Changes in the dimeric state of neuronal nitric oxide synthase affect the kinetics of secretagogue-induced insulin response

We previously showed that pancreatic beta-cells express a neuronal isoform of nitric oxide synthase (nNOS) that controls insulin secretion by exerting two enzymatic activities: nitric oxide (NO) production and cytochrome c reductase activity. We now bring evidence that two inhibitors of nNOS, N-omega-nitro-l-arginine methyl ester (l-NAME) and 7-nitroindazole (7-NI), increase glucose-induced insulin secretion but affect beta-cell function differently. In the presence of l-NAME, insulin response is monophasic, whereas 7-NI preserves the normal biphasic secretory pattern. In addition, the alterations of beta-cell functional response induced by the inhibitors also differ by their sensitivity to a substitutive treatment with sodium nitroprusside, a chemical NO donor. These differences are probably related to the nature of the two inhibitors. Indeed, using low-temperature SDS-PAGE and real-time analysis of nNOS dimerization by surface plasmon resonance, we could show that 7-NI, which competes with arginine and tetrahydrobiopterin (BH(4)), an essential cofactor for nNOS dimer formation, inhibits dimerization of the enzyme, whereas the substrate-based inhibitor l-NAME stabilizes the homodimeric state of nNOS. The latter effect could be reproduced by the two endogenous inhibitors of NOS, N-omega-methyl-l-arginine and asymmetric dimethylarginine, and resulted interestingly in a reduced ability of the protein inhibitor of nNOS (PIN) to dissociate nNOS dimers. We conclude that intracellular factors able to induce abnormalities in the nNOS monomer/dimer equilibrium could lead to pancreatic beta-cell dysfunction.

Monoclonal antibody 667 recognizes the variable region A motif of the ecotropic retrovirus CasBrE envelope glycoprotein and inhibits Env binding to the viral receptor

Monoclonal antibody (MAb) 667 is a neutralizing mouse monoclonal antibody recognizing the envelope glycoprotein (Env) of the ecotropic neurotropic murine retrovirus CasBrE but not that of other murine retroviruses. Since 667 can be used for preclinical studies of antiviral gene therapy as well as for studying the early events of retroviral infection, we have cloned its cDNAs and molecularly characterized it in detail. Spot technique-based experiments showed that 667 recognizes a linear epitope of 12 amino acids located in the variable region A of the receptor binding domain. Alanine scanning experiments showed that six amino acids within the epitope are critical for MAb binding. One of them, D(57), is not present in any other murine retroviral Env, which suggests a critical role for this residue in the selectivity of 667. MAb 667 heavy- and light-chain cDNAs were functionally characterized by transient transfection into Cos-7 cells. Enzyme-linked immunosorbent assays and Biacore studies showed that the specificities as well as the antigen-binding thermodynamic and kinetic properties of the recombinant 667 MAb (r667) produced by Cos-7 cells and those of the parental hybridoma-produced MAb (h667) were similar. However, h667 was shown to contain contaminating retroviral and/or retrovirus-like particles which interfere with both viral binding and neutralization experiments. These contaminants could successfully be removed by a stringent purification protocol. Importantly, this purified 667 could completely prevent retrovirus binding to target cells and was as efficient as the r667 MAb produced by transfected Cos-7 cells in neutralization assays. In conclusion, this study shows that the primary mechanism of virus neutralization by MAb 667 is the blocking of the retroviral receptor binding domain of CasBrE Env. In addition, the findings of this study constitute a warning against the direct use of hybridoma cell culture supernatants for studying the initial events of retroviral cell infection as well as for carrying out in vivo neutralization experiments and suggest that either recombinant antibodies or highly purified antibodies are preferable for these purposes.

A peptide mimetic of an anti-CD4 monoclonal antibody by rational design

The development of rational methods to design 'continuous' sequence mimetics of discontinuous regions of protein sequence has, to now, been only marginally successful. This has been largely due to the difficulty of constraining the recognition elements of a mimetic structure to the relative conformational and spatial orientations present in the parent molecule. Using peptide mapping to determine 'active' antigen recognition residues, molecular modeling, and a molecular dynamics trajectory analysis, we have developed a peptide mimic of an anti-CD4 antibody, containing antigen contact residues from multiple CDRs. The design described is a 27-residue peptide formed by juxtaposition of residues from 5 CDR regions. It displays an affinity for the antigen (CD4) of 0.9nM, compared to 2nM for the parent antibody ST40. Nevertheless, the mimetic shows low biological activity in an anti-retroviral assay.

Targeting of human breast cancer by a bispecific antibody directed against two tumour-associated antigens: ErbB-2 and carcinoembryonic antigen

Carcinoembryonic antigen (CEA) and ErbB-2 are expressed in about 50 and 30% of breast cancers, respectively. We hypothesised that targeting of these two antigens by a bispecific antibody (BAb) might provide efficient tumour uptake and prolonged tumour residence time. In the present study, we first studied the expression of CEA and ErbB-2 on primary breast tumours screened by immunohistochemistry. Of 106 primary breast cancers, 69 (65%) were positive for CEA, 20 (19%) were positive for ErbB-2, and 13 (12%) expressed both antigens. We then prepared and evaluated a BAb directed against CEA and ErbB-2. Using BIACORE technology, we showed that the BAb recognised both CEA and ErbB-2 with affinities of 0.9 x 10 and 0.8 x 10 M(-1), respectively. In vivo, BAb tumour localisation was compared with that of its parental homodimeric F(ab')(2)-ORTHO-phenylene- dimaleimide (PDM) fragments. Uptake of (125)I-BAb was lower than that of (131)I-35A7F(ab')(2)-PDM in LS174T tumours, used as a model of CEA expressing tumours, and was similar to that of (131)I-FWP51 F(ab')(2)-PDM in SKOv3 tumours, used as a model of ErbB-2 expressing tumours. In a double-positive model, the SKOv3-CEA-1B9 tumour, BAb showed a similar uptake to that of 35A7 F(ab')(2)-PDM and we demonstrated that, although BAb had double specificity, it internalised as a homodimeric anti-ErbB-2 antibody. BAb showed a greater uptake than that of FWP51 F(ab')(2)-PDM and this difference was even more important 72 h after injection with an uptake of 7.3 +/- 2.1 vs. 1.4 +/- 0.5% of the injected dose per gram of tissue. The results obtained with the BAb in the double-positive tumour-bearing nude mice suggest that targeting two distinct tumour-associated antigens on the same cell could improve tumour localisation.

Casein interactions studied by the surface plasmon resonance technique

Surface plasmon resonance technique was investigated for the first time to study the apparent hydrophobicity and association properties of the major bovine caseins: alpha(s)-(alpha(s1)- and alpha(s2)-caseins in a 4:1 proportion), beta-, and kappa-caseins. The apparent hydrophobicities of the caseins were evaluated by a new method based on the binding level of casein on a hydrophobic sensor chip, and kinetic and equilibrium affinity constants were determined for the following casein interactions: alpha(s)/alpha(s), alpha(s)/beta, alpha(s)/kappa, beta/beta, and beta/kappa, using a sensor chip modified with covalent immobilized caseins. The study by surface plasmon resonance technology of these casein interactions under different conditions (pH, ionic strength, calcium concentration, chemical modification) demonstrated that, at neutral pH, electrostatic repulsive forces play an important role since an increase in ionic strength of the medium resulted in a stronger interaction. When charge repulsions were reduced by either acidification, increase in ionic strength, or dephosphorylation, casein interactions were reinforced, presumably due to weak attractive forces. Moreover, in this molecular model, we showed that addition of calcium greatly increased the binding response between the most phosphorylated caseins and that the added calcium (2 mM) participated directly in the formation of bridges between the phosphate groups of the casein molecules.

Study of disabling T-cell activation and inhibiting T-cell-mediated immunopathology reveals a possible inverse agonist activity of CD4 peptidomimetics

We designed a new class of aromatically modified exocyclic peptides based on the structure of CD4 by engineering one of the cysteine residues in a peptidomimetic derived from the CDR3 region of the CD4 molecule. All three species mediate inhibition of T-cell proliferation at concentrations ranging from 10 to 100 microM. The mimetics CD4-Cys and CD4-Met bind to sCD4 with affinities ranging from 1 to 2 microM, while CD4-Ser shows poor binding in radioisotope assay. Though these mimetics have similar structures, they exhibit different biochemical and biological functions. Activation of T-cells as measured by thymidine incorporation or IL-2 production revealed that CD4-Cys and CD4-Ser mimetics behave as classical antagonists. On the other hand, the CD4-Met species inhibited T-cell proliferation with an IC(50) of 30 microM but unexpectedly increased IL-2 secretion modestly at a less than 3 microM concentration. In experimental autoimmune encephalitis (EAE), CD4-Ser and CD4-Cys mimetics reduced the severity of EAE symptoms while the CD4-Met mimetic exacerbated the conditions. We propose that CD4-Cys and CD4-Ser are classical antagonists, but CD4-Met may possess properties of an inverse agonist. The structure-activity relationship of mimetics reveals that a minor change in the net hydropathic value is enough to alter the dynamic nature of the receptor-ligand complex.

