Urokinase-type plasminogen activator: a paracrine factor regulating the bioavailability of IGFs in PA-III cell-induced osteoblastic metastases

Anticancer Res. 1993 Mar-Apr;13(2):481-6.


The transplantation of PA-III rat prostate cancer cells onto rat skeleton produces osteoblastic metastases. Therefore w e studied the paracrine interactions between the PA-III cells and osteoblast-derived osteosarcoma cells (UMR 106 cells). A serine protease secreted by PA-III cells hydrolyzed IGF-binding protein-1 and IGF-binding protein-2 (IGFBP-1 and IGFBP-2) detected in the cell culture media (CM) of OMR 106 cells by western ligand blotting. The serine protease of PA-III cell CM was purified using a benzamidine affinity column. This protease was a protein of 45-50 kDa on polyacrylamide gel electrophoresis under non-reducing conditions but generated two protein bands under reducing conditions; a) one of 33-35 kDa possessing protease activity and b) another of 20-25 kDa which was proteinolytically inactive. Sequence analysis identified the amino acid sequence of the a-chain (20-25 kDa band) and of the b-chain (33-35 kDa band) of rat urokinase-type plasminogen activator molecule. Urokinase purified from PA-III cell CM hydrolyzed IGFBPs of UMR 106 cells and stimulated the proliferation of UMR 106 cells in serum-free cultures. Its protease activity was abolished by benzamidine and aprotinin. Its mitogenic activity for osteoblasts was inhibited by anti-IGF-I monoclonal antibody. Northern blot analysis documented the expression of the urokinase-type plasminogen activator gene in the mRNA extracted from PA-III cells. Urokinase expression was inhibited by dexamethasone. Therefore, we conclude that urokinase-type plasminogen activator stimulates osteoblasts via an IGF-I dependent mechanism. Hydrolysis of the IGFBOPs at the sites of PA-III cell-induced bone tumors account for an increased bioavailability of IGFs. This may facilitate the development and the growth of PA-III cell-induced bone tumor and can also mediate the subsequent local osteoblastic reaction.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antibodies, Monoclonal
  • Aprotinin / pharmacology
  • Benzamidines / pharmacology
  • Biological Availability
  • Bone Neoplasms / enzymology
  • Bone Neoplasms / metabolism*
  • Bone Neoplasms / secondary*
  • Carrier Proteins / metabolism
  • Cell Division / drug effects
  • Culture Media
  • Dexamethasone / pharmacology
  • Down-Regulation / drug effects
  • Down-Regulation / physiology
  • Gene Expression / physiology
  • Hydrolysis
  • Insulin-Like Growth Factor Binding Protein 1
  • Insulin-Like Growth Factor Binding Protein 2
  • Insulin-Like Growth Factor I / metabolism*
  • Insulin-Like Growth Factor I / physiology
  • Kinetics
  • Male
  • Osteosarcoma / enzymology
  • Osteosarcoma / metabolism*
  • Osteosarcoma / secondary*
  • Prostatic Neoplasms / enzymology
  • Prostatic Neoplasms / genetics
  • Prostatic Neoplasms / pathology*
  • RNA, Messenger / metabolism
  • Rats
  • Stimulation, Chemical
  • Tumor Cells, Cultured
  • Urokinase-Type Plasminogen Activator / antagonists & inhibitors
  • Urokinase-Type Plasminogen Activator / pharmacology
  • Urokinase-Type Plasminogen Activator / physiology*


  • Antibodies, Monoclonal
  • Benzamidines
  • Carrier Proteins
  • Culture Media
  • Insulin-Like Growth Factor Binding Protein 1
  • Insulin-Like Growth Factor Binding Protein 2
  • RNA, Messenger
  • Insulin-Like Growth Factor I
  • Dexamethasone
  • Aprotinin
  • Urokinase-Type Plasminogen Activator
  • benzamidine