Proteolysis of highly polysialylated NCAM by the tissue plasminogen activator-plasmin system in rats

Tissue-type plasminogen activator (tPA), a serine protease which converts the zymogen plasminogen to the active protease plasmin, is believed to regulate neurite extension and neural cell migration by modulating extracellular metabolism. The highly polysialylated form of the neural cell adhesion molecule (NCAM-H) is strongly expressed in the developing brain and is believed to play a role in organizing the neural network. In this report, we incubated neonatal rat brain homogenates with human tPA and rat plasminogen in order to determine whether NCAM-H would be degraded. NCAM-H was degraded by plasmin which was formed from rat plasminogen by human tPA. The degradation was inhibited by the addition of plasminogen activator inhibitor type 1 (PAI-1) or aprotinin. These results suggest a possible contribution of the tPA-plasmin system to NCAM-H turnover in the developing brain.