TNF-binding Protein Research Articles

Tumor Necrosis Factor Inhibitors from Poxviruses with An Emphasis on Tanapoxvirus-2L Protein

Viruses have evolved strategies to counteract host defenses. Some tactics employ viral proteins to neutralize host immune effector proteins such as cytokines, chemokines and their receptors, which help coordinate the host responses against the virus. Tumor necrosis factor (TNF) is one of the crucial pro-inflammatory/anti-viral cytokines involved in inflammatory and autoimmune diseases. Poxvirus anti-immune proteins represent some of the most complex and efficient mechanisms of regulating TNF and its pathological effects. These proteins have considerable potential for treating TNF-related diseases. Here we discuss two major classes of poxvirus-TNF inhibitors focusing on the tanapoxvirus (TPV)-2L protein, previously called TPV-gp38. TPV-2L has been shown to interact and biologically neutralize human (h)TNF, and has been indirectly associated with the inhibition of other cytokines (hIFN-γ, hIL-2 and hIL-5). The TPV-2L protein alone has been expressed, purified and shown to bind with high affinity to hTNF, but lacked binding to the other cytokines. Further studies identified sequential binding of hβ2-microglobulin and hα2-macroglobulin to TPV-2L. The ability of a single viral protein to form multi-protein complexes suggests that TPV might also possess other novel strategies of evading the immune system. Reviewed here are patented poxvirus TNF-binding proteins and their genes to evaluate their potential therapeutic value.

The Immune System’s Moderating Response to Inflammation Relieves Autistic Behavior: Response to Peter Good

Authors Helt, Kelley, Boorstein, Pandey, and Fein, askedauthors Kinsbourne and Herbert to respond to the Goodletter because of their expertise in this area. Following isDr. Kinsbourne’s response.Curran et al. (2007) confirmed that children with autismbehaveless aberrantly when they are febrile due to infections,a phenomenon that might offer insight into the cause andtreatment of autistic symptoms. Good (2011) attributes theimprovement to an increase in cerebral blood flow. Somebrain regions related to autistic symptoms are indeed under-perfused (Ohnishi et al. 2000). However, because regionalcerebral blood flow is proportionate to metabolic need,diminished perfusion reflects diminished metabolism ratherthan cause it. Evidence is lacking that fever increases theperfusion of these regions, or that they would function betterif it did. Indeed, Curran et al. (2007) found no relationshipbetween degree of fever and degree of improvement.Fever is the presenting symptom of inflammatoryreactions to a pathogen. Absent inflammation, heat stressdoes not improve behavior in autism (Miles 2010, cited byGood). Therefore, the benefits do not accrue from the risingtemperature as such. I suggest that they derive from theimmune system’s efforts to limit the inflammatory reaction.The febrile inflammatory response to pathogens ismediated by proinflammatory cytokines, notably IL-1 betaand TNF-alpha (Mackowiak 1998) and promoted by thesympathetic nervous system. In excess, these cytokineswould be toxic. The proinflammatory cytokine response israpidly curtailed by IL-1ra, a specific IL-1 antagonist, andby anti-inflammatory cytokines, such as IL-10, TNF-binding protein and transforming growth factor-b (TGF-b)(Czura and Tracey 2005). Moreover, the inflammatoryreaction with its sympathetic activation is buffered by thevagal cholinergic anti-inflammatory system (CAIS) (Tracey2007; Thayer 2009).The inflammatory reflex of the vagus nerve preventsexcessive release of cytokines from macrophages. Whenthe CAIS of mice was inactivated, the cytokine response toendotoxin was excessive (Borovikova et al. 2000). Electri-cal vagal stimulation is used to treat inflammatory diseases,including depression, which features neuroinflammation(Pucak et al. 2007). Vagal stimulation also increases heartrate variability, as autonomic tone veers from sympathetictoward parasympathetic dominance.In controlling inflammation and sympathetic predomi-nance, the CAIS may lower arousal level. Much autisticbehavior appears to be a compensatory reaction to chronicpathologically heightened arousal (Kinsbourne 2011).Vargas et al. (2005)discoveredneuroinflammation in peoplewith autism, both in vivo and at autopsy. An outpouring ofcytokines from activated microglia, the CNS counterparts ofmacrophages, involves the excessive release of glutamate,the preponderant excitatory neurotransmitter, increasing thebrain activation toward hyperarousal. By subduing neuro-inflammation (Nizri et al. 2009), the CAIS would down-regulate arousal and enable adaptive behavior to emerge.Sympathetic hyperarousal in autism is also well docu-mented. By fostering parasympathetic (vagal) predominance,the CAIS might ameliorate the fearful sensory rejection andurge toward isolation and inward shift of attention thatcharacterizes the autistic state (Kinsbourne 2011).That autistic behavior can improve during fever demon-strates that it is not necessarily fixed but can constitute areaction to potentially remediable factors. If the suggested

