Zinc partitions IGFs from soluble IGF binding proteins (IGFBP)-5, but not soluble IGFBP-4, to myoblast IGF type 1 receptors

• Published in: Journal of endocrinology Vol. 180; no. 2; pp. 227 - 246
• Main Authors: McCusker, RH, Novakofski, J
• Format: Journal Article
• Language: English
• Published: Colchester BioScientifica 01.02.2004; Portland Press
• Subjects: Animals; Apud cells. Peptide and protein hormones. Growth factors; Binding, Competitive; Biological and medical sciences; Cells, Cultured; Dose-Response Relationship, Drug; Fundamental and applied biological sciences. Psychology; Insulin-Like Growth Factor Binding Protein 4 - metabolism; Mice; Myoblasts, Skeletal - metabolism; Receptor, IGF Type 1 - metabolism; Somatomedins - metabolism; Vertebrates: endocrinology; Zinc - metabolism; Zinc - pharmacology; Ligand binding; Rat; Rodentia; Striated muscle; In vitro; Zinc; Dose activity relation; Micronutrient; Insulin like growth factor binding protein; Vertebrata; Insulin like growth factor; Growth factor receptor; Mammalia; Cell line; Mouse; Myoblast; Affinity; Muscle; Biological receptor
• ISSN: 0022-0795; 1479-6805
• DOI: 10.1677/joe.0.1800227

Zinc (Zn(2+)), a multifunctional micronutrient, was recently shown to lower the affinity of cell-associated insulin-like growth factor (IGF) binding protein (IGFBP)-3 and IGFBP-5 for both IGF-I and IGF-II, but to increase the affinity of the cell surface type 1 IGF receptor (IGF-1R) for the same two ligands. However, there is a need for data concerning the effects of Zn(2+) on soluble IGFBPs and the type 2 IGF receptor (IGF-2R). In the current work, we demonstrate that Zn(2+) affects the affinity of IGFBP-5 secreted by myoblasts but not IGFBP-4. Zn(2+), at physiological levels, depressed binding of both IGF-I and IGF-II to IGFBP-5, affecting (125)I-IGF-I more than (125)I-IGF-II. Both (125)I-IGF-I and (125)I-IGF-II bound to high and low affinity sites on IGFBP-5. Zn(2+) converted the high affinity binding sites of IGFBP-5 into low affinity binding sites. An IGF-I analog, (125)I-R(3)-IGF-I, did not bind to the soluble murine IGFBP-5. Zn(2+) also decreased the affinity of the IGF-2R on L6 myoblasts. In contrast, Zn(2+) increased IGF-I, IGF-II and R(3)-IGF-I binding to the IGF-1R by increasing ligand binding affinity on both P(2)A(2a)-LISN and L6 myoblasts. Soluble IGFBP-5 and IGFBP-4 depressed the binding of (125)I-IGF-I and (125)I-IGF-II to the IGF-1R, but did not affect binding of (125)I-R(3)-IGF-I. By depressing the association of the IGFs with soluble IGFBP-5, Zn(2+) partitioned (125)I-IGF-I and (125)I-IGF-II from soluble IGFBP-5 onto cell surface IGF-1Rs. This effect is not seen when soluble L6-derived IGFBP-4 is present in extracellular fluids. We introduce a novel mechanism by which the trace micronutrient Zn(2+) may alter IGF distribution, i.e. Zn(2+) acts to increase IGF-1R binding at the expense of IGF binding to soluble IGFBP-5 and the IGF-2R.