Heterogeneity of the glycans O-glycosidically linked to the hinge region of secretory immunoglobulins from human milk

Pure secretory immunoglobulin A was isolated from human milk by fractionation in gradients of pH and (NH4)2SO4 concentration followed by gel filtration. The hinge region containing all the O-glycosidically linked oligosaccharides was isolated en bloc after trypsin and pepsin hydrolysis and separated by gel filtration. The mixture of O-glycosidically linked oligosaccharides contained N-acetylneuraminic acid (NeuAc), fucose (Fuc), galactose (Gal), N-acetylglucosamine (GlcNAc) and N-acetylgalactosamine (GalNAc) in the molar ratio of 0.2:0.5:2.5:2:1 respectively. After beta-elimination several oligosaccharides were separated by a combination of ion-exchange chromatography and gel-filtration chromatography. The complete structure of four of these oligosaccharides was determined by methanolysis, methylation and mass spectrometry. The structure of the four oligosaccharides which are linked to serine or threonine residues of the hinge region are as follows: beta-Gal-(1 leads to 3)-GalNAc-ol; alpha-HeuAc-(2 leads to 3)-beta-Gal-(1 leads to 3)-GalNAc-ol; beta-Gal-(1 leads to 3)-[beta-GlcNAc-(1 leads to 6)]-GalNAc-ol; beta-Gal-(1 leads to 3)-[beta-Gal-(1 leads to 4)-beta-GlcNac-(1 leads to 6)]-Gal-NAc-ol. These oligosaccharides are more complex and heterogenous than the oligosaccharides linked to serine residues of the hinge region from myeloma serum immunoglobulin A1.

The binding of lactoferrin to glycosaminoglycans on enterocyte-like HT29-18-C1 cells is mediated through basic residues located in the N-terminus

Although lactoferrins (Lfs) isolated from milk of various mammals exhibit a close structural relationship, they show species-specific binding to cells. To define the specificity of recognition of human (hLf), bovine (bLf) and murine (mLf) lactoferrin by human intestinal cells, we analysed the binding of the three proteins to a subclone derived from human carcinoma cell line HT29. We observed that hLf and bLf interact with two types of binding sites (K(d): 63+/-22 nM; 0.7+/-0.2 microM) while mLf was recognized only by the lowest affinity binding sites with a lower number of binding sites. Using N-terminal deleted human Lf variants, we found that the sequence G(1)RRRR(5) is mainly responsible for the interactions with HT29 cells. Lactoferrin-binding sites on the surface of HT29 cells were further identified as heparan sulphate and chondroitin sulphate glycosaminoglycans. We conclude that the presence of the sequence A(1)PRK(4) in bLf and K(1)ATT(4) in mLf provides an insight into why the interaction of bLf with cell membrane-associated glycosaminoglycans is similar to that of hLf and why binding of these lactoferrin species differs from that of murine Lf.

Delineation of the calcineurin-interacting region of cyclophilin B

The immunosuppressant drug cyclosporin A (CsA) inhibits T-cell function by blocking the phosphatase activity of calcineurin. This effect is mediated by formation of a complex between the drug and cyclophilin (CyP), which creates a composite surface able to make high-affinity contacts with calcineurin. In vitro, the CyPB/CsA complex is more effective in inhibiting calcineurin than the CyPA/CsA and CyPC/CsA complexes, pointing to fine structural differences in the calcineurin-binding region. To delineate the calcineurin-binding region of CyPB, we mutated several amino acids, located in two loops corresponding to CyPA regions known to be involved, as follows: R76A, G77H, D155R, and D158R. Compared to wild-type CyPB, the G77H, D155R, and D158R mutants had intact isomerase and CsA-binding activities, indicating that no major conformational changes had taken place. When complexed to CsA, they all displayed only reduced affinity for calcineurin and much decreased inhibition of calcineurin phosphatase activity. These results strongly suggest that the three amino acids G77, D155, and D158 are directly involved in the interaction of CyPB/CsA with calcineurin, in agreement with their exposed position. The G77, D155, and D158 residues are not maintained in CyPA and might therefore account for the higher affinity of the CyPB/CsA complex for calcineurin.

Lactoferrin upregulates the expression of CD4 antigen through the stimulation of the mitogen-activated protein kinase in the human lymphoblastic T Jurkat cell line

The main biological properties of lactoferrin are thought to concern inflammation and immunomodulation processes, including maturation of immature B and T cells. Lactoferrin accelerates T-cell maturation by inducing the expression of the CD4 surface marker. In this report, using the Jurkat T-cell line, we have shown that lactoferrin upregulates the expression of CD4 antigen through the activation of a transduction pathway. Using an anti-phosphotyrosine antibody, lactoferrin was demonstrated to induce a cascade of phosphorylation of numerous proteins on their tyrosine residues. This tyrosine-phosphorylation was transient, reaching maxima between 5 and 10 min. We also identified the mitogen-activated protein kinase (MAP kinase) which presented an enhanced catalytic activity, reaching a maximum at 10 min of incubation with lactoferrin. Moreover, the use of inhibitors such as genistein and PD98059, tyrosine kinases and MAP kinase kinase (or MEK) inhibitors respectively, allowed us to correlate the activation of MAP kinase with the upregulation of CD4 expression. Finally, using Lck-defective Jurkat cells, our results showed that the p56(lck) (Lck) kinase is necessary for MAP kinase activity and CD4 expression. This paper demonstrates that lactoferrin activates transduction pathway(s) in lymphoblastic T-cells, and that Lck and the Erk2 isoform of MAP kinase are implicated in the upregulation of CD4, induced by lactoferrin in these cells.

Structural analysis of trisialylated biantennary glycans isolated from mouse serum transferrin. Characterization of the sequence Neu5Gc(alpha 2-3)Gal(beta 1-3)[Neu5Gc(alpha 2-6)]GlcNAc(beta 1-2)Man

Five variants of mouse serum transferrin (mTf, designated mTf-I to mTf-V) with respect to carbohydrate composition have been isolated by DEAE-cellulose chromatography in the following relative percentages: mTf-I: 0.55; mTf-II: 0.79; mTf-III: 71.80; mTf-VI: 21. 90 and mTf-V: 4.96. The primary structures of the major glycans from mTf-III and mTf-IV were determined by methylation analysis and 1H-nuclear magnetic resonance (NMR) spectroscopy. All glycans possessed a common trimannosyl-N,N'-diacetylchitobiose core. From the glycovariant mTf-III two isomers of a conventional biantennary N-acetyllactosamine type were isolated, in which two N-glycolylneuraminic acid (Neu5Gc) residues are linked to galactose either by a (alpha 2-6) or (alpha 2-3) linkage. A subpopulation of this glycovariant contains a fucose residue (alpha 1-6)-linked to GlcNAc-1. The structure of the major glycan found in variant mTf-IV contained an additional Neu5Gc and possessed the following new type of linkage: Neu5Gc(alpha 2-3)Gal(beta 1-3)[Neu5Gc(alpha 2-6)]GlcNAc(beta 1-2 )Man(alpha 1-3). In addition to this glycan, a minor compound contained the same antennae linked to Man(alpha 1-6). In fraction mTf-V, which was found to be very heterogeneous by (1)H NMR analysis, carbohydrate composition and methylation analysis suggested the presence of tri'-antennary glycans sialylated by Neu5Gc alpha-2,6- and alpha-2, 3-linked to the terminal galactose residues. In summary, mTf glycans differed from those of other analyzed mammalian transferrins by the presence of Neu5Gc and by a Neu5Gc(alpha 2-6)GlcNAc linkage in trisialylated biantennary structures, reflecting in mouse liver, a high activity of CMP-Neu5Ac hydroxylase and (alpha 2-6)GlcNAc sialyltransferase.

