REGULATION OF TISSUE INHIBITOR OF METALLOPROTEINASES-3 GENE-EXPRESSION BY TRANSFORMING GROWTH-FACTOR-BETA AND DEXAMETHASONE IN BOVINE AND HUMAN ARTICULAR CHONDROCYTES

Physiological and pathological degradation of cartilage extracellular matrix (ECM) is regulated by the balance between tissue inhibitors of metalloproteinases (TIMPs) and matrix metalloproteinases (MMPs), We ex amined the potential of chondrocytes from normal bovine or human osteo arthritic (OA) cartilage to express RNA for the new inhibitor TIMP-3 a nd studied its regulation by an inducer of matrix synthesis, transform ing growth factor-beta (TGF-beta). Freshly released chondrocytes const itutively expressed three transcripts of TIMP-3 that are induced by se rum factors, In primary cultures of chondrocytes, one of these factors , TGF-beta, increased TIMP-3 mRNA in a dose-dependent fashion that req uired de novo protein synthesis and transcription, TGF-beta did not al ter stability of the TIMP-3 transcripts in RNA decay time-courses, sug gesting a transcriptional control, Nuclear run-on assays confirmed inc reased rate of TIMP-3 gene transcription by TGF-beta. An antiinflammat ory glucocorticoid, dexamethasone, inhibited the basal, and suppressed partially the TGF-beta-inducible, TIMP-3 expression in primary bovine and human chondrocytes, DNA sequencing of bovine TIMP-3 cDNA revealed an open reading frame of a 211-amino-acid protein containing signal p eptide and 12 conserved cysteines, The encoded protein differed from h uman TIMP-3 at four positions, The constitutive expression and evoluti onary conservation of TIMP-3 imply its important function, TIMP-3 indu ction by TGF-beta suggests the role of this factor and TIMP-3 in carti lage remodeling with important implications for arthritis.