Tumor necrosis factor-alpha induction of novel gene products in human endothelial cells including a macrophage-specific chemotaxin

Identification of a novel A20-binding inhibitor of nuclear factor-kappa B activation termed ABIN-2

The nuclear factor kappaB (NF-kappaB) plays a central role in the regulation of genes implicated in immune responses, inflammatory processes, and apoptotic cell death. The zinc finger protein A20 is a cellular inhibitor of NF-kappaB activation by various stimuli and plays a critical role in terminating NF-kappaB responses. The underlying mechanism for NF-kappaB inhibition by A20 is still unknown. A20 has been shown to interact with several proteins including tumor necrosis factor (TNF) receptor-associated factors 2 and 6, as well as the inhibitory protein of kappaB kinase (IKK) gamma protein. Here we report the cloning and characterization of ABIN-2, a previously unknown protein that binds to the COOH-terminal zinc finger domain of A20. NF-kappaB activation induced by TNF and interleukin-1 is inhibited by overexpression of ABIN-2. The latter also inhibits NF-kappaB activation induced by overexpression of receptor-interacting protein or TNF receptor-associated factor 2. In contrast, NF-kappaB activation by overexpression of IKKbeta or direct activators of the IKK complex, such as Tax, cannot be inhibited by ABIN-2. These results indicate that ABIN-2 interferes with NF-kappaB activation upstream of the IKK complex and that it might contribute to the NF-kappaB-inhibitory function of A20.

Detection of monocyte chemoattractant protein-1 receptor expression in experimental atherosclerotic lesions: an autoradiographic study

BACKGROUND

Monocytes, a common component of atheroma, are attracted to the lesion site in response to chemotactic signals, particularly expression of monocyte chemoattractant peptide 1 (MCP-1). This study assessed the feasibility of using radiolabeled MCP-1 to identify monocytes and macrophages that have localized at sites of experimental arterial lesions. Methods and Results-- The biodistribution of radiolabeled MCP-1 was determined in normal mice, and localization in experimental atheroma was determined in cholesterol-fed rabbits 4 weeks after arterial injury of the iliac artery (9 rabbits) and the abdominal aorta (1 rabbit). Vessels were harvested and autoradiographed after intravenous administration of (125)I-labeled MCP-1 and Evans blue dye. The arteries were evaluated histologically by hematoxylin and eosin staining and immune staining with a monoclonal antibody specific for rabbit macrophages (RAM-11). (125)I-MCP-1 has a blood clearance half-time of approximately 10 minutes and circulates in association with cells. The liver, lungs, and kidneys had the highest concentration of (125)I-MCP-1 at 5 and 30 minutes after tracer administration. Autoradiograms revealed accumulation of (125)I-MCP-1 in the damaged artery wall, with an average ratio of lesion to normal vessel of 6:1 (maximum 45:1). The accumulation of (125)I-MCP-1 in the reendothelialized (plaque formation) areas was greater than in the deendothelialized (Evans blue-positive) areas (6.55+/-2.26 versus 4.34+/-1.43 counts/pixel, P<0.05). The uptake of (125)I-MCP-1 correlated with the number of macrophages per unit area (r=0.85, P<0.0001).

CONCLUSIONS

Radiolabeled MCP-1 may be a useful tracer for imaging monocyte/macrophage-rich experimental atherosclerotic lesions.

Immunomodulatory effects of interferon-beta-1b in patients with multiple sclerosis

The mechanisms by which IFN beta-1b acts in the treatment of patients with multiple sclerosis (MS) are not completely known. Immunomodulatory effects of IFN beta-1b were investigated in patients with relapsing-remitting (RR) MS in vivo and in vitro. Compared to baseline and controls, defined as patients with RR-MS without immunomodulatory therapy, the expression of TGF beta-1-mRNA by peripheral blood mononuclear cells (PBMC) was persistently increased at week 6, month 3 and month 6 (p < or = 0.05), that of the TGF beta-1 receptor type II from day 5 up to month 6 (p < 0.01). The expression of TNF alpha-mRNA decreased from day 1 to month 3 compared to day 0 and the controls (p < 0.01). The in vitro investigations performed on isolated peripheral blood lymphocytes demonstrated that these effects were dose-dependent. The mRNA and protein expression of TNF alpha-R-I (55 kD-receptor) was only temporarily elevated at the beginning of the therapy in vivo. The expression of TNF alpha-R-I-mRNA increased dose-dependently after stimulation with IFN beta-1b for 24 h in vitro. Serum levels of soluble vascular cell adhesion molecule (sVCAM) were increased during the whole time of in vivo treatment (p < 0.01). The CD8CD38 lymphocyte subpopulation was continuously elevated from day 5 up to month 6 (p < 0.01) in the MS patients treated with IFN beta-1b in vivo. No persistent, significant changes were demonstrable concerning the percentage of total CD4, CD8, CD19 nor in CD4 subpopulations (CD4CD29, CD4CD45RA). The present data suggest that IFN beta-1b induces the mRNA expression of TGF beta-1 and TGF beta-R-II by PBMC, decreases that of TNF alpha and increases levels of sVCAM-1 and of circulating activated CD8 cells (CD8CD38) in blood. These might be other mechanisms by which IFN beta-1b mediates its positive effects in the treatment of MS patients.

Functional redundancy of the zinc fingers of A20 for inhibition of NF-kappaB activation and protein-protein interactions

The tumor necrosis factor (TNF) inducible protein A20 is a potent inhibitor of nuclear factor-kappaB (IkappaB)-mediated gene expression in response to TNF and several other stimuli. The C-terminal domain of A20 is characterized by seven zinc finger structures. Here, we show that a minimum of four zinc fingers is required to inhibit TNF-induced nuclear factor-kappaB (NF-kappaB) activation to a level that is comparable to that obtained with the wild-type A20 protein. However, there was no strict requirement for a particular zinc finger structure, since a mutant A20 protein containing only the first four zinc fingers was as potent as a mutant protein containing only the last four zinc fingers. A similar functional redundancy of the A20 zinc fingers was also observed for binding of A20 to a number of other proteins, including two novel NF-kappaB inhibitory proteins (ABIN-1, ABIN-2), A20 itself, the anti-apoptotic protein TXBP151, and a regulatory component of the IkappaB kinase complex, IKKgamma. Moreover, we demonstrate that complete loss of binding of any of these proteins correlates with complete loss of A20's ability to inhibit TNF-induced NF-kappaB activation. However, binding of IKKgamma as such is not sufficient for inhibition of NF-kappaB dependent gene expression in response to TNF.

A20 zinc finger protein inhibits TNF-induced apoptosis and stress response early in the signaling cascades and independently of binding to TRAF2 or 14-3-3 proteins

A20 zinc finger protein is a negative regulator of tumor necrosis factor (TNF)-induced signaling pathways leading to apoptosis, stress response and inflammation. A20 has been shown to bind to TNF-receptor-associated factor 2 (TRAF2) and 14-3-3 chaperone proteins. Our data indicate that the zinc finger domain of A20 is sufficient and that neither TRAF2 nor 14-3-3 binding is necessary for the inhibitory effects of A20. Mutations in the 14-3-3 binding site of A20 did, however, result in a partial cleavage of A20 protein suggesting that 14-3-3 chaperone proteins may stabilize A20. Furthermore, we show that A20 acts early in TNF-induced signaling cascades blocking both TNF-induced rapid activation of c-Jun N-terminal kinase and processing of the receptor-associated caspase-8. Taken together our data indicate that the zinc finger domain of A20 contains all necessary functional domains required for the inhibition of TNF signaling and that A20 may function at the level of the receptor signaling complex.

