Studies on the molecular composition and degradation of type IV procollagen.

The effects of trypsin on soluble type IV procollagen from the EHS mouse tumour were studied. The enzyme cleaved the pro alpha 1(IV) and pro alpha 2(IV) chains, causing only a minor decrease in the molecular weight of the pro alpha 1(IV) chain, whereas the pro alpha 2(IV) chain was degraded to at least two smaller peptides. Analyses of the uncleaved and trypsin-digested type IV procollagen by molecular sieving, with and without reduction and denaturation, were consistent with the two chains, pro alpha 1(IV) and pro alpha 2(IV), being in the same molecule, as a heterotrimer with the composition [pro alpha 1(IV)]2pro alpha 2(IV). It was also shown that the tumour promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) induces the secretion of a type IV collagen-degrading metal protease into media of cultured human skin fibroblasts. This result supports previously reported findings that such an enzyme is associated with malignant transformation of cells.