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Title: Contributions of the N- and C-terminal domains of IGF binding protein-6 to IGF binding.
Austin Authors: Headey, Stephen J;Leeding, Kerri S;Norton, Raymond S;Bach, Leon A
Affiliation: University of Melbourne, Department of Medicine, Austin Hospital, Heidelberg 3084, Australia
Issue Date: 1-Oct-2004
Publication information: Journal of Molecular Endocrinology; 33(2): 377-86
Abstract: Insulin-like growth factors IGF-I and IGF -II are important mediators of growth. A family of six high affinity IGF binding proteins (IGFBPs) modulate IGF action. IGFBPs have three domains, of which the N- and C-domains are involved in high affinity IGF binding. IGFBP-6 is unique in its 20-100-fold IGF-II binding specificity over IGF-I. The aim of this study was to determine the contributions of the N- and C-domains of IGFBP-6 to its IGF binding properties. We confirmed that differential dissociation kinetics are responsible for the IGF-II binding preference of IGFBP-6. The N-domain has rapid association kinetics, similar to full-length IGFBP-6, but both IGF-I and -II dissociate rapidly from this domain, thereby reducing its binding affinity for IGF-II approximately 50-fold. However, the N-domain binds IGF-I and -II with similar affinities and it has a similar IGF-I binding affinity to full-length IGFBP-6. This suggests that the C-domain confers the IGF-II binding preference of IGFBP-6; indeed, IGF-I bound inconsistently with very low affinity to the C-domain. Coincubation studies showed that isolated N- and C-domains of IGFBP-6 do not strongly cooperate to enhance IGF binding. The results of the binding studies are supported by the effects of the IGFBP-6 domains on IGF-induced colon cancer cell proliferation; the N-domain inhibited IGF-II induced proliferation with approximately 20-fold lower potency than IGFBP-6 and it was equipotent in inhibiting IGF-I- and IGF-II-induced proliferation. Coincubation of C-domain had no additional effect on N-domain-induced inhibition of proliferation. In conclusion, both the N- and C-domains of IGFBP-6 are involved in IGF binding, the C-domain is responsible for the IGF-II binding preference of IGFBP-6 and intact IGFBP-6 is necessary for high affinity IGF binding.
Gov't Doc #: 15525596
DOI: 10.1677/jme.1.01547
Type: Journal Article
Subjects: Biosensing Techniques
Cell Proliferation.drug effects
Colonic Neoplasms.drug therapy.metabolism.pathology
Insulin-Like Growth Factor Binding Protein 6.genetics.metabolism.pharmacology
Insulin-Like Growth Factor I.genetics.metabolism
Insulin-Like Growth Factor II.genetics.metabolism
Peptide Fragments.genetics.metabolism.pharmacology
Protein Structure, Tertiary
Tumor Cells, Cultured
Appears in Collections:Journal articles

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