Effective activation of the proenzyme form of the urokinase-type plasminogen activator (pro-uPA) by the cysteine protease cathepsin L.
Increased levels of both the cysteine protease, cathepsin L, and the serine protease, uPA (urokinase-type plasminogen activator), are present in solid tumors and are correlated with malignancy. uPA is released by tumor cells as an inactive single-chain proenzyme (pro-uPA) which has to be activated by proteolytic cleavage. We analyzed in detail the action of the cysteine protease, cathepsin L, on recombinant human pro-uPA. Enzymatic assays, SDS-PAGE and Western blot analysis revealed that cathepsin L is a potent activator of pro-uPA. As determined by N-terminal amino acid sequence analysis, activation of pro-uPA by cathepsin L is achieved by cleavage of the Lys158-Ile159 peptide bond, a common activation site of serine proteases such as plasmin and kallikrein. Similar to cathepsin B (Kobayashi et al., J. Biol. Chem. (1991) 266, 5147-5152) cleavage of pro-uPA by cathepsin L was most effective at acidic pH (molar ratio of cathepsin L to pro-uPA of 1:2,000). Nevertheless, even at pH 7.0, pro-uPA was activated by cathepsin L, although a 10-fold higher concentration of cathepsin L was required. As tumor cells may produce both pro-uPA and cathepsin L, implications for the activation of tumor cell-derived pro-uPA by cathepsin L may be considered. Different pathways of activation of pro-uPA in tumor tissues may coexist: (i) autocatalytic intrinsic activation of pro-uPA; (ii) activation by serine proteases (plasmin, kallikrein, Factor XIIa); and (iii) activation by cysteine proteases (cathepsin B and L).
Goretzki
L
L
Frauenklinik der Technischen Universität München, Klinikum rechts der Isar, Germany.
Schmitt
M
M
Mann
K
K
Calvete
J
J
Chucholowski
N
N
Kramer
M
M
Günzler
W A
WA
Jänicke
F
F
Graeff
H
H
D000595:Amino Acid Sequence; D015153:Blotting, Western; D056668:Cathepsin L; D002403:Cathepsins / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D003546:Cysteine Endopeptidases; D004591:Electrophoresis, Polyacrylamide Gel; D010450:Endopeptidases; D004789:Enzyme Activation; D004792:Enzyme Precursors / Q000378:metabolism*; D006801:Humans; D006868:Hydrolysis; D008969:Molecular Sequence Data; D011994:Recombinant Proteins / Q000378:metabolism; D014568:Urokinase-Type Plasminogen Activator / Q000378:metabolism*
D004792:Enzyme Precursors; D011994:Recombinant Proteins; D002403:Cathepsins; D010450:Endopeptidases; D014568:Urokinase-Type Plasminogen Activator; D003546:Cysteine Endopeptidases; C534281:CTSL protein, human; D056668:Cathepsin L