GlcNAc6ST2/CHST4 Is Essential for the Synthesis of R-10G-Reactive Keratan Sulfate/Sulfated N-Acetyllactosamine Oligosaccharides in Mouse Pleural Mesothelium

We recently showed that 6-sulfo sialyl N-acetyllactosamine (LacNAc) in O-linked glycans recognized by the CL40 antibody is abundant in the pleural mesothelium under physiological conditions and that these glycans undergo complementary synthesis by GlcNAc6ST2 (encoded by Chst4) and GlcNAc6ST3 (encoded by Chst5) in mice. GlcNAc6ST3 is essential for the synthesis of R-10G-positive keratan sulfate (KS) in the brain. The predicted minimum epitope of the R-10G antibody is a dimeric asialo 6-sulfo LacNAc. Whether R-10G-reactive KS/sulfated LacNAc oligosaccharides are also present in the pleural mesothelium was unknown. The question of which GlcNAc6STs are responsible for R-10G-reactive glycans was an additional issue to be clarified. Here, we show that R-10G-reactive glycans are as abundant in the pulmonary pleura as CL40-reactive glycans and that GlcNAc6ST3 is only partially involved in the synthesis of these pleural R-10G glycans, unlike in the adult brain. Unexpectedly, GlcNAc6ST2 is essential for the synthesis of R-10G-positive KS/sulfated LacNAc oligosaccharides in the lung pleura. The type of GlcNAc6ST and the magnitude of its contribution to KS glycan synthesis varied among tissues in vivo. We show that GlcNAc6ST2 is required and sufficient for R-10G-reactive KS synthesis in the lung pleura. Interestingly, R-10G immunoreactivity in KSGal6ST (encoded by Chst1) and C6ST1 (encoded by Chst3) double-deficient mouse lungs was markedly increased. MUC16, a mucin molecule, was shown to be a candidate carrier protein for pleural R-10G-reactive glycans. These results suggest that R-10G-reactive KS/sulfated LacNAc oligosaccharides may play a role in mesothelial cell proliferation and differentiation. Further elucidation of the functions of sulfated glycans synthesized by GlcNAc6ST2 and GlcNAc6ST3, such as R-10G and CL40 glycans, in pathological conditions may lead to a better understanding of the underlying mechanisms of the physiopathology of the lung mesothelium.

Hemolysis is associated with altered heparan sulfate of the endothelial glycocalyx and with local complement activation in thrombotic microangiopathies

The complement system plays a key role in the pathophysiology of kidney thrombotic microangiopathies (TMA), as illustrated by atypical hemolytic uremic syndrome. But complement abnormalities are not the only drivers of TMA lesions. Among other potential pathophysiological actors, we hypothesized that alteration of heparan sulfate (HS) in the endothelial glycocalyx could be important. To evaluate this, we analyzed clinical and histological features of kidney biopsies from a monocentric, retrospective cohort of 72 patients with TMA, particularly for HS integrity and markers of local complement activation. The role of heme (a major product of hemolysis) as an HS-degrading agent in vitro, and the impact of altering endothelial cell (ECs) HS on their ability to locally activate complement were studied. Compared with a positive control, glomerular HS staining was lower in 57 (79%) patients with TMA, moderately reduced in 20 (28%), and strongly reduced in 37 (51%) of these 57 cases. Strongly reduced HS density was significantly associated with both hemolysis at the time of biopsy and local complement activation (C3 and/or C5b-9 deposits). Using primary endothelial cells (HUVECs, Glomerular ECs), we observed decreased HS expression after short-term exposure to heme, and that artificial HS degradation by exposure to heparinase was associated with local complement activation. Further, prolonged exposure to heme modulated expression of several key genes of glycocalyx metabolism involved in coagulation regulation (C5-EPI, HS6ST1, HS3ST1). Thus, our study highlights the impact of hemolysis on the integrity of endothelial HS, both in patients and in endothelial cell models. Hence, acute alteration of HS may be a mechanism of heme-induced complement activation.

Complementary Role of GlcNAc6ST2 and GlcNAc6ST3 in Synthesis of CL40-Reactive Sialylated and Sulfated Glycans in the Mouse Pleural Mesothelium

Sialyl 6-sulfo Lewis X (6-sulfo sLe^X) and its derivative sialyl 6-sulfo N-acetyllactosamine (LacNAc) are sialylated and sulfated glycans of sialomucins found in the high endothelial venules (HEVs) of secondary lymphoid organs. A component of 6-sulfo sLe^X present in the core 1-extended O-linked glycans detected by the MECA-79 antibody was previously shown to exist in the lymphoid aggregate vasculature and bronchial mucosa of allergic and asthmatic lungs. The components of 6-sulfo sLe^X in pulmonary tissues under physiological conditions remain to be analyzed. The CL40 antibody recognizes 6-sulfo sLe^X and sialyl 6-sulfo LacNAc in O-linked and N-linked glycans, with absolute requirements for both GlcNAc-6-sulfation and sialylation. Immunostaining of normal mouse lungs with CL40 was performed and analyzed. The contribution of GlcNAc-6-O-sulfotransferases (GlcNAc6STs) to the synthesis of the CL40 epitope in the lungs was also elucidated. Here, we show that the expression of the CL40 epitope was specifically detected in the mesothelin-positive mesothelium of the pulmonary pleura. Moreover, GlcNAc6ST2 (encoded by Chst4) and GlcNAc6ST3 (encoded by Chst5), but not GlcNAc6ST1 (encoded by Chst2) or GlcNAc6ST4 (encoded by Chst7), are required for the synthesis of CL40-positive glycans in the lung mesothelium. Furthermore, neither GlcNAc6ST2 nor GlcNAc6ST3 is sufficient for in vivo expression of the CL40 epitope in the lung mesothelium, as demonstrated by GlcNAc6ST1/3/4 triple-knock-out and GlcNAc6ST1/2/4 triple-knock-out mice. These results indicate that CL40-positive sialylated and sulfated glycans are abundant in the pleural mesothelium and are synthesized complementarily by GlcNAc6ST2 and GlcNAc6ST3, under physiological conditions in mice.

