Annexin I surface binding sites and their regulation on human fibroblast-like synoviocytes

Objective, Annexin I is a glucocorticoid-inducible protein whose expression in rheumatoid synovium and inhibitory actions in animal models of arthriti s suggests its involvement in human arthritis. The present study explored t he potential for annexin I to mediate its antiinflammatory actions via spec ific cell-surface binding sites on human fibroblast-like synoviocytes (FLS) , Methods, Annexin I binding sites on cultured FLS from patients with osteoar thritis (OA) and rheumatoid arthritis (RA) were determined by ligand-bindin g flow cytometry, Phospholipase A(2) (PLA(2)) activity was determined by ar achidonic acid release. Results, FLS exhibited saturable, concentration-dependent cell-surface anne xin I binding, with >99% of the OA FLS exhibiting binding at an annexin I c oncentration of 10 muM, Annexin I binding of RA FLS was significantly lower than that of OA FLS. FLS annexin I binding sites were not affected by elas tase or a specific elastase inhibitor, and elastase release did not differ between RA and OA cells. In contrast, collagenase significantly increased a nnexin I binding sites on OA FLS and approached a significant effect on RA FLS, Tumor necrosis factor alpha increased annexin I binding sites on OA an d RA FLS, Similarly, interleukin-1 beta significantly increased annexin I b inding on OA FLS; but the increased binding on RA FLS was not significant. Dexamethasone exerted no significant effect on OA or RA FLS annexin I bindi ng sites. Treatment of RA FLS with an annexin I N-terminal peptide signific antly inhibited RA FLS PLA(2) activity. Conclusion. This is the first description of the expression, regulation, an d function of cell surface annexin I binding sites on FLS, Reduced annexin I binding sites in RA FLS may impair the sensitivity of certain proinflamma tory events to glucocorticoids.