Ubiquitin-like protein MNSFß noncovalently binds to molecular chaperone HSPA8 and regulates osteoclastogenesis.

MNSFß, a ubiquitin-like protein, covalently binds to various target proteins including proapoptotic Bcl-G. During the course of isolation of MNSFß-conjugating enzyme(s), we identified a novel target protein for MNSFß. MALDI-TOF MS fingerprinting revealed that the MNSFß-interacting protein is HSPA8 (heat shock 70-kDa protein 8). We observed that MNSFß noncovalently binds to HSPA8 in the presence of ATP in vitro. Double knockdown of MNSFß and HSPA8 strongly inhibited RANKL-induced osteoclastogenesis from Raw264.7 macrophage-like cells. The same treatment inhibited RANKL-induced ERK1/2 and p38 phosphorylation and TNFα production, suggesting that the association of MNSFß with HSPA8 may promote RANKL-induced osteoclastogenesis. This is the first report that MNSFß binds to a protein substrate via the noncovalent association and exerts biological effects.

Development of Phage-Based Antibody Fragment Reagents for Affinity Enrichment of Bacterial Immunoglobulin G Binding Proteins.

Disease and death caused by bacterial infections are global health problems. Effective bacterial strategies are required to promote survival and proliferation within a human host, and it is important to explore how this adaption occurs. However, the detection and quantification of bacterial virulence factors in complex biological samples are technically demanding challenges. These can be addressed by combining targeted affinity enrichment of antibodies with the sensitivity of liquid chromatography-selected reaction monitoring mass spectrometry (LC-SRM MS). However, many virulence factors have evolved properties that make specific detection by conventional antibodies difficult. We here present an antibody format that is particularly well suited for detection and analysis of immunoglobulin G (IgG)-binding virulence factors. As proof of concept, we have generated single chain fragment variable (scFv) antibodies that specifically target the IgG-binding surface proteins M1 and H of Streptococcus pyogenes. The binding ability of the developed scFv is demonstrated against both recombinant soluble protein M1 and H as well as the intact surface proteins on a wild-type S. pyogenes strain. Additionally, the capacity of the developed scFv antibodies to enrich their target proteins from both simple and complex backgrounds, thereby allowing for detection and quantification with LC-SRM MS, was demonstrated. We have established a workflow that allows for affinity enrichment of bacterial virulence factors.

Oxidative stress effect on progesterone-induced blocking factor (PIBF) binding to PIBF-receptor in lymphocytes.

Receptor-ligand binding is an essential interaction for biological function. Oxidative stress can modify receptors and/or membrane lipid dynamics, thus altering cell physiological functions. The aim of this study is to analyze how oxidative stress may alter receptor-ligand binding and lipid domain distribution in the case of progesterone-induced blocking factor/progesterone-induced blocking factor-receptor. For membrane fluidity regionalization analysis of MEC-1 lymphocytes, two-photon microscopy was used in individual living cells. Lymphocytes were also double stained with AlexaFluor647/progesterone-induced blocking factor and Laurdan to evaluate -induced blocking factor/progesterone-induced blocking factor-receptor distribution in the different membrane domains, under oxidative stress. A new procedure has been developed which quantitatively analyzes the regionalization of a membrane receptor among the lipid domains of different fluidity in the plasma membrane. We have been able to establish a new tool which detects and evaluates lipid raft clustering from two-photon microscopy images of individual living cells. We show that binding of progesterone-induced blocking factor to progesterone-induced blocking factor-receptor causes a rigidification of plasma membrane which is related to an increase of lipid raft clustering. However, this clustering is inhibited under oxidative stress conditions. In conclusion, oxidative stress decreases membrane fluidity, impairs receptor-ligand binding and reduces lipid raft clustering.

Ubiquitin-like protein MNSFß covalently binds to cytosolic 10-formyltetrahydrofolate dehydrogenase and regulates thymocyte function.