Design and Synthesis of 6-O-Phosphorylated Heparan Sulfate Oligosaccharides to Inhibit Amyloid β Aggregation

Dysregulation of amyloidogenic proteins and their abnormal processing and deposition in tissues cause systemic and localized amyloidosis. Formation of amyloid β (Aβ) fibrils that deposit as amyloid plaques in Alzheimer's disease (AD) brains is an earliest pathological hallmark. The polysulfated heparan sulfate (HS)/heparin (HP) is one of the non-protein components of Aβ deposits that not only modulates Aβ aggregation, but also acts as a receptor for Aβ fibrils to mediate their cytotoxicity. Interfering the interaction between HS/HP and Aβ could be a therapeutic strategy to arrest amyloidosis. Here we have synthesized the 6- O -phosphorylated HS/HP oligosaccharides and reported their competitive effects on the inhibition of HP-mediated Aβ fibril formation in vitro using a thioflavin T fluorescence assay and a tapping mode atomic force microscopy.

MO071: Hemolysis is Associated with Altered Heparan Sulfate of Endothelial Glycocalyx And with Local Complement Activation in Thrombotic Microangiopathies

BACKGROUND AND AIMS

The complement system plays a key role in the pathophysiology of renal thrombotic microangiopathies (TMA), as illustrated by atypical hemolytic uremic syndrome (HUS) characterized by a high rate of mutations in complement proteins. However, complement abnormalities are not fully sufficient to drive to TMA lesions. Among other suspected pathophysiological actors, we hypothesize that the alteration of heparan sulfate (HS) of endothelial glycocalyx—a cell membrane glycoaminoglycans and glycoproteins matrix able of regulating complement by binding factor H—may play a significant role.

METHOD

We recorded clinical and histological features in native kidney biopsies from a monocentric retrospective cohort of 72 TMA-patients. Glomerular HS integrity and local complement activation markers (C3 and C5b9 staining) were analyzed by immunofluorescence (IF) and immunohistochemistry. Using an in vitro endothelial cells model (human umbilical vein endothelial cells, HUVECs), we studied the impact of heme exposure (30’, 37°C)—a major product of hemolysis—on endothelial HS integrity by IF and flow cytometry (FCM). Heme-induced HS disruption was studied by slot blot of HS core-protein Syndecan (SDC) 1 and 4 in cells supernatant. Artificial enzymatic degradation of HS was achieved after exposure of HUVECs to a combination of heparinases I, II and III (30', 37°C), and we studied its effect on the ability of the HS-free cell membrane to locally activate complement by analyzing C3b deposition by IF and FCM, and the release of complement anaphylatoxins C3a and soluble attack complex membrane s-C5b9 in the cell supernatants by ELISA. The HS remodeling process induced by heme exposure (16 h, 37°C) were indirectly analyzed via a transcriptional profiling of the expression of the key enzymes involved in HS synthesis by RT–qPCR.

RESULTS

Glomerular HS staining decreased in 57 TMA-patients (79%), moderately (2+) or strongly (0–1+) in 20 (28%) and 37 (51%) cases, respectively. Reduced HS density was significantly associated with hemolysis at the time of biopsy (P = 0.008) and local complement activation (C3d and/or C5b-9 deposits, P < 0.001). Hemolysis at the time of biopsy was associated with more severe glomerular TMA lesions (P = 0.025), the presence of vascular thrombi (P = 0.007) and local complement activation (C3d and/or C5b-9 deposits, P = 0.006). On endothelial cells (HUVECs), we confirmed that HS expression was decreased after heme exposure in IF and FCM (P < 0.01). Coherently, HS core-proteins SDC-1 and 4 were significantly increased in HUVECs supernatant (P < 0.05), suggesting a negative heme-driven impact on HS integrity. Artificial HS degradation increased C3b membrane deposition on HUVECs on average ∼ 3 fold by FCM and ∼ 10 by IF, and we observed an increased release of complement C3a and s-C5b9 in cells supernatant (P < 0.05). Finally, we showed that prolonged exposure to heme induced a decreased of genic expression of C5-Epimerase and an increase in 6-OST1 and 3-OST1 expression (P < 0.05), the very three crucial genes of HS remodeling specifically and sequentially involved in the generation of anti-thrombin pattern, the well-known key regulator of the HS/heparin-driven inhibition of coagulation.

CONCLUSION

This study highlights the impact of hemolysis on the integrity of endothelial glycocalyx HS, both in kidney biopsy of TMA-patients and in an in vitro endothelial cell model, and suggests that acute alteration of HS is a mechanism of heme-induced complement activation. The endothelial glycocalyx appears then to be an important key in the understanding of TMA and could lead to the development of therapeutics targeting its preservation and/or reconstitution, in order to better control the disease.

Geniac: Automatic Configuration GENerator and Installer for nextflow pipelines

With the advent of high-throughput biotechnological platforms and their ever-growing capacity, life science has turned into a digitized, computational and data-intensive discipline. As a consequence, standard analysis with a bioinformatics pipeline in the context of routine production has become a challenge such that the data can be processed in real-time and delivered to the end-users as fast as possible. The usage of workflow management systems along with packaging systems and containerization technologies offer an opportunity to tackle this challenge. While very powerful, they can be used and combined in many multiple ways which may differ from one developer to another. Therefore, promoting the homogeneity of the workflow implementation requires guidelines and protocols which detail how the source code of the bioinformatics pipeline should be written and organized to ensure its usability, maintainability, interoperability, sustainability, portability, reproducibility, scalability and efficiency. Capitalizing on Nextflow, Conda, Docker, Singularity and the nf-core initiative, we propose a set of best practices along the development life cycle of the bioinformatics pipeline and deployment for production operations which target different expert communities including i) the bioinformaticians and statisticians ii) the software engineers and iii) the data managers and core facility engineers. We implemented Geniac (Automatic Configuration GENerator and Installer for nextflow pipelines) which consists of a toolbox with three components: i) a technical documentation available at https://geniac.readthedocs.io to detail coding guidelines for the bioinformatics pipeline with Nextflow, ii) a command line interface with a linter to check that the code respects the guidelines, and iii) an add-on to generate configuration files, build the containers and deploy the pipeline. The Geniac toolbox aims at the harmonization of development practices across developers and automation of the generation of configuration files and containers by parsing the source code of the Nextflow pipeline.