Does fusion of domains from unrelated proteins affect their folding pathways and the structural changes involved in their function? A case study with the diphtheria toxin T domain

We investigated whether the structural and functional behaviors of two unrelated protein domains were modified when fused. The IgG-binding protein ZZ derived from staphylococcal protein A was fused to the N- and/or C-terminus of the diphtheria toxin transmembrane domain (T). T undergoes a conformational change from a soluble native state at neutral pH to a molten globule-like state at acidic pH, leading to its interaction with membranes. We found that this molten globule state was not connected to the GdnHCl-induced unfolding pathway of T. The pH-induced transition of T, and also the unfolding of T and ZZ at neutral and acidic pH, were unchanged whether the domains were isolated or fused. The position of ZZ, however, influenced the solubility of T near its pK(i). SPR measurements revealed that T has a high affinity for membranes, isolated or within the fusion proteins (K(D)< 10(-11) M). This work shows that in the case of T and ZZ, the fusion of protein domains with different stabilities does not alter the structural changes involved in folding and function. This supports the use of T as a soluble membrane anchor.

Pertinence of kappa and lambda recombinant antibodies directed against thyroid peroxidase in thyroid autoimmune disease

Forty-one single-chain variable region fragments (scFvs) directed against thyroid peroxidase (TPO) were obtained by phage display libraries constructed from thyroid-infiltrating B cells of Graves' disease patients. Among these scFvs, 24.4% used a Vkappa light chain whereas 75.6% shows a light chain of Vlamda origin. Study of light chain gene usage in the TPO antibody repertoire demonstrated a dominance of the Vkappa 1-39 and Vlambda 1-51 genes. Thyroid peroxidase probing of overlapping peptides covering the amino acid sequences of anti-TPO T2/kappa and T13/lambda variable regions demonstrated a more restricted antigen recognition on T13/lambda than on T2/kappa. These two recombinant antibodies, expressed as whole IgG1 in the baculovirus/insect cell system, inhibited the binding to TPO of serum TPO autoantibodies whatever the light chain. Our study indicates that lambda as well as kappa light chain usage are found in the TPO antibody repertoire of thyroid-infiltrating B cells and are pertinent in the pathogenesis of autoimmune thyroid disease.

Intracellular distribution of viral gene products regulates a complex mechanism of cauliflower mosaic virus acquisition by its aphid vector

Interactions between Cauliflower mosaic virus (CaMV) and its aphid vector are regulated by the viral protein P2, which binds to the aphid stylets, and protein P3, which bridges P2 and virions. By using baculovirus expression of P2 and P3, electron microscopy, surface plasmon resonance, affinity chromatography, and transmission assays, we demonstrate that P3 must be previously bound to virions in order that attachment to P2 will allow aphid transmission of CaMV. We also show that a P2:P3 complex exists in the absence of virions but is nonfunctional in transmission. Hence, unlike P2, P3 and virions cannot be sequentially acquired by the vector. Immunogold labeling revealed the predominance of spatially separated P2:P3 and P3:virion complexes in infected plant cells. This specific distribution indicates that the transmissible complex, P2:P3:virion, does not form primarily in infected plants but in aphids. A model, describing the regulating role of P3 in the formation of the transmissible CaMV complex in planta and during acquisition by aphids, is presented, and its consequences are discussed.

Functional specific binding of testosterone to Schistosoma haematobium 28-kilodalton glutathione S-transferase

During parasitic disease such as schistosomiasis, sex hormones have an important influence on the age- and gender-dependent level of infection. Since mammal glutathione S-transferase (GST) has the ability to bind hormones and particularly sexual steroids to influence their transport, metabolism, and physiological action, we have evaluated the capacity of testosterone to bind the 28-kDa GST of the Schistosoma haematobium parasite (Sh28GST). For the first time, we have demonstrated a specific binding of testosterone to parasite GST protein with high affinity (K(d) = 2.57 x 10(-7) M). In addition, we have assessed the effect of this binding on Sh28GST enzymatic activity, a mechanism closely associated with the reduction of Schistosoma fecundity. We showed that testosterone has the functional ability to inhibit the Sh28GST enzymatic activity in a dose-dependent manner, suggesting that this hormone could be directly involved in an antifecundity mechanism. This effect seemed to be related to the binding of testosterone to one peptide involved in the enzymatic site (i.e., amino acids 24 to 43). During human infection, binding of sexual hormones to Schistosoma Sh28GST could play a key role in parasite metabolism, especially the decrease of fecundity, and could be involved in the sex-dependent immune response to Sh28GST that we have previously observed in infected adults.

Characterization of monoclonal antibodies against Escherichia coli core RNA polymerase

Multiple interactions with DNA, RNA and transcription factors occur in a transcription cycle. To survey the proximity of some of these factors to the Escherichia coli RNA polymerase surface, we produced a set of nine monoclonal antibodies (mAbs) against the enzyme. These mAbs, located at different places on the surface of the enzyme, were used in a co-immunopurification assay to investigate interference with the binding of NusA, sigma70, GreB and HepA to core RNA polymerase. One of these mAbs turned out to be the first antibody inhibitor of the binding of NusA and sigma70; it did not affect GreB and HepA interactions. Its epitope was located on the beta' subunit at the C-terminus of region G. The properties of this mAb reinforce the idea that the mutually exclusive binding of NusA and sigma70 to core RNA polymerase is due to, at least partially, overlapping binding sites, rather than allosteric interaction between two distant binding sites. This mAb is also useful to understand the occupancy of sigma70, NusA and Gre proteins on core RNA polymerase.

The chimeric mouse-human anti-CD4 Fab 13B8.2 expressed in baculovirus inhibits both antigen presentation and HIV-1 promoter activation

The anti-CD4 mAb 13B8.2, directed against the CDR3-like loop of the D1 domain of CD4, inhibits signal transduction pathways leading to both T cell activation and HIV replication. VH9/DSP2/JH2 and Vkappa12-13/Jkappa2 rearrangements, corresponding to genes encoding the heavy and light chain variable regions of the 13B8.2 mAb, were inserted into baculovirus cassettes upstream from pre-installed human Fdgamma1 and Ckappa genes, respectively. After expression in insect cells, a complete correctly-processed Fab was secreted into the culture medium; it was protein-G immunopurified with a yield of 5 mg/L. The chimeric Fab 13B8.2 showed anti-CD4 binding activity with an affinity value of 3.3 nM and recognized the same region on the CDR3-like loop as the parental mAb. The mouse-human Fab inhibited IL2 secretion following antigen presentation and displayed a strong capacity to prevent HIV-1 promoter activation. Taken together, these results indicate that the chimeric Fab retained a major part of the parental 13B8.2 mAb properties and suggest that it might be a valuable therapeutic tool.

Thyroid peroxidase autoantibodies obtained from random single chain FV libraries contain the same heavy/light chain combinations as occur in vivo

Three combinatorial libraries were constructed from unpurified, CD19(+), and antithyroid peroxidase (anti-TPO) B cells extracted from thyroid tissue of Graves' disease patients. Fifteen of the 41 randomly derived anti-TPO single chain variable region fragments (scFvs), showed VH1-3/V lambda 1-51 or VH1-69/V lambda 1-40 heavy/light chain pairing similar to that obtained with TPO-specific scFv derived from an in-cell library. One VH1-3/V lambda 1-51 scFv, A16, showed exactly the same nucleotide sequence as in-cell scFv ICB7, demonstrating that in vivo rearrangement can be obtained from a random combinatorial library. The majority of the scFvs used a heavy chain gene derived from the VH1-3 gene segment, whereas the light chain gene segments used were more heterogeneous, with dominance of the V kappa 1-39 and V lambda 1-51 gene segments. The anti-TPO scFvs showed high affinities to TPO, with values between 0.77 and 12.3 nM, and defined seven antigenic regions on the TPO molecule. The anti-TPO fragments, particularly VH1-3/V lambda 1-51 randomly associated scFv B4, which mimic natural H/L pairing, and VH1-3/V lambda 1-40 in-cell-derived scFv ICA5, efficiently displaced the TPO binding of serum autoantibodies from 20 Graves' disease patients. Our study directly demonstrates that antibodies derived from combinatorial libraries are likely to represent in vivo pairing, leading to high affinity antibody fragments mimicking the binding of serum autoantibodies to TPO.

