Journal of Clinical Endocrinology & Metabolism, Vol 80, 1318-1324, Copyright © 1995 by Endocrine Society

ARTICLES

Effect of the acid-labile subunit on the binding of insulin-like growth factor (IGF)-binding protein-3 to [125I]IGF-I

A Barreca, P Ponzani, M Arvigo, G Giordano and F Minuto
Department of Endocrinology and Metabolism, DiSEM, University of Genova, Italy.

In normal subjects, the major form of circulating insulin-like growth factor (IGF) is the GH-dependent 150K complex. This complex is formed by the IGF peptide, the acid-stable binding protein IG-FBP-3, and the acid-labile subunit (ALS), which, although not binding IGF, appears to be necessary to reconstitute the complex in its natural form. The ALS was purified in our laboratory from human serum by ammonium sulfate precipitation, ion exchange chromatography using DEAE-Sephadex A-50, Concanavalin-A-Sepharose-4B chromatography, and two sequential gel filtrations by fast performance liquid chromatography. As demonstrated by gel permeation chromatography on fast performance liquid chromatography, incubation for 2 h at 20 C of this preparation with [125I]IGF-I and recombinant IGFBP-3 (rIGFBP-3) allows the reconstitution of a complex of about 150 kilodaltons. In these experimental conditions, the ALS is not only able to increase the mol wt of the complex, but also to greatly increase the amount of IGF-I bound; in the absence of ALS, radioactivity in the mol wt volume of the complexed forms was lower than that in the mol wt volume of the free form (percentage of total [125I]IGF-I: rIGFBP-3 alone, 15% and 44%; in the presence of ALS, 41% and 24%, respectively). In both charcoal and polyethylene glycol ligand binding assays, competitive binding curves for the displacement of [125I]IGF-I from rIGFBP-3 by increasing concentrations of unlabeled IGF-I showed an increased binding activity of rIGFBP-3 in the presence of ALS. The effect of ALS on rIGFBP-3- binding activity was dose dependent. These data show that the non-IGF- binding ALS subunit of the 150-kilodalton complex can play an important role in the regulation of IGF-I or IGF-II binding to rIGFBP-3 and, therefore, on the levels of free IGF peptide, possibly by inducing conformational changes in rIGFBP-3. In addition, ligand and immunoblot reveal that ALS and rIGFBP-3 are able to form a high mol wt complex in the absence of IGF peptide. On the basis of these data, ALS seems to have a more complex function than that of simply increasing the mol wt of the IGF-IGFBP-3 complex.

This article has been cited by other articles:

				R. Pivonello, D. Ferone, W. W. de Herder, J. M. Kros, M. L. Del Basso De Caro, M. Arvigo, L. Annunziato, G. Lombardi, A. Colao, L. J. Hofland, et al. Dopamine Receptor Expression and Function in Corticotroph Pituitary Tumors J. Clin. Endocrinol. Metab., May 1, 2004; 89(5): 2452 - 2462. [Abstract] [Full Text] [PDF]

				M. Arosio, S. Garrone, P. Bruzzi, G. Faglia, F. Minuto, and A. Barreca Diagnostic Value of the Acid-Labile Subunit in Acromegaly: Evaluation in Comparison with Insulin-Like Growth Factor (IGF) I, and IGF-Binding Protein-1, -2, and -3 J. Clin. Endocrinol. Metab., March 1, 2001; 86(3): 1091 - 1098. [Abstract] [Full Text]

				T. Laursen, A. Flyvbjerg, J. O. L. Jørgensen, R. C. Baxter, and J. S. Christiansen Stimulation of the 150-Kilodalton Insulin-Like Growth Factor-Binding Protein-3 Ternary Complex by Continuous and Pulsatile Patterns of Growth Hormone (GH) Administration in GH-Deficient Patients J. Clin. Endocrinol. Metab., November 1, 2000; 85(11): 4310 - 4314. [Abstract] [Full Text]

				J. Khosravi, A. Diamandi, J. Mistry, and R. G. Krishna The High Molecular Weight Insulin-Like Growth Factor-Binding Protein Complex: Epitope Mapping, Immunoassay, and Preliminary Clinical Evaluation J. Clin. Endocrinol. Metab., August 1, 1999; 84(8): 2826 - 2833. [Abstract] [Full Text]

				D. R. Powell, S. K. Durham, F. Liu, B. K. Baker, P. D. K. Lee, S. L. Watkins, P. G. Campbell, E. D. Brewer, R. L. Hintz, and R. J. Hogg The Insulin-Like Growth Factor Axis and Growth in Children with Chronic Renal Failure: A Report of the Southwest Pediatric Nephrology Study Group J. Clin. Endocrinol. Metab., May 1, 1998; 83(5): 1654 - 1661. [Abstract] [Full Text]

				S. M. Twigg and R. C. Baxter Insulin-like Growth Factor (IGF)-binding Protein 5 Forms an Alternative Ternary Complex with IGFs and the Acid-labile Subunit J. Biol. Chem., March 13, 1998; 273(11): 6074 - 6079. [Abstract] [Full Text] [PDF]

				S. M. Firth, U. Ganeshprasad, and R. C. Baxter Structural Determinants of Ligand and Cell Surface Binding of Insulin-like Growth Factor-binding Protein-3 J. Biol. Chem., January 30, 1998; 273(5): 2631 - 2638. [Abstract] [Full Text] [PDF]

				S. Rajaram, D. J. Baylink, and S. Mohan Insulin-Like Growth Factor-Binding Proteins in Serum and Other Biological Fluids: Regulation and Functions Endocr. Rev., December 1, 1997; 18(6): 801 - 831. [Abstract] [Full Text]

				M. J. Khosravi, A. Diamandi, J. Mistry, R. G. Krishna, and A. Khare Acid-Labile Subunit of Human Insulin-Like Growth Factor-Binding Protein Complex: Measurement, Molecular, and Clinical Evaluation J. Clin. Endocrinol. Metab., December 1, 1997; 82(12): 3944 - 3951. [Abstract] [Full Text] [PDF]

				C. Y. Lee, H.-B. Wu, D.-S. Suh, and M. M. Rechler Insulin-Like Growth Factor-I (IGF-I) Concentration in 150-Kilodalton Complexes Containing Human IGF-Binding Protein-3 (hIGFBP-3) after Intravenous Injection of Adult Rats with hIGFBP-3 Endocrinology, April 1, 1997; 138(4): 1649 - 1657. [Abstract] [Full Text] [PDF]