Molecular Endocrinology, Vol 10, 622-630, Copyright © 1996 by Endocrine Society

ARTICLES

Insulin and insulin-like growth factor-I regulate hepatic insulin-like growth factor binding protein-3 by different mechanisms

BC Villafuerte, WN Zhang and LS Phillips
Division of Endocrinology and Metabolism, Emory University School of Medicine, Atlanta, Georgia 30322, USA.

Insulin-dependent diabetes mellitus is associated with decreased levels of circulating insulin-like growth factor binding protein-3 (IGFBP-3), which are restored toward normal by treatment with insulin and/or infusion of insulin-like growth factor-I (IGF-I). To understand underlying mechanisms, we studied IGFBP-3 production in cocultures of parenchymal and nonparenchymal cells from the livers of normal rats. Release of IGFBP-3 was measured by ligand blotting and was increased 1.9- and 15-fold by 10(-8) and 10(-8) M Insulin compared with 10(-10) M (P < 0.05 for 10(-6) vs. 10(-10) M). Expression of IGFBP-3 mRNA was increased concomitantly by 23 and 226% (P < 0.05 for 10(-6) M vs. 10(- 10) M), consistent with regulation in part at pretranslational levels. To evaluate mRNA stability, transcription was inhibited with 5,6- dichloro-1-beta-D-ribofuranosyl-benzimidazole (DRB): IGFBP-3 mRNA t1/2 was estimated at 13 h and 17 h with addition of 10(-5) M and 10(-10) M insulin, respectively, ruling out regulation at the level of mRNA turnover. IGFBP-3 gene transcription rates were evaluated by nuclear run-on assays and were increased 2,9-fold with the addition of 10(-6) M insulin, as compared with 10(-10) M insulin, comparable to stimulation of expression. Addition of IGF-I at 2.6 x 10(-8) M and 5.3 x 10(-8) M increased IGFBP-3 release by 5.2- and 8.2-fold (both P < 0.05 vs. no IGF-I), with concomitant increase in IGFBP-3 mRNA expression by 14- and 29-fold (both P < 0.05 vs. no IGF-I), suggesting regulation at a pretranslational level. Further studies showed that IGF-I did not have a significant effect on transcription initiation rates but prolonged the apparent half-life of IGFBP-3 mRNA about 2-fold. Stimulation of IGFBP-3 via type 1 IGF-I receptors was evaluated by studies with [QAYL] IGF-I; the analog increased IGFBP-3 mRNA expression 220 +/- 27% above the level obtained without IGF-I (vs. 133 +/- 9% with wild type IGF-I, P < 0.05), suggesting involvement of receptor-mediated synthesis. CONCLUSION: Insulin stimulates IGFBP-3 gene transcription but provides proportionally greater increases in IGFBP-3 release, consistent with regulation at both transcriptional and posttranslational levels; in contrast, IGF-I alters IGFBP-3 expression by decreasing IGFBP-3 mRNA degradation, consistent with regulation at pretranslational and posttranscriptional levels. Decreased IGFBP-3 levels in conditions of diabetes mellitus may be due to decreased hepatic IGFBP-3 release, and secondary both to decreased gene transcription (caused by insulin deficiency), as well as to decreased IGFBP-3 mRNA half-life (caused by low levels of IGF-I).

This article has been cited by other articles:

				J. Paquette, B. Bessette, E. Ledru, and C. Deal Identification of Upstream Stimulatory Factor Binding Sites in the Human IGFBP3 Promoter and Potential Implication of Adjacent Single-Nucleotide Polymorphisms and Responsiveness to Insulin Endocrinology, December 1, 2007; 148(12): 6007 - 6018. [Abstract] [Full Text] [PDF]

				B. D. Hand, M. C. Kostek, R. E. Ferrell, M. J. Delmonico, L. W. Douglass, S. M. Roth, J. M. Hagberg, and B. F. Hurley Influence of promoter region variants of insulin-like growth factor pathway genes on the strength-training response of muscle phenotypes in older adults J Appl Physiol, November 1, 2007; 103(5): 1678 - 1687. [Abstract] [Full Text] [PDF]

				B. C. Villafuerte and E. N. Kaytor An Insulin-response Element-binding Protein That Ameliorates Hyperglycemia in Diabetes J. Biol. Chem., May 20, 2005; 280(20): 20010 - 20020. [Abstract] [Full Text] [PDF]

				B. C. Villafuerte, L. S. Phillips, M. J. Rane, and W. Zhao Insulin-response Element-binding Protein 1: A NOVEL Akt SUBSTRATE INVOLVED IN TRANSCRIPTIONAL ACTION OF INSULIN J. Biol. Chem., August 27, 2004; 279(35): 36650 - 36659. [Abstract] [Full Text] [PDF]

				M. H. Vickers, B. A. Ikenasio, and B. H. Breier IGF-I Treatment Reduces Hyperphagia, Obesity, and Hypertension in Metabolic Disorders Induced by Fetal Programming Endocrinology, September 1, 2001; 142(9): 3964 - 3973. [Abstract] [Full Text] [PDF]

				W. S. Cohick, B. Wang, P. Verma, and Y. R. Boisclair Insulin-Like Growth Factor I (IGF-I) and Cyclic Adenosine 3',5'-Monophosphate Regulate IGF-Binding Protein-3 Gene Expression by Transcriptional and Posttranscriptional Mechanisms in Mammary Epithelial Cells Endocrinology, December 1, 2000; 141(12): 4583 - 4591. [Abstract] [Full Text] [PDF]

				J. M. Hayden, D. D. Strong, D. J. Baylink, D. R. Powell, T. K. Sampath, and S. Mohan Osteogenic Protein-1 Stimulates Production of Insulin-Like Growth Factor Binding Protein-3 Nuclear Transcripts in Human Osteosarcoma Cells Endocrinology, October 1, 1997; 138(10): 4240 - 4247. [Abstract] [Full Text] [PDF]

				B. C. Villafuerte, W. Zhao, A. C. Herington, R. Saffery, and L. S. Phillips Identification of an Insulin-responsive Element in the Rat Insulin-like Growth Factor-binding Protein-3 Gene J. Biol. Chem., February 21, 1997; 272(8): 5024 - 5030. [Abstract] [Full Text] [PDF]