Oxidized LDL suppresses NF-kappaB and overcomes protection from apoptosis in activated endothelial cells

Atherosclerosis is a chronic inflammatory disease associated with enhanced apoptotic cell death in vascular cells, partly induced by oxidized low-density lipoprotein (OxLDL). However, proinflammatory stimuli such as lipopolysaccharide (LPS) or tumor necrosis factor-alpha (TNF-alpha) activate endothelial cells (EC) and inhibit apoptosis through induction of nuclear factor kappaB (NF-kappaB)-dependent genes. This study therefore investigated whether OxLDL or its component, lysophosphatidylcholine (LPC), interacts with the effect of LPS or TNF-alpha on cell survival. Human EC were incubated with LPS, TNF-alpha, OxLDL, or LPC alone or in combinations. OxLDL (100 to 200 microg/ml) and LPC (100 to 300 microM) induced apoptosis dose-dependently. LPS and TNF-alpha had no effect on cell survival in the presence or absence of OxLDL or LPC. LPS and TNF-alpha both induced the antiapoptotic gene A20, whereas OxLDL and LPC suppressed its induction. Expression of A20 is regulated by NF-kappaB. OxLDL and LPC dose-dependently suppressed NF-kappaB activity. For functional analysis, bovine EC were transfected with A20 encoding expression constructs in sense and antisense orientation. Bovine EC that overexpressed A20 were protected against OxLDL-induced apoptosis, whereas expression of antisense A20 rendered cells more sensitive to OxLDL. These results suggest that OxLDL not only induces cell death, as has been shown before, but also compromises antiapoptotic protection of activated EC. OxLDL sensitizes EC to apoptotic triggers by interfering with the induction of A20 during the inflammatory response seen in atherosclerotic lesions. This inhibition is based on repression of NF-kappaB activation. The effect may be caused by the OxLDL component LPC.

Pleiotropic effects of HTLV type 1 Tax protein on cellular metabolism: mitotic checkpoint abrogation and NF-kappaB activation

Tax protein expressed by human T cell leukemia virus type 1 (HTLV-1) is a strong trans-activator of its own LTR promoter; it also affects the function of multiple cellular genes involved in cell cycle control and transcription. One way in which Tax exerts its pleiotropic effects is through protein-protein interaction with cellular cofactors. By using yeast two-hybrid technology, we have isolated several cellular proteins that bind to Tax. Two of these are MAD1, a mitotic checkpoint control protein, and TXBP151, a suppressor of tumor necrosis factor alpha-induced apoptosis. Here we discuss findings describing the role of MAD1 in exit of cells from mitosis and TXBP151 in NF-kappaB activation.

A20 and A20-binding proteins as cellular inhibitors of nuclear factor-kappa B-dependent gene expression and apoptosis

Proper gene expression and cell growth are critical for the survival of all organisms. Nuclear factor-kappa B (NF-kappa B)-dependent gene expression and apoptosis play crucial roles in numerous cellular processes, and defects in their regulation may contribute to a variety of diseases including inflammation and cancer. Although there has recently been tremendous progress in our understanding of the signaling pathways that lead to NF-kappa B activation and apoptosis, signaling mechanisms that negatively regulate these processes are only partially understood. This review deals with the zinc finger protein A20, which has been characterized as a dual inhibitor of NF-kappa B activation and apoptosis. Its inducible expression by a wide variety of stimuli, including cytokines such as tumor necrosis factor, interleukin-1, and CD40, as well as bacterial and viral products such as lipopolysaccharide, Epstein-Barr virus latent membrane protein 1, and human T-cell leukemia virus type I Tax, suggests that it is involved in the negative feedback regulation of signaling. We will discuss the possible underlying mechanisms, placing emphasis on the role of several A20-binding proteins that have recently been described. Moreover, evidence is presented that A20 and A20-binding proteins are potential novel therapeutic tools in the treatment of a variety of diseases.

Cloning and characterization of AWP1, a novel protein that associates with serine/threonine kinase PRK1 in vivo

We describe the cloning and expression of cDNAs encoding a novel human protein of 208 amino acid residues with a predicted molecular mass of 22.6kDa and its mouse homologue. We name this protein as AWP1 (associated with PRK1). AWP1 is a ubiquitously expressed protein, and the Awp1 gene is switched on during early human and mouse development. When expressed in COS-1 cells, the Myc-tagged AWP1 has an apparent molecular mass higher than that deduced from its amino acid sequence. AWP1 possesses a conserved zf-A20 zinc finger domain at its N-terminal and a zf-AN1 zinc finger domain at its C-terminal. Co-immunoprecipitation experiments revealed that mouse AWP1 specifically interacts with a rat serine/threonine protein kinase PRK1 in vivo. Hence, AWP1 may play a regulatory role in mammalian signal transduction pathways.

The Epstein-Barr virus latent membrane protein 1 (LMP1) enhances TNF alpha-induced apoptosis of intestine 407 epithelial cells: the role of LMP1 C-terminal activation regions 1 and 2

Epstein-Barr virus (EBV) latent membrane protein 1 (LMP1) can protect some kinds of lymphocytes from apoptotic cell death. In contrast, the present study showed that the expression of LMP1 induced high susceptibility to tumor necrosis factor alpha (TNFalpha)-induced apoptosis in intestine 407 epithelial cells, without affecting expression of TNF receptors I and II. LMP1-deletion mutants lacking either C-terminal activation region (CTAR)-1 or CTAR-2 had ability to enhance TNFalpha-induced apoptosis, whereas the deletion of both activation regions completely abolished the induction of high susceptibility to TNFalpha. Phosphorylation of the NFkB-inhibitory molecule IkB-alpha, another biological activity of TNFalpha, was not enhanced by LMP1-expression. LMP1 upregulated antiapoptotic gene A20 expression, suggesting that A20 can not block TNFalpha-induced apoptosis in this cell system. Apoptosis triggered by TNFalpha in LMP1-expressing intestine 407 cells was blocked by inhibitors of caspases-8 and -3. It is therefore concluded that in intestine 407 epithelial cells, LMP1 enhances primarily signal cascade responsible for TNFalpha-induced apoptosis, which occurs at a level upstream of acting site of caspases-8 and -3 and that CTAR-1 and CTAR-2 are involved in enhancement of TNFalpha-induced apoptosis.

Pharmacological manipulation of granulocyte apoptosis: potential therapeutic targets

Resolution of inflammation involves the clearance of excess or effete inflammatory cells by a process of physiological programmed cell death (apoptosis) and the subsequent recognition and removal of apoptotic cells by phagocytes. The therapeutic induction of apoptosis for the resolution of chronic inflammation and the general pharmacology of apoptosis have become subjects of increasing interest. In this article, some of the unique and important differences in the control of apoptosis of various inflammatory cells (particularly neutrophil and eosinophil granulocytes) are highlighted. It is suggested that apoptosis can be specifically regulated pharmacologically and could be exploited to develop new drug therapies.