Interaction of the octapeptide angiotensin II with a high-affinity single-chain Fv and with peptides derived from the antibody paratope

The amino-acid sequence of the very high-affinity anti-angiotensin II monoclonal antibody 4D8 was predicted from the nucleotide sequence of the heavy and light chain variable genes. The single-chain variable fragment (scFv) was constructed and expressed in Escherichia coli as a soluble protein and at the surface of the filamentous M13 phage and was compared with the full-length antibody (Ab). The scFv showed the same specificity profile and affinity constant as the intact antibody (5.0x10(10) and 8.0x10(10) M(-1), respectively, by Scatchard analysis). Several peptides from the set of overlapping dodecapeptides covering the variable domains of 4D8 mAb were found to specifically bind biotinylated angiotensin II: peptides from the L1, L2, L3 and H1 regions had the strongest capacity to bind the antigen.

Study of hydrophobic interactions between acylated proteins and phospholipid bilayers using BIACORE

Intracellular proteins of eukaryotic cells are frequently covalently modified by the addition of long chain fatty acids. These modifications are thought to allow otherwise soluble proteins to associate with membranes by lipid-lipid based hydrophobic interactions. The purpose of this work was to quantify the effect of acyl chain length on hydrophobic interactions between acylated proteins and phospholipid monolayers. The binding of an artificially acylated model protein to electrically neutral phospholipids was studied by surface plasmon resonance, using BIACORE. Kinetic rates for the binding of bovine pancreatic ribonuclease A (RNase A), monoacylated on its N-terminal lysine with fatty acids of 10, 12, 14, 16 or 18 carbon atoms, to phospholipids on hydrophobic sensor chips, were measured. Unlike unmodified ribonuclease, acylated RNase A bound to the phospholipids, and the association level increased with the acyl chain length to reach a maximum for C16. Reproducible kinetics were obtained which did not fit a 1:1 Langmuir model but rather a two-step binding profile.

Streptabody, a high avidity molecule made by tetramerization of in vivo biotinylated, phage display-selected scFv fragments on streptavidin

Phage display is a powerful method of isolating of antibody fragments from highly diverse naive human antibody repertoires. However, the affinity of the selected antibodies is usually low and current methods of affinity maturation are complex and time-consuming. In this paper, we describe an easy way to increase the functional affinity (avidity) of single chain variable fragments (scFvs) by tetramerization on streptavidin, following their site-specific biotinylation by the enzyme BirA. Expression vectors have been constructed that enable addition of the 15 amino acid biotin acceptor domain (BAD) on selected scFvs. Different domains were cloned at the C-terminus of scFv in the following order: a semi-rigid hinge region (of 16 residues), the BAD, and a histidine tail. Two such recombinant scFvs directed against the carcinoembryonic antigen (CEA) were previously selected from human non-immune and murine immune phage display libraries. The scFvs were first synthesized in Escherichia coli carrying the plasmid encoding the BirA enzyme, and then purified from the cytoplasmic extracts by Ni-NTA affinity chromatography. Purified biotinylated scFvs were tetramerized on the streptavidin molecule to create a streptabody (StAb). The avidity of various forms of anti-CEA StAbs, tested on purified CEA by competitive assays and surface plasmon resonance showed an increase of more than one log, as compared with the scFv monomer counterparts. Furthermore, the percentage of direct binding of 125I-labeled StAb or monomeric scFv on CEA-Sepharose beads and on CEA-expressing cells showed a dramatic increase for the tetramerized scFv (>80%), as compared with the monomeric scFv (<20%). Interestingly, the percentage binding of 125I-labeled anti-CEA StAbs to CEA-expressing colon carcinoma cells was definitely higher (>80%) than that obtained with a reference high affinity murine anti-CEA mAb (30%). Another advantage of using scFvs in a StAb format was demonstrated by Western blot analysis, where tetramerized anti-CEA scFv could detect a small quantity of CEA at a concentration 100-fold lower than the monomeric scFv.

Critical residues of epitopes recognized by several anti-p53 monoclonal antibodies correspond to key residues of p53 involved in interactions with the mdm2 protein

The aim of this work was to study the reactivity of antibodies directed against the N-terminus of p53 protein. First, we analysed the cross-reactivity of anti-p53 antibodies from human, mouse and rabbit sera with peptides derived from human, mouse and Xenopus p53. Next, we characterized more precisely a series of monoclonal antibodies directed against the N-terminal part of p53 and produced by immunizing mice with either full length human or Xenopus p53. For each of these mAbs we localized the epitope recognized on human p53 by the Spot method of multiple peptide synthesis, defined critical residues on p53 involved in the interaction by alanine scanning replacement experiments and determined kinetic parameters using real-time interaction analysis. These antibodies could be divided into two groups according to their epitopic and kinetic characteristics and their cross-reactivity with murine p53. Our results indicate that critical residues involved in the interaction of some of these mAbs with p53 correspond to key residues on p53 involved in its interaction with the mdm2 protein. These antibodies could, therefore, represent powerful tools for the study of p53 regulation.

Systematic mapping of regions of human cardiac troponin I involved in binding to cardiac troponin C: N- and C-terminal low affinity contributing regions

The Spot method of multiple peptide synthesis was used to map in a systematic manner regions of the human cardiac troponin I sequence (hcTnI) involved in interactions with its physiological partner, troponin C (cTnC). Ninety-six 20-mer peptides describing the entire hcTnI sequence were chemically assembled; their reactivity with [125I]cTnC, in the presence of 3 mM Ca2+, enabled the assignment of six sites of interaction (residues 19-32, 45-54, 129-138, 145-164, 161-178 and 191-210). For several sites, a good correlation with literature data was obtained, thus validating this methodological approach. Synthetic peptides, each containing in their sequence an interaction site, were prepared. As assessed by BIACORE, all of them exhibited an affinity for cTnC in the range of 10(-6)-10(-7) M, except for hcTnI [39-58] which showed a nanomolar affinity. This peptide was also able to block the interaction between hcTnI and cTnC. We therefore postulate that despite the existence of multiple cTnC interaction sites on the hcTnI molecule, only that region of hcTnI allows a stabilization of the complex. Residues 19-32 from the N-terminal cardio-specific extension of hcTnI were also found to be involved in interaction with cTnC; residues 19-32 may correspond to the minimal sequence of the extension which could switch between the N- and C-terminal TnC domains, depending on its phosphorylation state. Finally, two Ca(2+)-dependent cTnC binding domains within the C-terminal part of hcTnI (residues 164-178 and 191-210) were also mapped. The latter site may be linked with the cardiac dysfunction observed in stunned myocardium.

Affinity of recombinant antibody and antibody fragment binding to human thyroglobulin: potential applications in gene therapy

Recombinant antibodies and antibody fragments are currently being produced. They can be used in vitro for the structural study of antigen-antibody interactions for instance, but their in vivo production may have applications for gene therapy of certain cancers and severe viral diseases and in developing new animal models of autoimmune disease. We report here these two types of applications using a recombinant antihuman thyroglobulin (hTg) antibody.

Mapping the CD4 binding domain of gp17, a glycoprotein secreted from seminal vesicles and breast carcinomas

gp17, a secretory CD4-binding factor isolated from the human seminal plasma, is identical to the gross cystic disease fluid protein-15, a specific marker for primary and metastatic breast tumors. We previously demonstrated that gp17 binds to CD4 with high affinity and strongly inhibits T lymphocyte apoptosis induced by sequential cross-linking of CD4 and T cell receptor (TCR). To further characterize the gp17/CD4 interaction and map the gp17 binding site, we produced a secreted form of recombinant gp17 fused to human IgG1 Fc, gp17-Ig. We showed that gp17-Ig exhibits a binding affinity for CD4 similar to that of native gp17. As no information about gp17 structure is presently available, 99 overlapping gp17 peptides were synthesized by the Spot method, which allowed the mapping of two CD4 binding regions. Alanine scanning of CD4-reactive peptides identified critical residues, selected for site-directed mutagenesis. Nine gp17-Ig mutants were generated and characterized. Three residues within the carboxy-terminal region were identified as the major binding domain to CD4. The Spot method combined with mutagenesis represents a refined approach to distinguish the contact residues from the ones contributing to the conformation of the CD4-binding domain.

