Presence of cyclophilin A in synovial fluids of patients with rheumatoid arthritis.
Bottom Line: Sequencing of this protein revealed identity of the NH2-terminal amino acids with those of human cyclophilin A.The finding is unexpected since cyclophilin B rather than A is generally regarded as the secreted isoform, the presence of cyclophilin A being confined to the cytoplasm.This may offer a possible explanation of the effectiveness of cyclosporin A in RA, in addition to the known immunosuppressive effects of the drug.
Affiliation: Sandoz Research Institute, Vienna, Austria.
Cyclophilins have been suggested to act as leukocyte chemotactic factors produced in the course of inflammation. Therefore we looked for the presence of cyclophilins in the synovial fluids (SF) from patients with rheumatoid arthritis (RA). Peptidyl prolyl cis-trans isomerase activity (PPIase) was measured in SF from knee punctures of 26 patients with RA and five patients with knee osteoarthritis (OA). PPIase was detected in SF from RA patients, but not in samples from OA patients. Enzyme activity was sensitive to inhibition by cyclosporin A (IC50 = 28-50 nM). Estimated concentrations of the SF-derived cyclophilin based on the enzyme activity were in the range of 11 to 705 nM. The presence of cyclophilin in the SF showed disease correlation; its concentration correlated with the number of cells in the SF (r = 0.91, P < 0.0001) and with the percentage of neutrophils in the cellular infiltrate and was higher in more acute cases of joint swelling. In immunoblots of partially purified preparations of SF from RA patients, an approximately 18-kD protein band reacted with polyclonal antibodies that recognize cyclophilin A and B, but not with antibodies specific for cyclophilin B. Sequencing of this protein revealed identity of the NH2-terminal amino acids with those of human cyclophilin A. The finding is unexpected since cyclophilin B rather than A is generally regarded as the secreted isoform, the presence of cyclophilin A being confined to the cytoplasm. Our data support the hypothesis that cyclophilins may contribute to the pathogenesis of inflammatory diseases, possibly by acting as cytokines. This may offer a possible explanation of the effectiveness of cyclosporin A in RA, in addition to the known immunosuppressive effects of the drug.
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Mentions: To identify the protein responsible for the cyclophilinlike activity, we performed a fractionation of synovial fluids. Two separate experiments were performed with SF pools of patients KK, NN, and PH and patients KL and AA. First, fractionated ammonium sulfate precipitation was performed; the enzymatic activity precipitated between 20 and 60% saturation. This was followed by gel filtration chromatography on Superose 12; this step separated the bulk of protein contained in the SF from the enzymatic activity. In the pooled fractions containing the isomerase activity, SDS gel electrophoresis followed by Coomassie staining revealed the presence of a protein band that comigrates with cyclophilin A besides some other contaminating bands (Fig. 3 A). Using a polyclonal antiserum raised against cyclophilin A which cross-reacts with cyclophilin B, an immunoreactive band migrating to the same position as cyclophilin A was detected (Fig. 3 B). This protein did not react with antibodies specifically recognizing cyclophilin B (not shown). To further substantiate the assumption that the SF contain cyclophilin A, we performed NH2-terminal sequencing of the 18-kD protein partially purified from pooled SF of patients KL and AA after blotting from SDS gels. The sequence of the first 20 NH2-terminal amino acids was determined to Val-Asn-Pro-Thr-Val-Phe-Phe-Asp-Ile-Ala-ValAsp-Gly-Glu-Pro-Leu-Gly-Arg-Val-Ser. This is identical to the known sequence of human cyclophilin A (18).