Multiple levels of post‐transcriptional regulation of collagenase (matrix metalloproteinase 1) in an epithelial cell line

Multiple levels of regulation of collagenase (matrix metalloproteinase 1; MMP‐1), have been demonstrated in a clonal rat epithelial cell line (A5P/B10). Secreted enzyme could not be demonstrated in culture medium from A5P/B10 cells but, using antibodies specific for collagenase, the enzyme was detected within the cytoplasm and on the surface of the cells. A probe for rat collagenase could not detect a signal for mRNA in the cytoplasm while nuclear run‐on data demonstrated that the gene for collagenase was being transcribed. Incubating the cells with 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA) significantly increased cytoplasmic mRNA levels and slightly increased the intensity of staining in permeabilized cells, but collagenase activity was still not detected in the conditioned medium. This indicated that the protein was being synthesized by the TPA‐treated cells but was not being secreted into the medium. These data suggest that the secretion of collagenase may be regulated both following transcription and after the completion of translation and it is suggested that multiple levels of control may be operating to determine the rate of collagenase release and hence, the rate of collagen turnover.