Analysis of the structure-function relationship of tumour necrosis factor. Human/mouse chimeric TNF proteins: general properties and epitope analysis

Molecular cloning and phylogenetic analysis of inflammatory cytokines of the ferret (Mustela putorius furo)

The present study determined the cDNA and deduced amino acid sequences of ferret (Mustela putorius furo) inflammatory cytokines, interferon (IFN)-gamma, interleukin (IL)-1beta, IL-6, IL-8 and tumor necrosis factor (TNF)-alpha. The homologies of the nucleotide sequences of IFN-gamma, IL-1beta, IL-6, IL-8 and TNF-alpha of the ferret to those from other mammalian species ranged from 64.3-92.9%, 73.0-83.9, 58.1-84.8%, 58.1-89.7% and 79.0-95.0%, respectively. As distinctive amino acid residues constituting various motifs and ligand-binding sites and cysteine residues were highly conserved in ferret inflammatory cytokine proteins, ferret cytokines may have fundamentally similar functions to those of other mammals. Phylogenetic analyses based on the deduced amino acid sequences revealed that all ferret inflammatory cytokines were more closely related to those of the Carnivora order, specifically dog and cat, than to other species.

Comparative analyses of complex formation and binding sites between human tumor necrosis factor-alpha and its three antagonists elucidate their different neutralizing mechanisms

Tumor necrosis factor-alpha (TNFalpha)-blocking therapy, using biologic TNFalpha antagonists, has been approved for the treatment of several diseases including rheumatoid arthritis, psoriasis and Crohn's disease. There have been few detailed studies of binding characterizations for the complex formation by TNFalpha and clinically relevant antagonists, particularly Infliximab (Remicade) and Etanercept (Enbrel). Here we characterized the binding stoichiometry and size of soluble TNFalpha-antagonist complexes and identified energetically important binding sites on TNFalpha for the three antagonists, Etanercept, Infliximab, and the recently developed humanized TNFalpha neutralizing monoclonal antibody, YHB1411-2. Size-exclusion chromatography and dynamic light scattering analyses revealed that the three antagonists formed distinct thermodynamically stable TNFalpha-antagonist complexes that exhibited differences in their size and composition. Energetically important binding residues on TNFalpha were identified for each antagonist by a sequence of experiments that consisted of competition binding assays, fragmentations, loop mutations, and single-point mutations using yeast surface-displayed TNFalpha, which was further confirmed for solubly purified TNFalpha mutants by surface plasmon resonance technique. Analyses of the binding geometry based on binding site location, spatial constraints, and valency satisfaction allowed us to interpret the thermodynamically stable complexes as follows: one molecule of Etanercept and one molecule of trimeric TNFalpha (Etanercept1-TNFalpha1), Infliximab6-TNFalpha3, and YHB1411-2(4)-TNFalpha2. The distinct features of the soluble antagonist-TNFalpha complex formation among the antagonists may give further insights into their different neutralizing mechanisms and pharmacokinetic profiles.

Characterization of the interaction between murine tumour necrosis factor and monoclonal antibodies

We characterized the interaction between murine TNF (mTNF) and the neutralizing monoclonal antibodies TN3 and 1F3F3. The epitopes were localized by comparing the detection efficiency for a panel of TNF chimaeric proteins and site-specific muteins in ELISA. Mutation of mTNF amino acid Q131 inhibited the interaction with 1F3F3, whereas mutation of D71/Y72 inhibited the binding to TN3. As D71/Y72 are located in an exposed loop near the TNF intersubunit groove, binding of TN3 promoted the dissociation and/or interfered with the reassociation of subunits into mTNF trimers. 1F3F3, on the other hand, prevented the spontaneous dissociation of bound (hetero)trimeric mTNF.