Lactoferrin is synthesized by mouse brain tissue and its expression is enhanced after MPTP treatment

The presence of iron in brain tissue in increased concentrations in Parkinson's disease cases, where it might be responsible for oxidative stress, and the parallel observation that the iron transporter lactoferrin (Lf) was present in increased amounts in surviving neurons, led us to study the synthesis of Lf in a mouse model of Parkinson's disease. In this context, the origin and expression of brain Lf in normal, aged and MPTP (1-methyl-4-phenyl-1, 2,3,6-tetrahydropyridine)-treated mice were investigated. Lf immunostaining was observed mainly on microvessels in the cerebral cortex of the adult mice and to a greater extent in older mice. Lf immunoreactivity was also present in the hippocampus only in the aged mouse brains, associated with structures which seemed to be pyramidal neurons and fibers. After RT-PCR (polymerase chain reaction), Lf transcripts were found in mouse brain tissue whatever the age of the animals studied but the level of their expression was very low. No up-regulation of Lf was detectable during aging. Lf distribution and expression in the MPTP-induced Parkinsonian mouse model were also investigated. A marked depletion of dopamine (DA) occurred in the high dose MPTP-treated mice. The level of Lf expression was found to be markedly increased in the same animals and this up-regulation occurred on the first day after MPTP administration. When the brain was stressed by the neurotoxin MPTP, Lf expression increased in line with antioxidant enzymes such as catalase and gamma-glutamylcysteine synthetase, which may permit the protection of brain tissue from oxidative damage induced by the drug.

Regulatory effects of lactoferrin and lipopolysaccharide on LFA-1 expression on human peripheral blood mononuclear cells

The aim of this study was to investigate effects of human lactoferrin (hLF) with regard to LFA-1 expression on unstimulated and lipopolysaccharide (LPS)-activated human peripheral blood mononuclear cells (PBMC). The investigations were carried out on 30 healthy volunteers, males and females, 24-58 years old. We found that hLF, at an optimal dose of 5 microg/ml/10(6) cells in 24-hour culture, exerted regulatory effects on LFA-1 expression, depending on distribution of this molecule on cells in control cultures and on the effects of LPS. First, we revealed several patterns of LFA-1 distribution and density of this marker among studied individuals. The effects of LPS and hLF on LFA-1 expression patterns were differential. LFA-1 expression was stimulated by individual actions of LPS or hLF, additive or synergistic effects of both factors, it could be also inhibited by hLF alone or in combination with LPS. In about one third of cases no significant effects of LPS or hLF on LFA-1 expression were seen. Removal of monocytes from the PBMC population diminished LFA-1 expression in control cultures and abolished LPS- or hLF-elicited changes. The regulatory effects of hLF were also blocked by treatment of PBMC cultures with anti-tumor necrosis factor alpha (TNF-alpha) antibodies. Taken together, the data showed that hLF and LPS had immunoregulatory properties with respect to LFA-1 expression on human PBMC and that these actions were mediated by monocytes and TNF-alpha.

Lactoferrin inhibits G1 cyclin-dependent kinases during growth arrest of human breast carcinoma cells

Lactoferrin inhibits cell proliferation and suppresses tumor growth in vivo. However, the molecular mechanisms underlying these effects remain unknown. In this in vitro study, we demonstrate that treatment of breast carcinoma cells MDA-MB-231 with human lactoferrin induces growth arrest at the G1 to S transition of the cell cycle. This G1 arrest is associated with a dramatic decrease in the protein levels of Cdk2 and cyclin E correlated with an inhibition of the Cdk2 kinase activity. Cdk4 activity is also significantly decreased in the treated cells and is accompanied by an increased expression of the Cdk inhibitor p21(CIP1). Furthermore, we show that lactoferrin maintains the cell cycle progression regulator retinoblastoma protein pRb in a hypophosphorylated form. Additional experiments with synchronized cells by serum depletion confirm the anti-proliferative activity of human lactoferrin. These effects of lactoferrin occur through a p53-independent mechanism both in MDA-MB-231 cells and other epithelial cell lines such as HBL-100, MCF-7, and HT-29. These findings demonstrate that lactoferrin induces growth arrest by modulating the expression and the activity of key G1 regulatory proteins.

Cyclophilin B binding to platelets supports calcium-dependent adhesion to collagen

We have recently reported that cyclophilin B (CyPB), a secreted cyclosporine-binding protein, could bind to T lymphocytes through interactions with two types of binding sites. The first ones, referred to as type I, involve interactions with the conserved domain of CyPB and promote the endocytosis of surface-bound ligand, while the second type of binding sites, termed type II, are represented by glycosaminoglycans (GAG). Here, we further investigated the interactions of CyPB with blood cell populations. In addition to lymphocytes, CyPB was found to interact mainly with platelets. The binding is specific, with a dissociation constant (kd) of 9 +/- 3 nmol/L and the number of sites estimated at 960 +/- 60 per cell. Platelet glycosaminoglycans are not required for the interactions, but the binding is dramatically reduced by active cyclosporine derivatives. We then analyzed the biologic effects of CyPB and found a significant increase in platelet adhesion to collagen. Concurrently, CyPB initiates a transmembranous influx of Ca(2+) and induces the phosphorylation of the P-20 light chains of myosin. Taken together, the present results demonstrate for the first time that extracellular CyPB specifically interacts with platelets through a functional receptor related to the lymphocyte type I binding sites and might act by regulating the activity of a receptor-operated membrane Ca(2+) channel.

Receptor-mediated transcytosis of cyclophilin B through the blood-brain barrier

Cyclophilin B (CyPB) is a cyclosporin A (CsA)-binding protein mainly located in intracellular vesicles and secreted in biological fluids. In previous works, we demonstrated that CyPB interacts with T lymphocytes and enhances in vitro cellular incorporation and activity of CsA. In addition to its immunosuppressive activity, CsA is able to promote regeneration of damaged peripheral nerves. However, the crossing of the drug from plasma to neural tissue is restricted by the relative impermeability of the blood-brain barrier. To know whether CyPB might also participate in the delivery of CsA into the brain, we have analyzed the interactions of CyPB with brain capillary endothelial cells. First, we demonstrated that CyPB binds to two types of binding sites present at the surface of capillary endothelial cells from various species of tissues. The first type of binding sites (K(D) = 300 nM; number of sites = 3 x 10(6)) is related to interactions with negatively charged compounds such as proteoglycans. The second type of binding sites, approximately 50,000 per cell, exhibits a higher affinity for CyPB (K(D) = 15 nM) and is involved in an endocytosis process, indicating it might correspond to a functional receptor. Finally, the use of an in vitro model of blood-brain barrier allowed us to demonstrate that CyPB is transcytosed by a receptor-mediated pathway (flux = 16.5 fmol/cm2/h). In these conditions, CyPB did not significantly modify the passage of CsA, indicating that it is unlikely to provide a pathway for CsA brain delivery.

Porins OmpC and PhoE of Escherichia coli as specific cell-surface targets of human lactoferrin. Binding characteristics and biological effects

The binding of lactoferrin, an iron-binding glycoprotein found in secretions and leukocytes, to the outer membrane of Gram-negative bacteria is a prerequisite to exert its bactericidal activity. It was proposed that porins, in addition to lipopolysaccharides, are responsible for this binding. We studied the interactions of human lactoferrin with the three major porins of Escherichia coli OmpC, OmpF, and PhoE. Binding experiments were performed on both purified porins and porin-deficient E. coli K12 isogenic mutants. We determined that lactoferrin binds to the purified native OmpC or PhoE trimer with molar ratios of 1.9 +/- 0.4 and 1.8 +/- 0.3 and Kd values of 39 +/- 18 and 103 +/- 15 nM, respectively, but not to OmpF. Furthermore, preferential binding of lactoferrin was observed on strains that express either OmpC or PhoE. It was also demonstrated that residues 1-5, 28-34, and 39-42 of lactoferrin interact with porins. Based on sequence comparisons, the involvement of lactoferrin amino acid residues and porin loops in the interactions is discussed. The relationships between binding and antibacterial activity of the protein were studied using E. coli mutants and planar lipid bilayers. Electrophysiological studies revealed that lactoferrin can act as a blocking agent for OmpC but not for PhoE or OmpF. However, a total inhibition of the growth was only observed for the PhoE-expressing strain (minimal inhibitory concentration of lactoferrin was 2.4 mg/ml). These data support the proposal that the antibacterial activity of lactoferrin may depend, at least in part, on its ability to bind to porins, thus modifying the stability and/or the permeability of the bacterial outer membrane.

