. NF-kappa B/I kappa B signaling pathways are implicated in disease resistance responses in a range of organisms from Drosophila to mammals, suggesting that the SAR signaling pathway in plants is representative of an ancient and ubiquitous defense mechanism in higher organisms.

The Arabidopsis NIM1 protein shows homology to the mammalian transcription factor inhibitor I kappa B

The NIM1 (for noninducible immunity) gene product is involved in the signal transduction cascade leading to both systemic acquired resistance (SAR) and gene-for-gene disease resistance in Arabidopsis. We have isolated and characterized five new alleles of nim1 that show a range of phenotypes from weakly impaired in chemically induced pathogenesis-related protein-1 gene expression and fungal resistance to very strongly blocked. We have isolated the NIM1 gene by using a map-based cloning procedure. Interestingly, the NIM1 protein shows sequence homology to the mammalian signal transduction factor I kappa B subclass alpha. NF-kappa B/I kappa B signaling pathways are implicated in disease resistance responses in a range of organisms from Drosophila to mammals, suggesting that the SAR signaling pathway in plants is representative of an ancient and ubiquitous defense mechanism in higher organisms.

Early activation signals in endothelial cells. Stimulation by cytokines

With limitation to the "proinflammatory program" induced in endothelial cells by exposure to interleukin-1, tumor necrosis factor, and interleukin-6, we review the available data on the signaling for these three cytokines, from receptor engagement to induction of gene transcription. Only a few molecular pathways have been characterized so far, and key issues in endothelial biology, such as endothelial specificity of gene expression and heterogeneity of different endothelial populations, remain largely unexplored.

Notoginsenoside R1 counteracts endotoxin-induced activation of endothelial cells in vitro and endotoxin-induced lethality in mice in vivo

In this study we investigated a possible counteracting activity notoginsenoside R1 (NG-R1) on lipopolysaccharide (LPS)-induced effects in vitro and in vivo. The upregulation of plasminogen activator inhibitor-1 (PAI-1) antigen due to LPS (1 microgram/mL for 12 hours) in human umbilical vein endothelial cells (HUVECs) was prevented when the cells were incubated simultaneously with 100 micrograms/mL NG-R1 (PAI-1 antigen: LPS-treated cells, 969 +/- 54 ng/10(5) cells; control cells, 370 +/- 15 ng/10(5) cells; LPS + NG-R1-treated cells, 469 +/- 29 ng/10(5) cells; n = 6). The 2.5- and 3.4-fold (2.2- and 3.2-kb) increases in PAI-1 mRNA levels induced by LPS (1 microgram/mL for 6 hours) were reduced to 1.4- and 2.6-fold increases in the presence of both LPS and 100 micrograms/mL NG-R1. LPS-induced tissue factor (TF) activity in HUVECs was also counteracted when the cells were coincubated with both LPS and 100 micrograms/mL NG-R1 for 6 hours (TF activity: LPS-treated cells, 88.6 +/- 6.5 mU/10(6) cells; control cells, 0.7 +/- 0.01 mU/10(6) cells; LPS + NG-R1-treated cells, 56.0 +/- 1.9 mU/10(6) cells). The 26-fold increase in TF mRNA levels induced by LPS (1 microgram/mL for 2 hours) was reduced to a 13-fold increase in the presence of both LPS and 100 micrograms/mL NG-R1. PAI activity levels in the plasma of mice 4 hours after injection of LPS (10 ng/g body wt) increased 2.3-fold compared with a control group. In contrast, PAI activity from LPS + NG-R1 (1 microgram/g body wt NG-R1)-treated animals was at control level (PAI-1 activity: LPS-treated group, 11.3 +/- 3.1 U/mL; control group, 4.9 +/- 0.3 U/mL; LPS + NG-R1-treated group, 4.3 +/- 1.0 U/mL; n = 5 to 8). The production of TNF-alpha induced by 1 microgram/mL LPS by cultured human whole-blood cells was inhibited by 46% when the cells were incubated together with 100 micrograms/mL NG-R1. NG-R1 protected mice from the lethal effects of LPS. The 78% lethality induced by LPS/galactosamine was reduced to 23% when NG-R1 was administered simultaneously (P < .01 by chi 2 test). To extend this study to inflammatory cells, the effect of NG-R1 on LPS stimulation of the monocytic cell line THP-1 was investigated. NG-R1 inhibited the LPS-induced degradation of I kappa B-alpha and superinduced LPS-induced I kappa B-alpha mRNA, indicating that the effect of NG-R1 is not restricted to endothelial cells and is at least in part mediated by interference with the NF-kappa B/I kappa B-alpha pathway.

