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

Headey, SJ; Leeding, KS; Norton, RS; Bach, LA

Author(s): Headey, SJ; Leeding, KS; Norton, RS; Bach, LA;
Details: Publication Year 2004-10,Volume 33,Issue #2,Page 377-386
Journal Title: JOURNAL OF MOLECULAR ENDOCRINOLOGY
Publication Type: Journal Article
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 similar to50-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, IGR 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 similar to20-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.
Publisher: SOC ENDOCRINOLOGY
Keywords: INSULIN-LIKE-GROWTH; ACID-LABILE SUBUNIT; FACTOR-II; RECEPTOR INTERACTIONS; AMINO-ACIDS; FRAGMENTS; SITE; DETERMINANTS; AFFINITY; IGFBP-3
Publisher's Version: https://doi.org/10.1677/jme.1.01547
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Creation Date: 2004-10-01 12:00:00