Two distinct regions of cyclophilin B are involved in the recognition of a functional receptor and of glycosaminoglycans on T lymphocytes

Cyclophilin B is a cyclosporin A-binding protein exhibiting peptidyl-prolyl cis/trans isomerase activity. We have previously shown that it interacts with two types of binding sites on T lymphocytes. The type I sites correspond to specific functional receptors and the type II sites to sulfated glycosaminoglycans. The interactions of cyclophilin B with type I and type II sites are reduced in the presence of cyclosporin A and of a synthetic peptide mimicking the N-terminal part of cyclophilin B, respectively, suggesting that the protein possesses two distinct binding regions. In this study, we intended to characterize the areas of cyclophilin B involved in the interactions with binding sites present on Jurkat cells. The use of cyclophilin B mutants modified in the N-terminal region demonstrated that the 3Lys-Lys-Lys5 and 14Tyr-Phe-Asp16 clusters are probably solely required for the interactions with the type II sites. We further engineered mutants of the conserved central core of cyclophilin B, which bears the catalytic and the cyclosporin A binding sites as an approach to localize the binding regions for the type I sites. The enzymatic activity of cyclophilin B was dramatically reduced after substitution of the Arg62 and Phe67 residues, whereas the cyclosporin A binding activity was destroyed by mutation of the Trp128 residue and strongly decreased after modification of the Phe67 residue. Only the substitution of the Trp128 residue reduced the binding of the resulting cyclophilin B mutant to type I binding sites. The catalytic site of cyclophilin B therefore did not seem to be essential for cellular binding and the cyclosporin A binding site appeared to be partially involved in the binding to type I sites.

Receptor-mediated transcytosis of lactoferrin through the blood-brain barrier

Lactoferrin (Lf) is an iron-binding protein involved in host defense against infection and severe inflammation; it accumulates in the brain during neurodegenerative disorders. Before determining Lf function in brain tissue, we investigated its origin and demonstrate here that it crosses the blood-brain barrier. An in vitro model of the blood-brain barrier was used to examine the mechanism of Lf transport to the brain. We report that differentiated bovine brain capillary endothelial cells exhibited specific high (Kd = 37.5 nM; n = 90,000/cell) and low (Kd = 2 microM; n = 900,000 sites/cell) affinity binding sites. Only the latter were present on nondifferentiated cells. The surface-bound Lf was internalized only by the differentiated cell population leading to the conclusion that Lf receptors were acquired during cell differentiation. A specific unidirectional transport then occurred via a receptor-mediated process with no apparent intraendothelial degradation. We further report that iron may cross the bovine brain capillary endothelial cells as a complex with Lf. Finally, we show that the low density lipoprotein receptor-related protein might be involved in this process because its specific antagonist, the receptor-associated protein, inhibits 70% of Lf transport.

Lactoferrin: a multifunctional glycoprotein involved in the modulation of the inflammatory process

Lactoferrin is an iron-binding glycoprotein found in exocrine secretions of mammals and released from neutrophilic granules during inflammation. This review describes the biological roles of lactoferrin in host defence. Secreted lactoferrin exerts antimicrobial action either by chelation of iron or by destabilization of bacterial membranes. Furthermore, lactoferrin modulates the inflammatory process, mainly by preventing the release of cytokines from monocytes and by regulating the proliferation and differentiation of immune cells. Some of these activities are related to the ability of lactoferrin to bind lipopolysaccharides (LPS) with high affinity. Indeed, recent in vitro studies indicate that lactoferrin is able to compete with the LPS-binding protein for LPS binding and therefore to prevent the transfer of LPS to CD14 present at the surface of monocytes. Moreover, the prophylactic properties of lactoferrin against septicemia in vivo have been demonstrated. Taken as a whole, these observations strongly suggest that lactoferrin is one of the key molecules which modulate the inflammatory response.

Involvement of two classes of binding sites in the interactions of cyclophilin B with peripheral blood T-lymphocytes

Cyclophilin B (CyPB) is a cyclosporin A (CsA)-binding protein, mainly associated with the secretory pathway, and is released in biological fluids. We recently reported that CyPB specifically binds to T-lymphocytes and promotes enhanced incorporation of CsA. The interactions with cellular binding sites involved, at least in part, the specific N-terminal extension of the protein. In this study, we intended to specify further the nature of the CyPB-binding sites on peripheral blood T-lymphocytes. We first provide evidence that the CyPB binding to heparin-Sepharose is prevented by soluble sulphated glycosaminoglycans (GAG), raising the interesting possibility that such interactions may occur on the T-cell surface. We then characterized CyPB binding to T-cell surface GAG and found that these interactions involved the N-terminal extension of CyPB, but not its conserved CsA-binding domain. In addition, we determined the presence of a second CyPB binding site, which we termed a type I site, in contrast with type II for GAG interactions. The two binding sites exhibit a similar affinity but the expression of the type I site was 3-fold lower. The conclusion that CyPB binding to the type I site is distinct from the interactions with GAG was based on the findings that it was (1) resistant to NaCl wash and GAG-degrading enzyme treatments, (2) reduced in the presence of CsA or cyclophilin C, and (3) unmodified in the presence of either the N-terminal peptide of CyPB or protamine. Finally, we showed that the type I binding sites were involved in an endocytosis process, supporting the hypothesis that they may correspond to a functional receptor for CyPB.

Role of heparan sulphate proteoglycans in the regulation of human lactoferrin binding and activity in the MDA-MB-231 breast cancer cell line

We previously demonstrated that lactoferrin increases breast cell sensitivity to natural killer cell cytotoxicity whereas haematopoietic cells are unaffected by lactoferrin. It has been described that lactoferrin binds to various glycosaminoglycans. Compared to haematopoietic cells, breast cancer cells and particularly the breast cell line MDA-MB-231, possess a high level of proteoglycans. Scatchard analysis of 125I-lactoferrin binding to MDA-MB-231 cells revealed the presence of two classes of binding sites: a low affinity site with a Kd of about 700 nM and 3.9 x 10(6) sites and a higher affinity class with a Kd of 45 nM and 2.9 x 10(5) sites per cell. To investigate the potential regulation of lactoferrin activity by proteoglycans expressed on the MDA-MB-231 cells, we treated these cells with glycosaminoglycan-degrading enzymes or sodium chlorate, a metabolic inhibitor of proteoglycan sulphation. We showed that chondroitinase treatment has no effect, while heparinase or chlorate treatment significantly reduces both the binding of lactoferrin to cell surface sulphated molecules such as heparan sulphate proteoglycans (HSPG) and the affinity of lactoferrin for the higher affinity binding sites. The modulation of the lactoferrin binding was correlated with a decrease in lactoferrin activities on both MDA-MB-231 cell sensitisation to lysis and proliferation. Taken together, these results suggest that the presence of adequately sulphated molecules, in particular HSPG, is important for lactoferrin interaction and activity on the breast cancer cells MDA-MB-231.

Role of the first N-terminal basic cluster of human lactoferrin (R2R3R4R5) in the interactions with the Jurkat human lymphoblastic T-cells

We previously characterized a receptor of Mr 105,000 for human lactoferrin (hLf) on Jurkat human lymphoblastic T-cells. To delineate the role of R2R3R4R5 of hLf in the interaction with cells, we studied the binding of hLf variants obtained either by tryptic proteolysis (hLf-2N, hLF-3N and hLf-4N) or by mutagenesis (rhLf-5N). Consecutive removal of N-terminal arginine residues from hLf progressively increased the binding affinity but decreased the number of binding sites on the cells. The binding parameters of bovine Lf and native hLf did not differ, whereas the binding parameters of murine Lf resembled those of rhLf-5N. Culture of Jurkat cells in the presence of chlorate, which inhibits sulfation, reduced the number of binding sites for both native hLf and hLf-3N but not for rhLf-5N indicating that the hLf binding sites include sulfated molecules. The results suggest that the interaction of hLf with about 80,000 binding sites per Jurkat cell, mainly sulfated molecules, is dependent on R2R3R4, but not on R5. Interaction with about 20,000 binding sites per cell, presumably the hLf receptor, does not require the first N-terminal basic cluster of hLf. We conclude that the deletion of R2-R5 from hLf may serve to modulate the nature of its binding to cells and thereby its effects on cellular physiology.

