title: Insulin-like growth factor binding protein-3 in extracellular matrix stimulates adhesion of breast epithelial cells and activation of p44/42 mitogen-activated protein kinase.
abstract: IGF-binding protein-3 (IGFBP-3) is a multifunctional protein that regulates the potent mitogenic and antiapoptotic effects of IGF-I and IGF-II and exerts bioactivity independent of modulating IGF receptor activation. Previous studies have shown that in solution, IGFBP-3 binds constituent proteins of the extracellular matrix (ECM) such as fibronectin and collagen and is present in ECM deposited by fibroblasts in vitro; however, binding of IGFBP-3 to matrix has not been characterized, nor has its function in this environment been investigated. In this study, we show that IGFBP-3 binds to ECM deposited by human breast epithelial and cancer cells and neonatal human fibroblasts. IGF-I and heparin blocked binding of IGFBP-3 to matrix when added with the binding protein but were unable to displace IGFBP-3 already bound to the matrix. IGF-I bound to matrix-immobilized IGFBP-3 with approximately 25-fold reduced affinity compared with IGFBP-3 in solution. Mutation of the C-terminal basic domain of IGFBP-3 (228KGRKR-->MDGEA) resulted in markedly reduced binding to matrix compared with wild-type IGFBP-3, whereas mutation of the adjacent consensus heparin-binding domain (220KKK-->HSR) had relatively little effect. In the presence of matrix-bound IGFBP-3, adhesion of breast epithelial cells was increased by approximately 25%, and activation of the signaling pathway intermediate p44/42 MAPK was enhanced greater than 3-fold. These results indicate a previously unrecognized and potentially important role for IGFBP-3 in the extracellular matrix.
authors.affiliation: Kolling Institute of Medical Research, University of Sydney, Royal North Shore Hospital, St. Leonards, New South Wales 2065, Australia. janetlm@med.usyd.edu.au
authors.forename: Janet L
authors.initials: JL
authors.lastname: Martin
authors.forename: Stan
authors.initials: S
authors.lastname: Jambazov
mesh_terms: D001940:Breast / Q000166:cytology / Q000378:metabolism*; D001943:Breast Neoplasms / Q000378:metabolism; D002448:Cell Adhesion / Q000502:physiology*; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D004789:Enzyme Activation / Q000502:physiology; D004847:Epithelial Cells / Q000502:physiology; D005109:Extracellular Matrix / Q000378:metabolism*; D006493:Heparin / Q000494:pharmacology; D006801:Humans; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000502:physiology*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism / Q000494:pharmacology; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D015398:Signal Transduction; D012996:Solutions
chemical_list: D018972:Insulin-Like Growth Factor Binding Protein 3; D012996:Solutions; D007334:Insulin-Like Growth Factor I; D006493:Heparin; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3