Human anti-thyroid peroxidase single-chain fragment variable of Ig isolated from a combinatorial library assembled in-cell: insights into the in vivo situation

In an attempt to explore the natural variable heavy and light chain (VH/VL) pairing of autoantibodies involved in Graves' disease, we constructed a phage-displayed Ab library obtained by in-cell PCR of thyroid-infiltrating cells. We report here the molecular cloning and characterization of human single-chain fragment variable regions (scFv) specific for thyroid peroxidase (TPO) generated from this library. On the basis of the nucleotide sequences, three different scFvs were obtained (ICA1, ICB7, and ICA5). All were encoded by genes derived from the VH1 and Vlambda1 gene families. Using BIACORE for epitope mapping and kinetic analysis, we showed that these scFvs exhibited high affinity (Kd = 1 nM) for TPO and recognized three different epitopes. The biological relevance of these scFvs as compared with serum anti-TPO autoantibodies was assessed by competition studies. Sera from all the 29 Graves' disease patients tested were able to strongly inhibit (60-100%) the binding of the 3 scFvs to TPO. These data demonstrate that the in-cell PCR library generated human anti-TPO scFvs that retained the VH/VL pairing found in vivo and that the different epitope specificities defined by these scFvs overlapped with those found in the sera of patients with autoimmune thyroid disease.

alpha2-Macroglobulin, the main serum antiprotease, binds beta2-microglobulin, the light chain of the class I major histocompatibility complex, which is involved in human disease

beta(2)-Microglobulin, a 12 kDa protein forming part of the class I HLA (histocompatibility locus antigen) major histocompatibility complex, has been used as a prognosis factor for multiple myeloma and as a marker of renal function, and has been shown to be involved in the pathogenesis of dialysis-related amyloidosis. alpha(2)-Macroglobulin has the ability to bind a wide range of physiologically important molecules, thereby influencing their metabolic impact. In this study we show by Western blotting analysis that beta(2)-microglobulin binds to alpha(2)-macroglobulin in vitro. This binding was confirmed by BIAcore analysis, and was shown by ELISA to be concentration-dependent. The sequences of the binding peptides in the mature beta(2)-microglobulin molecule were identified by Spot multiple peptide synthesis and alpha(2)-macroglobulin binding studies. In conclusion, beta(2)-microglobulin interacts specifically with the universal antiprotease a(2)-macroglobulin. The identification of this interaction brings into question some of the axioms on the metabolism of beta(2)-microglobulin, and may help to explain the clinical findings observed in b(2)-microglobulin-related diseases.

Interactions of the human, rat, Saccharomyces cerevisiae and Escherichia coli 3-methyladenine-DNA glycosylases with DNA containing dIMP residues

In DNA, the deamination of dAMP generates 2'-deoxy-inosine 5'-monophosphate (dIMP). Hypoxanthine (HX) residues are mutagenic since they give rise to A.T-->G.C transition. They are excised, although with different efficiencies, by an activity of the 3-methyl-adenine (3-meAde)-DNA glycosylases from Escherichia coli (AlkA protein), human cells (ANPG protein), rat cells (APDG protein) and yeast (MAG protein). Comparison of the kinetic constants for the excision of HX residues by the four enzymes shows that the E.coli and yeast enzymes are quite inefficient, whereas for the ANPG and the APDG proteins they repair the HX residues with an efficiency comparable to that of alkylated bases, which are believed to be the primary substrates of these DNA glycosylases. Since the use of various substrates to monitor the activity of HX-DNA glycosylases has generated conflicting results, the efficacy of the four 3-meAde-DNA glycosylases of different origin was compared using three different substrates. Moreover, using oligo-nucleotides containing a single dIMP residue, we investigated a putative sequence specificity of the enzymes involving the bases next to the HX residue. We found up to 2-5-fold difference in the rates of HX excision between the various sequences of the oligonucleotides studied. When the dIMP residue was placed opposite to each of the four bases, a preferential recognition of dI:T over dI:dG, dI:dC and dI:dA mismatches was observed for both human (ANPG) and E.coli (AlkA) proteins. At variance, the yeast MAG protein removed more efficiently HX from a dI:dG over dI:dC, dI:T and dI:dA mismatches.

Affinity for the cognate monoclonal antibody of synthetic peptides derived from selection by phage display. Role of sequences flanking thebinding motif

Randomized peptide sequences displayed at the surface of filamentous phages are often used to select antibody ligands. The selected sequences are generally further used in the form of synthetic peptides; however, as such, their affinity for the selecting antibody is extremely variable and factors influencing this affinity have not been fully deciphered. We have used an f88.4 phage-displayed peptide library to identify ligands of mAb 11E12, an antibody reactive to human cardiac troponin I. A majority of the sequences thus selected showed a (T/A/I/L) EP(K/R/H) motif, homologous to the Y-TEPH motif identified by multiple peptide synthesis as the critical motif recognized by mAb 11E12 in the peptide epitope. A set of 15-mer synthetic peptides derived from the phage-selected sequences was used in BIACORE to characterize their interaction with mAb 11E12. Most peptides exhibited affinities in the 7-26 nM range. These affinities represented, however, only 1.9-7. 5% of the affinity of the 15-mer peptide epitope. In circular dichroism experiments, the peptide epitope showed a propensity to have some stabilized conformation, whereas a low-affinity peptide selected by phage-display did not. To try to decipher the molecular basis of this difference in affinity, new peptides were prepared by grafting the N- or the C-terminal sequence of the peptide epitope to the Y-TEPK motif of a low-affinity peptide selected by phage-display. These hybrid peptides showed marked increases both in affinity (as assessed using BIACORE) and in inhibitory potency (as assessed in competition ELISA), compared with the parent sequence. Thus, the sequences flanking the motif, although not containing critical residues, convey some determinants necessary for high affinity. The affinity of a given peptide strongly depends on its capacity to maintain the antigenically reactive structure it has on the phage, implying that it is impossible to predict whether high- or low-affinity peptides will be obtained from phage display.

Protein-disulfide isomerase (PDI) in FRTL5 cells. pH-dependent thyroglobulin/PDI interactions determine a novel PDI function in the post-endoplasmic reticulum of thyrocytes

Thyroglobulin (TG) is secreted by the thyrocytes into the follicular lumen of the thyroid. After maturation and hormone formation, TG is endocytosed and delivered to lysosomes. Quality control mechanisms may occur during this bidirectional traffic since 1) several molecular chaperones are cosecreted with TG in vivo, and 2) lysosomal targeting of immature TG is thought to be prevented via the interaction, in acidic conditions, between the Ser(789)-Met(1172) TG hormonogenic domain (BD) and an unidentified membrane receptor. We investigated the secretion and cell surface expression of PDI and other chaperones in the FRTL5 thyroid cell line, and then studied the characteristics of the interaction between TG and PDI. We demonstrated that PDI, but also other chaperones such as calnexin and KDEL-containing proteins are exposed at the cell surface. We observed on living cells or membrane preparations that PDI specifically binds TG in acidic conditions, and that only BD is involved in binding. Surface plasmon resonance analysis of TG/PDI interactions indicated: 1) that PDI bound TG but only in acidic conditions, and that it preferentially recognized immature molecules, and 2) BD is involved in binding even if cysteine-rich modules are deleted. The notion that PDI acts as an "escort" for immature TG in acidic post-endoplasmic reticulum compartments is discussed.

Biosynthesis and immunobiochemical characterization of gp17/GCDFP-15. A glycoprotein from seminal vesicles and from breast tumors, in HeLa cells and in Pichia pastoris yeast

The gp17 factor is a secretory product of human seminal vesicle cells which binds to CD4 and acts as a potent inhibitor of T lymphocyte apoptosis induced by CD4 crosslinking and subsequent T-cell receptor (TCR) activation. The protein is identical to gross cystic disease fluid protein-15 (GCDFP-15), a breast tumor secretory marker PIP (prolactin inducible protein), a prolactin-controlled and androgen-controlled protein; secretory actin binding protein (SABP), a seminal plasma actin binding protein and extra-parotid glycoprotein (EP-GP), a secretory protein from the salivary gland. The structure of this protein has not yet been elucidated and no biological function has been clearly attributed to date. Expression of recombinant gp17/GCDFP-15 cDNA in bacteria and insect cells leads to the production of a misfolded insoluble protein. In this study, we describe the production of gp17/GCDFP-15 in two different eukaryotic systems, namely HeLa cells and the Pichia pastoris yeast. Using constructs in which gp17/GCDFP-15 was tagged with enhanced green fluorescent protein (EGFP) in various combinations, we observed expression only when the fusion protein was directed to the secretory compartment by the correct signal peptide. The resulting fluorescent protein was inefficiently secreted, thus suggesting that gp17/GCDFP-15 is not appropriately post-translationally processed and/or transported in HeLa cells. The use of the P. pastoris secretory pathway allowed instead the accumulation in the culture medium of a GCDFP-15/gp17 species which retained the ability to bind to CD4 and also most of the biochemical and immunological properties of the native protein. The production of an active recombinant molecule opens the way to correlate the structural properties of this peculiar factor to its ability to bind several proteins, including CD4, and to block CD4-mediated T cell programmed death.