Lactoferrin is synthesized by mouse brain tissue and its expression is enhanced after MPTP treatment

The biological role and origin of human lactoferrin (Lf) within the brain in normal and disease processes are as yet uncharted. In this context the origin and expression of brain Lf in normal and MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine)-treated mice were investigated using immunohisto chemistry, PCR amplification and in situ hybridization. Lf immunostaining was observed both on sections of mouse lactating mammary gland, which was used as a positive control, and brains from young, adult and aged mice. Lf immunoreactivity was present in the pituitary gland, the hippocampus and the cortex of mouse brains and to a greater extent in older mice. After reverse transcription, Lf transcripts were also found in these brain sections. Lf distribution and expression in the MPTP-induced parkinsonian mouse model were next investigated. A marked depletion of dopamine and its metabolites: dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxy indole acetic acid (5-HIAA) occurs in the high dose MPTP-treated mice. The level of Lf expression was found to be greatly increased in the same animals but Lf immunoreactivity detected in the same brain region was not found increased in the affected areas.

Immunoregulatory effects of a nutritional preparation containing bovine lactoferrin taken orally by healthy individuals

The aim of this study was to monitor several immune parameters in 17 healthy volunteers taking orally commercially available capsules containing bovine lactoferrin (BLFT) for 10 days (40 mg of BLFT daily). We determined leukocyte number and content of main blood cell types, spontaneous and phytohemagglutinin A (PHA)-induced proliferation of lymphocytes, plasma levels of interleukin 6 (IL-6) and tumor necrosis factor alpha (TNF-alpha) as well as spontaneous and lipopolysaccharide (LPS)-induced production of these cytokines in peripheral blood cell cultures. All measurements were performed before, one day and 14 days following cessation of BLFT treatment. We established some, transient drop in the percentage of neutrophils accompanied by an opposite phenomenon with regard to lymphocyte levels. More profound changes were registered in the percentage of other cell types, for example a 100% increase in the level of immature cell forms (bands) was noted. At the same time the percentages of eosinophils and monocytes declined significantly. All these changes were, however, more individual and regulatory, the direction of these changes depended on initial picture of blood cells. Although the proliferative response of lymphocytes showed, on average, a transient decrease, differentiated effects of BLFT treatment were observed depending on initial ability of lymphocytes to proliferate. TNF-alpha serum levels showed a tendency to decrease during the monitoring time, the changes of IL-6 levels were, however, not significant. As in the case of the proliferative response, the treatment with BLFT was regulatory with respect to serum TNF-alpha levels. When we analyzed spontaneous and LPS-induced cytokine production in cell cultures we found that mainly the mean spontaneous response was affected (inhibition). We also observed a typical, regulatory action of BLFT on the level of spontaneously produced IL-6. This kind of regulatory action of BLFT was also found in the case of spontaneously produced TNF-alpha in cell cultures. The influence of other ingredients such as selenium or vitamins, contained in the capsules, cannot be excluded, although our latest data showed that orally taken bovine lactoferrin alone can induce identical changes as BLFT. Taken together, we revealed regulatory effects of oral treatment with commercially available capsules, containing BLFT. The results indicate that oral administration on BLFT-containing capsules may regulate some immune parameters in healthy individuals. In addition, the data suggest that bovine lactoferrin may be applied in clinic to improve the immune status of patients.

Production of human lactoferrin in transgenic tobacco plants

Production and characterization of human lactoferrin (hLf) in transgenic tobacco is reported. We have engineered two constructs containing either the native signal peptide from human lactoferrin or the signal peptide from sweet potato sporamin fused to human lactoferrin encoding cDNA. N-terminal sequences of rhLf purified from tobacco were identical to Lf from human milk for both constructs. The tobacco rhLf presents a molecular mass closely identical to native protein. Overall sugar composition shows the presence of plant specific xylose while sialic acid is absent. Binding parameters of the recombinant molecule to both Jurkat lymphoblastic T-cells or HT29-18-C1 enterocytes are similar to those of human lactoferrin isolated from milk.

Enhancing the effect of secreted cyclophilin B on immunosuppressive activity of cyclosporine

BACKGROUND

Cyclophilin B (CyPB) is a cyclosporine (CsA)-binding protein, located within intracellular vesicles and secreted in biological fluids. In previous works, we reported that CyPB specifically interacts with the T-cell membrane and potentiates the ability of CsA to inhibit CD3-induced proliferation of T lymphocytes.

METHODS

CyPB levels were measured in plasma from healthy donors and transplant patients. The role of extracellular CyPB on the distribution and activity of CsA was investigated first by studies on the uptake of free and CyPB-complexed drug by blood cells, and second by studies on the inhibitory effects of these two compounds on the CD3-induced proliferation of peripheral blood mononuclear cells.

RESULTS

A significant increase in plasma CyPB level was observed for CsA-treated patients (13+/-6.4 nM, n=42) in comparison with untreated donors (4.3+/-2.1 nM, n=34). In vitro, extracellular CyPB dose dependently modified CsA distribution between plasma, erythrocyte, and lymphocyte contents, by both retaining the complexed drug extracellularly and promoting its specific accumulation within peripheral blood mononuclear cells. Moreover, the enhanced ability of CyPB-complexed CsA to suppress CD3-induced T-cell proliferation was preserved in the presence of other blood cells, implying specific targeting of the drug to sensitive cells. Furthermore, although a large interindividual variability of sensitivity to the drug was confirmed for 18 individuals, we found that CyPB potentiated the activity of CsA in restoring a high sensitivity to the immunosuppressant.

CONCLUSION

These results suggest that plasma CyPB may contribute to the acceptance and the good maintenance of organ transplantation by enhancing the immunosuppressive activity of CsA through a receptor-mediated incorporation of CyPB-complexed CsA within peripheral blood lymphocytes.

Effects of human lactoferrin on NK cell cytotoxicity against haematopoietic and epithelial tumour cells

Lactoferrin is an iron-binding glycoprotein implicated in particular in the control of immune functions and cell proliferation. We have investigated its involvement, at inflammatory concentrations, in cancer progression. We report that lactoferrin has a significant effect on natural killer (NK) cell cytotoxicity against haematopoietic and breast epithelial cell lines. Lactoferrin increases cytolysis at a low concentration (10 micrograms/ml) while at a high concentration (100 micrograms/ml) it modulates cytolysis depending on the target cell phenotype. By pre-treatment of either NK cells or target cells with lactoferrin, we have demonstrated that the lactoferrin effect is due both to a modulation of NK cell cytotoxicity and the target cell sensitivity to lysis. Lactoferrin binds to 91% of the naturally heterogeneous CD56dim/bright NK cell population and increases the NK cell cytotoxic activity at low concentrations. High concentrations of lactoferrin seem to be toxic for the CD56bright NK cells and decrease NK cell cytotoxicity. Lactoferrin also exerts an effect on target cells depending on the cell phenotype. It does not modify the susceptibility to lysis of haematopoietic cells such as Jurkat and K-562 cells, but does significantly increase that of the breast and colon epithelial cells. We have also demonstrated that lactoferrin inhibits epithelial cell proliferation by blocking the cell cycle progression.

Effect of lactoferrin on proliferation and differentiation of the Jurkat human lymphoblastic T cell line

The effect of human lactoferrin on the human lymphoblastic T cell line (Jurkat) was tested with regard to proliferation and differentiation. Lactoferrin enhanced cell proliferation in a serum-reduced (1% fetal calf serum) culture. The stimulatory effect of lactoferrin on proliferation depended on the degree of iron saturation but the amplitude of the effect was low, similar to that obtained in the presence of serum transferrin. The proliferation stimulatory effect of lactoferrin was not observed in the presence of 10% fetal calf serum (FCS) in the culture medium. These results suggest that Fe-lactoferrin can substitute for Fe-transferrin during the prolonged culture of cells in a low serum concentration. Iron-saturated lactoferrin was also shown to promote T cell differentiation. Jurkat cells, when exposed to iron-saturated lactoferrin in the presence of 10% FCS, gradually exhibited a decrease in the cell volume, cell surface density of CD71 antigen, the nuclear incorporation of [methyl-3H]thymidine, but an increase of the percentage of cell population in the G0/1 phase of the cell cycle. These modifications were accompanied by the appearance of CD4 antigen at the cell surface. Therefore, in the continuous presence of lactoferrin, proliferating cells slowly enter into quiescence state, undergoing cell differentiation.

