Contributions of the N- and C-terminal domains of IGF binding protein-6 to IGF binding.

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.

• Authors: Stephen J Headey, Kerri S Leeding, Raymond S Norton, Leon A Bach
• Journal: Journal of molecular endocrinology (J Mol Endocrinol) Vol. 33 Issue 2 Pg. 377-86 (Oct 2004) ISSN: 0952-5041 [Print] England
• PMID: 15525596 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Insulin-Like Growth Factor Binding Protein 6
• Peptide Fragments
• Insulin-Like Growth Factor I
• Insulin-Like Growth Factor II

Topics

• Biosensing Techniques
• Cell Proliferation (drug effects)
• Colonic Neoplasms (drug therapy, metabolism, pathology)
• Humans
• Insulin-Like Growth Factor Binding Protein 6 (genetics, metabolism, pharmacology)
• Insulin-Like Growth Factor I (genetics, metabolism)
• Insulin-Like Growth Factor II (genetics, metabolism)
• Kinetics
• Peptide Fragments (genetics, metabolism, pharmacology)
• Protein Structure, Tertiary
• Tumor Cells, Cultured