3D structure modeling of complexes formed by CrmB TNF-binding proteins of Variola and cowpox viruses with murine and human TNFs

Orthopoxviral genomes bear genes for a series of homologous secreted proteins binding tumor necrosis factor (TNF). Orthopoxvirus species have different sets of these proteins. Variola virus has only one protein of this series, CrmB. Although CrmB protein sequences are similar to each other, their physicochemical and biological properties show certain species-specific features. We constructed 3D models of complexes formed by TNF-binding domains of variola and cowpox viruses with murine and human TNFs. We also constructed corresponding models with a mutant human TNF. In this mutant TNF, the arginine residue at position 31 involved in receptor binding was replaced by glutamine, characteristic of murine TNF. Analysis of the models showed that the least stable complex should be that formed by cowpox virus CrmB with human TNF, and the Arg31/Gln substitution should significantly stabilize the interaction between cowpox CrmB and mutant human TNF. Experimental comparison of the abilities of recombinant variola and cowpox CrmB proteins to inhibit the cytotoxic action of TNFs confirmed the predictions.

Recombinant TNF-binding protein from variola virus as a novel potential TNF antagonist

Gel-filtration chromatographic separation of the lysate of Sf21 insect cells infected with recombinant baculovirus BVi67 containing the gene for TNF-binding protein (CrmB) of variola virus (VARV) revealed that hTNF-cytotoxicity neutralization activity is associated with a fraction corresponding mainly to high molecular weight proteins (above 500 kDa) and less with fractions corresponding to proteins of 270 or 90 kDa. The recombinant VARV-CrmB protein has been purified by affinity chromatography. Difference in the experimentally determined and estimated (according to amino acid composition) VARV-CrmB molecular weight is due to glycosylation of the recombinant protein expressed in the insect cells. VARV-CrmB neutralizes in vitro the cytotoxic effect of hTNF and hLTalpha, and its TNF-neutralizing activity is two to three orders of magnitude higher compared to the analogous effects of type I and II soluble TNF receptors, comparable with the activity of mAb MAK195, and somewhat lower than the effect of the commercial drug Remicade.

Crystal structure of TNFalpha complexed with a poxvirus MHC-related TNF binding protein.

The poxvirus 2L protein binds tumor necrosis factor-alpha (TNFalpha) to inhibit host antiviral and immune responses. The 2.8-A 2L-TNFalpha structure reveals three symmetrically arranged 2L molecules per TNFalpha trimer. 2L resembles class I major histocompatibility complex (MHC) molecules but lacks a peptide-binding groove and beta2-microglobulin light chain. Overlap between the 2L and host TNF receptor-binding sites on TNFalpha rationalizes 2L inhibition of TNFalpha-TNF receptor interactions and prevention of TNFalpha-induced immune responses.

Interaction of human TNF and β2-microglobulin with Tanapox virus-encoded TNF inhibitor, TPV-2L

Tanapox virus (TPV) encodes and expresses a secreted TNF-binding protein, TPV-2L or gp38, that displays inhibitory properties against TNF from diverse mammalian species, including human, monkey, canine and rabbit. TPV-2L also has sequence similarity with the MHC-class I heavy chain and interacts differently with human TNF as compared to the known cellular TNF receptors or any of the known virus-encoded TNF receptor homologs derived from many poxviruses. In order to determine the TNF binding region in TPV-2L, various TPV-2L C-terminal truncations and internal deletions were created and the muteins were expressed using recombinant baculovirus vectors. C-terminal deletions from TPV-2L resulted in reduced binding affinity for human TNF and specific mutants of TNF that discriminate between TNF-R1 and TNF-R2. However, deletion of C-terminal 42 amino acid residues totally abolished the binding of human TNF and its mutants. Removal of any of the predicted internal domains resulted in a mutant TPV-2L protein incapable of binding to human TNF. Deletion of C-terminal residues also affected the ability of TPV-2L to block TNF-induced cellular cytotoxicity. In addition to TNF, TPV-2L can also form complexes with human β2-microglobulin to form a novel macromolecular complex. In summary, the TPV-2L protein is a bona fide MHC-1 heavy chain family member that binds and inhibits human TNF in a fashion very distinct from other known poxvirus-encoded TNF inhibitors, and also can form a novel complex with the human MHC-1 light chain, β2-microglobulin.