Structure of the O-glycopeptides isolated from bovine milk component PP3

The heat-stable acid-soluble phosphoglycoprotein component PP3 was isolated from the bovine milk proteose peptone fraction by concanavalin A affinity chromatography. Glycopeptides from the ConA-bound fraction corresponding to the component PP3 were obtained by Pronase digestion and were separated by gel filtration into high and low-molecular-mass glycopeptides. In a previous work, we have investigated the structure of the N-glycans from the high-molecular-mass glycopeptides [Girardet et al. (1995) Eur J Biochem 234: 939-46]. Here, we describe the structure of the O-glycans from the low-molecular-mass glycopeptides. By combining methylation analysis, mass spectrometry, 400 MHz 1H-NMR spectroscopy and peptide sequence analysis, we show that the low-molecular-mass fraction contains several neutral glycopeptides. A mixture of the following three glycan structures linked to the Thr86 has been identified: GalNac alpha1-O-Thr, Gal(beta1-3)GalNAc alpha1-O-Thr and Gal(beta1-4)GlcNAc(beta1-6)[Gal(beta1-3)]GalNAc alpha1-O-Thr.

Determination of glycan structures and molecular masses of the glycovariants of serum transferrin from a patient with carbohydrate deficient syndrome type II

Serum transferrin from a child with carbohydrate deficient syndrome type II was isolated by immunoaffinity chromatography and separated into minor and major fractions by fast protein liquid chromatography. The structure of the glycans released from the major fraction by hydrazinolysis was established by application of methanolysis and 1H-NMR spectroscopy. The results led to the identification of an N-acetyllactosamininic type monosialylated, monoantennary Man(alpha1-3) linked glycan. By electrospray-mass spectrometry analysis, the whole serum transferrin was separated into at least seven species (I to VII) with molecular masses ranging from 77,958 to 79,130 Da. On the basis of a polypeptide chain molecular mass of 75,143 Da, it was calculated that the major transferrin species III (78,247 Da) contains two monosialylated monoantennary glycans. The molecular mass of transferrin species V and VI (78,678 and 78,971 Da) suggests that one of their two glycans contains an additional N-acetyllactosamine and a sialylated N-acetyllactosamine units, respectively. Transferrin species I and V were found to correspond to the desialylated forms of species III and VI. The abnormal glycan structures can be explained by a defect in the N-acetylglucosaminyltransferase II activity [Charuk et al. (1995) Eur J Biochem 230: 797-805].

Lactoferrin inhibits the endotoxin interaction with CD14 by competition with the lipopolysaccharide-binding protein

Human lactoferrin (hLf), a glycoprotein released from neutrophil granules during inflammation, and the lipopolysaccharide (LPS)-binding protein (LBP), an acute-phase serum protein, are known to bind to the lipid A of LPS. The LPS-binding sites are located in the N-terminal regions of both proteins, at amino acid residues 28 to 34 of hLf and 91 to 108 of LBP. Both of these proteins modulate endotoxin activities, but they possess biologically antagonistic properties. In this study, we have investigated the competition between hLf and recombinant human LBP (rhLBP) for the binding of Escherichia coli 055:B5 LPS to the differentiated monocytic THP-1 cell line. Our studies revealed that hLf prevented the rhLBP-mediated binding of LPS to the CD14 receptor on cells. Maximal inhibition of LPS-cell interactions by hLf was raised when both hLf and rhLBP were simultaneously added to LPS or when hLf and LPS were mixed with cells 30 min prior to the incubation with rhLBP. However, when hLf was added 30 min after the interaction of rhLBP with LPS, the binding of the rhLPS-LBP complex to CD14 could not be reversed. These observations indicate that hLf competes with rhLBP for the LPS binding and therefore interferes with the interaction of LPS with CD14. Furthermore, experiments involving competitive binding of the rhLBP-LPS complex to cells with two recombinant mutated hLfs show that in addition to residues 28 to 34, another basic cluster which contains residues 1 to 5 of hLf competes for the binding to LPS. Basic sequences homologous to residues 28 to 34 of hLf were evidenced on LPS-binding proteins such as LBP, bactericidal/permeability-increasing protein, and Limulus anti-LPS factor.

The N-terminal Arg2, Arg3 and Arg4 of human lactoferrin interact with sulphated molecules but not with the receptor present on Jurkat human lymphoblastic T-cells

We previously characterized a 105 kDa receptor for human lactoferrin (hLf) on Jurkat human lymphoblastic T-cells. To delineate the role of the basic cluster Arg2-Arg3-Arg4-Arg5 of hLf in the interaction with Jurkat cells, we isolated N-terminally deleted hLf species of molecular mass 80 kDa lacking two, three or four N-terminal residues (hLf-2N, hLf-3N and hLf-4N) from native hLf that had been treated with trypsin. Native hLf bound to 102000 sites on Jurkat cells with a dissociation constant (Kd) of 70 nM. Consecutive removal of N-terminal arginine residues from hLf progressively increased the binding affinity but decreased the number of binding sites on the cells. A recombinant hLF mutant lacking the first five N-terminal residues (rhLf-5N) bound to 17000 sites with a Kd of 12 nM. The binding parameters of bovine lactoferrin (Lf) and native hLf did not significantly differ, whereas the binding parameters of murine Lf (8000 sites; Kd 30 nM) resembled those of rhLf-5N. Culture of Jurkat cells in the presence of chlorate, which inhibits sulphation, decreased the number of binding sites for both native hLf and hLf-3N but not for rhLf-5N, indicating that the hLf-binding sites include sulphated molecules. We propose that the interaction of hLf with a large number of binding sites (approx. 80000 per cell) on Jurkat cells is dependent on Arg2-Arg3-Arg4, but not on Arg5. Interaction with approx. 20000 binding sites per cell, presumably the hLf receptor, does not require the first N-terminal basic cluster of hLf. Moreover, the affinity of hLf for the latter binding site is enhanced approx. 6-fold after removal of the first basic cluster. Thus N-terminal proteolysis of hLf in vivo might serve to modulate the nature of its binding to cells and thereby its effects on cellular physiology.

Distribution of cyclophilin B-binding sites in the subsets of human peripheral blood lymphocytes

Cyclophilin B (CyPB) is a cyclosporin A (CsA)-binding protein, mainly associated with the secretory pathway and released in biological fluids. We have recently demonstrated that both free CyPB and CyPB-CsA complex specifically bind to peripheral blood T lymphocytes and are internalized. These results suggest that CyPB might promote the targeting of the drug into sensitive cells. Peripheral blood lymphocytes are subdivided in several populations according to their biological functions and sensitivity to CsA. We have investigated the binding of CyPB to these different subsets using a CyPB derivatized by fluorescein through its single cysteine which retains its binding properties. We have confirmed that only T cells were involved in the interaction with CyPB. The ligand binding was found to be heterogeneously distributed on the different T-cell subsets and surface-bound CyPB was mainly associated with the CD4-positive cells. No significant difference was noted between the CD45RA and CD45RO subsets, demonstrating that CyPB-binding sites were equally distributed between native and memory T cells. CD3 stimulation of T lymphocytes led to a decrease in the CyPB-binding capacity, that may be explained by a down-regulation of the CyPB-receptor expression upon T-cell activation. Finally, we demonstrated that CyPB-receptor-positive cells, isolated on CyPB sulphydryl-coupled affinity matrices, are more sensitive to CyPB-complexed CsA than mixed peripheral blood lymphocytes, suggesting that CyPB potentiates CsA activity through the binding of the complex. Taken together, our results demonstrate that CyPB-binding sites are mainly associated with resting cells of the helper T lymphocyte, and that CyPB might modulate the distribution of CsA through the drug targeting to sensitive cells.

