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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
Author(s) -
RemacleBonnet Maryse M.,
Garrouste Françoise L.,
Pommier Gilbert J.
Publication year - 1997
Publication title -
international journal of cancer
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.475
H-Index - 234
eISSN - 1097-0215
pISSN - 0020-7136
DOI - 10.1002/(sici)1097-0215(19970904)72:5<835::aid-ijc21>3.0.co;2-6
Subject(s) - proteolysis , plasmin , growth factor , autocrine signalling , urokinase receptor , insulin like growth factor binding protein , biology , proteases , receptor , insulin like growth factor , cell growth , stromal cell , microbiology and biotechnology , vitronectin , chemistry , biochemistry , cancer research , enzyme , integrin
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 125 I‐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.