Identification of tumor necrosis factor (TNF) amino acids crucial for binding to the murine p75 TNF receptor and construction of receptor-selective mutants

The bioactivity of tumor necrosis factor (TNF) is mediated by two TNF receptors (TNF-Rs), more particularly TNF-RI and TNF-RII. Although human TNF (hTNF) and murine TNF (mTNF) are very homologous, hTNF binds only to mTNF-RI. By measuring the binding of a panel of mTNF/hTNF chimeras to both mTNF-R, we pinpointed the TNF region that mediates the interaction with mTNF-RII. Using site-specific mutagenesis, we identified amino acids 71-73 and 89 as the main interacting residues. Mutein hTNF-S71D/T72Y/H73 Delta/T89E interacts with both types of mTNF-R and is active in CT6 cell proliferation assays mediated by mTNF-RII. Mutein mTNF-D71S/Y72T/Delta 73H/E89T binds to mTNF-RI only and is no longer active on CT6 cells. However, the L929s cytotoxicity of this mutein (an effect mediated by mTNF-RI triggering) was also 100-fold lower than that of wild-type mTNF due to enhanced dissociation during incubation at subnanomolar concentrations. The additional mutation of amino acid 102, resulting in the mutein mTNF-D71S/Y72T/Delta 73H/E89T/P102Q, restored the trimer stability, which led to an enhanced specific activity on L929s cells. Hence the specific activity of a TNF species is governed not only by its receptor binding characteristics but also by its trimer stability after incubation at subnanomolar concentrations. In conclusion, the mutation of TNF amino acids 71-73, 89, and 102 is sufficient to obtain a mTNF mutein selective for mTNF-RI and a hTNF mutein that, unlike wild-type hTNF, also acts on mTNF-RII.

Molecular cloning and functional characterization of bottlenose dolphin (Tursiops truncatus) tumor necrosis factor alpha

Bottlenose dolphin tumor necrosis factor alpha (doTNF-alpha) cDNA was cloned by reverse transcription polymerase chain reaction (RT-PCR) and the nucleic and deduced amino acid sequences were determined. The sequence of the cDNA clones shows that doTNF-alpha has an open reading frame of 699bp encoding 233 amino acids. The nucleic acid sequence of doTNF-alpha indicates 90, 88, 87, and 79% similarity with the cattle, pig, human, and mouse TNF-alpha gene, respectively. Based on the analysis of human and mouse TNF-alpha molecules, doTNF-alpha is processed to a mature protein with 157 amino acids. The 233 amino acids precursor has a hydrophobic region that could serve as a transmembrane domain. The recombinant doTNF-alpha expressed in Escherichia coli as a glutathione S-transferase fusion protein reacted with anti-human TNF-alpha antibody and exerted cytotoxity to the TNF-alpha sensitive murine cell line L929.

Heterotrimers Formed by Tumor Necrosis Factors of Different Species or Muteins

Incubation of murine tumor necrosis factor (mTNF) at subnanomolar concentrations results in partial dissociation of the trimers, coinciding with a decrease in bioactivity. Using size-exclusion chromatography, we observed that the conversion of labeled mTNF to monomers is not only prevented by coincubation with an excess of unlabeled mTNF but also with unlabeled human TNF (hTNF). Moreover, after coincubation of mTNF and hTNF four different TNF complexes were revealed by native polyacrylamide gel electrophoresis, viz. homotrimeric mTNF and hTNF, as well as two complexes with an intermediate migration pattern. Analytical gel filtration in combination with native polyacrylamide gel electrophoresis and Western blot immunodetection indicated that these new complexes consisted of heterotrimeric TNF molecules. We conclude that an exchange of monomers takes place during coincubation of two different species of TNF, which results in homotrimeric and heterotrimeric TNF. To assess receptor interaction in vitro, TNF heterotrimeric molecules were used as obtained after incubation of mTNF with labeled hTNF (which only binds to mTNF receptor I) or with labeled mutein mTNF75 (specific for mTNF receptor II). These heterotrimers were retained by both mTNF receptors, which means that the mTNF subunits incorporated in heterotrimeric complexes still can bind to both types of TNF receptor. In addition, the gradual decrease in mTNF bioactivity during preincubation at subnanomolar concentrations was prevented by the presence of mutein mTNF75, which is inactive in an L929 cytotoxicity assay, indicating that heterotrimerization can influence the overall bioactivity.

