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Multiple insulin-responsive elements regulate transcription of the GAPDH gene.
M Alexander-Bridges1, I Dugast, L Ercolani
1Department of Medicine, Massachusetts General Hospital, Harvard Medical School, Howard Hughes Medical Institute, Boston 02114.
Advances in Enzyme Regulation
|January 1, 1992
Summary
Insulin regulates GAPDH gene expression through multiple upstream elements, including IRE-A and IRE-B, involving specific DNA-binding proteins like IREA-BP. These factors are crucial for insulin signaling in metabolic tissues.
Area of Science:
- Molecular Biology
- Gene Regulation
- Metabolic Signaling
Background:
- Insulin acutely and chronically affects GAPDH gene expression.
- Multiple regulatory elements in the GAPDH gene's upstream region mediate this effect.
- Understanding these regulatory mechanisms is key to metabolic research.
Purpose of the Study:
- To investigate the specific elements and DNA-binding proteins involved in insulin-mediated GAPDH gene regulation.
- To elucidate the role of IREA-BP and IRP-B in insulin signal transduction.
- To understand tissue-specific and differentiation-dependent regulation of GAPDH.
Main Methods:
- Analysis of cis-acting factors (g/TRE, IRE-A, IRE-B) in gene regulation.
- Detection and characterization of insulin-sensitive DNA-binding proteins (IREA-BP, IRP-B) using electrophoretic mobility shift assays.
- In vivo studies in rats (fasting/refeeding) and cell culture models (H35 hepatoma, 3T3 adipocytes/preadipocytes).
- Footprint and cotransfection studies to identify regulatory motifs and transcription factors (C/EBP).
Main Results:
- IRE-A and IRE-B collectively mediate a significant insulin effect on GAPDH-CAT expression in cell lines.
- An insulin-sensitive DNA-binding protein, IREA-BP, was identified and its levels increase with insulin treatment.
- IREA-BP and IRP-B are induced by fasting/refeeding in vivo, correlating with cell culture findings.
- IREA-BP is present in preadipocytes and induced upon differentiation; IRE-B binding protein is absent in preadipocytes.
- C/EBP transcription factor regulates GAPDH gene transcription via a proximal promoter motif.
Conclusions:
- IREA-BP and IRP-B are essential components of insulin signal transduction for GAPDH gene expression in liver and fat tissues.
- Multiple regulatory elements and transcription factors, including C/EBP, contribute to the differentiation-dependent and tissue-specific regulation of GAPDH.
- Cloning of IRE-A and IRE-B binding proteins is in progress to further define their roles.