Beta3Gn-T7 Is a Keratan Sulfate β1,3 N-Acetylglucosaminyltransferase in the Adult Brain

Keratan sulfate (KS) glycan is covalently attached to a core protein of proteoglycans. KS is abundant in neuropils and presents densely in close proximity to the perineuronal region of the perineuronal net-positive neurons in the adult brain under physiological conditions. We previously showed that the synthesis of KS positive for the R-10G antibody in the adult brain is mediated by GlcNAc-6-sulfotransferase 3 (GlcNAc6ST3; encoded by Chst5). Deficiency in both GlcNAc6ST3 and GlcNAc6ST1, encoded by Chst2, completely abolished KS. Protein-tyrosine phosphatase receptor type z1 (Ptprz1)/phosphacan was identified as a KS scaffold. KS requires the extension of GlcNAc by β1,3 N-acetylglucosaminyltransferase (Beta3Gn-T). Members of the Beta3Gn-T family involved in the synthesis of adult brain KS have not been identified. In this study, we show by a method of gene targeting that Beta3Gn-T7, encoded by B3gnt7, is a major Beta3Gn-T for the synthesis of KS in neuropils and the perineuronal region in the adult brain. Intriguingly, the B3gnt7 gene is selectively expressed in oligodendrocyte precursor cells (OPCs) and oligodendrocytes similar to that of GlcNAc6ST3. These results indicate that Beta3Gn-T7 in oligodendrocyte lineage cells may play a role in the formation of neuropils and perineuronal nets in the adult brain through the synthesis of R-10G-positive KS-modified proteoglycan.

Synthesis of new sulfated disaccharides for the modulation of TLR4-dependent inflammation

Natural sulfated glycans are key players in inflammation through TLR4 activation; therefore synthetic exogenous sulfated saccharides can be used to downregulate inflammation processes. We have designed and synthesized new sulfated compounds based on small and biocompatible carbohydrates that are able to cross the BBB. A suitable protected donor and acceptor, obtained from a unique precursor, have been stereoselectively glycosylated to give an orthogonally protected cellobiose disaccharide. Selective deprotection and sulfation allowed the syntheses of four differentially sulfated disaccharides, which have been characterized by NMR, HRMS and MS/MS. Together with their partially protected precursors, the new compounds were tested on HEK-TLR4 cells. Our results show the potential of small oligosaccharides to modulate TLR4 activity, confirming the need for sulfation and the key role of the 6-sulfate groups to trigger TLR4 signalization.

ARIAweb: a server for automated NMR structure calculation

Nuclear magnetic resonance (NMR) spectroscopy is a method of choice to study the dynamics and determine the atomic structure of macromolecules in solution. The standalone program ARIA (Ambiguous Restraints for Iterative Assignment) for automated assignment of nuclear Overhauser enhancement (NOE) data and structure calculation is well established in the NMR community. To ultimately provide a perfectly transparent and easy to use service, we designed an online user interface to ARIA with additional functionalities. Data conversion, structure calculation setup and execution, followed by interactive visualization of the generated 3D structures are all integrated in ARIAweb and freely accessible at https://ariaweb.pasteur.fr.

Glycosylation changes in inflammatory diseases

Glycosylation is one of the most important modifications of proteins and lipids, and cell surface glycoconjugates are thought to play important roles in a variety of biological functions including cell-cell and cell-substrate interactions, bacterial adhesion, cell immunogenicity and cell signaling. Alterations of glycosylation are observed in a number of inflammatory diseases. Pro-inflammatory cytokines have been shown to modulate cell surface glycosylation by regulating the expression of glycosyltransferases and sulfotransferases involved in the biosynthesis of glycan chains, inducing the expression of specific carbohydrate antigens at the cell surface that can be recognized by different types of lectins or by bacterial adhesins, contributing to the development of diseases. Glycosylation can also regulate biological functions of immune cells by recruiting leukocytes to inflammation sites with pro- or anti-inflammatory effects. Cell surface proteoglycans provide a large panel of binding sites for many mediators of inflammation, and regulate their bio-availability and functions. In this review, we summarize the current knowledge of the glycosylation changes occurring in mucin type O-linked glycans, glycosaminoglycans, as well as in glycosphingolipids, with a particular focus on cystic fibrosis and neurodegenerative diseases, and their consequences on cell interactions and disease progression.

The Emerging Roles of Heparan Sulfate 3-O-Sulfotransferases in Cancer

Alteration in the expression of heparan sulfate (HS)-modifying enzymes has been frequently observed in cancer. Consequently, dysregulation of the HS biosynthetic machinery results in dramatic changes in the HS structure, thereby impacting a range of pivotal cellular processes involved in tumorigenesis and cancer progression including proliferation, migration, apoptosis, and immune escape. HS 3-O-sulfotransferases (HS3STs) catalyse the maturation step of glucosaminyl 3-O-sulfation within HS chains. Although seven HS3ST isozymes have been described in human, 3-O-sulfation is a rare modification and only a few biological processes have been described to be influenced by 3-O-sulfated HS. An aberrant expression of HS3STs has been reported in a variety of cancers. Thus, it was suggested that changes in the expression of these enzymes as a result of tumorigenesis or tumor growth may critically influence cancer cell behavior. In accordance with this assumption, a number of studies have documented the epigenetic repression of HS3ST2 and HS3ST3A in many cancers. However, the situation is not so clear, and there is accumulating evidence that HS3ST2, HS3ST3A, HS3ST3B, and HS3ST4 may also act as tumor-promoting enzymes in a number of cancer cells depending on their phenotypes and molecular signatures. In this mini-review, we focus on the recent insights regarding the abnormal expression of HS3STs in cancer and discuss the functional consequences on tumor cell behavior. In term of clinical outcome, further investigations are needed to explore the potential value of HS3STs and/or their 3-O-sulfated products as targets for therapeutic strategies in cancer treatment.

Cancer cells induce immune escape via glycocalyx changes controlled by the telomeric protein TRF2

Myeloid-derived suppressor cells (MDSCs) are immature myeloid cells with strong immunosuppressive activity that promote tumor growth. In this study, we describe a mechanism by which cancer cells control MDSCs in human cancers by upregulating TRF2, a protein required for telomere stability. Specifically, we showed that the TRF2 upregulation in cancer cells has extratelomeric roles in activating the expression of a network of genes involved in the biosynthesis of heparan sulfate proteoglycan, leading to profound changes in glycocalyx length and stiffness, as revealed by atomic force microscopy. This TRF2-dependent regulation facilitated the recruitment of MDSCs, their activation via the TLR2/MyD88/IL-6/STAT3 pathway leading to the inhibition of natural killer recruitment and cytotoxicity, and ultimately tumor progression and metastasis. The clinical relevance of these findings is supported by our analysis of cancer cohorts, which showed a correlation between high TRF2 expression and MDSC infiltration, which was inversely correlated with overall patient survival.

