METALLOPROTEINASE ACTIVITY SECRETED BY FIBROGENIC CELLS IN THE PROCESSING OF PROLYSYL OXIDASE - POTENTIAL ROLE OF PROCOLLAGEN C-PROTEINASE

Lysyl oxidase is secreted from fibrogenic cells as a 50-kDa proenzyme that is proteolytically processed to the mature enzyme in the extracel lular space. To characterize the secreted proteinase activity, a trunc ated, recombinant form of lysyl oxidase was prepared as a proteinase s ubstrate containing the sequence of the propeptide cleavage region, Th e processing proteinase activity secreted by cultured fibrogenic cells resists inhibitors of serine or aspartyl proteinases as well as tissu e inhibitor of matrix metalloproteinases-2 (MMP-2) but is completely i nhibited by metal ion chelators. Known metalloproteinases were tested for their activity toward this substrate. Carboxyl-terminal procollage n proteinase (C-proteinase), MMP-2, and conditioned fibrogenic cell cu lture medium cleave the lysyl oxidase substrate to the size of the mat ure enzyme. The NH2-terminal sequence generated by arterial smooth mus cle conditioned medium and the C-proteinase but not by MMP-2, i.e. Asp -Asp Pro-Tyr, was identical to that previously identified in mature ly syl oxidase isolated from connective tissue, The C-proteinase activity against the model substrate was inhibited by a synthetic oligopeptide mimic of the cleavage sequence (Ac-Met-Val-Gly-Asp-Asp-Pro-Tyr-Asn-am ide), whereas this peptide also inhibited the generation of lysyl oxid ase activity in the medium of fetal rat lung fibroblasts in culture. I n toto, these results identify a secreted metalloproteinase activity p articipating in the activation of prolysyl oxidase, identify inhibitor s of the processing activity, and implicate procollagen C-proteinase i n this role.