Pathophysiological mechanisms of TNF during intoxication with natural or man-made toxins

Intoxication with different natural toxins or man-made toxicants has been associated with the induction of tumor necrosis factor alpha (TNF). These include endotoxin, superantigens, Pseudomonas aeruginosa exotoxin A, bacterial DNA, T cell stimulatory agents such as agonistic anti-CD3 mAbs or concanavalin A, alpha-amanitin, paracetamol, ethanol, carbon tetrachloride, dioxin, and dimethylnitrosamine. In this paper we compile and discuss the current knowledge on the pathophysiological role of TNF during intoxication with all mentioned toxins and toxicants. A possible role of gut-derived endotoxin in several TNF-dependent toxic events has been considered. The development of pharmaceuticals that selectively interfere with the detrimental pathways induced by TNF during intoxication with bacteria, viruses, drugs, or other chemicals requires detailed knowledge of the signaling pathways originating from the two TNF receptors (TNFR1 and TNFR2). Major characteristics of these signaling pathways are described and put together.

The zinc finger protein A20 interacts with a novel anti-apoptotic protein which is cleaved by specific caspases

A20 is a Cys2/Cys2 zinc finger protein which is induced by a variety of inflammatory stimuli and which has been characterized as an inhibitor of cell death by a yet unknown mechanism. In order to clarify its molecular mechanism of action, we used the yeast two-hybrid system to screen for proteins that interact with A20. A cDNA fragment was isolated which encoded a portion of a novel protein (TXBP151), which was recently found to be a human T-cell leukemia virus type-I (HTLV-I) Tax-binding protein. The full-length 2386 bp TXBP151 mRNA encodes a protein of 86 kDa. Like A20, overexpression of TXBP151 could inhibit apoptosis induced by tumour necrosis factor (TNF) in NIH3T3 cells. Moreover, transfection of antisense TXBP151 partially abolished the anti-apoptotic effect of A20. Furthermore, apoptosis induced by TNF or CD95 (Fas/APO-1) was associated with proteolysis of TXBP151. This degradation could be inhibited by the broad-spectrum caspase inhibitor zVAD-fmk or by expression of the cowpox virus-derived inhibitor CrmA, suggesting that TXBP151 is a novel substrate for caspase family members. TXBP151 was indeed found to be specifically cleaved in vitro by members of the caspase-3-like subfamily, viz. caspase-3, caspase-6 and caspase-7. Thus TXBP151 appears to be a novel A20-binding protein which might mediate the anti-apoptotic activity of A20, and which can be processed by specific caspases.

The zinc finger protein A20 inhibits TNF-induced NF-kappaB-dependent gene expression by interfering with an RIP- or TRAF2-mediated transactivation signal and directly binds to a novel NF-kappaB-inhibiting protein ABIN

The zinc finger protein A20 is a tumor necrosis factor (TNF)- and interleukin 1 (IL-1)-inducible protein that negatively regulates nuclear factor-kappa B (NF-kappaB)-dependent gene expression. However, the molecular mechanism by which A20 exerts this effect is still unclear. We show that A20 does not inhibit TNF- induced nuclear translocation and DNA binding of NF-kappaB, although it completely prevents the TNF- induced activation of an NF-kappaB-dependent reporter gene, as well as TNF-induced IL-6 and granulocyte macrophage-colony stimulating factor gene expression. Moreover, NF-kappaB activation induced by overexpression of the TNF receptor-associated proteins TNF receptor-associated death domain protein (TRADD), receptor interacting protein (RIP), and TNF recep- tor-associated factor 2 (TRAF2) was also inhibited by expression of A20, whereas NF-kappaB activation induced by overexpression of NF-kappaB-inducing kinase (NIK) or the human T cell leukemia virus type 1 (HTLV-1) Tax was unaffected. These results demonstrate that A20 inhibits NF-kappaB-dependent gene expression by interfering with a novel TNF-induced and RIP- or TRAF2-mediated pathway that is different from the NIK-IkappaB kinase pathway and that is specifically involved in the transactivation of NF-kappaB. Via yeast two-hybrid screening, we found that A20 binds to a novel protein, ABIN, which mimics the NF-kappaB inhibiting effects of A20 upon overexpression, suggesting that the effect of A20 is mediated by its interaction with this NF-kappaB inhibiting protein, ABIN.

Immunomodulatory effects of IFNbeta-1b on the mRNA-expression of TGFbeta-1 and TNFalpha in vitro

The mechanisms by which IFNbeta-1b acts in the treatment of multiple sclerosis (MS) patients are not completely known. We investigated the influence of IFNbeta-1b on the mRNA-expression of the immunosuppressive cytokine TGFbeta-1 and the proinflammatory mediator TNFalpha in an in vitro model by the method of non-radioactive in situ hybridization. Peripheral blood lymphocytes (PBL) were isolated from eight patients with relapsing remitting form of MS during remission and from six healthy controls. They were stimulated with IFNbeta-1b in different concentrations for 24 h. In both groups a statistically significant dose-dependent increase of TGFbeta-1-mRNA and decrease of TNFalpha-mRNA was demonstrable in the cultured stimulated blood lymphocytes compared to unstimulated cells. Stimulations with lipopolysaccharide (LPS) led to an increase of both cytokine-mRNAs in the lymphocytes. These data suggest specific and dose-dependent effects of IFNbeta-1b and hint at immunomodulatory properties of this drug to regulate the cytokine dysbalance in MS. This might be one mechanism by which IFNbeta-1b mediates its beneficial effects on the course of the disease.

Vascular Endothelial Genes That Are Responsive to Tumor Necrosis Factor- In Vitro Are Expressed in Atherosclerotic Lesions, Including Inhibitor of Apoptosis Protein-1, Stannin, and Two Novel Genes

Activation and dysfunction of endothelial cells play a prominent role in patho-physiological processes such as atherosclerosis. We describe the identification by differential display of 106 cytokine-responsive gene fragments from endothelial cells, activated by monocyte conditioned medium or tumor necrosis factor-. A minority of the fragments (22/106) represent known genes involved in various processes, including leukocyte trafficking, vesicular transport, cell cycle control, apoptosis, and cellular protection against oxidative stress. Full-length cDNA clones were obtained for five novel transcripts that were induced or repressed more than 10-fold in vitro. These novel human cDNAs CA2_1, CG12_1, GG10_2, AG8_1, and GG2_1 encode inhibitor of apoptosis protein-1 (hIAP-1), homologues of apolipoprotein-L, mouse rabkinesin-6, rat stannin, and a novel 188 amino acid protein, respectively. Expression of 4 novel transcripts is shown by in situ hybridization on healthy and atherosclerotic vascular tissue, using monocyte chemotactic protein-1 as a marker for inflammation. CA2_1 (hIAP-1) and AG8_1 are expressed by endothelial cells and macrophage foam cells of the inflamed vascular wall. CG12_1 (apolipoprotein-L like) was specifically expressed in endothelial cells lining the normal and atherosclerotic iliac artery and aorta. These results substantiate the complex change in the gene expression pattern of vascular endothelial cells, which accompanies the inflammatory reaction of atherosclerotic lesions.