The serine/threonine phosphatase inhibitor calyculin A induces rapid degradation of IkappaBbeta. Requirement of both the N- and C-terminal sequences

Signal-initiated activation of the transcription factor NF-kappaB is mediated through proteolysis of its cytoplasmic inhibitory proteins IkappaBalpha and IkappaBbeta. While most NF-kappaB inducers trigger the degradation of IkappaBalpha, only certain stimuli are able to induce the degradation of IkappaBbeta. The degradation of IkappaBalpha is targeted by its site-specific phosphorylations, although the mechanism underlying the degradation of IkappaBbeta remains elusive. In the present study, we have analyzed the effect of phosphatase inhibitors on the proteolysis of IkappaBbeta. We show that the serine/threonine phosphatase inhibitor calyculin A induces the hyperphosphorylation and subsequent degradation of IkappaBbeta in both human Jurkat T cells and the murine 70Z-3 preB cells, which is associated with the nuclear expression of active NF-kappaB. The calyculin A-mediated degradation of IkappaBbeta is further enhanced by the cytokine tumor necrosis factor-alpha (TNF-alpha), although TNF-alpha alone is unable to induce the degradation of IkappaBbeta. Mutational analyses have revealed that the inducible degradation of IkappaBbeta induced by calyculin A, and TNF-alpha requires two N-terminal serines (serines 19 and 23) that are homologous to the inducible phosphorylation sites present in IkappaBalpha. Furthermore, the C-terminal 51 amino acid residues, which are rich in serines and aspartic acids, are also required for the inducible degradation of IkappaBbeta. These results suggest that the degradation signal of IkappaBbeta may be controlled by the opposing actions of protein kinases and phosphatases and that both the N- and C-terminal sequences of IkappaBbeta are required for the inducible degradation of this NF-kappaB inhibitor.

Accommodation of vascularized xenografts: expression of "protective genes" by donor endothelial cells in a host Th2 cytokine environment

Organ xenografts under certain circumstances survive in the presence of anti-graft antibodies and complement, a situation referred to as "accommodation." We find that the endothelial cells (ECs) in hamster hearts that accommodate themselves in rats express genes, such as A20 and bcl-2, that in vitro protect ECs from apoptosis and prevent upregulation in those cells of proinflammatory genes such as cytokines, procoagulant and adhesion molecules. Hearts that are rejected do not express these genes. In addition, vessels of rejected hearts show florid transplant arteriosclerosis whereas those of accommodated hearts do not. Accommodated xenografts have an ongoing T helper cell type 2 (Th2) cytokine immune response, whereas the rejected grafts have a Th1 response. We propose a model for factors that contribute to the survival of xenografts and the avoidance of transplant arteriosclerosis.

Gem, a GTP-binding protein from mitogen-stimulated T cells, is induced in endothelial cells upon activation by inflammatory cytokines

Using differential screening of cytokine-activated versus resting porcine aortic endothelial cells (PAEC), we have isolated a member of the family of Ras/GTP-binding proteins. The cDNA encodes a 34-kilodalton protein showing 97% homology to Gem, a gene recently isolated from activated T cells, likely representing its porcine homologue. The amino acid sequence differs from the Ras consensus by the absence of a C-terminal isoprenylation site and a glycine to glutamic acid substitution in the third GTP-binding domain. We report here, that pigGem mRNA is strongly inducible in PAEC upon activation by either IL-1 alpha, TNF alpha or lipopolysaccharide (LPS). Low constitutive expression is found in several organs. Epitope-tagged pigGem transfected into endothelial cells (EC) localizes to the cytoplasm and to the inner side of the plasma membrane. Structural features of Gem and its inducibility apparently restricted to T cells and endothelial cells, together with Rad, a GTPase overexpressed in skeletal muscle cells of type II diabetic individuals, define a new branch within the superfamily of GTP-binding proteins.

Site-specific tyrosine phosphorylation of IkappaBalpha negatively regulates its inducible phosphorylation and degradation