The heparan sulfate 3-O-sulfotransferases (HS3ST) 2, 3B and 4 enhance proliferation and survival in breast cancer MDA-MB-231 cells

Heparan sulfate 3-O-sulfotransferases (HS3STs) catalyze the final maturation step of heparan sulfates. Although seven HS3ST isozymes have been described in human, 3-O-sulfation is a relatively rare modification, and only a few biological processes have been described to be influenced by 3-O-sulfated motifs. A conflicting literature has recently reported that HS3ST2, 3A, 3B and 4 may exhibit either tumor-promoting or anti-oncogenic properties, depending on the model used and cancer cell phenotype. Hence, we decided to compare the consequences of the overexpression of each of these HS3STs in the same cellular model. We demonstrated that, unlike HS3ST3A, the other three isozymes enhanced the proliferation of breast cancer MDA-MB-231 and BT-20 cells. Moreover, the colony forming capacity of MDA-MB-231 cells was markedly increased by the expression of HS3ST2, 3B and 4. No notable difference was observed between the three isozymes, meaning that the modifications catalyzed by each HS3ST had the same functional impact on cell behavior. We then demonstrated that overexpression of HS3ST2, 3B and 4 was accompanied by increased activation of c-Src, Akt and NF-κB and up-regulation of the anti-apoptotic proteins survivin and XIAP. In line with these findings, we showed that HS3ST-transfected cells are more resistant to cell death induction by pro-apoptotic stimuli or NK cells. Altogether, our findings demonstrate that HS3ST2, 3B and 4 share the same pro-tumoral activity and support the idea that these HS3STs could compensate each other for loss of their expression depending on the molecular signature of cancer cells and/or changes in the tumor environment.

Use of Toll-like receptor assays for the detection of bacterial contaminations in icodextrin batches released for peritoneal dialysis

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Monocyte test assays were poorly efficient for the detection of little bacterial contamination in icodextrin batches.

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TLR2- and TLR4-transfected cell lines were appropriate for detecting PGN and LPS contaminations.

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Mutanolysin treatment of icodextrins enhanced the response of TLR2-transfected cells to contaminating PGN.

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Using TLR-transfected cell lines is a valuable approach for selecting icodextrin batches for peritoneal dialysis solutions.

Icodextrin is a starch derivative used for preparing solutions of peritoneal dialysis. Unfortunately, peptidoglycans (PGN) and lipopolysaccharides (LPS) have been reported to contaminate certain icodextrin batches and to contribute to the development of sterile peritonitis. The decision of selecting or rejecting icodextrin batches is however difficult, because of limitations in the detection of these bacterial contaminants. Besides monocyte activation tests of cytokine release, a number of bio-assays using stably TLR-transfected cell lines have been developed. Here, we compared the efficacy of TLR2- and TLR4-transfected cells to detect bacterial contamination with the responses of monocytes exposed to the same icodextrin samples. In contrast to monocyte models of cytokine release, we found that TLR2- and TLR4-transfected cell lines are highly sensitive to detect little PGN and LPS contaminations in the presence of icodextrin. With the intent to increase PGN reactivity, mutanolysin was used to generate soluble fragments in icodextrin samples. We found that such an enzymatic treatment led to an enhanced response of TLR2-transfected cells, even though parental icodextrin samples were poorly reactive. Altogether, these findings indicate that the use of TLR2- and TLR4-transfected cell lines is a valuable approach for helping to the decision of selecting icodextrin batches for peritoneal dialysis.

Radiation-induced changes in the glycome of endothelial cells with functional consequences

As it is altered by ionizing radiation, the vascular network is considered as a prime target in limiting normal tissue damage and improving tumor control in radiation therapy. Irradiation activates endothelial cells which then participate in the recruitment of circulating cells, especially by overexpressing cell adhesion molecules, but also by other as yet unknown mechanisms. Since protein glycosylation is an important determinant of cell adhesion, we hypothesized that radiation could alter the glycosylation pattern of endothelial cells and thereby impact adhesion of circulating cells. Herein, we show that ionizing radiation increases high mannose-type N-glycans and decreases glycosaminoglycans. These changes stimulate interactions measured under flow conditions between irradiated endothelial cells and monocytes. Targeted transcriptomic approaches in vitro in endothelial cells and in vivo in a radiation enteropathy mouse model confirm that genes involved in N- and O-glycosylation are modulated by radiation, and in silico analyses give insight into the mechanism by which radiation modifies glycosylation. The endothelium glycome may therefore be considered as a key therapeutic target for modulating the chronic inflammatory response observed in healthy tissues or for participating in tumor control by radiation therapy.

Participation of 3-O-sulfated heparan sulfates in the protection of macrophages by herpes simplex virus-1 glycoprotein D and cyclophilin B against apoptosis

Heparan sulfates (HS) are involved in numerous biological processes, which rely on their ability to interact with a large panel of proteins. Although the reaction of 3‐O‐sulfation can be catalysed by the largest family of HS sulfotransferases, very few mechanisms have been associated with this modification and to date, only glycoprotein D (gD) of herpes simplex virus‐1 (HSV‐1 gD) and cyclophilin B (CyPB) have been well‐described as ligands for 3‐O‐sulfated HS. Here, we hypothesized that both ligands could induce the same responses via a mechanism dependent on 3‐O‐sulfated HS. First, we checked that HSV‐1 gD was as efficient as CyPB to induce the activation of the same signalling events in primary macrophages. We then demonstrated that both ligands efficiently reduced staurosporin‐induced apoptosis and modulated the expression of apoptotic genes. In addition to 3‐O‐sulfated HS, HSV‐1 gD was reported to interact with other receptors, including herpes virus entry mediator (HVEM), nectin‐1 and ‐2. Thus, we decided to identify the contribution of each binding site in the responses triggered by HSV‐1 gD and CyPB. We found that knock‐down of 3‐O‐sulfotransferase 2, which is the main 3‐O‐sulfated HS‐generating enzyme in macrophages, strongly reduced the responses induced by both ligands. Moreover, silencing the expression of HVEM rendered macrophages unresponsive to either HSV‐1 gD and CyPB, thus indicating that both proteins induced the same responses by interacting with a complex formed by 3‐O‐sulfated HS and HVEM. Collectively, our results suggest that HSV‐1 might hijack the binding sites for CyPB in order to protect macrophages against apoptosis for efficient infection.