Normal human serum contains natural antibodies reactive with autologous ABO blood group antigens

It is widely accepted that the serum of healthy individuals contains natural antibodies only against those blood group A or B antigens that are not expressed on the individual's red blood cells. The mechanisms involved in tolerance to autologous blood group antigens remain unclear. In the present study, we show that IgM and IgG antibodies reactive with autologous blood group antigens are present in the immunoglobulin fraction of normal human serum. Natural IgG anti-A antibodies purified by affinity chromatography from IgG of individuals of blood group A exhibited an affinity for A trisaccharide antigen in the micromolar range and agglutinated A red cells at sixfold higher concentrations than those required for agglutination with affinity-purified anti-A IgG of individuals of blood group B. Whereas autoantibodies reactive with self A and B antigens are readily detected in purified IgG and IgM fractions, their expression is restricted in whole serum as a result of complementary interactions between variable regions of antibodies. These observations suggest that tolerance to autologous ABO blood group antigens is dependent on peripheral control of antibody autoreactivity.

Inhibition of cell adhesion by antibodies to Arg-Gly-Asp (RGD) in normal immunoglobulin for therapeutic use (intravenous immunoglobulin, IVIg)

Intravenous immunoglobulin (IVIg) therapy is associated with a broad range of immunomodulatory activities. Several of the postulated mechanisms of IVIg action relate to the presence of antibodies to molecules relevant for regulation of the immune response. This article reports that IVIg contains antibodies to the Arg-Gly-Asp (RGD) sequence, and the attachment site of a number of adhesive extracellular matrix proteins, including ligands for beta1, beta3, and beta5 integrins. Anti-RGD antibodies were identified in IVIg by enzyme-linked immunosorbent assay and by using the BIAcore (BIAcore, Uppsala, Sweden) technology. The affinity of anti-RGD antibodies to a synthetic RGD-containing peptide and to fibronectin (Fn) was found to be in the micromolar range. F(ab')2 fragments specific for RGD were purified from IVIg by affinity chromatography. Anti-RGD F(ab')2 antibodies inhibited adenosine diphosphate induced alphaIIb/beta3 integrin-mediated platelet aggregation and the adhesion of activated alpha4beta1 integrin-expressing B cells to Fn. Adhesion of unstimulated platelets to fibrinogen (Fg) involving both the gamma-chain dodecapeptide sequence and the RGD sequence was inhibited by anti-RGD antibodies. In addition, adhesion of thrombin-stimulated platelets to von Willebrand factor or Fg was completely inhibited by affinity-purified anti-RGD antibodies. Our results suggest that the presence of natural IgG antibodies to the RGD motif may contribute to the immunomodulatory and anti-inflammatory effects of therapeutic preparations of normal IgG.

Tumor targeting with newly designed biparatopic antibodies directed against two different epitopes of the carcinoembryonic antigen (CEA)

In an attempt to improve tumor targeting and tumor retention time of monoclonal antibodies (MAbs), we prepared biparatopic antibodies (BpAbs) having the capability of binding 2 different non-overlapping epitopes on the same target antigen molecule, namely, the carcinoembryonic antigen (CEA). Six BpAbs were constructed by coupling 2 different Fab' fragments from 4 different specific anti-CEA MAbs recognizing 4 CEA epitopes (Gold 1-4). Demonstration of the double paratopic binding of these antibodies for CEA was confirmed in vitro by inhibition radioimmunoassay and cross-inhibition analysis by surface plasmon resonance (SPR; BIACORE) technology. Using the latter technique, the affinity constants for CEA immobilized onto the sensor chip were found to range from 0.37 to 1.54 x 10(9) M(-1) for the 4 parental F(ab')2 fragments and from 1.88 to 10.14 x 10(9) M(-1) for the BpAbs, demonstrating the advantage of biparatopic binding over conventional F(ab')2 binding. The Ka improvement was particularly high for BpAb F6/35A7 and BpAb F6/B17 with a 9.5- and 8.1-fold increase, respectively, as compared with the parental F(ab')2. In vivo, the 6 BpAbs were compared with their 2 respective parental F(ab')2 by injection of 131I-BpAb/125I-F(ab')2 parental fragments into nude mice xenografted with the human colon carcinoma T380. Dissection 72 hr post-injection demonstrated that BpAb B17/CE25 and BpAb F6/B17 gave higher tumor uptake than that of their parental F(ab')2. This finding is particularly interesting for BpAb F6/B17, which compared favorably with the F6 F(ab')2, one of the best parental F(ab')2 fragments used in our study.

High-affinity antibodies from hen's-egg yolks against human mannose-6-phosphate/insulin-like growth-factor-II receptor (M6P/IGFII-R): characterization and potential use in clinical cancer studies

The mannose-6-phosphate/insulin-like growth-factor-II receptor (M6P/IGFII-R) involved in trafficking of newly synthesized lysosomal enzymes, degradation of IGFII and activation of TGFbetaI, was suggested as being coded by a tumor-suppressor gene. No specific antibodies are currently available for clinical studies. Since M6P/IGFII-R is a highly conserved protein in mammals, we immunized chicken with human M6P/IGFII-R. Up to 200 mg of specific IgY from weekly pooled egg yolk was extracted by the polyethylene glycol procedure. Chicken IgY antibodies specifically recognized the human and bovine 270-kDa M6P/IGFII-R but not the 46-kDa M6P-R, as documented by immunoprecipitation and immunobloting. Using biosensor analysis, IgY antibodies were shown to bind M6P/IGFII-R with high affinity (K(D) = 7.5 x 10(-9) M). A solid-phase competitive ELISA using bovine M6P/IGFII-R coated on 96-well microplates, allowed us to titrate the M6P/IGFII-R in human sera at a sensitivity of 300 ng/ml. The M6P/IGFII-R was stained by immunoperoxidase in breast- and ovarian-cancer cell lines (T47D, MDA-MB231, MCF7 and BG1) and in frozen breast-cancer tissues, showing predominant localization in the trans-Golgi network. Staining specificity was shown with irrelevant IgY and by extinction with antigen excess. Quantitative immunohistochemical analysis of frozen sections from 40 invasive breast carcinomas indicated varying levels (from 5 to 400 units) of the M6P/IGFII-R protein which were not correlated with tumor size, histological grade and estrogen receptor or progesterone receptor. There was a trend (p = 0.08) between lymph-node invasiveness and low receptor level. Moreover, the M6P/IGFII-R level was significantly lower in cancer cells than in normal cells in 10 out of the 21 tumors in which the peritumoral normal glands could be quantified in parallel. These 2 last results agree with the hypothesis of a tumor-suppressor gene for this receptor and suggest more basic and clinical studies to prove it.

Interleukin-6 receptor signaling. I. gp80 and gp130 receptor interaction in the absence of interleukin-6

Interleukin-6 (IL-6) is used as a growth factor by various tumor cells. It binds to a gp80 specific receptor (IL-6R) and then to a gp130 transducing chain. Both receptor chains are released as soluble functional proteins which circulate in biological fluids. To study the physiological role of these soluble receptors, both proteins were purified from human plasma and the kinetic constants of equilibria between IL-6 and its natural soluble IL-6R (sIL-6R) and gp130 receptor (sgp130) were measured using surface plasmon resonance analysis. Unexpectedly, natural sIL-6R and natural sgp130 were found to interact (Kd = 2.8 nM) in the absence of IL-6. No interaction was seen between the recombinant soluble receptors or between either natural soluble receptor and its recombinant partner. This binary complex was not due to copurification of IL-6 and was detected in human plasma of healthy donors. It results from either direct interaction between the two natural soluble receptors or indirect binding mediated by a yet unidentified copurified plasma molecule playing the role of an IL-6 antagonist. Once formed, the binary complex was found to be unable to bind IL-6. Soluble gp130 had already been shown to inhibit IL-6 signaling by inactivating the IL-6/IL-6R complex. In addition we show that, in the absence of IL-6, circulating natural sgp130 is able to inhibit directly the circulating sIL-6R that is a strong synergic molecule of IL-6 signaling.