The transcription factor NF-kappaB is retained in the cytoplasm by its interaction with the inhibitory subunit known as IkappaB. Signal-induced serine phosphorylation and subsequent ubiquitination of IkappaBalpha target it for degradation by the 26 S proteasome. Recently, pervanadate, a protein-tyrosine phosphatase inhibitor, was shown to block the degradation of IkappaBalpha, thus inhibiting NF-kappaB activation. We investigated the mechanism by which pervanadate inhibits the degradation of IkappaBalpha. Western blot analysis of IkappaBalpha from tumor necrosis factor-treated cells revealed a slower migrating IkappaBalpha species that was subsequently degraded. However, pervanadate-treated cells also revealed a slower migrating species of IkappaBalpha that appeared in a time- and dose-dependent manner and was not degraded by tumor necrosis factor. The slower migrating species of IkappaBalpha from pervanadate-treated cells was tyrosine-phosphorylated as revealed by cross-reactivity with anti-phosphotyrosine antibodies, by the ability of the specific tyrosine phosphatase PTP1B to dephosphorylate it, and by phosphoamino acid analysis of IkappaBalpha immunoprecipitated from 32P-labeled cells. By site-specific mutagenesis and deletion analysis, we identified Tyr-42 on IkappaBalpha as the phosphoacceptor site. Furthermore, in an in vitro reconstitution system, tyrosine-phosphorylated IkappaBalpha was protected from degradation. Our results demonstrate that inducible phosphorylation and degradation of IkappaBalpha are negatively regulated by phosphorylation at Tyr-42, thus preventing NF-kappaB activation.

Different mechanisms control signal-induced degradation and basal turnover of the NF-kappaB inhibitor IkappaB alpha in vivo

The transcription factor NF-kappaB is sequestered in the cytoplasm by a family of IkappaB molecules. Upon cellular stimulation with diverse agents, one of these molecules, IkappaB alpha, is rapidly phosphorylated and subsequently degraded. This process triggers nuclear translocation of NF-kappaB and the successive activation of target genes. Independent of its rapid stimulation-induced breakdown, IkappaB alpha is inherently unstable and undergoes a continuous turnover. To compare the mechanisms and protein domains involved in inducible and basal degradation of IkappaB alpha in intact cells we employed a transfection strategy using tagged IkappaB alpha and ubiquitin molecules. We show that tumor necrosis factor alpha (TNFalpha) induced breakdown of IkappaB alpha but not its basal turnover coincides with ubiquitination in the amino-terminal signal response domain (SRD) of IkappaB alpha. Neither the SRD nor the carboxy-terminal PEST sequence is needed for basal turnover, which instead depends only on the core ankyrin repeat domain. Despite the differences in the requirements of protein domains and ubiquitin-conjugation for both degradation pathways, each one is mediated by the proteasome. This finding is important for understanding alternative modes of controlling NF-kappaB activity.

Human lymphocyte adhesion to xenogeneic porcine endothelial cells: modulation by human TNF-alpha and involvement of VLA-4 and LFA-1

Considering that in the allogeneic situation the adhesion of recipient lymphocytes to donor endothelial cells initiates the cellular rejection, we questioned the possible occurrence of a similar process in the xenogeneic situation. The adhesion of human peripheral blood lymphocytes (PBL) to porcine aortic endothelial cells (PAEC) was thus studied in an in vitro porcine-to-human xenogeneic model. It was found that 25.9% of human PBL adhered to resting PAEC. Furthermore, this adhesion increased significantly when the PAEC were stimulated by the human cytokine TNF-alpha (tumor necrosis factor-alpha). The effect of human TNF-alpha was concentration- and time-dependent and was maximal (from 25.9% to 35.6%) with 100 U/ml during 6 h. Moreover, blocking experiments with monoclonal antibody (mAb) demonstrated the role of the PBL adhesion molecules LFA-1 and especially VLA-4. Indeed, an anti-CD11a mAb decreased PBL adhesion to resting PAEC by 17.1% and to TNF-alpha stimulated PAEC by 16.9%, whereas an anti-CD49d mAb decreased dramatically PBL adhesion to resting PAEC by 53.1% and to TNF-alpha stimulated PAEC by 41.0%. Finally, phenotypic analysis of the adherent PBL showed that 50.5% of adherent cells to resting PAEC were NK (natural killer) cells, whereas 50.7% of adherent cells to TNF-alpha stimulated PAEC were T lymphocytes, showing the preferential adhesion of NK cells to resting PAEC, and that the stimulation of the PAEC with human TNF-alpha affects predominantly T lymphocyte adhesion. These results indicate that human PBL could bind to xenogeneic PAEC and that this interaction could be a first step of a xenogeneic cellular rejection.

An IkappaB homolog encoded by African swine fever virus provides a novel mechanism for downregulation of proinflammatory cytokine responses in host macrophages