Tumour-necrosis factor-α induces heparan sulfate 6-O-endosulfatase 1 (Sulf-1) expression in fibroblasts

Heparan sulfate (HS) 6-O-endosulfatases (Sulfs) have emerged recently as critical regulators of many physiological and pathological processes. By removing 6-O-sulfates from specific HS sequences, they modulate the activities of a variety of growth factors and morphogens, including fibroblast growth factor (FGF)-1. However, little is known about the functions of Sulfs in inflammation. Tumour-necrosis factor (TNF)-α plays an important role in regulating the behaviour of fibroblasts. In this study, we examined the effect of this inflammatory cytokine on the expression of Sulfs in human MRC-5 fibroblasts. Compositional analysis of HS from TNF-α-treated cells showed a strong reduction in the amount of the trisulfated UA2S-GlcNS6S disaccharide, which suggested a selective reaction of 6-O-desulfation. Real-time PCR analysis revealed that TNF-α increased Sulf-1 expression in a dose- and time-dependent manner, via a mechanism involving NF-ĸB, ERK1/2 and p38 MAPK. In addition, we confirmed that cell stimulation with TNF-α was accompanied by the secretion of an active form of Sulf-1. To study the function of Sulf- 1, we examined the responses induced by FGF-1. We showed that ERK1/2 activation and cell proliferation were markedly reduced in TNF-α-treated MRC-5 cells compared with untreated cells. Silencing the expression of Sulf-1 by RNA interference restored the responses induced by FGF-1, which indicated that TNF-α-mediated induction of the sulfatase indeed resulted in alterations of HS biological properties. Taken together, our results indicate that Sulf-1 is responsive to TNF-α stimulation and may function as an autocrine regulator of fibroblast expansion in the course of an inflammatory response.

Regulation of the Expression of Heparan Sulfate 3-O-Sulfotransferase 3B (HS3ST3B) by Inflammatory Stimuli in Human Monocytes

Heparan sulfate (HS) is recognized as an important player in a wide range of dynamic steps of inflammatory reactions. Thereby, structural HS remodeling is likely to play an important role in the regulation of inflammatory and immune responses; however, little is known about underlying mechanism. In this study, we analyzed the regulation of expression of HS 3-O-sulfotransferases (HS3STs) in response to inflammatory stimuli. We found that among the seven HS3ST isoenzymes, only the expression of HS3ST3B was markedly up-regulated in human primary monocytes and the related cell line THP1 after exposure to TLR agonists. TNF-α was also efficient, to a lesser extent, to increase HS3ST3B expression, while IL-6, IL-4, and IFN-γ were poor inducers. We then analyzed the molecular mechanisms that regulate the high expression of HS3ST3B in response to LPS. Based on the expression of HS3ST3B transcripts and on the response of a reporter gene containing the HS3ST3B1 promoter, we provide evidence that LPS induces a rapid and strong transcription of HS3ST3B1 gene, which was mainly dependent on the activation of NF-κB and JNK signaling pathways. Additionally, active p38 MAPK and de novo synthesized proteins are involved in post-transcriptional mechanisms to maintain a high level of HS3ST3B mRNA to a steady state. Altogether, our findings indicate that HS3ST3B1 gene behaves as a primary response gene, suggesting that it may play an important role in making 3-O-sulfated HS with specific functions in the regulation of inflammatory and immune responses. J. Cell. Biochem. 117: 1529-1542, 2016. © 2015 Wiley Periodicals, Inc.

Macrophage polarization alters the expression and sulfation pattern of glycosaminoglycans

Macrophages are major cells of inflammatory process and take part in a large number of physiological and pathological processes. According to tissue environment, they can polarize into pro-inflammatory (M1) or alternative (M2) cells. Although many evidences have hinted to a potential role of cell-surface glycosaminoglycans (GAGs) in the functions of macrophages, the effect of M1 or M2 polarization on the biosynthesis of these polysaccharides has not been investigated so far. GAGs are composed of repeat sulfated disaccharide units. Heparan (HS) and chondroitin/dermatan sulfates (CS/DS) are the major GAGs expressed at the cell membrane. They are involved in numerous biological processes, which rely on their ability to selectively interact with a large panel of proteins. More than 20 genes encoding sulfotransferases have been implicated in HS and CS/DS biosynthesis, and the functional repertoire of HS and CS/DS has been related to the expression of these isoenzymes. In this study, we analyzed the expression of sulfotransferases as a response to macrophage polarization. We found that M1 and M2 activation drastically modified the profiles of expression of numerous HS and CS/DS sulfotransferases. This was accompanied by the expression of GAGs with distinct structural features. We then demonstrated that GAGs of M2 macrophages were efficient to present fibroblast growth factor-2 in an assay of tumor cell proliferation, thus indicating that changes in GAG structure may contribute to the functions of polarized macrophages. Altogether, our findings suggest a regulatory mechanism in which fine modifications in GAG biosynthesis may participate to the plasticity of macrophage functions.

A systems biology approach for defining the molecular framework of the hematopoietic stem cell niche

Despite progress in identifying the cellular composition of hematopoietic stem/progenitor cell (HSPC) niches, little is known about the molecular requirements of HSPC support. To address this issue, we used a panel of six recognized HSPC-supportive stromal lines and less-supportive counterparts originating from embryonic and adult hematopoietic sites. Through comprehensive transcriptomic meta-analyses, we identified 481 mRNAs and 17 microRNAs organized in a modular network implicated in paracrine signaling. Further inclusion of 18 additional cell strains demonstrated that this mRNA subset was predictive of HSPC support. Our gene set contains most known HSPC regulators as well as a number of unexpected ones, such as Pax9 and Ccdc80, as validated by functional studies in zebrafish embryos. In sum, our approach has identified the core molecular network required for HSPC support. These cues, along with a searchable web resource, will inform ongoing efforts to instruct HSPC ex vivo amplification and formation from pluripotent precursors.