Human Cytomegalovirus Binding to Human Monocytes Induces Immunoregulatory Gene Expression

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

A20 RNA expression is associated with undifferentiated nasopharyngeal carcinoma and poorly differentiated head and neck squamous cell carcinoma

A20 is an anti-apoptotic gene that can be induced in human epithelial cell lines in response to expression of the Epstein-Barr virus (EBV) gene product latent membrane protein 1 (LMP1). EBV is a ubiquitous, persistent human herpesvirus that is consistently associated with undifferentiated nasopharyngeal carcinoma (NPC), in which antigen expression includes LMP1. Consistent with a potential role in the development of NPC, LMP1 has profound effects on epithelial cell growth. A20 may be a key downstream effector of LMP1 in NPC, as LMP1-induced A20 blocks p53-mediated apoptosis in H1299 epithelial cells and most NPCs have wild-type p53. Moreover, the potential role of A20 in the development of epithelial malignancies may extend to tumours not associated with EBV. The purpose of this study was to develop an in situ hybridization assay to assess expression of A20 RNA in undifferentiated NPC and in non-EBV-associated poorly differentiated head and neck squamous cell carcinomas (SCCs) and well-differentiated SCCs of the skin. A20 RNA expression was also examined in normal samples of oral mucosa and skin. Expression of A20 was demonstrated in 76 per cent of undifferentiated NPCs and in 80 per cent of poorly differentiated head and neck SCCs, suggesting a role for A20 in the pathogenesis of these epithelial malignancies. By contrast, A20 RNA was not detected in well-differentiated SCCs of the skin, or in any normal samples of squamous epithelial tissue. The pathway leading to A20 expression in non-EBV-associated poorly differentiated head and neck SCCs is clearly LMP1-independent. LMP1 expression was demonstrated in 29 per cent of NPC biopsies, suggesting an LMP1-independent pathway to A20 induction in undifferentiated NPC.

Astrocyte-Derived Monocyte-Chemoattractant Protein-1 Directs the Transmigration of Leukocytes Across a Model of the Human Blood-Brain Barrier

The migration of leukocytes across the blood-brain barrier (BBB) into the central nervous system is critical in the pathogenesis of central nervous system inflammatory diseases. The production of chemokines, such as monocyte-chemoattractant protein-1 (MCP-1), by endothelial cells (EC) and astrocytes may initiate and amplify this process. Using a coculture of human EC and astrocytes to model the BBB, we demonstrated that exogenous MCP-1 induces the transmigration of monocytes in a dose-dependent manner. TNF-α, IFN-γ, or IL-1β treatment of cocultures also induced significant migration of monocytes that correlates with the induction of MCP-1 protein. TGF-β, previously shown to induce MCP-1 expression in astrocytes, but not in EC, caused migration of monocytes across cocultures, but not across EC grown alone. Monocytes and lymphocytes transmigrated across cytokine-treated cocultures in greater numbers than across EC alone. Astrocytes were the main source of cytokine-induced MCP-1, supporting a role for astrocytes in facilitating leukocyte transmigration. A blocking Ab to MCP-1 inhibited MCP-1- and cytokine-induced transmigration of monocytes by 85–90%. Cytokine treatment of cocultures also resulted in the transmigration of activated, CD69-positive lymphocytes. The MCP-1-mediated transmigration of monocytes across cocultures was blocked using an Ab to ICAM-1 and inhibited by 55% using an Ab to E-selectin. These data suggest a central role for astrocyte-derived MCP-1 in directing the migration of monocytes and lymphocytes across the BBB.

Nuclear factor kB-independent cytoprotective pathways originating at tumor necrosis factor receptor-associated factor 2

Most normal and neoplastic cell types are resistant to tumor necrosis factor (TNF) cytotoxicity unless cotreated with protein or RNA synthesis inhibitors, such as cycloheximide and actinomycin D. Cellular resistance to TNF requires TNF receptor-associated factor 2 (TRAF2), which has been hypothesized to act mainly by mediating activation of the transcription factors nuclear factor kB (NFkB) and activator protein 1 (AP1). NFkB was proposed to switch on transcription of yet unidentified anti-apoptotic genes. To test the possible existence of NFkB-independent cytoprotective pathways, we systematically compared selective trans-dominant inhibitors of the NFkB pathway with inhibitors of TRAF2 signaling for their effect on TNF cytotoxicity. Blockade of TRAF2 function(s) by signaling-deficient oligomerization partners or by molecules affecting TRAF2 recruitment to the TNF receptor 1 complex completely abrogated the cytoprotective response. Conversely, sensitization to TNF cytotoxicity induced by a selective NFkB blockade affected only a fraction of TNF-treated cells in an apparently stochastic manner. No cytoprotective role for c-Jun amino-terminal kinases/stress-activated protein kinases (JNKs/SAPKs), which are activated by TRAF2 and contribute to stimulation of activator protein 1 activity, could be demonstrated in the cellular systems tested. Although required for cytoprotection, TRAF2 is not sufficient to protect cells from TNF + cycloheximide cytotoxicity when overexpressed in transfected cells, thus indicating an essential role of additional TNF receptor 1 complex components in the cytoprotective response. Our results indicate that TNF-induced cytoprotection is a complex function requiring the integration of multiple signal transduction pathways.

Identification of Four Genes in Endothelial Cells Whose Expression Is Affected by Tumor Cells and Host Immune Status—A Study in Ex Vivo–Isolated Endothelial Cells

A spontaneously metastasizing, well-defined mouse lymphoma was chosen as an in vivo model to study the effect of tumor-host interaction on gene expression in liver sinusoidal endothelial cells. Forty-nine bovine aortic endothelial cell (BAEC) genes, recently isolated by a differential screening approach of a cDNA library enriched for tumor necrosis factor- (TNF-) suppressed genes, were investigated. Four of these genes were finally selected because they were affected differentially by host immuno-competence, TNF-, and tumor cells. Sequence analysis showed them to encode the bovine polyubiquitin (A4), elongation factor 1 (B2), the acidic ribosomal phosphoprotein PO (C3), and the ribosomal protein S2 (E10). Gene expression was analyzed by dot-blot or Northern blot analysis. TNF- and tumor cell conditioned supernatant suppressed the genes additive in BAEC but not in other endothelial cells except for bovine capillary endothelial cells. Ex vivo–isolated liver endothelial cells of tumor-bearing syngeneic DBA/2 mice showed strong downregulation of these four genes in comparison to normal control values. In contrast, endothelial cells of tumor-bearing immuno-incompetent Balb/c (nu/nu) mice showed no downregulation but upregulation of these genes. Consistently, all four genes were also downregulated when BAEC were incubated with supernatants derived from ex vivo–isolated liver metastases from immuno-competent but not from -incompetent mice. Thus, the expression of a group of genes involved in protein translation and processing was more profoundly altered in endothelial cells in vivo than in vitro, suggesting that microenviromental factors and cell-cell and cell-matrix interactions play an important role.

© 1998 by The American Society of Hematology.

