Autoregulation of collagenase production by a protein synthesized and secreted by synovial fibroblasts: cellular mechanism for control of collagen degradation.

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 3Hleucine. Collagenase production was measured by immunoprecipitation of culture medium with monospecific antibody. 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 synovial fibroblasts autoregulate collagenase production and suggest that the low levels of collagenase seen in resting cultures result from an active suppression of collagenase synthesis.