Insulin-like growth factors (IGFs) are important regulators of cell growth and differentiation in many tissues. IGFs circulate in association with specific binding proteins (IGFBPs). Studies in this and other laboratories indicate that IGFBP-1 is a major short-term modulator of IGF bioavailability and that hepatic production of IGFBP-1 is rapidly regulated by glucocorticoids and insulin at the level of gene transcription. Changes in IGFBP-1 expression and IGF bioavailability may play an important role in the pathogenesis of complications of both hypo- and hyperinsulinemic states. Moreover, studies to date indicate that IGFBP-1 provides in important model system for understanding basic mechanisms by which insulin and glucocorticoids interact to regulate hepatic gene transcription. During an NIH FIRST Award, we identified and purified rat IGFBP-1, identified and utilized in vivo and cell culture model systems to examine the regulation of IGFBP-1, cloned the IGFBP-1 gene and its 5' promoter region and identified contiguous glucocorticoid (GRE) and insulin (IRS) response sequences in the proximal IGFBP-1 promoter. Competitive binding and supershift studies show that the major protein binding to this sequence is hepatocyte nuclear factor-3 (HNF-3) and that C/EBP proteins also interact with this sequence. To our knowledge, this represented the first demonstration that HNF-3 proteins may interact with an IRS and potentially contribute to effects of insulin on gene expression. Functional studies confirm that HNF-3 proteins enhance IGFBP-1 promoter activity at this site and mutation of this HNF-3 binding site also disrupts glucocorticoid effects and reduces the effect of insulin and glucocorticoids on promoter function. Gel shift studies indicate that C/EPB proteins in nuclear extracts also interact with this site and that still other factors may be required for insulin to exert its effects on basal IGFBP-1 promoter function. Based on these observations, we now will utilize fine mapping, site directed mutagenesis and co-transfection systems to examine the role of HNF-3 and/or C/EBP proteins in mediating interactions between glucocorticoids and insulin on IGFBP-1 promoter activity, and examine the role that interactions between and/or modifications on HNF-3, C/EBP and other factors may play in mediating effects of insulin on IGFBP-1 expression. In vivo footprinting will also be performed to determine whether insulin alters access of specific factors this site or the conformation of the IGFBP-1 promoter. The results of these studies should provide insight into specific mechanisms by which glucocorticoids and insulin interact to regulate hepatic gene expression and modulate biological effects of IGFs in disorders of metabolism.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
5R01DK041430-09
Application #
2701084
Study Section
Endocrinology Study Section (END)
Program Officer
Sato, Sheryl M
Project Start
1990-01-01
Project End
2000-03-31
Budget Start
1998-06-17
Budget End
2000-03-31
Support Year
9
Fiscal Year
1998
Total Cost
Indirect Cost
Name
University of Illinois at Chicago
Department
Internal Medicine/Medicine
Type
Schools of Medicine
DUNS #
121911077
City
Chicago
State
IL
Country
United States
Zip Code
60612
Deng, Xiong; Zhang, Wenwei; O-Sullivan, InSug et al. (2012) FoxO1 inhibits sterol regulatory element-binding protein-1c (SREBP-1c) gene expression via transcription factors Sp1 and SREBP-1c. J Biol Chem 287:20132-43
Cypess, Aaron M; Zhang, Hongbin; Schulz, Tim J et al. (2011) Insulin/IGF-I regulation of necdin and brown adipocyte differentiation via CREB- and FoxO1-associated pathways. Endocrinology 152:3680-9
Ganjam, Goutham Kumar; Dimova, Elitsa Y; Unterman, Terry G et al. (2009) FoxO1 and HNF-4 are involved in regulation of hepatic glucokinase gene expression by resveratrol. J Biol Chem 284:30783-97
Carroll, Robert E; Goodlad, Robert A; Poole, Aleksandra J et al. (2009) Reduced susceptibility to azoxymethane-induced aberrant crypt foci formation and colon cancer in growth hormone deficient rats. Growth Horm IGF Res 19:447-56
McLoughlin, Thomas J; Smith, Sierra M; DeLong, Alissa D et al. (2009) FoxO1 induces apoptosis in skeletal myotubes in a DNA-binding-dependent manner. Am J Physiol Cell Physiol 297:C548-55
Ono, Mitsuru; Chia, Dennis J; Merino-Martinez, Roxana et al. (2007) Signal transducer and activator of transcription (Stat) 5b-mediated inhibition of insulin-like growth factor binding protein-1 gene transcription: a mechanism for repression of gene expression by growth hormone. Mol Endocrinol 21:1443-57
Allen, David L; Unterman, Terry G (2007) Regulation of myostatin expression and myoblast differentiation by FoxO and SMAD transcription factors. Am J Physiol Cell Physiol 292:C188-99
Park, Youngkyu; Maizels, Evelyn T; Feiger, Zachary J et al. (2005) Induction of cyclin D2 in rat granulosa cells requires FSH-dependent relief from FOXO1 repression coupled with positive signals from Smad. J Biol Chem 280:9135-48
Gan, Lixia; Zheng, Wenhua; Chabot, Jean-Guy et al. (2005) Nuclear/cytoplasmic shuttling of the transcription factor FoxO1 is regulated by neurotrophic factors. J Neurochem 93:1209-19
Purple, C R; Untermann, T G; Pichika, R et al. (2002) Fibronectin fragments upregulate insulin-like growth factor binding proteins in chondrocytes. Osteoarthritis Cartilage 10:734-46

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