Cytokines Link Toll-Like Receptor 4 Signaling to Cardiac Dysfunction After Global Myocardial Ischemia

Although Toll-like receptor 4 (TLR4) has been implicated in the myocardial injury caused by regional ischemia/reperfusion, its role in the myocardial inflammatory response and in contractile dysfunction after global ischemia/reperfusion is unclear. Cytokines, particularly tumor necrosis factor-alpha (TNF-alpha), contribute to the mechanism of myocardial dysfunction after global ischemia/reperfusion. We hypothesized that a TLR4-mediated cytokine cascade modulates myocardial contractile function after global ischemia/reperfusion. This study examined whether TLR4 regulates TNF-alpha and interleukin (IL)-1beta peptide production during global ischemia/reperfusion and whether TLR4 signaling influences postischemic cardiac function through TNF-alpha and IL-1beta. Isolated hearts from wild-type mice, two strains of TLR4 mutants, TNF-alpha knockouts, and IL-1beta knockouts underwent global ischemia/reperfusion. Cardiac contractile function was analyzed, and myocardial nuclear factor-kappaB activity and TNF-alpha and IL-1beta levels were measured. In wild-type hearts, global ischemia/reperfusion induced nuclear factor-kappaB activation and the production of TNF-alpha and IL-1beta peptides. In TLR4-mutant hearts, these changes were significantly reduced and postischemic functional recovery was improved. Application of TNF-alpha and IL-1beta to TLR4-mutant hearts abrogated this improvement in postischemic functional recovery. Postischemic functional recovery also improved in TNF-alpha knockout and IL-1beta knockout hearts, as well as in wild-type hearts treated with TNF-binding protein or IL-1 receptor antagonist. This study demonstrates that TLR4 signaling contributes to cardiac dysfunction after global ischemia/reperfusion. TLR4 signaling mediates the production of TNF-alpha and IL-1beta peptides, and these two cytokines link TLR4 signaling to postischemic cardiac dysfunction.

Tumor Necrosis Factor-α Regulates Inflammatory and Mesenchymal Responses via Mitogen-Activated Protein Kinase Kinase, p38, and Nuclear Factor κB in Human Endometriotic Epithelial Cells

Tumor necrosis factor (TNF)-alpha is central to the endometriotic disease process. TNF-alpha receptor signaling regulates epithelial cell secretion of inflammation and invasion mediators. Because epithelial cells are a disease-inducing component of the endometriotic lesion, we explored the response of 12Z immortalized human epithelial endometriotic cells to TNF-alpha. This report reveals the impact of disruption of established TNF-alpha-induced signaling cascades on the expression of biomarkers of inflammation and epithelial-mesenchymal transition (EMT) from endometriotic epithelial cells. Note that we show the molecular potential of soluble TNF-R1 [TNF binding protein (TBP)] and a panel of small molecule kinase inhibitors to block endometriotic gene expression directly. The TNF-alpha receptor is demonstrated to signal through IkappaB kinase complex (IKK) 2 > IkappaB > nuclear factor kappaB, extracellular signal-regulated kinase > mitogen-activated protein kinase kinase (MEK), p38, and phosphatidylinositol 3-kinase (PI3K) > Akt1/2. TNF-alpha induces the expression of transcripts for inflammatory mediators interleukin (IL)-6, IL-8, regulated on activation normal T cell expressed and secreted, TNF-alpha, granulocyte macrophage-colony-stimulating factor (GM-CSF), and monocyte chemoattractant protein (MCP)-1 and also invasion mediators matrix metalloproteinase (MMP)-7, MMP-9, and intracellular adhesion molecule-1. Indeed, TBP inhibits the TNF-alpha-induced expression of all the above endometriotic genes in 12Z endometriotic epithelial cells. The secretion of IL-6, IL-8, GMCSF, and MCP-1 by TNF-alpha is blocked by TBP. Interestingly, MEK, p38, and IKK inhibitors block TNF-alpha-induced IL-8, IL-6, and GM-CSF secretion and 12z invasion, whereas the PI3K inhibitors do not. The only inhibitor to block MCP-1 expression is the p38 inhibitor. Last, TBP, MEK inhibitor, or p38 inhibitor also block cell surface expression of N-cadherin, a marker of mesenchymal cells. Taken together, these results demonstrate that interruption of TNF-alpha-induced signaling pathways in human endometriotic epithelial cells results in decreased expression and secretion of biomarkers for inflammation, EMT, and disease progression.

