Rabbit proactivator is a neutral metalloproteinase that activates another metalloproteinase, procollagenase, and degrades noncollagenous matrix. We describe the construction of an activator complementary DNA (cDNA) clone, which is 1.9 kb, that selects a 2.1-kb messenger RNA (mRNA) in Northern blot hybridizations. Nucleic acid sequence studies of the activator cDNA indicate 1) that it encodes protein M , 53,881, 2) that this protein exhibits -80% homology with rat transin, an oncogene-induced protein with a previously unknown function, and 3) that, in the first 172 residues, it is virtually identical to the rabbit metalloproteinase, stromelysin. Homology between rabbit activator and human skin collagenase is approximately 50%. Activator and collagenase mRNA are coordinately regulated; untreated cultures of rabbit synovial fibroblasts produce low levels of each protein, but addition of phorbol myristate acetate ( W M ) results in an increase in mRNA for both proteins by 2.5-5 hours. Adding alltrans-retinoic acid (lo-%) or dexamethasone (lO-'M) to phorbol-stimulated cells coordinately suppresses both activator and collagenase mRNA. Our data suggest the existence of coordinately regulated metalloproteinases that are important in the modulation of connective tissue metabolism.The metalloproteinase, collagenase (EC 3.2.24.7), is the only neutral proteinase able to initiate degradation of the interstitial collagens, types I, 11, and I11 (for review, see refs. 1 and 2). As such, collagenase plays a crucial role in the degradation of collagen that occurs as a result of both normal physiologic and disease processes (3). To study mechanisms that control the synthesis of collagenase, we have developed a model system of cultured rabbit synovial fibroblasts. These cells are readily available from the synovium of the knees of young rabbits and grow well in culture. Of experimental value is the fact that they make only minimal amounts of collagenase unless stimulated with such agents as interleukin-I , crystals of monosodium urate monohydrate, or the tumor promoter, phorbol myristate acetate (PMA) (r18). Addition of an inducer results in an increase in collagenase messenger RNA (mRNA), which is followed by rapid synthesis and secretion of collagenase protein (6,9). Equally valuable is the fact that collagenase synthesis can be antagonized by glucocorticoids and by retinoids (10,ll). It is believed that both compounds act at the level of transcription to decrease collagenase mRNA and protein, but do not affect the half-life of collagenase mRNA (12). This system has thus allowed us to study both the induction and suppression of collagenase synthesis.Rabbit synovial fibroblast collagenase is synthesized and secreted as an inactive polypeptide, procollagenase ( M , 57,000), with a minor species of glycosylated enzyme (M, 61,000) (9,13). Activation of

We used a subclone of a rabbit genomic clone for collagenase that cross-hybridizes with human synovial cell messenger RNA (mRNA) to identify a human collagenase complementary DNA (cDNA) clone. The human cDNA clone is 2.1 kilobases (kb) and selects a mRNA transcript of approximately the same size from primary cultures of rheumatoid synovial cells that produce collagenase, but no mRNA is selected from control (nonproducing) synovial fibroblasts. Restriction enzyme analysis and DNA sequence data indicate that our cDNA clone is full length and that it is identical to that recently described for human skin fibroblast collagenase. The cDNA clone identified a single collagenase gene of 17 kb from blots of human genomic DNA. The identity of human skin and synovial cell collagenase and the ubiquity of this enzyme and of its substrates, the interstitial collagens types I, II, and III, imply that common mechanisms controlling collagenolysis throughout the human body may be operative in both normal and disease states.

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