MNSFß is a ubiquitously expressed member of the ubiquitin-like family that has been involved in various biological functions. Previous studies have demonstrated that MNSFß covalently binds to various target proteins including Bcl-G, a proapoptotic protein. In this study, we purified a 115 kDa MNSFß adduct from murine liver lysates by sequential chromatography on DEAE and anti-MNSFß IgG-conjugated Sepharose in the presence of ATP. MALDI-TOF MS fingerprinting revealed that this MNSFß adduct consists of an 8.5 kDa MNSFß and 10-formyltetrahydrofolate dehydrogenase (FDH), an abundant enzyme of folate metabolism. Interestingly, MNSFß preferably binds to cytosolic but not mitochondrial FDH. Fingerprinting analysis of the MNSFß adduct demonstrate that MNSFß conjugates to cytosolic FDH with a linkage between the C-terminal Gly74 and Lys72. The 115 kDa MNSFß/FDH complex was not expressed in any of the tissues examined, indicating that this adduct formation is not ubiquitous. We found that MNSFß/FDH complex formation was induced by dexamethasone in thymocytes. Double knockdown of MNSFß and FDH strongly reduced dexamethasone-induced apoptosis. Collectively, MNSFß/FDH complex formation may positively regulate apoptosis in thymocytes.

[Cloning, eukaryotic expression and spatial expression patterns of porcine MNSFbeta].

MNSFbeta (Monoclonal nonspecific suppressor factor beta) is a natural immunosuppressive factor which has been reported to be involved in various biological processes, such as immune responses, cell division, stress response, cell apoptosis, and nuclear transport. However, study on porcine MNSFbeta has been rarely reported. In this study, the full-length sequence of porcine MNSFbeta (GenBank accession number: KF77642500) was predicted in silicon and its cDNA sequence was obtained through RT-PCR from porcine spleen. The nucleic acid and protein sequences were analyzed. Then, the gene was subcloned into pEGFP-C1 to construct a recombinant plasmid pEGFP-MNSFbeta which was transfected into swine umbilical vein endothelial cells (SUVECs) using Lipofectamine 2000. The expression of GFP was detected by fluorescence microscopy, Western blot, and laser confocal fluorescence microscopy. The spatial expression patterns of porcine MNSFbeta were detected by real-time qPCR. Results showed that the full length of porcine MNSFbeta was 402 bp encoding 133 amino acids with only one exon. Bioinformatics analysis showed that porcine MNSFbeta protein was a stable protein consisting of a ubiquitin-like domain fused to the ribosomal protein S30 with no signal peptide. The analyses of homology and phylogenetic tree of porcine MNSFbeta and its homologs in other 18 species showed that the identities of MNSFbeta protein sequence were higher than 91% among different species and the evolutionary distance was less than 0.05. It indicates that MNSFbeta is highly conserved in the process of evolution. Fluorescence signal showed that the fusion protein GFP-MNSFbeta was successfully expressed in SUVECs which was then confirmed by Western blot. Laser confocal fluorescence microscopy showed that MNSFbeta was expressed in both nucleus and cytoplasm. Analysis of spatial expression patterns showed that procine MNSFbeta was widely expressed in immune tissues, but not in lung, suggesting that MNSFbeta may play an important role in immune response.

Structural basis for the structural dynamics of human mitochondrial chaperonin mHsp60.

Human mitochondrial chaperonin mHsp60 is essential for mitochondrial function by assisting folding of mitochondrial proteins. Unlike the double-ring bacterial GroEL, mHsp60 exists as a heptameric ring that is unstable and dissociates to subunits. The structural dynamics has been implicated for a unique mechanism of mHsp60. We purified active heptameric mHsp60, and determined a cryo-EM structure of mHsp60 heptamer at 3.4 Å. Of the three domains, the equatorial domains contribute most to the inter-subunit interactions, which include a four-stranded ß sheet. Our structural comparison with GroEL shows that mHsp60 contains several unique sequences that directly decrease the sidechain interactions around the ß sheet and indirectly shorten ß strands by disengaging the backbones of the flanking residues from hydrogen bonding in the ß strand conformation. The decreased inter-subunit interactions result in a small inter-subunit interface in mHsp60 compared to GroEL, providing a structural basis for the dynamics of mHsp60 subunit association. Importantly, the unique sequences are conserved among higher eukaryotic mitochondrial chaperonins, suggesting the importance of structural dynamics for eukaryotic chaperonins. Our structural comparison with the single-ring mHsp60-mHsp10 shows that upon mHsp10 binding the shortened inter-subunit ß sheet is restored and the overall inter-subunit interface of mHsp60 increases drastically. Our structural basis for the mHsp10 induced stabilization of mHsp60 subunit interaction is consistent with the literature that mHsp10 stabilizes mHsp60 quaternary structure. Together, our studies provide structural bases for structural dynamics of the mHsp60 heptamer and for the stabilizing effect of mHsp10 on mHsp60 subunit association.