Identification of Four Genes in Endothelial Cells Whose Expression Is Affected by Tumor Cells and Host Immune Status—A Study in Ex Vivo–Isolated Endothelial Cells

A spontaneously metastasizing, well-defined mouse lymphoma was chosen as an in vivo model to study the effect of tumor-host interaction on gene expression in liver sinusoidal endothelial cells. Forty-nine bovine aortic endothelial cell (BAEC) genes, recently isolated by a differential screening approach of a cDNA library enriched for tumor necrosis factor- (TNF-) suppressed genes, were investigated. Four of these genes were finally selected because they were affected differentially by host immuno-competence, TNF-, and tumor cells. Sequence analysis showed them to encode the bovine polyubiquitin (A4), elongation factor 1 (B2), the acidic ribosomal phosphoprotein PO (C3), and the ribosomal protein S2 (E10). Gene expression was analyzed by dot-blot or Northern blot analysis. TNF- and tumor cell conditioned supernatant suppressed the genes additive in BAEC but not in other endothelial cells except for bovine capillary endothelial cells. Ex vivo–isolated liver endothelial cells of tumor-bearing syngeneic DBA/2 mice showed strong downregulation of these four genes in comparison to normal control values. In contrast, endothelial cells of tumor-bearing immuno-incompetent Balb/c (nu/nu) mice showed no downregulation but upregulation of these genes. Consistently, all four genes were also downregulated when BAEC were incubated with supernatants derived from ex vivo–isolated liver metastases from immuno-competent but not from -incompetent mice. Thus, the expression of a group of genes involved in protein translation and processing was more profoundly altered in endothelial cells in vivo than in vitro, suggesting that microenviromental factors and cell-cell and cell-matrix interactions play an important role.

© 1998 by The American Society of Hematology.

Apoptotic, non-apoptotic, and anti-apoptotic pathways of tumor necrosis factor signalling

Early events in the signalling of tumor necrosis factor-receptor 1 (TNF-R1), which is the main TNF receptor on most cell types, have been clarified recently. A multimolecular signal transducing complex from which several pathways originate rapidly forms upon TNF-induced aggregation of the receptor. Although fully capable of transducing apoptotic signals, which depend on the adapter Fas-associated death domain protein (FADD) and on the subsequent recruitment/activation of the apoptotic proteases, TNF-R1 usually does not kill cells; this is due to the induction of a complex cytoprotective response that requires TNF-receptor associated factor 2 (TRAF2), a signal transducer that couples TNF-R1 to both nuclear factor kappaB (NFkappaB)-dependent and NFkappaB-independent transcriptional events implicated in induction of genes protecting from TNF cytotoxicity. Although absolutely required for cytoprotection, TNF-receptor associated factor 2 is not sufficient to protect cells from TNF, thus suggesting that it may act in concert with additional TNF-R1 complex components. In this commentary, we will discuss some critical aspects of TNF-R1 signal transduction that are not fully understood: Why do cells not die before the protective protein synthesis has occurred? What are the mechanisms implicated in the termination of each TNF-R1-elicited response? Are there regulatory mechanisms capable of influencing the composition of the TNF-R1 complex and, consequently, the propagation of specific signals?

Lipopolysaccharide Induces the Antiapoptotic Molecules, A1 and A20, in Microvascular Endothelial Cells

The effect of lipopolysaccharide (LPS) on endothelial cells is a key component of the inflammatory response seen in Gram-negative sepsis. LPS does not cause death of cultured human endothelial cells. However, when the expression of new proteins is inhibited by cycloheximide, microvascular endothelial cells in culture undergo apoptosis. This finding suggests that LPS induces apoptotic and antiapoptotic pathways, with the antiapoptotic response being dependent on the synthesis of new proteins. Concurrent activation of apoptotic and antiapoptotic pathways has previously been documented for tumor necrosis factor (TNF). In the case of TNF, the antiapoptotic signal has been attributed to at least two cytoprotective proteins: the Bcl-2 homologue, A1, and the zinc-finger protein, A20. In this study, we demonstrate that both these molecules are induced in microvascular endothelial cells by LPS. Enforced overexpression of either A1 or A20 inhibits LPS and cycloheximide-initiated apoptosis. Induction of A1 and A20 does not require synthesis of intermediary proteins, but is dependent on the presence of soluble CD14. In addition, we show that inhibition of signaling by the transcription factor, NF-κB, blocks accumulation of A1 and A20 mRNA. Taken together, our findings suggest that LPS directly induces expression of the cytoprotective proteins, A1 and A20, via a CD14-dependent pathway requiring activation of NF-κB.

© 1998 by The American Society of Hematology.

Complement-Induced Expression of Chemokine Genes in Endothelium: Regulation by IL-1-Dependent and -Independent Mechanisms

Activation of complement in the vicinity of endothelium is thought to contribute to the tissue manifestations of inflammatory and immune responses. Endothelial cells contribute to these processes in part by the elaboration of chemokines that activate various leukocytes and direct their migration into tissues. We investigated the mechanisms by which activation of complement on endothelial cell surfaces might influence the expression of chemokine genes in endothelial cells. In a model for the immune reaction occurring in a xenograft, human serum, as a source of xenoreactive anti-endothelial Abs and complement, induced expression of the monocyte chemotactic protein-1 (MCP-1), IL-8, and RANTES genes. The MCP-1 and IL-8 genes were expressed within 3 h as a first phase and at &gt;12 h as a second phase. The RANTES gene was expressed in porcine endothelial cells only 12 h after exposure to human serum. The expression of these genes required activation of complement and assembly of membrane attack complex, as it was inhibited by soluble CR1 and did not occur in the absence of C8. The early phase of MCP-1 and IL-8 gene expression did not require de novo protein synthesis. The late phase of MCP-1, IL-8, and RANTES gene expression predominantly required the production of IL-1α as an intermediate step. The results indicate that the expression of chemokine genes in endothelial cells occurs as a function of differential responses to complement and may in part be conditioned by the availability of IL-1α.

Lipopolysaccharide Induces the Antiapoptotic Molecules, A1 and A20, in Microvascular Endothelial Cells

The effect of lipopolysaccharide (LPS) on endothelial cells is a key component of the inflammatory response seen in Gram-negative sepsis. LPS does not cause death of cultured human endothelial cells. However, when the expression of new proteins is inhibited by cycloheximide, microvascular endothelial cells in culture undergo apoptosis. This finding suggests that LPS induces apoptotic and antiapoptotic pathways, with the antiapoptotic response being dependent on the synthesis of new proteins. Concurrent activation of apoptotic and antiapoptotic pathways has previously been documented for tumor necrosis factor (TNF). In the case of TNF, the antiapoptotic signal has been attributed to at least two cytoprotective proteins: the Bcl-2 homologue, A1, and the zinc-finger protein, A20. In this study, we demonstrate that both these molecules are induced in microvascular endothelial cells by LPS. Enforced overexpression of either A1 or A20 inhibits LPS and cycloheximide-initiated apoptosis. Induction of A1 and A20 does not require synthesis of intermediary proteins, but is dependent on the presence of soluble CD14. In addition, we show that inhibition of signaling by the transcription factor, NF-κB, blocks accumulation of A1 and A20 mRNA. Taken together, our findings suggest that LPS directly induces expression of the cytoprotective proteins, A1 and A20, via a CD14-dependent pathway requiring activation of NF-κB.

© 1998 by The American Society of Hematology.

