Autoregulation of collagenase prod and secreted by synovial fibroblast control of collagen degradation (phorbol myristate acetate/connective tissue regulation/immunopreci

Conditioned medium taken from cultures of resting rabbit synovial fibroblasts contained a protein that prevented the synthesis of the neutral proteinase collagenase. Conditioned medium was concentrated 10-fold and placed on cultures of rabbit synovial fibroblasts along with an inducer of collagenase (phorbol myristate acetate or latex particles) and (3H)leucine. Collagenase production was measured by immu- noprecipitation of culture medium with monospecific anti- body. Gel filtration showed that the inhibitory factor had MrS of 12,500, 25,000-50,000, and 150,000, suggesting that the protein may exist as aggregates. Activity was destroyed by boiling, by trypsin, and by dithiothreitol. Production of the inhibitory protein was prevented by cycloheximide. Isoelectric focusing purified the protein 100- to 150-fold and revealed pIs in the range of 3.2-3.7. Glycosylation was demonstrated by binding to Con A-Sepharose. Our data indicate that rabbit sy- novial fibroblasts autoregulate collagenase production and suggest that the low levels of collagenase seen in resting cul- tures result from an active suppression of collagenase synthe- sis.