Surface‐bound plasmin induces selective proteolysis of insulin‐like‐growth‐factor (IGF)‐binding protein‐4 (IGFBP‐4) and promotes autocrine IGF‐II bio‐availability in human colon‐carcinoma cells

• Published in: International journal of cancer 1997-09, Vol.72 (5), p.835-843
• Main Authors: Remacle‐Bonnet, Maryse M., Garrouste, Françoise L., Pommier, Gilbert J.
• Format: Article
• Language: English
• Subjects: Adenocarcinoma - metabolism; Aprotinin - pharmacology; Biological and medical sciences; Blotting, Western; Colonic Neoplasms - metabolism; Culture Media, Conditioned - chemistry; Culture Media, Conditioned - metabolism; Endopeptidases - analysis; Endopeptidases - metabolism; Extracellular Matrix - metabolism; Fibrinolysin - metabolism; Gastroenterology. Liver. Pancreas. Abdomen; Humans; Insulin-Like Growth Factor Binding Protein 4 - analysis; Insulin-Like Growth Factor Binding Protein 4 - metabolism; Insulin-Like Growth Factor II - analysis; Insulin-Like Growth Factor II - metabolism; Medical sciences; Plasminogen - pharmacology; Stomach. Duodenum. Small intestine. Colon. Rectum. Anus; Tumor Cells, Cultured; Tumors
• ISSN: 0020-7136; 1097-0215
• DOI: 10.1002/(SICI)1097-0215(19970904)72:5<835::AID-IJC21>3.0.CO;2-6

Limited proteolysis of insulin‐like‐growth‐factor (IGF)‐binding proteins (IGFBPs) represents a key process to modulate IGF bio‐availability at the cellular level. In human colon carcinomas, urokinase‐type plasminogen activator (u‐PA) produced by stroma cells can bind to cancer‐cell‐associated u‐PA receptor (u‐PAR), and then catalyze the conversion of plasminogen (Pg) into plasmin (Pm). We therefore investigated the interplay between the IGF and Pm systems in the HT29‐D4 human colon‐carcinoma‐cell model. HT29‐D4 cells secreted IGF‐II totally complexed to IGFBP‐2, IGFBP‐4 and IGFBP‐6. Approximately 15% of IGFBP‐4 was associated with the extracellular matrix. HT29‐D4 cells produced neither u‐PA‐ nor IGFBP‐specific proteases. However, activation of Pm at the HT29‐D4 cell surface obtained by the sequential addition of exogenous u‐PA and Pg to mimic the stromal complementation induced selective proteolysis targeted to IGFBP‐4 only (>95%). IGFBP‐2 and IGFBP‐6, though sensitive to proteolysis by soluble Pm, were not altered by cell‐bound Pm. IGFBP‐4 proteolysis yielded 18‐ and 14‐kDa immunoreactive fragments which were not detectable by Western ligand blotting, indicating that they bound IGF‐II with poor affinity. Release of IGF‐II from IGF‐II‐IGFBP complexes after IGFBP‐4 proteolysis by cell‐bound Pm was indicated by the observation that approximately 20% of the 125I‐IGF‐II initially associated with endogenous IGFBP in reconstituted complexes was transferred to HT29‐D4 cell‐surface IGF‐I receptors. These results suggest that IGFBP‐4 proteolysis by cell‐bound Pm can promote autocrine/paracrine IGF‐II bio‐availability in colon‐cancer cells. This may have important consequences on the behavior of cancer cells at the interface between stroma and malignant cells in carcinomas of the colon in vivo. Int. J. Cancer 72:835–843, 1997. © 1997 Wiley‐Liss, Inc.