Characterization of human lactoferrin produced in the baculovirus expression system

Lactoferrin, an iron-binding 80-kDa glycoprotein, is a major component of human milk whose structure is now well defined. The binding site of lactoferrin to the membrane receptor of lymphocyte has been located in the region 4-52, but the amino acids directly involved in the interaction have not been identified yet. To gain further insights into the structure-function relationships of the lactoferrin binding site, we first expressed the cDNA encoding human lactoferrin in the lepidoptera Spodoptera frugiperda cells (Sf9) using a recombinant baculovirus. The selected transformant secreted and N-glycosylated protein of 78 kDa which was immunoprecipitated by specific anti-lactoferrin antibodies. To confirm the structure and the function of the recombinant lactoferrin, the protein was purified by ion-exchange chromatography and its physical, biochemical, and biological properties were compared with those of the native protein. In particular, the N-terminal amino acid sequence and the iron-binding stability as a function of pH, of both proteins, were identical. The main difference concerns the glycosylation which leads to glycans of lower molecular masses as detected by the electrophoretic mobility of lactoferrin after N-glycosidase F treatment and matrix-assisted laser desorption ionization/time-of-flight mass spectrometry. Despite the different glycosylation features, the recombinant lactoferrin retained the binding property to the Jurkat human lymphoblastic T-cell line of the native lactoferrin. On the basis of these analyses, production of protein mutants generated by site-directed mutagenesis is now in process.

Cyclophilin B mediates cyclosporin A incorporation in human blood T-lymphocytes through the specific binding of complexed drug to the cell surface

Cyclophilin B (CyPB) is a cyclosporin A (CsA)-binding protein located within intracellular vesicles and released in biological fluids. We recently reported the specific binding of this protein to T-cell surface receptor which is internalized even in the presence of CsA. These results suggest that CyPB might target the drug to lymphocytes and consequently modify its activity. To verify this hypothesis, we have first investigated the binding capacity and internalization of the CsA-CyPB complex in human peripheral blood T-lymphocytes and secondly compared the inhibitory effect of both free and CyPB-complexed CsA on the CD3-induced activation and proliferation of T-cells. Here, we present evidence that both the CsA-CyPB complex and free CyPB bind to the T-lymphocyte surface, with similar values of Kd and number of sites. At 37 degrees C, the complex is internalized but, in contrast to the protein, the drug is accumulated within the cell. Moreover, CyPB receptors are internalized together with the ligand and rapidly recycled to the cell surface. Finally, we demonstrate that CyPB-complexed CsA remains as efficient as uncomplexed CsA and that CyPB enhances the immunosuppressive activity of the drug. Taken together, our results support the hypothesis that surface CyPB receptors may be related to the selective and variable action of CsA, through specific binding and targeting of the CyPB-CsA complex to peripheral blood T-lymphocytes.

Involvement of the N-terminal part of cyclophilin B in the interaction with specific Jurkat T-cell binding sites

Cyclophilin B (CyPB) is secreted in biological fluids such as blood or milk and binds to a specific receptor present on the human lymphoblastic cell line Jurkat and on human peripheral blood lymphocytes. This study was intended to specify the areas of CyPB that are involved in the interaction with the receptor. A synthetic peptide corresponding to the first 24 N-terminal amino acid residues of CyPB was shown to specifically recognize the receptor. Moreover, modification of Arg18 of CyPB by p-hydroxyphenlglyoxal led to a dramatic loss of affinity for the receptor. However, when this residue was replaced by an alanine residue using site-directed mutagenesis, no modification of the binding properties was found, suggesting that Arg18 is not directly involved but is sufficiently close to the interaction site to interfere with the binding when modified. Competitive binding experiments using a chimaeric protein made up of the 24 N-terminal amino acid residues of CyPB fused to the cyclophilin A core sequence confirmed the involvement of this region of CyPB in receptor binding.

Solution structure of bovine angiogenin by 1H nuclear magnetic resonance spectroscopy

The three-dimensional structure of bovine angiogenin has been determined using two- and three-dimensional proton NMR spectroscopy. The solution structure is very close to that recently determined by X-ray diffraction analysis. This structure appears well defined, even if five loops and one helix exhibit greater flexibility. Analysis of the active site geometry confirms the position of the Glu-118 residue which obstructs the pyrimidine binding site. There is no experimental evidence of an unobstructed conformation of angiogenin in solution. In addition, it appears that the Glu-118 and Ser-119 residues and the cell receptor binding loop may play an important role in the differences of C-terminal fragment organization and ribonucleolytic activity observed between angiogenins and ribonuclease A.

Cellular distribution of the iron-binding protein lactotransferrin in the mesencephalon of Parkinson's disease cases

Changes in the distribution of the iron-binding protein lactotransferrin have recently been described in the central nervous system during a variety of neurodegenerative disorders. To investigate whether lactotransferrin is associated with the neuropathological changes that characterize Parkinson's disease, we analyzed the distribution of this protein in the mesencephalon of neurologically normal individuals and patients affected with Parkinson's disease using quantitative immunohistochemical methods. High levels of lactotransferrin were observed in a large population of neurons in the substantia nigra of control cases. Lactotransferrin-positive neurons were severely affected by the neurodegenerative process that occurs in Parkinson's disease as indicated by a severe decrease in the number of immunolabeled neurons in all of these cases. Quantitative analysis also demonstrated higher immunolabeling levels of lactotransferrin in the surviving neurons in the substantia nigra and ventral tegmental area of Parkinson's disease cases compared to control cases. These results suggest that lactotransferrin may participate actively in the mechanism of neuronal degeneration in Parkinson's disease.

Evidence that human milk isolated cyclophilin B corresponds to a truncated form

Cyclophilin B (CyPB) is a member of the cyclophilin family (cyclosporin A-binding proteins) with specific N- and C-terminal extensions. In contrast to cyclophilin A, CyPB owns a signal sequence leading to its translocation in the endoplasmic reticulum. CyPB was reported to be present in human blood and milk, suggesting it is secreted. For this purpose, CyPB was purified to homogeneity from human milk and compared to recombinant CyPB expressed in E. coli. Ion spray mass spectrometry revealed that CyPB secreted in human milk exhibits a lower molecular mass than the one expected. Identification of phenylalanine as the C-terminus amino-acid residue of human milk CyPB indicates that the difference in molecular mass may be explained by the absence of the five C-terminal amino-acid residues AIAKE. These results suggest that in the sequence VEKPFAIAKE known to be responsible for retention of CyPB in the endoplasmic reticulum, the sequence AIAKE is more particularly necessary. Our findings raise the possibility that the CyPB may be processed to promote its release. As recombinant CyPB was shown to bind specifically to Jurkat cells, a lymphoblastic T-cell line, we then wanted to investigate the binding of human milk CyPB to these cells. Despite lacking the five C-terminal amino-acid residues, human milk CyPB is able to inhibit the binding of recombinant CyPB to Jurkat T cells.

Internalization of human lactoferrin by the Jurkat human lymphoblastic T-cell line

Binding of either iron-saturated or iron-free lactoferrin to the Jurkat human lymphoblastic T-cell line was saturable with a dissociation constant Kd of 40 nM. The total number of binding sites was estimated to be approximately 300,000. Non-specific binding did not exceed 30% of the total binding. Removal of the 4 clustered arginine residues of lactoferrin at position 2 to 5, which are involved in the interactions with heparan sulfate, did not modify the binding parameters. Therefore, the high number of low affinity binding sites previously described as responsible for the interaction of lactoferrin with either hepatocytes, enterocytes or the U937 monocytic cell line, is not involved in the binding of lactoferrin to Jurkat cells. After binding at 4 degrees C, a shift to 37 degrees C causes cell to internalize lactoferrin, with the maximum intracellular concentration found at 3 to 8 and 5 to 15 min for iron-saturated and iron-free forms, respectively. Addition of colchicine had no effect on binding or internalization. These results suggest that endocytosis of lactoferrin by Jurkat cells occurs through a receptor-mediated process. Jurkat cells internalize lactoferrin monophasically with a first-order endocytic constant K(in) of 0.060 min-1 at 37 degrees C. Confocal microscopic analysis, using fluorescein-carbohydrate-labeled lactoferrin showed that lactoferrin was mainly localized in intracellular vesicles. Following uptake, the endocytic path utilized by fluorescein-carbohydrate-labeled lactoferrin was shown to diverge from that of rhodamine-labeled serum transferrin; after internalization, lactoferrin and serum transferrin did not fully colocalize. Intracellular lactoferrin was found in endosome vesicles as assessed by electron microscopy. Raising the pH in endosomes using chloroquine led to the accumulation of lactoferrin into endosomes (acidic compartment). After internalization, Jurkat cells released both degraded and intact lactoferrin into the culture medium, suggesting that a fraction (30-40%) of the ligand is degraded at each round of endocytosis.