The cysteine-cysteine family of chemokines RANTES, MIP-1alpha, and MIP-1beta induce trypanocidal activity in human macrophages via nitric oxide

This paper describes a new role for the cysteine-cysteine (CC) chemokines RANTES, MIP-1alpha, and MIP-1beta on human macrophage function, which is the induction of nitric oxide (NO)-mediated trypanocidal activity. In a previous report, we showed that RANTES, MIP-1alpha and MIP-1beta enhance Trypanosoma cruzi uptake and promote parasite killing by human macrophages (M. F. Lima, Y. Zhang, and F. Villalta, Cell. Mol. Biol. 43:1067-1076, 1997). Here we study the mechanism by which RANTES, MIP-1alpha, and MIP-1beta activate human macrophages obtained from healthy individuals to kill T. cruzi. Treatment of human macrophages with different concentrations of RANTES, MIP-1alpha, and MIP-1beta enhances T. cruzi trypomastigote phagocytosis in a dose peak response. The optimal response induced by the three CC chemokines is attained at 500 ng/ml. The macrophage trypanocidal activity induced by CC chemokines can be completely inhibited by L-N-monomethyl arginine (L-NMMA), a specific inhibitor of the L-arginine:NO pathway, but not by its D-enantiomer. Culture supernatants of chemokine-treated human macrophages contain increased NO2- levels, and NO2- production is also specifically inhibited by L-NMMA. The amount of NO2- induced by these chemokines in human macrophages is comparable to the amount of NO2- induced by gamma interferon. The killing of trypomastigotes by NO in cell-free medium is blocked by an NO antagonist or a NO scavenger. This data supports the hypothesis that the CC chemokines RANTES, MIP-1alpha, and MIP-1beta activate human macrophages to kill T. cruzi via NO, which is an effective trypanocidal mechanism.

Lipopolysaccharide-induced NF-kappaB activation in human endothelial cells involves degradation of IkappaBalpha but not IkappaBbeta

We studied the signal transduction pathways involved in NF-kappaB activation and the induction of the cytoprotective A20 gene by lipopolysaccharide (LPS) in human umbilical vein endothelial cells (HUVEC). LPS induced human A20 mRNA expression with a maximum level 2 h after stimulation. The proteasome inhibitor N-acetyl-leucinyl-leucinyl-norleucinal-H (ALLN) and the tyrosine kinase inhibitor herbimycin A (HMA) blocked A20 mRNA expression and partially inhibited NF-kappaB DNA-binding activity induced by LPS treatment. LPS induced IkappaBalpha degradation at 30-60 min after treatment, but did not induce IkappaBbeta degradation up to 120 min. In contrast, TNF-alpha rapidly induced IkappaBalpha degradation within 5 min and IkappaBbeta degradation within 15 min. Cycloheximide did not prevent LPS-induced IkappaBalpha degradation, indicating that newly synthesized proteins induced by LPS were not involved in LPS-stimulated IkappaBalpha degradation. LPS-induced IkappaBalpha degradation was inhibited by ALLN, confirming that ALLN inhibits NF-kappaB activation by preventing IkappaBalpha degradation. Of note, HMA also inhibited LPS-induced IkappaBalpha degradation. However, tyrosine phosphorylation of IkappaBalpha itself was not elicited by LPS stimulation, suggesting that tyrosine phosphorylation of a protein(s) upstream of IkappaBalpha is required for subsequent degradation. We conclude that in HUVEC, LPS induces NF-kappaB-dependent genes through degradation of IkappaBalpha, not IkappaBbeta, and propose that this degradation is induced in part by HMA-sensitive kinase(s) upstream of IkappaBalpha.

TNF-induced mitochondrial changes and activation of apoptotic proteases are inhibited by A20

A20 zinc finger protein is a product of a cytokine-induced primary response gene. It functions as a negative regulator of the tumor necrosis factor (TNF) inhibiting both TNF-mediated apoptosis and activation of transcription factors. We demonstrated that A20 overexpression blocks early TNF-induced signaling events including the generation of free radicals, the fall in mitochondrial transmembrane potential (delta psi(m)), and the activation of caspase-3-like apoptotic proteases. General inhibitor of caspases, cow pox virus-derived CrmA, also inhibited TNF-induced mitochondrial changes indicating that early caspase activation occurs upstream from mitochondrial changes. Interestingly, changes in mitochondrial function or induction of caspase-3-like activity induced by anti-Fas or doxorubicin were not inhibited by A20. The data show that A20 is a specific inhibitor of TNF signaling and acts upstream of INF-induced free radical formation, fall in mitochondrial transmembrane potential (delta psi(m)), and activation of caspase-3-like proteases.

Epithelial cell kinase-B61: an autocrine loop modulating intestinal epithelial migration and barrier function

Epithelial cell kinase (Eck) is a member of a large family of receptor tyrosine kinases whose functions remain largely unknown. Expression and regulation of Eck and its cognate ligand B61 were analyzed in the human colonic adenocarcinoma cell line Caco-2. Immunocytochemical staining demonstrated coexpression of Eck and B61 in the same cells, suggestive of an autocrine loop. Eck levels were maximal in preconfluent cells. In contrast, B61 levels were barely detectable in preconfluent cells and increased progressively after the cells reached confluence. Caco-2 cells cultured in the presence of added B61 showed a significant reduction in the levels of dipeptidyl peptidase and sucrase-isomaltase mRNA, markers of Caco-2 cell differentiation. Cytokines interleukin-1beta (IL-1beta), basic fibroblast growth factor, IL-2, epidermal growth factor, and transforming growth factor-beta modulated steady-state levels of Eck and B61 mRNA and regulated Eck activation as assessed by tyrosine phosphorylation. Functionally, stimulation of Eck by B61 resulted in increased proliferation, enhanced barrier function, and enhanced restitution of injured epithelial monolayers. These results suggest that the Eck-B61 interaction, a target of regulatory peptides, plays a role in intestinal epithelial cell development, migration, and barrier function, contributing to homeostasis and preservation of continuity of the epithelial barrier.

A20 inhibits NF-kappaB activation independently of binding to 14-3-3 proteins

The A20 protein, which belongs to a class of Cys2/Cys2 zinc finger proteins, has been characterized as an inhibitor of NF-kappaB activation. In order to clarify its molecular mechanism of action, the yeast two-hybrid system was used to screen for interacting proteins. We report that different isoforms of 14-3-3 proteins, viz. eta and zeta, are able to bind A20, involving the 14-3-3-binding motif RSKSDP located between zinc fingers 3 and 4. However, A20 mutants that no longer associated with 14-3-3 proteins could still fully inhibit NF-kappaB activation induced by tumor necrosis factor, interleukin-1beta or phorbol 12-myristate 13-acetate, thus excluding a crucial role for 14-3-3 interaction in this A20 function.

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.

Novel regulation of the helix-loop-helix protein Id1 by S5a, a subunit of the 26 S proteasome

Id proteins negatively regulate the dimerization, DNA binding, and biological properties of basic helix-loop-helix proteins. In a search for novel factors that interact with Id1, we identified a component of the 26 S proteasome, S5a, that has previously been implicated only in the recognition of ubiquitinated polypeptides destined for proteolysis. S5a interacts strongly with Id1, less strongly with the basic helix-loop-helix proteins MyoD and E12, and not at all with other Id proteins. S5a restores DNA binding by MyoD-Id1 and E12-Id1 heterodimers, enhances DNA binding by MyoD and E12 homodimers, and reverses Id1-mediated repression of the muscle creatine kinase promoter during myogenic differentiation. Mutagenesis experiments showed that amino acids flanking the helix-loop-helix domain plus three residues in the first helix of Id1 impart S5a recognition. This requires only the NH2-terminal half of S5a. S5a thus appears to promote the positive regulation of myogenic genes through ubiquitin-independent mechanisms involving inhibition of Id1 and the enhancement of DNA binding by MyoD and E12. This latter property may permit the selection of novel promoter binding sites during myogenesis.