Tumor Necrosis Factor (TNF)-Soluble High-Affinity Receptor Complex as a TNF Antagonist

A novel high-affinity inhibitor of tumor necrosis factor (TNF) is described, which is created by the fusion of the extracellular domains of TNF-binding protein 1 (TBP-1) to both the alpha and beta chains of an inactive version of the heterodimeric protein hormone, human chorionic gonadotropin. The resulting molecule, termed TNF-soluble high-affinity receptor complex (SHARC), self-assembles into a heterodimeric protein containing two functional TBP-1 moieties. The TNF-SHARC is a potent inhibitor of TNF-alpha bioactivity in vitro and has a prolonged pharmacokinetic profile compared with monomeric TBP-1 in vivo. Consistent with the long half-life, the duration of action in an lipopolysaccharide-mediated proinflammatory mouse model is prolonged similarly. In a collagen-induced arthritis mouse model, this molecule demonstrates improved efficacy over monomeric TBP-1. Based on these results, we demonstrated that inactivated heterodimeric protein hormones are flexible and efficient scaffolds for the creation of soluble high-affinity receptor complexes.

Characterization of the febrile response induced by fibroblast-stimulating lipopeptide-1 in guinea pigs

Recently, it has been shown that the Toll-like receptors-2 and -6 agonist fibroblast-stimulating lipopeptide-1 (FSL-1) have the capacity to induce fever and sickness behavior in rats. Since the mechanisms of the fever-inducing effects of FSL-1 are still unknown, we tested the pyrogenic properties of FSL-1 in guinea pigs and assessed a role for TNF-alpha and prostaglandins in the manifestation of the febrile response to this substance. Intra-arterial and intraperitoneal injections of FSL-1 caused dose-dependent fevers that coincided with elevated plasma levels of TNF and IL-6, the intraperitoneal route of administration being more effective than the intra-arterial route. Intra-arterial or intraperitoneal injection of a soluble form of the TNF type 1 receptor, referred to as TNF binding protein (TNFbp), together with FSL-1, completely neutralized FSL-1-induced circulating TNF and reduced fever and circulating IL-6. Intra-arterial or intraperitoneal injection of the nonselective cyclooxygenase (COX)-inhibitor diclofenac depressed fever and FSL-1-induced elevations of circulating PGE2. Circulating TNF and IL-6, however, remained unimpaired by treatment with diclofenac. In conclusion, FSL-1-induced fever in guinea pigs depends, in shape and duration, on the route of administration and is, to a high degree, mediated by pyrogenic cytokines and COX products.

Sepsis-induced suppression of skeletal muscle translation initiation mediated by tumor necrosis factor α

Inhibition of translational efficiency is responsible at least in part for the sepsis-induced decrease in protein synthesis observed in skeletal muscle. Moreover, infusion of the inflammatory cytokine tumor necrosis factor α (TNF- α) into naive rats produces a comparable decrement. Therefore, the purpose of the present study was to determine whether inhibition of TNF action under in vivo conditions could prevent the sepsis-induced decrease in translation initiation observed in the postabsorptive state. To address this aim, sepsis was produced by cecal ligation and puncture (CLP) and rats were studied in the fasted condition 20 to 24 hours thereafter. Both septic and time-matched nonseptic control rats were pretreated with TNF-binding protein (TNF BP) before CLP or sham surgery to neutralize endogenously produced TNF. Sepsis altered the distribution of eukaryotic initiation factor 4E (eIF4E) in the gastrocnemius by increasing the amount associated with 4E-BP1 (inactive complex) and decreasing the amount bound to eIF4G (active complex). This change in eIF4E availability was associated with a decreased phosphorylation of 4E-BP1. Furthermore, the phosphorylation of ribosomal protein S6 and mammalian target of rapamycin (mTOR) was also decreased in the gastrocnemius from septic rats. Pretreatment of septic rats with TNF BP largely ameliorated the altered distribution of eIF4E as well as the reduced phosphorylation of 4E-BP1, S6, and mTOR. In contrast, sepsis did not change either the total amount or the phosphorylation state of eIF2 α or eIF2B ε. Furthermore, no sepsis-induced change in eIFs was detected in the slow-twitch soleus muscle. The ability of TNF BP to prevent the sepsis-induced alterations in translation initiation was independent of change in plasma insulin and proportional to the insulinlike growth factor I content in blood and muscle but was associated with a reduction in plasma corticosterone. Hence, the decreased constitutive protein synthesis observed in fast-twitch skeletal muscle in response to peritonitis is mediated by a TNF-dependent mechanism affecting mTOR regulation of translation initiation.