Lactoferrin-lipopolysaccharide interaction: involvement of the 28-34 loop region of human lactoferrin in the high-affinity binding to Escherichia coli 055B5 lipopolysaccharide

The ability of lactoferrin (Lf), an iron-binding glycoprotein that is also called lactotransferrin, to bind lipopolysaccharide (LPS) may be relevant to some of its biological properties. A knowledge of the LPS-binding site on Lf may help to explain the mechanism of its involvement in host defence. Our report reveals the presence of two Escherichia coli 055B5 LPS-binding sites on human Lf (hLf): a high-affinity binding site (Kd 3.6 +/- 1 nM) and a low-affinity binding site (Kd 390 +/- 20 nM). Bovine Lf (bLf), which shares about 70% amino acid sequence identity with hLf, exhibits the same behaviour towards LPS. Like hLf, bLf also contains a low- and a high-affinity LPS-binding site. The Kd value (4.5 +/- 2 nM) corresponding to the high-affinity binding site is similar to that obtained for hLf. Different LPS-binding sites for human serum transferrin have been suggested, as this protein, which is known to bind bacterial endotoxin, produced only 12% inhibition of hLf-LPS interaction. Binding and competitive binding experiments performed with the N-tryptic fragment (residues 4-283), the C-tryptic fragment (residues 284-692) and the N2-glycopeptide (residues 91-255) isolated from hLf have demonstrated that the high-affinity binding site is located in the N-terminal domain I of hLf, and the low-affinity binding site is present in the C-terminal lobe. The inhibition of hLf-LPS interaction by a synthetic octadecapeptide corresponding to residues 20-37 of hLf and lactoferricin B (residues 17-41), a proteolytic fragment from bLf, revealed the importance of the 28-34 loop region of hLf and the homologous region of bLf for LPS binding. Direct evidence that this amino acid sequence is involved in the high-affinity binding to LPS was demonstrated by assays carried out with EGS-loop hLf, a recombinant hLf mutated at residues 28-34.

Structure of glycopeptides isolated from bovine milk component PP3

The heat-stable acid-soluble phosphoglycoprotein component PP3 was isolated from the bovine milk proteose peptone fraction by concanavalin A affinity chromatography. Glycopeptides were released by pronase digestion of the milk component PP3 and were subsequently separated by high-pH anion-exchange chromatography on CarboPac PA-1. The primary structures of the glycan and peptide moieties of eight N-glycopeptides have been established by combining methylation analysis, mass spectrometry, 400-MHz 1H-NMR spectroscopy, and peptide sequence analysis. All the analyzed fractions contained biantennary N-acetyllactosamine-type carbohydrate chains, some of them with a GalNAc(beta 1-4)GlcNAc or a NeuAc(alpha 2-6)GalNAc(beta 1-4)GlcNAc group. This particular sequence did or did not replace the Gal(beta 1-4)GlcNAc group usually found in most N-linked glycans. Moreover, the sialylated Gal and GalNAc residues were only found on the Man(alpha 1-3) antenna.

Expression of lactoferrin receptors is increased in the mesencephalon of patients with Parkinson disease

The degeneration of nigral dopaminergic neurons in Parkinson disease is believed to be associated with oxidative stress. Since iron levels are increased in the substantia nigra of parkinsonian patients and this metal catalyzes the formation of free radicals, it may be involved in the mechanisms of nerve cell death. The cause of nigral iron increase is not understood. Iron acquisition by neurons may occur from iron-transferrin complexes with a direct interaction with specific membrane receptors, but recent results have shown a low density of transferrin receptors in the substantia nigra. To investigate whether neuronal death in Parkinson disease may be associated with changes in a pathway supplementary to that of transferrin, lactoferrin (lactotransferrin) receptor expression was studied in the mesencephalon. In this report we present evidence from immunohistochemical staining of postmortem human brain tissue that lactoferrin receptors are localized on neurons (perikarya, dendrites, axons), cerebral microvasculature, and, in some cases, glial cells. In parkinsonian patients, lactoferrin receptor immunoreactivity on neurons and microvessels was increased and more pronounced in those regions of the mesencephalon where the loss of dopaminergic neurons is severe. Moreover, in the substantia nigra, the intensity of immunoreactivity on neurons and microvessels was higher for patients with higher nigral dopaminergic loss. These data suggest that lactoferrin receptors on vulnerable neurons may increase intraneuronal iron levels and contribute to the degeneration of nigral dopaminergic neurons in Parkinson disease.

Characterization of sheep hemopexin glycovariants

The hemopexin phenotype HpxB1 isolated from sheep serum, yields three major bands when subjected to starch gel and/or polyacrylamide gel electrophoresis which are here designated as subcomponents HpxB1-I, HpxB1-II and HpxB1-III. Electrospray mass spectrometric analysis of samples of the isolated subcomponents prepared by ion exchange chromatography showed that each was composed of three glycoproteins and that the major difference between the subcomponents was due to their constituent glycoproteins possessing different numbers of sialic acid residues. Combined analysis of the ESI-MS data and of the overall carbohydrate compositional data obtained by colorimetric procedures, leads to the composition of the glycan of each glycoprotein, and a combined methylation and 400 MHz H-NMR analysis of the alkaline cleaved glycans identified them as being of only the biantennary N-acetyllactosamine type. Taking into account the molecular mass, the carbohydrate content and structure it may be concluded that each of the constituent glycoproteins contain five N-glycosidically linked glycans.

Human lactoferrin induces phenotypic and functional changes in murine splenic B cells

The immunotropic activities of human lactoferrin were studied with respect to phenotypic and functional changes in murine splenic B cells. Phenotypic changes were induced by human lactoferrin in splenic B-cell fractions separated by buoyant density. B cells from 7-8-day-old BALB/c mice isolated from a 50/60% Percoll gradient, gained characteristic features of more mature B cells manifested by an increase of surface IgD and complement receptor expression. Incubation of the analogous B-cell fraction from adult mice with human lactoferrin resulted in minor changes in relation to IgM and IgD expression. Besides induction of phenotypic changes on immature B cells, human lactoferrin enabled B cells from normal newborn and adult immunodeficient CBA/N mice to present antigen to an antigen-specific T-helper type 2 (Th2) cell line. We conclude that human lactoferrin acts as a maturation factor for B cells with regard to their phenotype and function.