Structure and DNA binding of the human Rtf1 Plus3 domain.

The yeast Paf1 complex consists of Paf1, Rtf1, Cdc73, Ctr9, and Leo1 and regulates histone H2B ubiquitination, histone H3 methylation, RNA polymerase II carboxy-terminal domain (CTD) Ser2 phosphorylation, and RNA 3' end processing. We provide structural insight into the Paf1 complex with the NMR structure of the conserved and functionally important Plus3 domain of human Rtf1. A predominantly beta-stranded subdomain displays structural similarity to Dicer/Argonaute PAZ domains and to Tudor domains. We further demonstrate that the highly basic Rtf1 Plus3 domain can interact in vitro with single-stranded DNA via residues on the rim of the beta sheet, reminiscent of siRNA binding by PAZ domains, but did not detect binding to double-stranded DNA or RNA. We discuss the potential role of Rtf1 Plus3 ssDNA binding during transcription elongation.

Ingested (oral) SIRS peptide 1-21 inhibits acute EAE by inducing Th2-like cytokines.

OBJECTIVE: Ingested type I IFN inhibits clinical attacks, relapses and inflammation in murine chronic relapsing EAE by inhibiting Th1-like cytokines. Type I IFN activates human suppressor T cells that produce SIRS. METHODS: We examined whether oral (ingested) SIRS peptide inhibits EAE by decreasing Th1-like cytokines. RESULTS: Parenteral SIRS peptide 1-21 showed a significant inhibition of disease severity in murine EAE. Ingested SIRS peptide at 10 and 100 microg SIRS peptide showed a significant inhibition of disease severity but also a prolonged delay in the onset of disease compared to placebo. There were significantly less inflammatory foci in the SIRS peptide fed group compared to the control mock fed group. Splenocytes from SIRS peptide 1-21 fed mice showed increased production of Th2-like CD30L, IL-13, TCA-3 cytokines/chemokines and decreased production of Th1-like cytokine lymphotactin. INTERPRETATION: Ingested (oral) SIRS peptide significantly inhibits both clinical EAE and inflammation predominately via counter-regulatory type 2-like cytokines/chemokines IL-13, CD30L and TCA-3.

TIP, a T-cell factor identified using high-throughput screening increases survival in a graft-versus-host disease model.

A coordinated effort combining bioinformatic tools with high-throughput cell-based screening assays was implemented to identify novel factors involved in T-cell biology. We generated a unique library of cDNAs encoding predicted secreted and transmembrane domain-containing proteins generated by analyzing the Human Genome Sciences cDNA database with a combination of two algorithms that predict signal peptides. Supernatants from mammalian cells transiently transfected with this library were incubated with primary T cells and T-cell lines in several high-throughput assays. Here we describe the discovery of a T cell factor, TIP (T cell immunomodulatory protein), which does not show any homology to proteins with known function. Treatment of primary human and murine T cells with TIP in vitro resulted in the secretion of IFN-gamma, TNF-alpha, and IL-10, whereas in vivo TIP had a protective effect in a mouse acute graft-versus-host disease (GVHD) model. Therefore, combining functional genomics with high-throughput cell-based screening is a valuable and efficient approach to identifying immunomodulatory activities for novel proteins.

Beyond Antibodies: Development of a Novel Protein Scaffold Based on Human Chaperonin 10.

Human Chaperonin 10 (hCpn10) was utilised as a novel scaffold for presenting peptides of therapeutic and diagnostic significance. Molecular dynamic simulations and protein sizing analyses identified a peptide linker (P1) optimal for the formation of the quarternary hCpn10 heptamer structure. hCpn10 scaffold displaying peptides targeting Factor VIIa (CE76-P1) and CD44 (CP7) were expressed in E. coli. Functional studies of CE76-P1 indicated nanomolar affinity for Factor VIIa (3 nM) similar to the E-76 peptide (6 nM), with undetectable binding to Factor X. CE76-P1 was a potent inhibitor of FX activity (via inhibition of Factor VIIa) and prolonged clot formation 4 times longer than achieved by E-76 peptide as determined by prothrombin time (PT) assays. This improvement in clotting function by CE76-P1, highlights the advantages of a heptamer-based scaffold for improving avidity by multiple peptide presentation. In another example of hCPn10 utility as a scaffold, CP7 bound to native CD44 overexpressed on cancer cells and bound rCD44 with high affinity (KD 9.6 nM). The ability to present various peptides through substitution of the hCpn10 mobile loop demonstrates its utility as a novel protein scaffold.

