Urokinase - type plasminogen activator also known as PLAU and UPA, a serine protease with extremely limited substrate specificity, cleaving the sequence Cys - Pro - Gly - Arg560 - Val561 - Val - Gly - Gly - Cys in plasminogen to form plasmin. uPA is a potent marker of invasion and metastasis in a variety of human cancers associated with breast, stomach, colon, bladder, ovary, brain and endometrium. The human PLAU is initially synthesized as 431 amino acid precursor with a N-terminal signal peptide (20 residues). The single chain molecule is processed into a disulfide-linked two-chain molecule of different molecular weights. Two forms of the A chain exist, starting at Ser21 (the long form) and Lys156 (the short form). The long and short A ch