CYTOKINE-TRIGGERED DECREASES IN LEVELS OF PHOSPHORYLATED EUKARYOTIC INITIATION FACTOR 4G IN SKELETAL MUSCLE DURING SEPSIS

Chronic septic abscess formation causes an inhibition of protein synthesis in gastrocnemius that is not observed in rats with a sterile abscess. The inhibition is associated with an impaired translation initiation. The present study was designed to investigate the effects of sepsis on the level of phosphorylated eukaryotic initiation factor (eIF) 4G in gastrocnemius after induction of a chronic intra-abdominal sterile or septic abscess as a possible mechanism to account for the impairment of translation initiation during sepsis. The extent of phosphorylated eIF4G was reduced by more than 50% (P< 0.05) and 68% (P < 0.01) in gastrocnemius after 3 and 5 days, respectively, and returned to control values after 14 days of abscess formation in septic rats compared with sterile inflammatory animals. To examine the mediators of the septic process contributing to the decreased levels of phosphorylated eIF4G, the cytokine response to sepsis was pharmacologically modulated. First, treatment of septic rats with tumor necrosis factor (TNF) binding protein or interleukin (IL) 1 receptor antagonist increased the level of phosphorylated eIF4G. Second, infusion of TNF-alpha for 24 h in control rats resulted in a 70% decrease in phosphorylated eIF4G. Third, infusion of IL-1ra led to an increase in the level of phosphorylation of eIF4G in rats infused with TNF-alpha. Taken together, the data indicate that a cytokine-dependent decrease in the steady state phosphorylation of eIF4G is a possible mechanism accounting for the inhibition of skeletal muscle protein synthesis during sepsis. Furthermore, the findings support a role of IL-1 as the proinflammatory mediator responsible for the reduced level of phosphorylated eIF4G.

Glucocorticoids and TNFalpha interact cooperatively to mediate sepsis-induced leucine resistance in skeletal muscle.

Sepsis blunts the ability of nutrient signaling by leucine to stimulate skeletal muscle protein synthesis by impairing translation initiation. The present study tested the hypothesis that overproduction of either tumor necrosis factor (TNF)-alpha or glucocorticoids mediate the sepsis-induced leucine resistance. Prior to producing peritonitis, rats received either vehicle, TNF binding protein (TNF(BP)) to inhibit endogenous TNFalpha action, and/or the glucocorticoid receptor antagonist RU486. Leucine was orally administered to all rats 24 h thereafter and the gastrocnemius removed 20 min later to assess protein synthesis and signaling components important in controlling peptide-chain initiation. Muscle protein synthesis was 65% lower in septic rats administered leucine than in leucine-treated control animals. This reduction was not prevented by either TNF(BP) or RU486 alone, but was completely reversed by the combination. This sepsis-induced leucine resistance was associated with an 80% reduction in the amount of active eIF4E.eIF4G complex, a 5-fold increase in the formation of the inactive eIF4E.4E-BP1 complex as well as markedly reduced (at least 70%) phosphorylation of 4E-BP1, eIF4G, S6K1, S6, and mTOR. Pretreatment of septic rats with either TNF(BP) or RU486 individually only nominally improved the leucine action as assessed by the above-mentioned endpoints. In contrast, when TNF(BP) and RU486 were co-administered, the ability of sepsis to impair the leucine-stimulated phosphorylation of 4E-BP1, eIF4G, S6K1, and S6 as well as the redistribution of eIF4E was essentially prevented. No differences in the total amount or phosphorylation of eIF2alpha and eIF2Bepsilon were detected between the different groups, and changes could not be attributed to differences in the prevailing plasma concentration of insulin or leucine. Our data demonstrate the sepsis-induced leucine resistance in skeletal muscle results from the cooperative interaction of both TNFalpha and glucocorticoids.

