Urokinase-type plasminogen activator: a paracrine factor regulating the bioavailability of IGFs in PA-III cell-induced osteoblastic metastases.
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.
Koutsilieris
M
M
Hormonal Bioregulation Laboratory, Hospital Center Laval University (C.H.U.L.), Ste. Foy, Quebec, Canada.
Frenette
G
G
Lazure
C
C
Lehoux
J G
JG
Govindan
M V
MV
Polychronakos
C
C
D000818:Animals; D000911:Antibodies, Monoclonal; D007611:Aprotinin / Q000494:pharmacology; D001550:Benzamidines / Q000494:pharmacology; D001682:Biological Availability; D001859:Bone Neoplasms / Q000201:enzymology / Q000378:metabolism* / Q000556:secondary*; D002352:Carrier Proteins / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects; D003470:Culture Media; D003907:Dexamethasone / Q000494:pharmacology; D015536:Down-Regulation / Q000187:drug effects / Q000502:physiology; D015870:Gene Expression / Q000502:physiology; D006868:Hydrolysis; D018970:Insulin-Like Growth Factor Binding Protein 1; D018971:Insulin-Like Growth Factor Binding Protein 2; D007334:Insulin-Like Growth Factor I / Q000378:metabolism* / Q000502:physiology; D007700:Kinetics; D008297:Male; D012516:Osteosarcoma / Q000201:enzymology / Q000378:metabolism* / Q000556:secondary*; D011471:Prostatic Neoplasms / Q000201:enzymology / Q000235:genetics / Q000473:pathology*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D013268:Stimulation, Chemical; D014407:Tumor Cells, Cultured; D014568:Urokinase-Type Plasminogen Activator / Q000037:antagonists & inhibitors / Q000494:pharmacology / Q000502:physiology*
D000911:Antibodies, Monoclonal; D001550:Benzamidines; D002352:Carrier Proteins; D003470:Culture Media; D018970:Insulin-Like Growth Factor Binding Protein 1; D018971:Insulin-Like Growth Factor Binding Protein 2; D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I; D003907:Dexamethasone; D007611:Aprotinin; D014568:Urokinase-Type Plasminogen Activator; C032157:benzamidine