Over-sulfated glycosaminoglycans are alternative selectin ligands: insights into molecular interactions and possible role in breast cancer metastasis

Distant metastasis account for about 90 % of cancer associated deaths, and yet the oncology field is cruelly lacking tools to accurately predict and/or prevent metastasis. Distant metastasis occurs when circulating tumor cells interact with the endothelium of distant organs and extravasate from the blood vessel into the surrounding tissue. Selectins are a family of carbohydrate receptors well depicted for their role in tumor cells extravasation. They mediate primary interactions of cancer cells with endothelial cells, as well as secondary interactions with leucocytes and platelets, which are also promoting metastasis. The cancer associated carbohydrate antigen sialyl-Lewis x (sLe(x)) has been repeatedly shown to be involved, as selectin ligand, in these interactions. However, recent studies have highlighted that glycosaminoglycans (GAGs), another class of glycans, may also serve as ligands for selectins. We report herein that cancer-associated GAGs are differentially recognized by selectins according to their density of sulfation and the pH conditions of the binding. We also show that these parameters regulate platelets-cancer cells heterotypic aggregation, supporting the idea that GAGs may have pro-metastatic function. Combining our experimental results with in depth analyses of molecular dockings, we propose a model of GAG/selectin interactions robust enough to recapitulate the differential binding of selectins to GAGs, the competition between GAGs and sLe(x) for selectin binding and the effect of sub-physiological pH on GAGs affinities towards selectins. Altogether, our data suggest GAGs to be good ligands for selectins, potentially promoting distant metastasis in a complementary way to sLe(x).

Differential contribution of the repeats to heparin binding of HBHA, a major adhesin of Mycobacterium tuberculosis

BACKGROUND

Tuberculosis remains one of the most important causes of global mortality and morbidity, and the molecular mechanisms of the pathogenesis are still incompletely understood. Only few virulence factors of the causative agent Mycobacterium tuberculosis are known. One of them is the heparin-binding haemagglutinin (HBHA), an important adhesin for epithelial cells and an extrapulmonary dissemination factor. HBHA mediates mycobacterial adherence to epithelial cells via the interactions of its C-terminal, lysine rich repeat domain with sulfated glycoconjugates on the surface of epithelial cells.

METHODOLOGY/PRINCIPAL FINDINGS

Using defined heparin sulfate (HS) analogs, we determined the minimal heparin fragment length for HBHA binding and structural adaptations of the HBHA heparin-binding domain (HBD) upon binding to heparin. The NMR studies show significant shifts of all residues in the HBD upon interaction with heparin, with stronger shifts in the last repeats compared to the upstream repeats, and indicated that the HS fragments with 14 sugar units cover the entire C-terminal lysine-rich domain of HBHA. The differential implication of the repeats is determined by the relative position of prolines and lysines within each repeat, and may contribute to binding specificity. GAG binding induces a non-homogeneous structural rearrangement in the HBD, with stabilization of a nascent α-helix only in the last penta-repeats.

CONCLUSION/SIGNIFICANCE

Mycobacterial HBHA undergoes structural adaptation upon interaction with GAGs, which is likely involved in binding specificities of the adhesin, and mycobacterial pathogens may use HBD polymorphisms for host or organ specificity. Further studies will aim at decoding the complementarity between HBD repeats and HS sequence.

Synthesis of heparan sulfate with cyclophilin B-binding properties is determined by cell type-specific expression of sulfotransferases

Cyclophilin B (CyPB) induces migration and adhesion of T lymphocytes via a mechanism that requires interaction with 3-O-sulfated heparan sulfate (HS). HS biosynthesis is a complex process with many sulfotransferases involved. N-Deacetylases/N-sulfotransferases are responsible for N-sulfation, which is essential for subsequent modification steps, whereas 3-O-sulfotransferases (3-OSTs) catalyze the least abundant modification. These enzymes are represented by several isoforms, which differ in term of distribution pattern, suggesting their involvement in making tissue-specific HS. To elucidate how the specificity of CyPB binding is determined, we explored the relationships between the expression of these sulfotransferases and the generation of HS motifs with CyPB-binding properties. We demonstrated that high N-sulfate density and the presence of 2-O- and 3-O-sulfates determine binding of CyPB, as evidenced by competitive experiments with heparin derivatives, soluble HS, and anti-HS antibodies. We then showed that target cells, i.e. CD4+ lymphocyte subsets, monocytes/macrophages, and related cell lines, specifically expressed high levels of NDST2 and 3-OST3 isoforms. Silencing the expression of NDST1, NDST2, 2-OST, and 3-OST3 by RNA interference efficiently decreased binding and activity of CyPB, thus confirming their involvement in the biosynthesis of binding sequences for CyPB. Moreover, we demonstrated that NDST1 was able to partially sulfate exogenous substrate in the absence of NDST2 but not vice versa, suggesting that both isoenzymes do not have redundant activities but do have rather complementary activities in making N-sulfated sequences with CyPB-binding properties. Altogether, these results suggest a regulatory mechanism in which cell type-specific expression of certain HS sulfotransferases determines the specific binding of CyPB to target cells.

Structural and functional characterization of the interaction between cyclophilin B and a heparin-derived oligosaccharide

The chemotaxis and integrin-mediated adhesion of T lymphocytes triggered by secreted cyclophilin B (CypB) depend on interactions with both cell surface heparan sulfate proteoglycans (HSPG) and the extracellular domain of the CD147 membrane receptor. Here, we use NMR spectroscopy to characterize the interaction of CypB with heparin-derived oligosaccharides. Chemical shift perturbation experiments allowed the precise definition of the heparan sulfate (HS) binding site of CypB. The N-terminal extremity of CypB, which contains a consensus sequence for heparin-binding proteins was modeled on the basis of our experimental NMR data. Because the HS binding site extends toward the CypB catalytic pocket, we measured its peptidyl-prolyl cis-trans isomerase (PPIase) activity in the absence or presence of a HS oligosaccharide toward a CD147-derived peptide. We report the first direct evidence that CypB is enzymatically active on CD147, as it is able to accelerate the cis/trans isomerization of the Asp(179)-Pro(180) bond in a CD147-derived peptide. However, HS binding has no significant influence on this PPIase activity. We thus conclude that the glycanic moiety of HSPG serves as anchor for CypB at the cell surface, and that the signal could be transduced by CypB via its PPIase activity toward CD147.