Glucocorticoids and TNFα Interact Cooperatively to Mediate Sepsis-Induced Leucine Resistance in Skeletal Muscle

Sepsis blunts the ability of nutrient signaling by leucine to stimulate skeletal muscle protein synthesis by impairing translation initiation. The present study tested the hypothesis that overproduction of either tumor necrosis factor (TNF)-alpha or glucocorticoids mediate the sepsis-induced leucine resistance. Prior to producing peritonitis, rats received either vehicle, TNF binding protein (TNF(BP)) to inhibit endogenous TNFalpha action, and/or the glucocorticoid receptor antagonist RU486. Leucine was orally administered to all rats 24 h thereafter and the gastrocnemius removed 20 min later to assess protein synthesis and signaling components important in controlling peptide-chain initiation. Muscle protein synthesis was 65% lower in septic rats administered leucine than in leucine-treated control animals. This reduction was not prevented by either TNF(BP) or RU486 alone, but was completely reversed by the combination. This sepsis-induced leucine resistance was associated with an 80% reduction in the amount of active eIF4E.eIF4G complex, a 5-fold increase in the formation of the inactive eIF4E.4E-BP1 complex as well as markedly reduced (at least 70%) phosphorylation of 4E-BP1, eIF4G, S6K1, S6, and mTOR. Pretreatment of septic rats with either TNF(BP) or RU486 individually only nominally improved the leucine action as assessed by the above-mentioned endpoints. In contrast, when TNF(BP) and RU486 were co-administered, the ability of sepsis to impair the leucine-stimulated phosphorylation of 4E-BP1, eIF4G, S6K1, and S6 as well as the redistribution of eIF4E was essentially prevented. No differences in the total amount or phosphorylation of eIF2alpha and eIF2Bepsilon were detected between the different groups, and changes could not be attributed to differences in the prevailing plasma concentration of insulin or leucine. Our data demonstrate the sepsis-induced leucine resistance in skeletal muscle results from the cooperative interaction of both TNFalpha and glucocorticoids.

Hormone, cytokine, and nutritional regulation of sepsis-induced increases in atrogin-1 and MuRF1 in skeletal muscle

Various atrophic stimuli increase two muscle-specific E3 ligases, muscle RING finger 1 (MuRF1) and atrogin-1, and knockout mice for these "atrogenes" display resistance to denervation-induced atrophy. The present study determined whether increased atrogin-1 and MuRF1 mRNA are mediated by overproduction of endogenous glucocorticoids or inflammatory cytokines in adult rats and whether atrogene expression can be downregulated by anabolic agents such as insulin-like growth factor (IGF)-I and the nutrient-signaling amino acid leucine. Both atrogin-1 and MuRF1 mRNA in gastrocnemius was upregulated dose and time dependently by endotoxin. Additionally, peritonitis produced by cecal ligation and puncture increased atrogin-1 and MuRF1 mRNA in gastrocnemius (but not soleus or heart) by 8 h, which was sustained for 72 and 24 h, respectively. Whereas the sepsis-induced increase in atrogin-1 expression was completely prevented by IGF-I, the increased MuRF1 was not altered. In contrast to the IGF-I effect, the sepsis-induced increased mRNA of both atrogenes was unresponsive to either acute or repetitive administration of leucine. Whereas exogenous infusion of TNF-alpha increased atrogin-1 and MuRF1 in gastrocnemius, pretreatment of septic rats with the TNF antagonist TNF-binding protein did not prevent increased expression of either atrogene. Similarly, whereas dexamethasone increased atrogene expression, pretreatment with the glucocorticoid receptor antagonist RU-486 failed to ameliorate the sepsis-induced increase in atrogin-1 and MuRF1. Thus, under in vivo conditions in mature adult rats, the sepsis-induced increase in muscle atrogin-1 and MuRF1 mRNA appears both glucocorticoid and TNF independent and is unresponsive to leucine.