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.

Expression of tumor necrosis factor-alpha and transforming growth factor-beta 1 in cerebrospinal fluid cells in meningitis

Meningitis is an acute inflammatory disease of the pia and arachnoid and the fluid in the subarachnoid space, in which a participation of cytokines can be expected. While tumor necrosis factor-alpha (TNF alpha) promotes inflammatory reactions, transforming growth factor-beta 1 (TGF beta 1) has antagonistic effects and suppresses the inflammation in the subarachnoid space. We investigated the protein concentration and mRNA expression of TNF alpha and TGF beta 1 in cerebrospinal fluid (CSF) by ELISA and intracellularly by non-radioactive in situ hybridization in 23 patients with bacterial or viral meningitis. A higher amount of both cytokines on protein and mRNA level, especially of TNF alpha, could be detected in bacterial infection. While an imbalance of both cytokines with a preponderance of TNF alpha- compared to TGF beta 1-mRNA was visible in CSF cells of patients with bacterial meningitis, a balance of TNF alpha- and TGF beta 1-mRNA or a higher expression of TGF beta 1-mRNA could be detected in viral meningitis. In the acute phase of the disease neutrophil granulocytes expressed more TNF alpha- and TGF beta 1-mRNA than lymphocytes and monocytes/macrophages, while these cell types were dominating the cytokine synthesis during the healing phase. These data indicate that immunomodulatory mechanisms take place in the CSF compartment itself, regulated by CSF cells in different but specific ways. In addition, TGF beta 1 seems to be involved in the down-regulation of the inflammatory activity and to be one factor in the cytokine network, which could contribute to a lower rate of complications and positive outcomes. Moreover this study favors the possibility to monitor the immunomodulatory mechanisms by non-radioactive in situ hybridization.

Cell-cell adhesion mediated by binding of membrane-anchored ligand LERK-2 to the EPH-related receptor human embryonal kinase 2 promotes tyrosine kinase activity

Human embryonal kinase 2 (HEK2) is a protein-tyrosine kinase that is a member of the EPH family of receptors. Transcripts for HEK2 have a wide tissue distribution. Recently, a still growing family of ligands, which we have named LERKs, for ligands of the eph-related kinases, has been isolated. In order to analyze functional effects between the LERKs and the HEK2 receptor, we expressed HEK2 cDNA in an interleukin-3-dependent progenitor cell line 32D that grows as single cells in culture. Within the group of LERKs, LERK-2 and -5 were shown to bind to HEK2. Membrane-bound and soluble forms of LERK-2 were demonstrated to signal through HEK2 as judged by receptor phosphorylation. Coincubation of HEK2 and LERK-2 expressing cells induced cell-cell adhesion and formation of cell aggregates. This interaction could be inhibited by preincubation of HEK2 expressing cells with soluble LERK-2. Coexpression of HEK2 and LERK-2 in 32D cells showed reduced kinase activity and autophosphorylation of HEK2 compared with the juxtacrine stimulation, which seems to be due to a reduced sensitivity of the receptor.

14-3-3 proteins associate with A20 in an isoform-specific manner and function both as chaperone and adapter molecules

A20, a novel zinc finger protein, is an inhibitor of tumor necrosis factor-induced apoptosis. The mechanism by which A20 exerts its protective effect is currently unknown. Several isoforms of the 14-3-3 proteins were found to interact with A20 in a yeast two-hybrid screen. A20 bound several 14-3-3 isoforms in vitro. Moreover, transfected A20 was found to preferentially bind the endogenous eta14-3-3 isoform, whereas the beta/zeta isoforms co-immunoprecipitated much less efficiently, and epsilon14-3-3 had an intermediate affinity. Importantly, c-Raf, a previously described 14-3-3-interacting protein, also preferentially bound the eta isoform. The cellular localization and subcellular fractionation of A20 was dramatically altered by co-transfected 14-3-3, providing the first experimental evidence for the notion that 14-3-3 can function as a chaperone. Furthermore, c-Raf and A20 co-immunoprecipitated in a 14-3-3-dependent manner, suggesting that 14-3-3 can function as a bridging or adapter molecule.

A20 blocks endothelial cell activation through a NF-kappaB-dependent mechanism

The A20 gene product is a novel zinc finger protein originally described as a tumor necrosis factor alpha (TNF)-inducible early response gene in human umbilical vein endothelial cells (HUVEC). Its described function is to block TNF-induced apoptosis in fibroblasts and B lymphocytes, but more recently it has also been shown to play a role in lymphoid cell maturation. The mechanism of action of A20 is unknown. The aim of our study was to assess the effect of A20 upon endothelial cell activation. By transfecting bovine aortic endothelial cells (BAEC) with A20 as well as reporter constructs consisting of the promoters of genes known to be up-regulated during endothelial cell activation, i.e. E-selectin, interleukin (IL)-8, tissue factor (TF), and inhibitor of nuclear factor kappaBalpha (IkappaBalpha), we demonstrate that A20 expression inhibits gene up-regulation associated with TNF, lipopolysaccharide (LPS), phorbol 12-myristate 13-acetate (PMA), and hydrogen peroxide (H2O2)-induced endothelial cell (EC) activation. The mechanism of action of A20 is in part, or totally, due to the blockade of nuclear factor kappaB (NF-kappaB), as shown by its ability to suppress the activity of a NF-kappaB reporter. This effect is specific, as A20 does not block a noninducible, constitutively expressed reporter, Rous sarcoma virus-luciferase (RSV-LUC); nor does it block the c-Tat-inducible, NF-kappaB-independent reporter, human immunodeficiency virus-chloramphenicol acetyltransferase (HIV-CAT). How A20 blocks NF-kappaB is unclear, although we demonstrate that it does not affect p65 (RelA)-mediated gene transactivation. The inhibition of endothelial cell activation by A20 is a novel function for A20.

Induction of macrophage antiprotozoal activity by monocyte chemotactic and activating factor

To determine if monocyte chemotactic and activating factor (MCAF) induces intracellular antimicrobial activity, human monocyte-derived macrophages were treated with MCAF and challenged with Toxoplasma gondii and Leishmania donovani. Pretreatment with MCAF induced macrophages to inhibit protozoal replication by approximately 50%. These findings suggest a potential host defense role for MCAF in the inflammatory response to intracellular pathogens.

A20, an inhibitor of cell death, self-associates by its zinc finger domain

A20 is a primary response gene which is induced after monocyte adherence or cytokine stimulation of a variety of cells. The A20 protein belongs to a novel class of Cys2/Cys2 zinc finger proteins, and has been characterized as an inhibitor of both apoptotic and necrotic cell death. In order to clarify its molecular mechanism of action, we used the yeast-based two-hybrid system to screen for A20-associated proteins. Here we report that A20 is able to self-associate, and demonstrate that the latter interaction is mediated by its zinc finger domain.

Eph receptor tyrosine kinases and their ligands in neural development

Receptor tyrosine kinases play important roles in many developmental phenomena, including the regulation of cell proliferation, differentiation, and survival. The largest subfamily of receptor tyrosine kinases are the Eph receptors, which are widely expressed in the nervous system. With the recent identification of several Eph ligands, it has become evident that Eph receptors and their ligands are involved in the guidance of retinal axons and in the process of hindbrain segmentation.