Synthetic peptides derived from the variable regions of an anti-CD4 monoclonal antibody bind to CD4 and inhibit HIV-1 promoter activation in virus-infected cells

The monoclonal antibody (mAb) ST40, specific for the immunoglobulin complementarity-determining region (CDR) 3-like loop in domain 1 of the CD4 molecule, inhibits human immunodeficiency virus type 1 (HIV-1) promoter activity and viral transcription in HIV-infected cells. To design synthetic peptides from the ST40 paratope that could mimic these biological properties, a set of 220 overlapping 12-mer peptides frameshifted by one residue, corresponding to the deduced ST40 amino acid sequence, was synthesized by the Spot method and tested for binding to recombinant soluble CD4 antigen. Several peptides that included in their sequences amino acids from the CDRs of the antibody and framework residues flanking the CDRs were found to bind soluble CD4. Eleven paratope-derived peptides (termed CM1-CM11) were synthesized in a cyclic and soluble form. All the synthetic peptides showed CD4 binding capacity with affinities ranging from 1.6 to 86.4 nM. Moreover, peptides CM2, CM6, CM7, CM9, and CM11 were able to bind a cyclic peptide corresponding to the CDR3-like loop in domain 1 of CD4 (amino acids 81-92 of CD4). Peptide CM9 from the light chain variable region of mAb ST40 and, to a lesser extent, peptides CM2 and CM11 were able to inhibit HIV-1 promoter long terminal repeat-driven beta-galactosidase gene expression in the HeLa P4 HIV-1 long terminal repeat beta-galactosidase indicator cell line infected with HIV-1. The binding of mAb ST40 to CD4 was also efficiently displaced by peptides CM2, CM9, and CM11. Our results indicate that the information gained from a systematic exploration of the antigen binding capacity of synthetic peptides from immunoglobulin variable sequences can lead to the identification of bioactive paratope-derived peptides of potential pharmacological interest.

Characterization of a new intrabody directed against the N-terminal region of human p53

Genes encoding the rearranged immunoglobulin heavy and light chain variable regions of DO-1, a monoclonal antibody directed against human p53, have been used to construct a single-chain antibody. DO-1 recognizes an N-terminal epitope in the region involved in the transactivation function of p53 and the binding of Mdm2. The DO-1 single chain scFv expressed in the periplasm of E. coli or at the surface of the filamentous phage M13 retained the immunological specificity and affinity of the full length antibody. Furthermore, the DO-1 recombinant antibody was able to inhibit the in vitro binding of Hdm2, and was shown to be a powerful protecting agent of p53's DNA binding activity at 37 degrees C. The DO-1 single-chain antibody has been used to construct single-chain intracellular antibodies (intrabodies) for expression in the cytoplasm and the nucleus of mammalian cells. These anti-p53 intrabodies were additionally modified by addition of a Ckappa domain to increase cytoplasmic and nuclear stability. Here we show that expression of the DO-1 single-chain antibody in the H1299 cell line results in an inhibition of p53's transactivation function. The DO-1 intrabody is a useful tool to study those functions of p53 driven by the N-terminal region of the protein.

Soluble CD21 (sCD21) forms biologically active complexes with CD23: sCD21 is present in normal plasma as a complex with trimeric CD23 and inhibits soluble CD23-induced IgE synthesis by B cells

A soluble form of CD21 (sCD21) of 135 kDa is spontaneously released by human B and T lymphocytes upon shedding of the extracellular domain of the molecule. By Western blotting, we have now identified two forms of sCD21 of Mr 135 and 90 kDa in normal human serum. We further demonstrate that sCD21 circulates in a complexed form with cleavage fragments of C3 and CD23, two previously identified ligands of the membrane CD21 receptor. The CD23 molecule was in the form of a trimer in the soluble complex purified from plasma by affinity chromatography on anti-CD21 Sepharose. The serum sCD21 complex was also found to contain IgE. The presence of IgE and of CD21 in a soluble complex that contains trimeric CD23 as the only form of soluble CD23 (sCD23) is in agreement with a model in which two of the three lectin heads of CD23 bind to the Cepsilon3 domain of IgE, thus leaving one of the heads available for interaction with CD21. We further demonstrate that sCD21 inhibits sCD23-induced IgE synthesis by IL-4-stimulated B cells. The results indicate that sCD21 in plasma retains the ligand-binding properties of the membrane CD21 receptor and exhibits immunoregulatory properties that may be relevant to allergic and inflammatory disorders.

Differential antibody reactivity and CD4 binding of the mammary tumor marker protein GCDFP-15 from breast cyst and its counterparts from exocrine epithelia

Analysis of biopsies from breast cancer patients demonstrated that GCDFP-15 (gross cystic disease fluid protein-15) is a specific immunocytochemical marker of primary and secondary apocrine breast tumors. The protein has an amino acid sequence identical to SABP (secretory actin-binding protein), to PIP (prolactin-inducible protein) and to gp17, a protein isolated from human seminal plasma. The latter was found to bind to CD4, a T-cell co-receptor involved in antigen recognition, thereby inhibiting the ability of the receptor to interact with the HIV-1 envelope protein gp120. We compare here the ability of independently purified GCDFP-15, SABP and gp17 and of recombinant PIP both to cross-react with a panel of monoclonal antibodies (MAbs) raised against GCDFP-15 or gp17, respectively, and to bind to CD4. We show that, although the various factors share the ability to bind to the panel of antibodies used, differences in the pattern of MAb recognition can be demonstrated. By comparing the kinetic constants for binding of GCDFP-5 and gp17 to CD4 by biosensor technology, significant differences in binding affinities were observed between the 2 factors, thus reflecting structural differences. Surface plasmon resonance analysis also showed that anti-GCDFP-15 and anti-gp17 antibodies inhibit the binding of CD4 to GCDFP-15 and gp17, respectively, to different extents. Our data thus indicate that, while the various forms of the protein are encoded by the same cDNA, tissue specificities due to post-translational modifications exist. This information may be relevant for developing more sensitive and accurate tests for the use of GCDFP-15 as a diagnostic mammary tumor marker and, most importantly, raises the possibility that GCDFP-15 may constitute a breast tumor-specific antigen.

Peptide specificity of high-titer anti-glutamic acid decarboxylase (GAD)65 autoantibodies

To study systematically the linear epitope specificity of anti-glutamic acid decarboxylase (GAD) autoantibodies associated with insulin-dependent diabetes mellitus (IDDM), we produced 93 overlapping 12-residue synthetic peptides derived from the sequence of the human GAD65 protein and covering the entire length of the protein. These peptides were used as antigens in an enzyme immunoassay to screen the sera from 10 IDDM patients, all of which contained at high level autoantibodies directed against GAD65. Three out of ten (30%) IDDM patients had antibodies that reacted with one or more of the synthetic peptides. Two of the peptide-reactive IDDM sera, which also bound denatured recombinant GAD65 on western blots, had the highest titers of anti-GAD antibodies in ELISA assay. Moreover, the anti-GAD antibodies-GAD complexes formed with these sera were characterized by low dissociation rates, indicative of their good stability. A fine specificity analysis, using analogs of antigen peptide 1 (residues 1-12), allowed us to identify the residues at positions 5-9 (GSGFW) as critical for antibody recognition.

Human cardiac troponin I: precise identification of antigenic epitopes and prediction of secondary structure

The presence of human cardiac troponin I (hcTnI) in serum is considered to be a highly specific biochemical marker of acute myocardial infarction. To better understand the antigenic properties of hcTnI, a set of 68 overlapping peptides covering the complete amino acid sequence of hcTnI was prepared and used in epitope mapping experiments. All 16 anti-hcTnI monoclonal antibodies tested were found to recognize a peptide epitope, indicating that recognition by anti-hcTnI monoclonal antibodies was not dependent on the tertiary structure of the protein. Furthermore, the peptide reactivity with anti-hcTnI polyclonal antibodies indicated that most of the sequence of the protein was antigenic; in particular, the N- and C-terminal extremities were found to be the strongest antigenic regions. By using accurate secondary structure prediction methods, hcTnI was found to be an all-alpha type protein, with five regions predicted as helices. Matching the results of the epitope analysis with the structural prediction led us to the view that hcTnI is not a globular protein but probably adopts an extended conformation, allowing a large part of the amino acid sequence of this molecule to be recognized by the immune system. This improved knowledge of the antigenic and structural properties of hcTnI may help in developing new antibodies and immunoassays for use in diagnosing myocardial infarction.