Properties of the recombinant TNF-binding proteins from variola, monkeypox, and cowpox viruses are different

Tumor necrosis factor (TNF), a potent proinflammatory and antiviral cytokine, is a critical extracellular immune regulator targeted by poxviruses through the activity of virus-encoded family of TNF-binding proteins (CrmB, CrmC, CrmD, and CrmE). The only TNF-binding protein from variola virus (VARV), the causative agent of smallpox, infecting exclusively humans, is CrmB. Here we have aligned the amino acid sequences of CrmB proteins from 10 VARV, 14 cowpox virus (CPXV), and 22 monkeypox virus (MPXV) strains. Sequence analyses demonstrated a high homology of these proteins. The regions homologous to cd00185 domain of the TNF receptor family, determining the specificity of ligand–receptor binding, were found in the sequences of CrmB proteins. In addition, a comparative analysis of the C-terminal SECRET domain sequences of CrmB proteins was performed. The differences in the amino acid sequences of these domains characteristic of each particular orthopoxvirus species were detected. It was assumed that the species-specific distinctions between the CrmB proteins might underlie the differences in these physicochemical and biological properties. The individual recombinant proteins VARV-CrmB, MPXV-CrmB, and CPXV-CrmB were synthesized in a baculovirus expression system in insect cells and isolated. Purified VARV-CrmB was detectable as a dimer with a molecular weight of 90 kDa, while MPXV- and CPXV-CrmBs, as monomers when fractioned by non-reducing SDS-PAGE. The CrmB proteins of VARV, MPXV, and CPXV differed in the efficiencies of inhibition of the cytotoxic effects of human, mouse, or rabbit TNFs in L929 mouse fibroblast cell line. Testing of CrmBs in the experimental model of LPS-induced shock using SPF BALB/c mice detected a pronounced protective effect of VARV-CrmB. Thus, our data demonstrated the difference in anti-TNF activities of VARV-, MPXV-, and CPXV-CrmBs and efficiency of VARV-CrmB rather than CPXV- or MPXV-CrmBs against LPS-induced mortality in mice.

Variation in Ligand Binding Specificities of a Novel Class of Poxvirus-encoded Tumor Necrosis Factor-binding Protein

The Yatapoxviruses encode a distinct class of secreted TNF-binding protein (TNF-BP) that resembles an MHC class I heavy chain but distinct from any other known TNF inhibitor. Characterization of these viral TNF inhibitors from Tanapox virus, Yaba monkey tumor virus (YMTV) and a closely related version from Swinepox virus revealed dramatically differential TNF binding specificities for different mammalian species. The Tanapox virus 2L protein (TPV-2L) formed inhibitory complexes with human TNF, and interacted with monkey and canine TNF with high affinity but rabbit TNF with low affinity. On the other hand, YMTV-2L bound human and monkey TNF with high affinity but rabbit TNF with only low affinity. The TNF-BP from swinepox virus (SPV003/148) only interacted with porcine TNF with high affinity. The observed TNF binding analysis mirrored the biological activity of these TNF-binding protein to block TNF-induced cellular cytolysis. TPV-2L and YMTV-2L also inhibited the human TNF-mediated signaling in cells but TPV-2L exhibited higher affinity for human TNF (KD, 43 pm) compared with monkey (KD, 120 pm) whereas for YMTV-2L, the affinities were reversed (human TNF KD, 440 pm; monkey TNF KD, 230 pm). The interaction domain of human TNF with TNF-binding proteins is significantly different from that of TNFRs, as determined using human TNF mutants. We conclude that these poxvirus TNF-binding proteins represent a new class of TNF inhibitors and are distinct from the viral TNF receptor homologues characterized to date.

Onercept for Moderate-to-Severe Crohn’s Disease: A Randomized, Double-Blind, Placebo-Controlled Trial

Onercept is a recombinant, soluble human p55 receptor to tumor necrosis factor-alpha. A randomized, double-blind, placebo-controlled, dose-ranging trial was performed to evaluate the efficacy of onercept induction therapy in patients with Crohn's disease (CD). Patients (n = 207) with moderate-to-severe acute or chronic active CD were randomized to receive subcutaneous onercept (10, 25, 35, or 50 mg) or placebo 3 times weekly for 8 weeks. Primary analysis was induction of remission (defined as a CD activity index score < or = 150) at week 8. A total of 104 patients had acute active CD. Remission rates at week 8 were 23.5% for placebo (n = 17), and 34.8%, 20.0%, 26.1%, and 28.6% for onercept 10 mg (n = 23), 25 mg (n = 20), 35 mg (n = 23), and 50 mg (n = 21), respectively (P = .98). A total of 103 patients had chronic active CD. Remission rates at week 8 were 23.8% for placebo (n = 21), and 23.8%, 9.1%, 35.3%, and 13.6% for onercept 10 mg (n = 21), 25 mg (n = 22), 35 mg (n = 17), and 50 mg (n = 22), respectively (P = .66). There were no differences between treatment groups in the incidence of adverse events. However, mild-to-moderate injection-site reactions occurred in up to 12% of onercept-treated patients. Onercept was well tolerated but was not effective at the doses studied in patients with active CD.