The heparin/heparan sulfate sequence that interacts with cyclophilin B contains a 3-O-sulfated N-unsubstituted glucosamine residue

Many of the biological functions of heparan sulfate (HS) proteoglycans can be attributed to specialized structures within HS moieties, which are thought to modulate binding and function of various effector proteins. Cyclophilin B (CyPB), which was initially identified as a cyclosporin A-binding protein, triggers migration and integrin-mediated adhesion of peripheral blood T lymphocytes by a mechanism dependent on interaction with cell surface HS. Here we determined the structural features of HS that are responsible for the specific binding of CyPB. In addition to the involvement of 2-O,6-O, and N-sulfate groups, we also demonstrated that binding of CyPB was dependent on the presence of N-unsubstituted glucosamine residues (GlcNH2), which have been reported to be precursors for sulfation by 3-O-sulfotransferases-3 (3-OST-3). Interestingly, 3-OST-3B isoform was found to be the main 3-OST isoenzyme expressed in peripheral blood T lymphocytes and Jurkat T cells. Moreover, down-regulation of the expression of 3-OST-3 by RNA interference potently reduced CyPB binding and consequent activation of p44/42 mitogen-activated protein kinases. Altogether, our results strongly support the hypothesis that 3-O-sulfation of GlcNH2 residues could be a key modification that provides specialized HS structures for CyPB binding to responsive cells. Given that 3-O-sulfation of GlcNH2-containing HS by 3-OST-3 also provides binding sites for glycoprotein gD of herpes simplex virus type I, these findings suggest an intriguing structural linkage between the HS sequences involved in CyPB binding and viral infection.

Syndecan-1/CD147 association is essential for cyclophilin B-induced activation of p44/42 mitogen-activated protein kinases and promotion of cell adhesion and chemotaxis

Many of the biological functions attributed to cell surface proteoglycans are dependent on the interaction with extracellular mediators through their heparan sulphate (HS) moieties and the participation of their core proteins in signaling events. A class of recently identified inflammatory mediators is secreted cyclophilins, which are mostly known as cyclosporin A-binding proteins. We previously demonstrated that cyclophilin B (CyPB) triggers chemotaxis and integrin-mediated adhesion of T lymphocytes mainly of the CD4+/CD45RO+ phenotype. These activities are related to interactions with two types of binding sites, CD147 and cell surface HS. Here, we demonstrate that CyPB-mediated adhesion of CD4+/CD45RO+ T cells is related to p44/42 mitogen-activated protein kinase (MAPK) activation by a mechanism involving CD147 and HS proteoglycans (HSPG). Although HSPG core proteins are represented by syndecan-1, -2, -4, CD44v3 and betaglycan in CD4+/CD45RO+ T cells, we found that only syndecan-1 is physically associated with CD147. The intensity of the heterocomplex increased in response to CyPB, suggesting a transient enhancement and/or stabilization in the association of CD147 to syndecan-1. Pretreatment with anti-syndecan-1 antibodies or knockdown of syndecan-1 expression by RNA interference dramatically reduced CyPB-induced p44/p42 MAPK activation and consequent migration and adhesion, supporting the model in which syndecan-1 serves as a binding subunit to form the fully active receptor of CyPB. Altogether, our findings provide a novel example of a soluble mediator in which a member of the syndecan family plays a critical role in efficient interaction with signaling receptors and initiation of cellular responses.

Octasaccharide is the minimal length unit required for efficient binding of cyclophilin B to heparin and cell surface heparan sulphate

Cyclophilin B (CyPB) is a heparin-binding protein first identified as a receptor for cyclosporin A. In previous studies, we reported that CyPB triggers chemotaxis and integrin-mediated adhesion of T-lymphocytes by way of interaction with two types of binding sites. The first site corresponds to a signalling receptor; the second site has been identified as heparan sulphate (HS) and appears crucial to induce cell adhesion. Characterization of the HS-binding unit is critical to understand the requirement of HS in pro-adhesive activity of CyPB. By using a strategy based on gel mobility shift assays with fluorophore-labelled oligosaccharides, we demonstrated that the minimal heparin unit required for efficient binding of CyPB is an octasaccharide. The mutants CyPB(KKK-) [where KKK- refers to the substitutions K3A(Lys3-->Ala)/K4A/K5A] and CyPB(DeltaYFD) (where Tyr14-Phe-Asp16 has been deleted) failed to interact with octasaccharides, confirming that the Y14FD16 and K3KK5 clusters are required for CyPB binding. Molecular modelling revealed that both clusters are spatially arranged so that they may act synergistically to form a binding site for the octasaccharide. We then demonstrated that heparin-derived octasaccharides and higher degree of polymerization oligosaccharides inhibited the interaction between CyPB and fluorophore-labelled HS chains purified from T-lymphocytes, and strongly reduced the HS-dependent pro-adhesive activity of CyPB. However, oligosaccharides or heparin were unable to restore adhesion of heparinase-treated T-lymphocytes, indicating that HS has to be present on the cell membrane to support the pro-adhesive activity of CyPB. Altogether, these results demonstrate that the octasaccharide is likely to be the minimal length unit required for efficient binding of CyPB to cell surface HS and consequent HS-dependent cell responses.

Interactions of multiple heparin binding growth factors with neuropilin-1 and potentiation of the activity of fibroblast growth factor-2

The hypothesis that neuropilin-1 (Npn-1) may interact with heparin-binding proteins other than vascular endothelial growth factor has been tested using an optical biosensor-based binding assay. The results show that fibroblast growth factor (FGF) 1, 2, 4, and 7, FGF receptor 1, hepatocyte growth factor/scatter factor (HGF/SF), FGF-binding protein, normal protease sensitive form of prion protein, antithrombin III, and Npn-1 itself are all able to interact with Npn-1 immobilized on the sensor surface. FGF-2, FGF-4, and HGF/SF are also shown to interact with Npn-1 in a solution assay. Moreover, these protein-protein interactions are dependent on the ionic strength of the medium and are inhibited by heparin, and the kinetics of binding of FGF-2, FGF-4 and HGF/SF to Npn-1 are characterized by fast association rate constants (270,000-1,600,000 m(-1) s(-1)). These results suggest that Npn-1 possesses a "heparin" mimetic site that is able to interact at least in part through ionic bonding with the heparin binding site on many of the proteins studied. Npn-1 was also found to potentiate the growth stimulatory activity of FGF-2 on human umbilical vein endothelial cells, indicating that Npn-1 may not just bind but also regulate the activity of heparin-binding proteins.

