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The major excreted protein of transformed fibroblasts is an activable acid-protease

S Gal, M M Gottesman

    The Journal of Biological Chemistry
    |February 5, 1986
    PubMed

    Insights

    Malignant mouse cells secrete a major excreted protein (MEP) that acts as an acid-activable protease. This protease digests extracellular matrix proteins and may represent a novel acid-protease in mouse cells.

    Area of Science:

    • Biochemistry
    • Cell Biology
    • Oncology

    Background:

    • Malignant transformation in mouse cells, induced by various agents or specific promoters, leads to elevated synthesis and secretion of a 39,000-dalton protein known as major excreted protein (MEP).
    • The functional role and enzymatic activity of MEP in the context of cellular transformation and extracellular matrix interaction remain to be fully elucidated.

    Purpose of the Study:

    • To characterize the enzymatic activity of the secreted major excreted protein (MEP) from transformed mouse cells.
    • To determine the optimal conditions for MEP protease activity and identify its substrate specificity.
    • To investigate the potential novelty of MEP as an acid-protease distinct from known cathepsins.

    Main Methods:

    • Analysis of protein synthesis and secretion in mouse cells undergoing malignant transformation.
    • Biochemical assays to assess protease activity of purified secreted MEP.
    • Determination of optimal pH, temperature, and substrate concentration for MEP activity.
    • Inhibition studies using various classes of protease inhibitors (sulfhydryl, metallo-, seryl-, carboxyprotease inhibitors).
    • Comparison of MEP protease characteristics with known cathepsins.

    Main Results:

    • Secreted MEP functions as an acid-activable protease, with auto-activation occurring at low pH.
    • The MEP protease exhibits optimal activity within a pH range of 3.3-3.6.
    • MEP effectively digests various proteins, including extracellular matrix components like fibronectin, collagen, and laminin.
    • MEP activity is dependent on temperature and concentration, and is specifically inhibited by sulfhydryl protease inhibitors (e.g., leupeptin, iodoacetic acid).
    • MEP protease displays distinct characteristics compared to previously reported cathepsins.

    Conclusions:

    • Secreted major excreted protein (MEP) is a novel acid-activable protease involved in the degradation of extracellular matrix proteins.
    • MEP protease activity is regulated by acidic pH and is sensitive to sulfhydryl protease inhibitors.
    • The unique properties of MEP suggest it represents a new class of acid-protease in mouse cells with potential implications in malignant transformation.

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