Cytokines stimulate inflammatory defenses against viral infections. In order to evade host defenses, viruses have developed strategies to counteract antiviral cytokines. African swine fever virus (ASFV) is a large, double-stranded DNA virus that infects macrophages. This study demonstrates that ASFV effectively inhibited phorbol myristic acid-induced synthesis of antiviral, proinflammatory cytokines alpha interferon, tumor necrosis factor alpha, and interleukin-8 in infected macrophages as assessed by enzyme-linked immunosorbent assay and reverse transcriptase PCR. In contrast, levels of mRNA and protein for transforming growth factor beta, an anti-inflammatory cytokine, were increased by ASFV infection, suggesting that ASFV-induced inhibition of cytokine synthesis may be limited to cytokines activated by NFkappaB. An interleukin-8 promoter, containing an NFkappaB enhancer site, driving expression of a luciferase reporter gene was used to show that NFkappaB-dependent transcription was inhibited by the virus and by a cloned ASFV gene, A238L. This gene encodes a protein with homology to IkappaB, the inhibitor of NFkappaB. Electrophoretic mobility shift assay showed that cells expressing the A238L gene inhibited NFkappaB binding to DNA. These results suggest that the A238L gene product interacts with NFkappaB to prevent transcription and downregulate proinflammatory cytokine production. This novel viral evasion strategy encoded in a single IkappaB-like protein may be capable of inhibiting most macrophage NFkappaB-dependent antiviral mechanisms and may provide insights into how ASFV causes a fatal hemorrhagic disease of domestic pigs and a persistent infection in the African warthog, which is its natural permissive host.

In vitro accommodation of immortalized porcine endothelial cells: resistance to complement mediated lysis and down-regulation of VCAM expression induced by low concentrations of polyclonal human IgG antipig antibodies

The capacity of vascularized xenografts to survive in the face of normal levels of circulating antigraft antibodies and complement has been ascribed to a phenomenon referred to as "endothelial cell accommodation." The mechanisms whereby accommodation might occur have remained obscure. We have investigated this phenomenon in an in vitro system. A preparation of polyclonal immunoglobulin, human normal globulin (HNG), induced a change in the phenotype of immortalized porcine endothelial cells (IPEC) suggestive of accommodation; the cells became resistant to complement mediated lysis and displayed a reduced expression of surface VCAM and MHC class I. The accommodated phenotype only manifested after 72 hr incubation with HNG and was optimal after 120 hr. In an analysis of all the experiments performed, the development of resistance to complement mediated lysis appeared independent of the inducing dose of HNG. However, down-regulation of VCAM was only manifest when subsaturating doses were used. Our results suggest that IgG xenoreactive antibodies can mediate changes in porcine endothelial cell phenotype consistent with accommodation. The dependence on both time and dose of antibody applied might explain why accommodation has been difficult to achieve consistently in in vivo models of discordant xenotransplantation. By demonstrating a functional interaction between human VLA-4 and porcine VCAM, we speculate that the down-regulation in expression of VCAM on accommodated endothelium may have an important regulatory effect on traffic of inflammatory cells into xenografts. Our results have important implications for the development of strategies to promote accommodation of xenografts.

Synergistic activation of interleukin-8 gene transcription by all-trans-retinoic acid and tumor necrosis factor-alpha involves the transcription factor NF-kappaB

Induction of interleukin-8 (IL-8) by IL-1 or tumor necrosis factor (TNF), and repression by interferons or glucocorticoids have been shown to involve sequences between nucleotides -94 and -71 of the 5'-flanking region, and the transcription factors NF-IL-6 and NF-kappaB. The A3 cell line was derived from the human melanoma cell line G-361 by stable transfection with part of the IL-8 promoter (nucleotides -101 to +40 from transcription start) fused to the luciferase coding region. These regulatory sequences were sufficient for transcriptional activation by all-trans-retinoic acid (ATRA), 9-cis-retinoic acid, IL-1beta, or TNF-alpha. Simultaneous treatment of A3 cells with ATRA and TNF-alpha resulted in a dose- and time-dependent synergistic increase in luciferase expression and IL-8 mRNA levels. Transient transfections of the parental cell line demonstrated that the NF-kappaB binding site is essential for this synergistic transactivation. Electrophoretic mobility shift assays with nuclear extracts of A3 cells showed that stimulation with ATRA and TNF-alpha for more than 16 h resulted in enhanced NF-kappaB binding compared to that induced by TNF-alpha alone. The simultaneous treatment with ATRA and TNF-alpha also resulted in changes in the composition of NF-kappaB complexes bound to the IL-8 NF-kappaB site, preventing the formation of two TNF-alpha-inducible binding activities. We suggest that these complexes consist of repressive factors which, when removed, allow enhanced binding of NF-kappaB to its cognate site.

The intron-exon structure of the porcine E-selectin-encoding gene

We have cloned and sequenced the gene encoding porcine E-selectin. The gene comprises 12 exons and 11 introns. Two pseudoexons are contained within intron 4 and intron 6. These sequences are similar to the corresponding exons in the human E-selectin sequence; however, they are not present in the porcine E-selectin-encoding cDNA. Transcription starts at position -498 relative to the translation initiation site. The first ATG is located within exon 2. Translation stops in exon 11 leaving exon 12 untranslated in its entirety.