Tissue-type plasminogen activator is a target of the tumor suppressor gene maspin

Abstract
The maspin protein has tumor suppressor activity in breast and prostate cancers. It inhibits cell motility and invasion in vitro and tumor growth and metastasis in nude mice. Maspin is structurally a member of the serpin (serine protease inhibitors) superfamily but deviates somewhat from classical serpins. We find that single-chain tissue plasminogen activator (sctPA) specifically interacts with the maspin reactive site loop peptide and forms a stable complex with recombinant maspin [rMaspin(i)]. Major effects of rMaspin(i) are observed on plasminogen activation by sctPA. First, rMaspin(i) activates free sctPA. Second, it inhibits sctPA preactivated by poly- d -lysine. Third, rMaspin(i) exerts a biphasic effect on the activity of sctPA preactivated by fibrinogen/gelatin, acting as a competitive inhibitor at low concentrations (in vitro suggest a mechanism by which maspin regulates plasminogen activation by sctPA bound to the epithelial cell surface.

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