Human cardiac troponin I: precise identification of antigenic epitopes and prediction of secondary structure

The presence of human cardiac troponin I (hcTnI) in serum is considered to be a highly specific biochemical marker of acute myocardial infarction. To better understand the antigenic properties of hcTnI, a set of 68 overlapping peptides covering the complete amino acid sequence of hcTnI was prepared and used in epitope mapping experiments. All 16 anti-hcTnI monoclonal antibodies tested were found to recognize a peptide epitope, indicating that recognition by anti-hcTnI monoclonal antibodies was not dependent on the tertiary structure of the protein. Furthermore, the peptide reactivity with anti-hcTnI polyclonal antibodies indicated that most of the sequence of the protein was antigenic; in particular, the N- and C-terminal extremities were found to be the strongest antigenic regions. By using accurate secondary structure prediction methods, hcTnI was found to be an all-alpha type protein, with five regions predicted as helices. Matching the results of the epitope analysis with the structural prediction led us to the view that hcTnI is not a globular protein but probably adopts an extended conformation, allowing a large part of the amino acid sequence of this molecule to be recognized by the immune system. This improved knowledge of the antigenic and structural properties of hcTnI may help in developing new antibodies and immunoassays for use in diagnosing myocardial infarction.

Anti-digoxin scFv fragments expressed in bacteria and in insect cells have different antigen binding properties

A gene encoding a single-chain antibody fragment directed against digoxin (named 1C10 scFv) was cloned in two expression systems. For this purpose, a new baculovirus transfer cassette fully compatible with the procaryotic pHEN vector was constructed. Baculovirus production led to higher yield than did Escherichia coli expression. The procaryotic fragment showed variations in the fine specificity profile but an affinity constant nearly identical to that of the 1C10 Fab, whereas the eucaryotic scFv fragment had a lower affinity with a specificity profile identical to original mAb. The half-lives of the digoxin:scFv complexes and the global specificity are compatible with therapeutic use of this antibody fragment.

The antibiotic rifampicin is a nonsteroidal ligand and activator of the human glucocorticoid receptor

The glucocorticoid receptor (GR) belongs to a superfamily of ligand-regulated nuclear steroid hormone receptors. The steps in the signal transduction pathway leading to the biological effects of glucocorticoids (GCs) include sequentially binding of the steroid to the GR ligand binding domain (LBD), receptor transformation, nuclear translocation and either positive or negative gene transactivation. Rifampicin (RIF) is a macrocyclic antibiotic used as an antituberculosis agents. As the incidence of tuberculosis has been increasing, in part because of the AIDS epidemic, a growing number of patients are being exposed to the adverse effects of this antibiotic. Indeed, this compound, as are the GCs, is often implicated in noxious drug interactions, because of its strong ability to induce drug-metabolizing enzymes. Moreover, in humans, RIF, as are the GCs, has been described as a potential immunodepressor, associated notably with the reduction of mitogenic responsiveness of human peripheral blood lymphocytes. Here, we report that RIF activates the human glucocorticoid receptor (hGR). Transient expression of wild-type, deleted or mutated GRs; sucrose density gradient sedimentation; and the BIAcore technique strongly suggest that RIF binds to the receptor with the physiological consequence that this antibiotic acts as an immunodepressor. Given the wide use of RIF in the treatment of coinfection of tuberculosis and HIV, this report is highly relevant to current medical practice.

Systematic exploration of the antigen binding activity of synthetic peptides isolated from the variable regions of immunoglobulins

Sets of short (12 residues) cellulose-bound synthetic overlapping peptides derived from the sequences of the variable regions of the heavy and light chains of three different antibodies (an anti-thyroglobulin antibody, the HyHEL-5 anti-lysozyme antibody, and an anti-angiotensin II antibody) were used to systematically assess the antigen binding capacity of peptides from the antibody paratope outside their natural molecular context. Peptides enclosing one or several of the complementarity determining region (CDR) residues had antigen binding activity, although the most active peptides were not necessarily those bearing the greatest number of CDR residues. Several residues from the framework region, preceding or following the CDR, were found to play a role in binding. Affinity constants from 4.1 x 10(-7) to 6.7 x 10(-8) M-1 for the soluble form of 9 lysozyme-binding dodecapeptides were measured by BIAcore analysis. Alanine scanning of lysozyme-binding hexapeptides from the HyHEL-5 sequence identified 38 residues important for binding, of which 22 corresponded to residues that had been shown by x-ray crystallography to be at the interface between HyHEL-5 and lysozyme. Our results could be of interest for the rational identification of biologically active peptides derived from antibody sequences and in providing an experimental basis for mutagenesis of the antibody paratope.

Increased cathepsin D level in the serum of patients with metastatic breast carcinoma detected with a specific pro-cathepsin D immunoassay

BACKGROUND

An increased cathepsin D (cath-D) level in breast carcinoma cytosol has been proposed as a prognostic parameter. However, no increase had been previously detected in serum when assaying total cath-D concentration.

METHODS

The authors compared 2 radioimmunoassays of total cath-D and pro-cath-D in the serum of 3 groups of patients: those with metastatic breast carcinomas (n = 30), those with nonmetastatic breast carcinomas (n = 24), and healthy women (n = 21).

RESULTS

There was a significant increase of total cath-D and pro-cath-D in the serum of 18 of the 30 patients with metastatic breast carcinoma. No increase was observed in any of the patients with nonmetastatic disease compared with healthy women. Moreover, the level of pro-cath-D was often superior to that of total cath-D in the same patients, suggesting that the total cath-D assay in serum underestimates the actual concentration of pro-cath-D. This is not believed to be due to the masking of cath-D with the circulating mannose-6-phosphate/insulin-like growth factor II receptor because the purified receptor did not interfere in the binding of the monoclonal antibodies used in the assay to cath-D.

CONCLUSIONS

An increased level of cath-D in the serum of breast carcinoma patients is a late event observed only in patients with metastatic disease. This increased circulating level is more likely due to increased secretion of the proenzyme rather than to tumor cell lysis.

In vitro and in vivo secretion of cloned antibodies by genetically modified myogenic cells

In vivo production of recombinant antibodies by engineered cells may have applications for gene therapy of certain cancers and of certain severe viral diseases. It would also permit the development of new animal models of autoimmune diseases and new approaches for in vivo ablation of specific cell types for fundamental purposes. Using gene transfer of an anti-human thyroglobulin monoclonal antibody, we show here that several cell types permitting autologous grafting of genetically engineered cells are efficiently able to secrete antibodies in vitro. Those cells include skin fibroblasts, hepatocytes, and myogenic cells. We also show that the secreted antibodies display an affinity for the antigen close to that of the parental antibody, with, however, slight differences varying according to the cell type. This indicates that the foldings of antigen combining sites of antibodies produced in B cell- and non-B cell contexts are very similar. Finally, we report that, when implanted in the forelimb of a mouse, genetically modified myogenic cells are able to secrete antibodies for at least 4 months. Taken together, our observations point to the notion that genetic modification of patient cells may be used for long-term antibody-based gene therapies.

Accurate topological comparison of two recombinant human growth hormones by optical surface plasmon resonance

A strategy for the comparison of two recombinant derived human growth hormones (r-hGH) has been developed using surface plasmon resonance (SPR). Statistical analysis was systematically used on the results obtained with several batches derived from two different Escherichia coli strains. Monoclonal antibodies (MAb) directed against four different domains in the tertiary structure of natural human growth hormone were used to compare the epitopic maps of the three (two recombinant and one natural) hGH by SPR analysis. Topological studies show the homogeneity of the epitopic maps of the three hGH. The kinetic parameters, association rate, and dissociation rate constants were also analyzed for the binding of each hGH batch to all MAbs. They were found to be homogeneous between the three hormones. Furthermore, the two r-hGH were compared by more classical approaches examining recognition of lactogenic or somatogenic receptors using, respectively, a bioassay of Nb2 cell proliferation and binding to rat liver microsomes. Specific bioactivities and IC50 values calculated in radioreceptor assays did not significantly differ between different r-hGH. The method was sensitive enough to show slight differences on koff value for one MAb (3C11) between (natural) hormone and two r-hGH. These differences are discussed in relation to previous observation made in the literature and the presence of isoforms in the natural product. The strategy developed here was very useful as a new tool to establish the equivalence of the two r-hGH.

