ABSTRACT
FK506 (Tacrolimus) and cyclosporin A exert their immunosuppressive effects via a common mechanism, calcineurin inhibition, after binding to intracellular proteins termed immunophilins: FK506-binding protein (FKBP) and cyclophilin. In this study, FK506 was found to induce chondrogenic differentiation of ATDC5 cells (clonal mouse embryonal carcinoma cells) in a concentration-dependent manner (0.1-1000 ng/ml). Immunohistochemical staining showed that ATDC5 cells induced to differentiate by FK506 produced proteoglycan and type II collagen, main components of the extracellular matrix of cartilage. Rapamycin, an immunosuppressant that binds to FKBP, antagonized the effect of FK506. Cyclosporin A did not induce chondrogenesis at concentrations up to 1000 ng/ml. Taken together, these results suggest that FK506 induces chondrogenic differentiation of ATDC5 cells via a calcineurin-independent mechanism, after binding to FKBP.