Extracellular TNFR1 Release Requires the Calcium-dependent Formation of a Nucleobindin 2-ARTS-1 Complex

Extracellular tumor necrosis factor (TNF) receptors function as TNF-binding proteins that modulate TNF activity. In human vascular endothelial cells (HUVEC), extracellular TNFR1 (type I TNF receptor, TNFRSF1A) is generated by two mechanisms, proteolytic cleavage of soluble TNFR1 ectodomains and the release of full-length 55-kDa TNFR1 in the membranes of exosome-like vesicles. TNFR1 release from HUVEC is known to involve the association between ARTS-1 (aminopeptidase regulator of TNFR1 shedding), an integral membrane aminopeptidase, and TNFR1. The goal of this study was to identify ARTS-1 binding partners that modulate TNFR1 release to the extracellular space. A yeast two-hybrid screen of a human placenta cDNA library showed that NUCB2 (nucleobindin 2), via its helix-loop-helix domains, binds the ARTS-1 extracellular domain. The association between endogenous ARTS-1 and NUCB2 in HUVEC was demonstrated by co-immunoprecipitation experiments, which showed the formation of a calcium-dependent NUCB2.ARTS-1 complex that associated with a subset of total cellular TNFR1. Confocal microscopy experiments demonstrated that this association involved a distinct population of NUCB2-containing intracytoplasmic vesicles. RNA interference was utilized to specifically knock down NUCB2 and ARTS-1 expression, which demonstrated that both are required for the constitutive release of a full-length 55-kDa TNFR1 within exosome-like vesicles as well as the inducible proteolytic cleavage of soluble TNFR1 ectodomains. We propose that calcium-dependent NUCB2.ARTS-1 complexes, which associate with TNFR1 prior to its commitment to pathways that result in either the constitutive release of TNFR1 exosome-like vesicles or the inducible proteolytic cleavage of TNFR1 ectodomains, play an important role in mediating TNFR1 release to the extracellular compartment.

NUCB2, an ARTS‐1 Interacting and Calcium‐Binding Protein, that Promotes the Extracellular Release of TNFR1

Extracellular tumor necrosis factor (TNF) receptors function as TNF-binding proteins that modulate TNF bioactivity. ARTS-1 (Aminopeptidase Regulator of Type 1 TNF Receptor Shedding), a type II integral membrane protein expressed by human epithelial vascular endothelial (HUVEC) cells, binds to and promotes the release of soluble type I TNF receptors (sTNFR1). A yeast two-hybrid screen, utilizing the ARTS-1 extracellular domain as bait, and co-immunoprecipitation experiments identified the calcium binding protein, NUCB2 (nucleobindin 2), as an ARTS-1 interacting protein. NUCB2-specific siRNA selectively down-regulated NUCB2 mRNA and protein levels in HUVEC cells by 73 and 54%, respectively and resulted in a 73% decrease in constitutive sTNFR1 release into HUVEC culture supernatants over 24 h. IL-1β-stimulated TNFR1 release was decreased by 84% in siRNA-treated HUVEC cells. The intracellular calcium chelator, BAPTA-AM, inhibited the co-immunoprecipitation of NUCB2 and ARTS-1. Ionomycin increased TNFR1 release by 25%, whereas HUVEC treated with the intracellular calcium-depleting agent, thapsigargin reduced TNFR1 release by 49%. These experiments demonstrate that the effects of intracellular calcium are mediated via NUCB2 and both calcium and NUCB2 are required for maximal constitutive TNFR1 release. In conclusion, we have identified NUCB2 as an ARTS-1-interacting protein that promotes the extracellular release of TNFR1. We propose that a calcium-dependent, NUCB2-ARTS-1 complex regulates the intracellular trafficking and the extracellular release of TNFR1. This abstract is funded by: DIR, NHLBI, NIH.