Schwann cell proliferation and localized proteolysis: expression of plasminogen-activator activity predominates in the proliferating cell populations.

The role of the serum proteolytic system plasminogen/plasminogen activator as a biochemical tool used by the glia or neurons, or both, for maintaining their temporary and flexible cellular interactions during histogenesis of the nervous system is under study. The present report identifies a glia cell type, the Schwann cell, as one of the cellular components of the nervous system that uses extracellular proteolysis at the time of the tissue construction. Purified dividing mouse Schwann cells in culture produce extracellular plasminogen activator. The levels of extracellular plasminogen-activator activity, as measured by the biochemical fibrinolytic assay, were directly related to the proliferation rates of the Schwann cells. The cellular plasminogen-activator specific activity at the maximal rate of cell proliferation was 3-4 times higher than that of the cells at low rate of mitosis. It is concluded that plasminogen-activator activity is expressed predominantly by the proliferating Schwann cell populations, suggesting that the extracellular proteolysis is used by the tissue at those stages when the cells divide.