A neutralizing monoclonal antibody specific for the dimer interface region of IL-8

We have generated two mAbs, 6G4.2.5 and A5.12.14, that are similarly capable of neutralizing the biologic activity of wild-type IL-8. To characterize these antibodies further, their reactivity against a series of engineered IL-8 monomer and dimer variants was examined using a neutrophil degranulation assay. While 6G4.2.5 was found to block effectively the biologic activity of all variants regardless of their dimerization status, the results for A5.12.14 differed dramatically. A5.12.14 fully inhibited the agonist activity of one of the monomer variants, partially blocked the activity of another, and had no effect on the activity of two other variants. These results suggested that the binding epitope of A5.12.14 was being affected by the particular amino acid substitutions introduced into the dimer interface region of the variants to disfavor dimerization. If A5.12.14 indeed binds to the dimer interface region of IL-8, it could be predicted that this mAb would be unable to inhibit the activity of dimeric IL-8. This was confirmed in studies which showed that A5.12.14 had no demonstrable effect on the activity of a constitutively dimeric IL-8 variant. These studies represent the first example of a mAb specific for the dimerization status of IL-8.

Generation and biological characterization of membrane-bound, uncleavable murine tumor necrosis factor

Tumor necrosis factor (TNF) is produced as a membrane-bound, 26-kDa proform from which the mature, 17-kDa TNF subunit is released by proteolytic cleavage. In order to compare the biological activity of membrane-bound versus soluble TNF, mutational analysis of potential cleavage sites in murine TNF was carried out. The biological activity was assessed after transfection in L929 cells. Deletion of the first nine codons of the mature part of the murine TNF gene still led to the production of secretable TNF, indicating alternative cleavage sites separate from the -1/+1 junction. However, an additional deletion of 3 amino acids, generating TNF delta 1-12, resulted in a membrane-bound form of TNF. Site-directed mutagenesis revealed Lys11 as the critical residue for alternative cleavage. Mutation of this residue to Glu in a TNF delta 1-9 mutant gave rise to uncleavable, membrane-bound TNF with biological activities similar to wild-type TNF. Induction of apoptosis, proliferation, or cytokine production by triggering of either 55-kDa or 75-kDa TNF receptors in appropriate cell lines occurred efficiently both with soluble and with membrane-bound TNF. The latter was, however, less active in the cytotoxic assays on U937 cells in which the 75-kDa TNF receptor is not signaling, but contributes to maximal TNF activity by ligand passing. This indicates that membrane-bound TNF cannot be passed from the 75-kDa to the 55-kDa TNF receptor.

Efficient secretion of biologically active mouse tumor necrosis factor alpha by Streptomyces lividans

We have studied the production of mouse tumor necrosis factor alpha (mTNF) with Streptomyces lividans as host. mTNF cDNA was fused to the alpha-amylase-encoding gene (aml) of Streptomyces venezuelae ATCC15068 at 12 amino acids (aa) downstream from the signal-peptidase cleavage site so that the aa surrounding this processing site were conserved. S. lividans containing this construct secreted mTNF at moderately high levels (1-10 micrograms/ml) as a biologically active compound of high specific activity (1 x 10(8) units/mg protein). No unprocessed pre-protein and virtually no processed protein could be detected in the cell lysates. N-terminal aa sequence analysis indicated microheterogeneity (-3 to -6 forms) at the N-terminal site of secreted mTNF. It was demonstrated that this microheterogeneity was due to aminopeptidase activity.

Human tumor necrosis factor mutants with preferential binding to and activity on either the R55 or R75 receptor

Previously, we reported that the cytotoxic activity of human (h) tumor necrosis factor (TNF) on murine (m) L929 cells requires the integrity of three loops (positions 30-36, 84-88 and 138-150) which cluster around the interface between each two subunits of the trimeric hTNF structure. The collection of hTNF mutants was further characterized by their activity on various human cell systems as well as by their binding to the two types of hTNF receptor (R), R55 and R75. It turned out that two amino acids (Leu29 and Arg32) were specifically involved in hR75 binding, as Leu29-->Ser (L29S) and Arg32-->Trp (R32W) mutant molecules had largely lost binding to hR75, but not to hR55. In order to screen for more highly R55-specific mutants, nine other amino acids were inserted at these two positions; only the substitutions L29G and L29Y showed an increased differential binding as compared to L29S, while no further improvement was found with mutations at position 32 compared to R32W. Biological assays mediated either by hR55 or hR75 confirmed the results obtained by physical binding to purified receptors. A similar substitution in mTNF, Arg32-->Tyr, also resulted in a preferential loss of binding to hR75 and a large decrease in mR75-mediated bioactivity. Except for the double mutant L29S-R32W, all other tested amino acid substitutions in the loops at positions 30-36 or 84-88 of hTNF led to a substantial loss of affinity for both receptors and a concomitant reduction of biological activity. In the loop at positions 138-150, the non-conservative replacement of Glu by Lys at position 146 (E146K) resulted in an even lower binding to R75 as compared to R32W, while binding on and bioactivity through R55 was only slightly reduced. Remarkably, a reversed differential binding was observed after substitution at position 143 in hTNF; replacing Asp by non-conservative residues such as Tyr, Phe or Asn resulted in a much larger decrease in binding to R55 than to R75. In conclusion, receptor-specific mutants such as R32W, E146K and D143N can be used to study the function either of R55 or R75 on different human cell types. In vivo, we presume that the R55-specific mutants will retain antitumor activity in the absence of R75-dependent, severe side effects.