Effect of intracellular iron depletion by picolinic acid on expression of the lactoferrin receptor in the human colon carcinoma cell subclone HT29-18-C1

A lactoferrin receptor has been found on the brush-border membrane of intestinal epithelial cells of several species, including humans. A role for this receptor in intestinal iron absorption, which is well regulated in response to body iron stores, has been proposed. We have investigated the effect of intracellular iron depletion by picolinic acid, an iron chelator, on the cell surface binding of human lactoferrin to human enterocytes and its intracellular uptake, using HT29-18-C1 cells, an enterocyte-like differentiable cell line. The confluent cells exhibited 5.8 x 10(6) specific binding sites per cell for diferric human 125I-labelled lactoferrin with relatively low affinity (Kd 8.4 x 10(-7) M). The addition of picolinic acid to the culture medium resulted in a concentration- and time-dependent increase in lactoferrin binding that was correlated with a decrease in intracellular iron content. The maximum effect of picolinic acid on lactoferrin binding (approx. 2-fold increase), which appeared between 12 and 18 h after its addition, was obtained at a picolinic acid concentration of 2 mM. Scatchard analysis showed that the enhanced lactoferrin binding resulted from an increase in the number of lactoferrin receptors rather than an alteration in the binding affinity for lactoferrin. The time-dependent effect of picolinic acid was completely abolished in the presence of 1 microM anisomycin, a protein synthesis inhibitor, indicating that ongoing protein synthesis is involved in this effect. The enhanced lactoferrin binding induced by picolinic acid produced an increase of approx. 30% in the uptake of lactoferrin-bound 59Fe, indicating the existence of functional receptors. These results suggest that biosynthesis of lactoferrin receptors in intestinal epithelial cells can be regulated in response to the levels of intracellular chelatable iron, consistent with intestinal iron absorption dependent on body iron stores.

Structural determination of two N-linked glycans isolated from recombinant human lactoferrin expressed in BHK cells

A full-length cDNA coding for human lactoferrin was isolated from a mammary gland library and the recombinant protein was expressed in BHK cells as described by Stowell K. M. et al. [1991, Biochem. J. 276, 349-355]. Two N-linked glycans from purified recombinant lactoferrin were released by hydrazinolysis and analyzed by 400-MHz 1H-NMR spectroscopy. The identified structures corresponded to N-acetyllactosaminic biantennary glycans and were alpha-2,3-disialylated forms (80%) or alpha-2,3-monosialylated (20%) forms. Moreover, 70% of total glycans were alpha-1,6-fucosylated at the GlcNAc residue linked to asparagine. In regard to its glycan moiety, the recombinant glycoprotein is close to native lactoferrins from milk or leucocytes but shows specific structural features which should be taken into account prior to in vivo and in vitro biological studies.

Rat mammary-gland transferrin: nucleotide sequence, phylogenetic analysis and glycan structure

The complete cDNA for rat mammary-gland transferrin (Tf) has been sequenced and also the native protein isolated from milk in order to analyse the structure of the main glycan variants present. A lactating-rat mammary-gland cDNA library in lambda gt10 was screened with a partial cDNA copy of rat liver Tf and subsequently rescreened with 5' fragments of the longest clones. This produced a 2275 bp insert coding for an open reading frame of 695 amino acid residues. This includes a 19-amino acid signal sequence and the mature protein containing 676 amino acids and one N-glycosylation site in the C-terminal domain at residue 490. Phylogenetic analysis was carried out using 14 translated Tf nucleotide sequences, and the derived evolutionary tree shows that at least three gene duplication events have occurred during Tf evolution, one of which generated the N- and C-terminal domains and occurred before separation of arthropods and chordates. The two halves of human melanotransferrin are more similar to each other than to any other sequence, which contrasts with the pattern shown by the remaining sequences. Native rat milk Tf is separated into four bands on native PAGE that differ only in their sialic acid content: one biantennary glycan is present containing either no sialic acid residues or up to three. The complete structures of the two major variants were determined by methylation, m.s. and 400 MHz 1H-n.m.r. spectroscopy. They contain either one or two neuraminic acid residues (alpha 2-->6)-linked to galactose in conventional biantennary N-acetyl-lactosamine-type glycans. Most contain fucose (alpha 1-->6)-linked to the terminal non-reducing N-acetylglucosamine.

Analysis of the N-linked oligosaccharides of human C1s using electrospray ionisation mass spectrometry

Information on the structures of the oligosaccharides linked to Asn residues 159 and 391 of the human complement protease C1s was obtained using mass spectrometric and monosaccharide analyses. Asn159 is linked to a complex-type biantennary, bisialylated oligosaccharide NeuAc2 Gal2 GlcNAc4 Man3 (molecular mass = 2206 +/- 1). Asn391 is occupied by either a biantennary, bisialylated oligosaccharide, or a triantennary, trisialylated species NeuAc3 Gal3 GlcNAc5 Man3 (molecular mass = 2861 +/- 1), or a fucosylated triatennary, trisialylated species NeuAc3 Gal3 GlcNAc5 Man3 Fuc1 (molecular mass = 3007 +/- 1), in relative proportions of approximately 1:1:1. The carbohydrate heterogeneity at Asn391 gives rise to three major types of C1s molecules of molecular masses 79,318 +/- 8 (A), 79,971 +/- 8 (B), and 80,131 +/- 8 (C), with an average mass of 79,807 +/- 8. A minor modification, yielding an extra mass of 132 +/- 2, is also detected within positions 1-153.

Selective assay for CyPA and CyPB in human blood using highly specific anti-peptide antibodies

Cyclophilins A and B (CyPA and CyPB) are known to be the main binding proteins for cyclosporin A (CsA), a potent immunosuppressive drug. Due to the high homology between the two proteins, antibodies to CyPB were found to cross-react with CyPA. In order to avoid this phenomenon, we raised specific antibodies against peptides copying the most divergent parts of the two sequences. These antibodies allowed us to develop an ELISA capture assay selective for either isotype. Thus, we showed that leukocyte CyPB concentration was almost ten times lower than that of CyPA, and that in contrast to the results described in the literature, only CyPB was released in plasma. Moreover, CyPB levels in leukocytes and plasma were found to correlate for the same donor, but no relationship was found with CyPA level.

Change in glycosylation of chicken transferrin glycans biosynthesized during embryogenesis and primary culture of embryo hepatocytes

Transferrins were isolated by immunoaffinity chromatography from chicken serum, chicken embryo serum and from the culture medium of chicken embryo hepatocytes in primary culture. The glycovariants of these three transferrins were separated by ion-exchange chromatography using a fast protein liquid chromatography (FPLC) system. The structures of the oligosaccharide-alditols released by hydrazinolysis from the glycovariants were compared after analysis by a combination of methanolysis, methylation analysis and 1H-NMR spectroscopy. In the three transferrins analysed, the oligosaccharides were of the biantennary N-acetyllactosaminic type, having several prominent features. In particular, the embryo serum transferrin glycan differed from that of chicken serum transferrin by the presence of a bisecting N-acetylglucosamine, suggesting a developmental change in glycosylation. The glycan structure of the transferrin secreted by the embryo hepatocytes in primary culture was marked by the presence of fucose (alpha 1-6) linked to the core N-acetylglucosamine, suggesting that expression of the fucosyltransferase activity is dependent on cell culture conditions. Moreover, comparative analysis of chicken serum transferrin and ovotransferrin glycans reinforces the idea that the glycosylation of two identical polypeptide chains is organ specific.

Immunolocalization of the lactotransferrin receptor on the human T lymphoblastic cell line Jurkat

Monoclonal antibodies have been raised against the soluble lactotransferrin binding protein purified from the cell culture supernatant of Jurkat cell line, a human T-lymphoblastic cell. All monoclonal antibodies were able to specifically bind to the membrane of Jurkat cells. One of the monoclonal antibodies, DP5B3G10, recognized both the soluble lactotransferrin-binding protein and the membrane lymphocyte lactotransferrin receptor after SDS-PAGE in presence of 2-mercaptoethanol and electrotransfer on nitrocellulose. The monoclonal antibody DP5B3G10 inhibited the binding of lactotransferrin to Jurkat cells and human peripheral activated lymphocytes. In addition, lactotransferrin inhibited the binding of the monoclonal antibody to the cell surface. These results suggest that the 95 kDa lactotransferrin-binding protein isolated from the cell culture medium corresponds to the soluble form of the 105 kDa lymphocyte lactotransferrin receptor. Corresponding proteins of 105 kDa molecular mass were identified in Jurkat and CEM T-cells and Raji B-cells. Finally, the monoclonal antibody DP5B3G10 was used to immunolocalize the lactotransferrin receptor on the Jurkat cells. Using fluorescence and electron microscopy, the receptor was localized both inside and at the cell surface. The cell membrane receptor was associated into clusters. After permeabilization of the plasma membrane, the staining was positive in the peri-membrane area. The region near the nucleus was devoid of receptor.