Specific inhibition of IL-6 signalling with monoclonal antibodies against the gp130 receptor

A family of cytokines [IL-6, IL-11, oncostatin M (OM), leukaemia inhibitory factor (LIF), ciliary neurotrophic factor (CNTF) and cardiotrophin-1] involved in various inflammatory or tumoral diseases share the same gp130 signal transducer chain. The complex formed with their specific receptors associates with a common transducing gp130 membrane protein (gp130) resulting in the formation of high avidity receptor and activation of tyrosine kinases. With the view of identifying gp130 domains specifically involved in IL-6 signalling, the authors prepared 37 new anti-gp130 mAb and analysed the structure-function relationship of the molecule. By cross-competition ELISA, the mAb were classified in 10 subgroups called A to J. By ELISA and BIAcore analysis, the mAb were found to recognize at least 18 antigenic specificities of the gp130 chain. The mAb reacted against the soluble and the membrane forms of gp130 as well. Their ability to inhibit the proliferation of the human myeloma cell line XG-4 of which the growth is strictly dependent on the presence of either exogenous IL-6, or LIF, or OM, or CNTF was studied. Besides mAb with no evident neutralizing effect (G and H) and mAb which neutralized equally well the activity of all tested cytokines (all mAb of groups A, I and J), some showed a selective effect. Those of group F inhibited also the proliferation induced by the 4 cytokines, but more specifically that dependent on the CNTF. mAb of groups B and E specifically inhibited the growth induced by IL-6, whereas those of group C inhibited that induced by LIF and OM. These results show the presence of different gp130 epitopes specifically involved in the signaling induced by the cytokines of the gp130 family. In ELISA, only mAb of group B and E were found to inhibit the binding of the IL-6-IL-6R complex to gp130, showing that they identified one or two domains of gp130 involved in its interaction with the IL-6-IL-6R complex. Precise identification of this(ese) epitope(s) would be useful to better understand the mechanisms of the IL-6 signalling.

Surface plasmon resonance analysis of gp17, a natural CD4 ligand from human seminal plasma inhibiting human immunodeficiency virus type-1 gp120-mediated syncytium formation

We have previously isolated from human seminal plasma a CD4 ligand, the gp17 glycoprotein, which shares sequence identity with three previously identified proteins: secretory actin-binding protein (SABP) from seminal plasma, gross-cystic-disease fluid protein-15 (GCDFP-15) and prolactin-inducible protein (PIP) from breast tumor cells. Functions of these glycoproteins are unknown. To further characterize the physical interaction between gp17 and CD4 we used surface plasmon resonance and demonstrated that gp17-CD4 binding affinity is high. Competition experiments indicated that gp17 interferes with human immunodeficiency virus (HIV) envelope protein/CD4 binding, although it binds to a site distinct from but close to the gp120-binding site. We observed moreover that gp17 inhibits syncytium formation between transfected cells expressing the wild-type HIV-1 envelope glycoprotein and CD4, respectively. Our results suggest that gp17, which may function as an immunomodulatory CD4-binding factor playing a role at insemination, may also play a role in controlling HIV spread in the sexual tract.

Cytokine targeting in tumors using a bispecific antibody directed against carcinoembryonic antigen and tumor necrosis factor alpha

The use of tumor necrosis factor alpha (TNFalpha) in cancer therapy is limited by its short circulatory half-life and its severe systemic side effects. To overcome these limitations, we evaluated the capability of a bispecific antibody (BAb) directed against carcinoembryonic antigen (CEA) and human TNFalpha to target this cytokine in tumors. A BAb was constructed by coupling the Fab' fragments from an anti-CEA monoclonal antibody (MAb) to the Fab' fragments from an anti-TNFalpha MAb via a stable thioether linkage. The double specificity of the BAb for CEA and TNFalpha was demonstrated using a BIAcoreTM two-step analysis. The affinity constants of the BAb for CEA immobilized on a sensor chip and for soluble TNFalpha added to the CEA-BAb complex were as high as those of the parental MAbs (1.7 x 10(9) M-1 and 6.6 x 10(8) M-1, respectively). The radiolabeled 125I-labeled BAb retained high immunoreactivity with both CEA and TNFalpha immobilized on a solid phase. In nude mice xenografted with the human colorectal carcinoma T380, the 125I-labeled BAb showed a tumor localization and biodistribution comparable to that of 131I-labeled anti-CEA parental F(ab')2 with 25-30% of the injected dose (ID)/g tumor at 24 h and 20% ID/g tumor at 48 h. To target TNFalpha to the tumor, a two-step i.v. injection protocol was used first, in which a variable dose of 125I-labeled BAb was injected, followed 24 or 48 h later by a constant dose of 131I-labeled TNFalpha (1 microg). Mice pretreated with 3 microg of BAb and sacrificed 2, 4, 6, or 8 h after the injection of TNFalpha showed a 1.5- to 2-fold increased concentration of 131I-labeled TNFalpha in the tumor as compared to control mice, which received TNFalpha alone. With a higher dose of BAb (25 microg), mice showed a better targeting of TNFalpha with a 3.2-fold increased concentration of 131I-labeled TNFalpha in the tumor: 9.3% versus 2.9% ID/g in control mice 6 h after TNFa injection. In a one-step injection protocol using a premixed BAb-TNFalpha preparation, similar results were obtained 6 h postinjection (3.5-fold increased TNFalpha tumor concentration). A longer retention time of TNFalpha was observed leading to an 8.1-fold increased concentration of TNFalpha in the tumor 14 h postinjection (4.4 versus 0.5% ID/g tumor for BAb-treated and control mice, respectively). These results show that our BAb is able, first, to localize in a human colon carcinoma and, there, to immunoabsorb the i.v.-injected TNFalpha, leading to its increased concentration at the tumor site.

Selective recognition of M235T angiotensinogen variants and their determination in human plasma by monoclonal antibody-based immunoanalysis

The common M235T mutation of human angiotensinogen has been shown to be associated with a 10-20% increase in plasma angiotensinOgen level and increased frequency of essential and pregnancy-induced hypertension. The detection of such a common factor in the plasma of individuals at risk could be a useful tool for modern molecular-based medicine. The recognition of M235T variants was investigated using four monoclonal antibodies (mAbs) directed against human angiotensinogen; two immunometric assays were developed. The first assay (using mAbS 7B2 and 4G3) allowed the direct determination of angiotensinogen concentrations and did not show a significant difference with the enzymatic measurement of angiotensinogen. The second assay (using mAbs 1H8 and 1C11) showed a fine distinction between the T235 mutant and M235 wild-type forms of angiotensinogen, with a greater affinity for the latter, as confirmed by biosensor BIAcore experiments. This assay was extremely sensitive in measuring the proportions of the M235 and T235 forms present in the test samples, the first time such a distinction has been achieved in the serpin family. The simple immunoanalysis of the plasma allowed the direct determination of the M235T genotype of the individual tested. Furthermore, it was shown that the T174M mutation, described as being in complete linkage disequilibrium with the M235T mutation, had no influence on these results. Moreover, this assay suggested the presence of the M235 and T235 angiotensinogens in approximately equal amounts in heterozygous plasmas. In conclusion, the immunometric assay described in this study should provide original tools for investigating the relationship between M235T genotype, plasma angiotensinogen levels, and regulation of blood pressure.

Identification of a novel antigenic structure of the human receptor for interleukin-6 involved in the interaction with the glycoprotein 130 chain

The receptor for interleukin-6 (IL-6) is characterized by a ligand-binding glycoprotein 80 (gp80) transmembrane chain (IL-6R) which associates with a signal-transducer gp130 chain. We previously raised a series of monoclonal antibodies (mAb) recognizing different epitopes of the human IL-6R and interfering with the function of the receptor. One of them, M182, was able to diminish the proliferation of IL-6-dependent plasmacytoma cell lines although it was found unable to inhibit the binding of IL-6 to its receptor. Using an enzyme-linked immunosorbent assay for measuring the binding of IL-6 IL-6R to the gp130 chain, we showed that M182 was directed against a structure directly involved in the IL-6R gp130 interaction. M182 was able to potentiate the inhibitor effect of anti-IL-6R mAB which interfere with the binding of IL-6, leading to complete inhibition of the proliferation of IL-6-dependent cell lines. M182 was also found to synergize with inhibitory anti-IL-6 mAb. Therefore this structure appears to be an important regulatory domain of the IL-6R and a valuable target for inhibiting IL-6 signalling.