Soluble Immune Response Suppressor (SIRS): Reassessing the immunosuppressant potential of an elusive peptide.

A previously studied immunosuppressive cytokine, Soluble Immune Response Suppressor (SIRS), may have relevance to current studies of immune suppression in a variety of human disease states. Despite extensive efforts using experimental models, mainly in mice, much remains to be discovered as to how autoimmune cells in mice and humans escape normal regulation and, conversely, how tumor cells evade evoking an immune response. It is the contention of this commentary that the literature pre-2000 contain results that might inform current studies. The broadly immunosuppressive protein, SIRS, was studied extensively from the 1970s to 1990s and culminated in the determination of the n-terminal 21mer sequence of this 15kDa protein which had high homology to the short neurotoxins from sea snakes, that are canonical members of the three finger neurotoxin superfamily (3FTx). It was not until 2007 that the prophylactic administration of the synthetic N-terminal peptide of the SIRS 21mer, identical to the published sequence, was reported to inhibit or delay the development of two autoimmune diseases in mice: experimental allergic encephalomyelitis (EAE) and type I diabetes (T1D). These findings were consistent with other studies of the 3FTx superfamily as important probes in the study of mammalian pharmacology. It is the perspective of this commentary that SIRS, SIRS peptide and the anti-peptide mAb, represent useful, pharmacologically-active probes for the study of the immune response as well as in the potential treatment of autoimmune, inflammatory diseases and cancer.

Biochemical analysis of a T cell receptor alpha-like molecule involved in antigen-nonspecific suppression.

Monoclonal nonspecific suppressor factor (MNSF), a lymphokine produced by murine T cell hybridoma, possesses a pleiotropic antigen-nonspecific suppressive function. We have shown that 70 kDa MNSF comprises an 8 kDa ubiquitin-like polypeptide (Ubi-L) and 62 kDa T cell receptor (TCR) alpha-like molecule. Ubi-L binds specifically to its 82 kDa receptor protein on target cells. In the current study, we have further characterized the biochemical nature of the TCR(alpha)-like molecule. The 62 kDa protein was separated into two species of 46 kDa and 16 kDa on reverse-phase HPLC. Anti-TCR(alpha) monoclonal antibody recognized the 46 kDa, but not the 16 kDa protein. Anti-TCRbeta monoclonal antibody failed to recognize these proteins. Ubi-L conjugated to the 46 kDa protein, whereas Ubi-L lacking its C-terminal Gly-Gly did not. Although Ubi-L was labile both to heating at 56 degrees C and to acidification to pH 4, the Ubi-L-46 kDa protein complex was unaffected by these treatments. In addition, the 46 kDa protein elongated the Ubi-L-induced protein tyrosine phosphorylation in a concanavalin A-activated murine T helper type 2 clone, D10 cells. One of the four tryptic peptide sequences derived from the 46 kDa protein was in alignment with a related sequence found in the J(alpha) region of the TCR(alpha), including the highly conserved motif F-G-X-G-T-X-L.

Noncovalent interaction of MNSFbeta, a ubiquitin-like protein, with histone 2A.

Monoclonal nonspecific suppressor factor (MNSF), a lymphokine produced by murine T cell hybridoma, possesses pleiotrophic antigen-nonspecific suppressive functions. A cDNA clone encoding MNSFbeta, an isoform of the MNSF, has been isolated and characterized. MNSFbeta cDNA encodes a fusion protein consisting of a ubiquitin-like segment (Ubi-L) and ribosomal protein S30. Most recently, we observed that Ubi-L covalently conjugates to Bcl-G, a novel pro-apoptotic protein. In this study, we observed that Ubi-L noncovalently and specifically binds to histone 2A. The maximum binding was observed at a molar ratio equal to 1 for GST-Ubi-L and 2 for histone 2A. Ubi-L formed complex with histone 2A in the presence of 1% Triton X-100. Free Ubi-L was detected in nuclei from unstimulated murine helper T cell line, D10. The increased amounts of free Ubi-L and some Ubi-L adducts were observed in nuclei from mitogen-activated D10 cells. Interestingly, two Ubi-L adducts were unique to the chromatin fraction of nuclei from the activated D10 cells.