Interleukin 8 secretion by colonic crypt cells in vitro: response to injury suppressed by butyrate and enhanced in inflammatory bowel disease

Epithelia from several sites exhibit inducible secretion of interleukin 8 (IL-8). This study aimed to characterise secretion of IL-8 by colonic epithelial cells in vitro. Colonic crypt cells were isolated enzymatically from resected colon and the IL-8 content of culture supernates was measured by ELISA. The rate of secretion of IL-8 accelerated and levels of IL-8 transcripts increased appreciably during culture. Exposure to tumour necrosis factor alpha (TNF alpha) failed to increase secretion further. Secretion was not induced by the enzymatic digestion or by serum used in the culture medium but was significantly inhibited by butyrate, by a mean of 23%. Control experiments indicated that colonic crypt cells were the likely source. The secretion of IL-8 over 24 hours by cells from uninflamed mucosa of patients with ulcerative colitis or Crohn's disease was more than twofold that from normal cells, while that from cancer bearing colons was normal. TNF alpha (10 mM) significantly suppressed IL-8 secretion only in the ulcerative colitis group and the change was different to those in the normal (p = 0.007) and Crohn's disease groups (p = 0.012). Cells from inflamed areas secreted more IL-8 than those from autologous uninflamed areas (p = 0.009) but responses to modulating factors were no different. The induction of IL-8 secretion by colonic crypt cells in vitro is probably a response to injury associated with isolation and culture. It is suppressed by butyrate and increased in inflammatory bowel disease independently of the presence of mucosal inflammation. Whether epithelial derived IL-8 plays a part in the pathogenesis of inflammatory bowel disease is not yet clear.

Lipopolysaccharide-inducible and salicylate-sensitive nuclear factor(s) on human tumor necrosis factor alpha promoter

Lipopolysaccharide (LPS) is one of the most potent trigger substances for monocytes and macrophages causing secretion of tumor necrosis factor alpha (TNF-alpha) and other inflammatory mediators. The nature of the nuclear factors involved in human TNF-alpha gene regulation is still unknown. Nuclear factor kappa B (NF-kappa B) proteins have been suggested to play an important role in gene transcription of inflammatory mediators when monocytes are stimulated with LPS. However, it remains unclear whether these nuclear factors are the only ones involved in human TNF-alpha gene regulation. In this report, to further the identification of nuclear factor(s) involved in TNF-alpha gene regulation, human monocytic THP-1 cells were transfected with a series of truncated versions of human TNF-alpha promoter. A 98-bp region located from nucleotides -584 to -487 demonstrated strong promoter activity. Electrophoretic mobility shift assays demonstrated that a 64-bp fragment located within the 98-bp region and lacking any potential NF-kappa B-binding sites avidly bound LPS-challenged THP-1 nuclear protein. Although this binding was inhibited in salicylate-treated cells, as was binding of NF-kappa B, the pattern of binding was found to differ from that noted for NF-kappa B. Analysis of this 64-bp fragment disclosed the absence of an NF-kappa B consensus sequence, suggesting a novel nuclear DNA-binding protein necessary for the initiation of human TNF-alpha transcription other than, or in addition to, NF-kappa B.

Differential expressions of the eph family of receptor tyrosine kinase genes (sek, elk, eck) in the developing nervous system of the mouse

To examine the roles of the eph subfamily of receptor tyrosine kinase (RTK), we isolated mouse cDNAs for sek, elk, and eck and localized their mRNAs in the developing mouse, with particular reference to the CNS development, by in situ hybridization. sek mRNA is most abundantly expressed throughout development; sek was detected in the germinal layer of the embryonic CNS during mid- to late-gestation and was widely expressed in the early postnatal brain. elk was expressed in the mantle layer of the embryonic CNS and showed a distribution complementary to that of sek. Differential expression of sek and elk was also observed in the early postnatal cerebellum; sek was expressed in the Purkinje cells, while elk was detected in the granule cells. eck was moderately expressed in the germinal layer of the embryonic CNS at mid-gestation, but its expression decreased as development proceeded. These spatio-temporally different patterns of gene expression suggest that these RTKs have distinct roles in mouse development despite their structural homology.

Fas- and tumor necrosis factor-induced apoptosis is inhibited by the poxvirus crmA gene product

crmA is a cowpox virus gene that encodes a protease inhibitor of the serpin family. The only reported target for the CrmA protein is the cysteine protease interleukin-1 beta converting enzyme (ICE). ICE, by virtue of its homology to the Caenorhabditis elegans cell death protein Ced-3, has been suggested to play a fundamentally important role in mammalian apoptosis. We hypothesized that a function of crmA may be to inhibit cell death, since a major mechanism of viral clearance is the immune system-mediated induction of apoptosis of infected cells. The tumor necrosis factor receptor and the Fas antigen are two cytokine receptors which, by engaging and activating the death pathway, can eliminate virus-infected cells. Remarkably, crmA was found to be an exceptionally potent inhibitor of apoptosis induced by both these receptors, capable of blocking the cell death program even at pharmacological doses of the death stimulus. Therefore, an important new function for crmA is the inhibition of cytokine-induced apoptosis. Further, the data suggest that a protease, either ICE or a related crmA-inhibitable protein, is a component of the Fas- and tumor necrosis factor-induced cell death pathways.

Upregulation of NF-kappa B-dependent gene expression mediated by the p75 tumor necrosis factor receptor

Tumor necrosis factor (TNF-alpha) interacts with two transmembrane receptor proteins, p55TNFR and p75TNFR, which are members of a family of cell surface molecules that include the Fas antigen, CD27, CD30, CD40, OX40, a Shope fibroma viral protein, and the low-affinity p75 neurotrophin receptor. Although the p55 TNF receptor has been shown to be primarily responsible for the biologic responses of TNF-alpha, the exact involvement of the p75 TNF receptor in signaling events is unclear. Here we show that expression of a human cDNA clone for p75 in COS-1 and 3T3 cells results in the constitutive activation of an TNF-inducible NF-kappa B-containing promoter. Analysis of a number of chimeric p75 receptor cDNA constructs further suggests that this activity requires the cytoplasmic domain of the p75 receptor. These results therefore indicate that the p75 TNF receptor is capable of mediating signal transduction.

Fas ligation triggers apoptosis in macrophages but not endothelial cells

The reticuloendothelial system includes macrophages and endothelial cells. These cells are produced and destroyed in vivo with a precision that implies the existence of homeostatic mechanisms. The stimuli for endothelial cell proliferation and monocyte production are becoming well characterized. However, the mechanisms involved in eliminating these cells are poorly understood. One mechanism involved in cellular elimination is apoptosis, which can be triggered in some cells by ligation of the Fas molecule. In this report we have investigated whether macrophages and endothelial cells express the Fas molecule, and whether Fas transmits an apoptosis-inducing signal in these cells. We demonstrate that macrophages express Fas and readily undergo apoptosis when cultured with anti-Fas. In contrast, while endothelial cells can express the Fas molecule, Fas ligation is insufficient to induce apoptosis. These results suggest differential regulation of Fas function among cells of the reticuloendothelial system, and imply different mechanisms of homeostasis.