High binding capacity of cyclophilin B to chondrocyte heparan sulfate proteoglycans and its release from the cell surface by matrix metalloproteinases: possible role as a proinflammatory mediator in arthritis

OBJECTIVE

To study cyclophilin B, a protein newly identified as a secretion product of cultured chondrocytes, in the context of chondrocyte pathobiology.

METHODS

Cyclophilin B was purified by sequential chromatographic processing of the secretion medium of cultured guinea pig chondrocytes. Its presence both at the surface of chondrocyte monolayers and in cartilage was demonstrated by immunohistochemistry. Binding sites at the surface of chondrocytes were characterized by Scatchard plot analysis using (125)I-labeled cyclophilin B, and by glycosidase treatments. The release of cyclophilin B from chondrocytes by activated matrix metalloproteinases (MMPs) was studied by Western blot analysis.

RESULTS

Cyclophilin B was present at the surface of cultured chondrocytes and within cartilage, both in cells and in the extracellular matrix, with a particularly intense staining in the superficial layer. It was secreted constitutively by chondrocytes and cartilage explants. Its secretion was enhanced after treatment with its pharmacologic binding partner, cyclosporin A (CSA). Experiments with (125)I-labeled cyclophilin B demonstrated the presence of high-capacity, low-affinity, NaCl-sensitive binding sites at the surface of chondrocytes. Cell-bound cyclophilin B could be released by heparinase treatment, demonstrating binding to pericellular heparan sulfate proteoglycans (HSPGs). Chondroitinase or keratanase treatments had no effect. MMPs 1, 2, 3, 9, and 13 released intact cyclophilin B from the cell surface, probably by cleavage of HSPGs. This effect was reversed by the broad-spectrum MMP inhibitor, marimastat.

CONCLUSION

Cyclophilin B is a secreted CSA-binding protein involved in inflammatory events. It can induce chemotaxis in human neutrophils and T lymphocytes. The finding that cyclophilin B is an intrinsic component of cartilage and that it can be released by MMPs suggests that it has a role in the pathogenesis of arthritic diseases, even more so since its signaling receptor is present within the inflamed joint both on T cells and in the rheumatoid synovium.

Preliminary study of the stability of calix[4]arene crown compounds under radiolysis

The extraction of (135)Cs from high activity waste arising from reprocessing of spent fuel can be achieved by using calix[4]arene crown compounds. The radiolytic degradation of calix[4]arene crowns as well as their solvent, o-nitrophenyloctyl ether (NPOE), was studied using electrospray ionization mass spectrometry (ESI-MS) (that formed Cs(+) or Na(+) adducts) in nitric acid, as well as by chemical ionization tandem mass spectrometry (MS/MS) experiments. The structures of major degradation products were identified with MS and specifically labelled nitric acid. Although NPOE and calix[4]arene crowns alone are relatively stable, under simulated conditions resembling the real industrial processes involving radiolysis in the presence of nitric acid, several products resulting from nitration and oxidation were observed.

Receptor type I and type II binding regions and the peptidyl-prolyl isomerase site of cyclophilin B are required for enhancement of T-lymphocyte adhesion to fibronectin

Cyclophilin B (CyPB), a cyclosporin A (CsA) binding protein, interacts with two types of binding sites at the surface of T-lymphocytes. The type I sites correspond to functional receptors involved in endocytosis and the type II sites to sulfated glycosaminoglycans (GAGs). Mutational analysis of CyPB has revealed that W128, which is part of the CsA-binding pocket, is implicated in the binding to the functional type I receptors and that two amino acid clusters located in the N-terminus ensure the binding to GAGs. The peptidyl-prolyl isomerase activity of CyPB is not required for receptor binding. We have recently demonstrated that CyPB enhances adhesion of peripheral blood T-lymphocytes to fibronectin, a component of the extracellular matrix. We intended to identify additional amino acids involved in the binding of CyPB to its functional type I receptor and to determine regions responsible for the stimulation of peripheral blood T-lymphocyte adhesion. We determined that residues R76, G77, K132, D155, and D158 of the calcineurin (CN) interacting region were implicated in the recognition of type I receptor but not of GAGs. We also found that two different changes in the N-terminal extension that abated binding to GAGs prevented adhesion of peripheral blood T-lymphocytes to coated CyPB, whereas abbrogation of the PPIase activity had no effect. On the other hand, the adhesion of peripheral blood T-lymphocytes to coated fibronectin was not stimulated by CyPB mutants devoid of either type I receptor or GAGs binding activity or by mutants of the PPIase site. Altogether, the results demonstrate that different regions of CyPB are involved in peripheral blood T-lymphocyte activation and imply a novel important physiological function for peptidyl-prolyl isomerase activity.

Interaction with glycosaminoglycans is required for cyclophilin B to trigger integrin-mediated adhesion of peripheral blood T lymphocytes to extracellular matrix

Cyclophilins A and B (CyPA and CyPB) are cyclosporin A-binding proteins that are involved in inflammatory events. We have reported that CyPB interacts with two types of cell-surface-binding sites. The first site corresponds to a functional receptor and requires interaction with the central core of CyPB. This region is highly conserved in cyclophilins, suggesting that CyPA and CyPB might share biological activities mediated by interaction with this receptor. The second site is identified with glycosaminoglycans (GAGs), the binding region located in the N terminus of CyPB. The difference in the N-terminal extensions of CyPA and CyPB suggests that a unique interaction with GAGs might account for selective activity of CyPB. To explore this hypothesis, we analyzed the lymphocyte responses triggered by CyPA, CyPB, and CyPB(KKK-), a mutant unable to interact with GAGs. The three ligands seemed capable enough to elicit calcium signal and chemotaxis by binding to the same signaling receptor. In contrast, only CyPB enhanced firm adhesion of T cells to the extracellular matrix. This activity depended on the interactions with GAGs and signaling receptor. CyPB-mediated adhesion required CD147 presumably because it was a costimulatory molecule and was related to an activation of alpha4beta1 and alpha4beta7 integrins. Finally, we showed that CyPB was capable mainly to enhance T cell adhesion of the CD4+CD45RO+ subset. The present data indicate that CyPB rather than CyPA is a proinflammatory factor for T lymphocytes and highlight the crucial role of CyPB-GAG interaction in the chemokine-like activity of this protein.

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.

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.

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.

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.

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.

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.

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.

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.