Murine soluble Fc gamma receptors/IgG-binding factors (IgG-BF): analysis of the relation to Fc gamma RII and production of milligram quantities of biologically active recombinant IgG-BF.

The production of soluble forms of low-affinity Fc gamma R by cells expressing recombinant or natural membrane Fc gamma RII, and the structural relationships between these soluble receptors and membrane Fc gamma RII are described. We show that 37-40 kD soluble Fc gamma RII, corresponding to the two N-terminal domains of Fc gamma RII and binding to IgG, are spontaneously produced in vitro by cleavage of membrane Fc gamma RII. Moreover, we describe methods to produce and purify to homogeneity large quantities of endotoxin-free recombinant IgG-binding factor (rIgG-BF) from the culture medium of a cell line transfected with a mutated Fc gamma RII cDNA. These methods include the use of bioreactors for culturing transfected fibroblasts and the purification of rIgG-BF by ion-exchange chromatography and hydrophobic-interaction chromatography. By using such procedures, about 2.4 mg of rIgG-BF were purified from 1 liter of culture medium of transfected fibroblasts. Like natural IgG-BF, the 95-99% pure rIgG-BF suppressed, in a dose-dependent manner, secondary in vitro IgG antibody responses to sheep red blood cells.

Immunosuppressive activity in the rat seminiferous tubules.

Rat seminiferous tubule segments in defined stages of the epithelial cycle were isolated by transillumination-assisted microdissection. The segments were cultured together with ConA-stimulated peripheral blood lymphocytes (PBL) and incorporation of 3H-labelled thymidine was measured. Tubule segments in stages II-VIII of the seminiferous epithelial cycle inhibited PBL proliferation significantly more than stages IX-I. Inhibition was lowest in stages IX-XII and increased progressively to reach a maximum in stages II-VIII. In a more detailed analysis, tubules in stages V and VI inhibited PBL proliferation significantly less than stage II tubules. No significant difference was observed between stages II and VII. The immunosuppressive activity had molecular weights of approximately 25 kDa and approximately 65 kDa in stage II-VIII seminiferous tubules. In stage II-VI seminiferous tubules activity was present also at approximately 10 kDa. The results suggest that the seminiferous tubules produce high-molecular weight immunosuppressive activity in a stage-dependent way. In addition to its contribution to the immunologically privileged milieu of the testis this activity may also be involved in the physiological regulation of DNA synthesis in the seminiferous epithelium.

Glycoprotein glycosylation and the immunosuppressive effects of human pregnancy serum.

Pregnancy serum contains a factor or factors which suppress T lymphocyte proliferation, although the identity of the factor(s) is still unclear. We have demonstrated that the immunosuppressive activity of pregnancy sera can be destroyed by treatment with periodate which oxidises protein-linked oligosaccharides. Similar effects have been noted with uromodulin, a potent immunosuppressive glycoprotein initially isolated from pregnancy urine. We find, however, that uromodulin is present in both pregnancy and non-pregnancy sera, and that removal of uromodulin from pregnancy serum by lectin affinity chromatography is not associated with loss of activity, ruling out this glycoprotein as the immunosuppressive factor. The possible role of protein-linked oligosaccharides of other serum glycoproteins in causing the pregnancy-related immunosuppression is discussed.

Bovine early pregnancy factor (EPF) activity dependent on a 67-kDa polypeptide.

