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.


CONCLUSIONS
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.
De Ceuninck
Frédéric
F
Division de Rheumatologie, Institut de Recherches Servier, 11 rue des Moulineaux, 92150 Suresnes, France. frederic.deceuninck@fr.netgrs.com
Allain
Fabrice
F
Caliez
Audrey
A
Spik
Geneviève
G
Vanhoutte
Paul M
PM
D000818:Animals; D018501:Antirheumatic Agents / Q000494:pharmacology; D001168:Arthritis / Q000276:immunology / Q000378:metabolism; D002358:Cartilage, Articular / Q000166:cytology; D002478:Cells, Cultured; D019902:Chondrocytes / Q000166:cytology / Q000201:enzymology* / Q000378:metabolism; D021983:Cyclophilins / Q000378:metabolism*; D016572:Cyclosporine / Q000494:pharmacology; D006026:Glycoside Hydrolases / Q000378:metabolism; D006168:Guinea Pigs; D019812:Heparan Sulfate Proteoglycans / Q000378:metabolism*; D007150:Immunohistochemistry; D018836:Inflammation Mediators / Q000378:metabolism*; D007457:Iodine Radioisotopes; D020782:Matrix Metalloproteinases / Q000378:metabolism*; D019696:Peptidylprolyl Isomerase; D011485:Protein Binding / Q000187:drug effects / Q000502:physiology
D018501:Antirheumatic Agents; D019812:Heparan Sulfate Proteoglycans; D018836:Inflammation Mediators; D007457:Iodine Radioisotopes; C081786:cyclophilin B; D016572:Cyclosporine; D006026:Glycoside Hydrolases; D020782:Matrix Metalloproteinases; D021983:Cyclophilins; D019696:Peptidylprolyl Isomerase