High-resolution mapping of the HyHEL-10 epitope of chicken lysozyme by site-directed mutagenesis

The complex formed between hen egg white lysozyme (HEL) and the monoclonal antibody HyHEL-10 Fab fragment has an interface composed of van der Waals interactions, hydrogen bonds, and a single ion pair. The antibody overlaps part of the active site cleft. Putative critical residues within the epitope region of HEL, identified from the x-ray crystallographic structure of the complex, were replaced by site-directed mutagenesis to probe their relative importance in determining affinity of the antibody for HEL. Twenty single mutations of HEL at three contact residues (Arg-21HEL, Asp-101HEL, and Gly-102HEL) and at a partially buried residue (Asn-19HEL) in the epitope were made, and the effects on the free energies of dissociation were measured. A correlation between increased amino acid side-chain volume and reduced affinity for HELs with mutations at position 101 was observed. The D101GHEL mutant is bound to HyHEL-10 as tightly as wild-type enzyme, but the delta delta Gdissoc is increased by about 2.2 kcal (9.2 kJ)/mol for the larger residues in this position. HEL variants with lysine or histidine replacements for arginine at position 21 are bound 1.4-2.7 times more tightly than those with neutral or negatively charged amino acids in this position. These exhibit 1/40 the affinity for HyHEL-10 Fab compared with wild type. There is no side-chain volume correlation with delta delta Gdissoc at position 21. Although Gly-102HEL and Asn-19HEL are in the epitope, replacements at these positions have no effect on the affinity of HEL for the antibody.

Tumor necrosis factor activities and cancer therapy--a perspective

Tumor necrosis factor (TNF) is a multifunctional cytokine which has excited and fascinated numerous investigators and commercial entities due to its promise as a therapeutic agent against cancer and as a target for drugs treating septic shock. TNF is a protein having cytotoxic, cytostatic, immunomodulatory as well as several other activities and is also involved in septic shock. This review covers the structure of TNF and its receptors, various in vitro activities and in vivo activities based on studies in animal model systems. The role of TNF as an anticancer therapeutic agent, based on various phase I and phase II clinical studies, has also been considered. The review concludes with several considerations for increasing the therapeutic utility of TNF in terms of targeting, toxicity and half-life.

The molecular action of tumor necrosis factor-alpha

Tumor necrosis factor-alpha (TNF-alpha) is a polypeptide hormone newly synthesized by different cell types upon stimulation with endotoxin, inflammatory mediators (C5a anaphylatoxin), or cytokines such as interleukin-1 and, in an autocrine manner, TNF itself. The net biological effect of TNF-alpha may vary depending on relative concentration, duration of cell exposure and presence of other mediators which may act in synergism with this cytokine. TNF-alpha may be relevant either in pathological events occurring in cachexia and endotoxic shock and inflammation or in beneficial processes such as host defense, immunity and tissue homeostasis. The biological effects of TNF-alpha are triggered by the binding to specific cell surface receptors. The formation of TNF-alpha-receptor complex activates a variety of biochemical pathways that include the transduction of the signal at least in part controlled by guanine-nucleotide-binding regulatory proteins (G proteins), its amplification through activation of adenyl cyclase, phospholipases and protein kinases with the generation of second messenger pathways. The transduction of selected genes in different cell types determines the characteristics of the cell response to TNF-alpha. The full understanding of the molecular mechanisms of TNF-alpha will provide the basis for a pharmacological approach intended to inhibit or potentiate selected biological actions of this cytokine.