Maternal bovine EPF activity can be reduced to one single polypeptide enriched and identified from serum of cows in early pregnancy. The relative molecular weight of this active polypeptide was estimated at 67 kDa. This bovine EPF was labelled by 125I and peroxidase. In parallel investigations of non-pregnant animals a 67-kDa polypeptide was additionally identified in the last purification step, but without EPF activity in the rosette inhibition test. This indicated occurrence of an inactive pre-compound (or carrier protein) of the EPF in the non-pregnant state. On pre-incubation of lymphocytes with EPF analogues (inactive polypeptide from nonpregnancy serum) EPF retained its optimal activity, its lymphocyte receptors being unaffected. Monoclonal antibodies produced against HPLC-enriched EPF were reactive to the 67-kDa polypeptide in pregnancy material as well as in nonpregnancy material and were not able to differentiate between 'pregnant' and 'nonpregnant'. A mouse anti-EPF serum produced against highly purified EPF isolated from SDS PAGE showed reactivity only against the 67-kDa polypeptide of pregnancy serum but not against that of non-pregnancy serum. This is the first evidence for a difference in antigenic determinants of the two 67-kDa proteins found in pregnancy and non-pregnancy serum. Furthermore, a second higher molecular weight protein could be identified by this antiserum in pregnancy and non-pregnancy serum.

Secretion of suppressor factors by EBV infected B cell lines.

The infection of human peripheral blood B cells with Epstein-Barr Virus (EBV), induced the production of suppressor factor(s) which were released into the supernatant of the B-cell cultures. The induction of suppressive activity was independent of T-cell presence. The suppression was exhibited both against T-cell activity (MLR and mitogenic stimulation) as well as against B-cell mitogenic stimulation of human or murine B lymphocytes. The suppressive factor(s) was of a low molecular weight (equal or less than 5,000), resistant to trypsin and heating at 80 degrees C and its activity was partially inhibited by neuraminidase treatment. These findings indicate that the suppressive factor(s) is not correlated to immunoglobulin production, is not apparently of a protein nature, and might be of ganglioside or siaylated glycoprotein structure. Our present findings suggest that, in addition to T cells, B cells might also play an immunoregulatory role in the expression of immune response potential.

Immunomodulatory activity of plasmatic substances.

In order to study circulating substances which could be involved in uremic immunodeficiency, the activity of plasma and plasmatic fractions of different molecular weight MW (A and B) from 12 patients with chronic renal failure (CRF) and 12 normal subjects (N) was assayed in vitro on PHA stimulated normal lymphocyte cultures. Plasma from CRF patients inhibited lymphoproliferation compared to normal plasma activity (mean +/- SD: 9,990 +/- 3,980 cpm vs. 22,163 +/- 3,054 cpm; p < 0.001). Nevertheless, the corresponding plasmatic fractions failed to induce similar effects. Both normal fractions showed inhibitory effects on proliferation while most of the CRF fractions allowed greater cellular proliferation than the former. The dose-response curves showed that all the normal fractions contained inhibitor(s) whose effect decreased with increasing dilution. Most of the B normal fractions also produced stimulatory effects when they were diluted between 1:5 and 1:25. Variable dose-response curves were obtained in the presence of CRF fractions. However, the lack of inhibitory activity in 9 of 12 patients and the stimulatory effects produced by several A-CRF fractions suggest qualitative differences between CRF and normal fractions. Present findings demonstrate inhibitory and stimulatory activities in the normal fractions which might be due to immunomodulator substances. Disorders in this immunomodulator system could be responsible for the immunodeficiency described in CRF patients.

[Analysis of antigen non-specific suppressor T cells factor (TsF) which suppresses the generation of cytotoxic T lymphocytes].

Anti-mouse melanoma suppressor T cells clone (F12) secreted a functional factor (TsF) which suppresses the generation of cytotoxic T lymphocytes (CTL). Ts clone F12 secreted TsF into culture supernatant by stimulating for more than 12 hours with anti-CD3 monoclonal Ab. In syngeneic CTL induction system, TsF suppresses the generation of both anti-melanoma and anti-lymphoma CTL. Moreover, TsF suppresses allogeneic CTL not only from C57BL/6 mice but also from C3H mice. Analysis of the biochemical and physiochemical character of TsF shows that TsF is stable for variance of pH and freeze and thawing, but unstable for heat in region of 100 degrees C. and in acetonitorile. It is also suggested that the molecular weight of TsF is in the vicinity of 12,000 daltons on the analysis in high performance liquid chromatography. F12 clone secretes other suppressive cytokine, TGF-beta and INF-gamma. However, TsF seems different from these suppressive cytokine, because anti-TGF-beta serum which blocks the suppressive function of TGF-beta 1 for CTL generation does not block TsF function. Moreover, recombinant INF-gamma does not suppress the generation of CTL.