Conserved Amino Acids within CCAAT Enhancer-binding Proteins (C/EBPα and β) Regulate Phosphoenolpyruvate Carboxykinase (PEPCK) Gene Expression

Luis A Jurado,Shulan Song,William J Roesler,Edwards A Park

doi:10.1074/jbc.m201429200

Abstract

Thyroid hormone and cAMP stimulate transcription of the gene for phosphoenolpyruvate carboxykinase (PEPCK). CCAAT enhancer-binding proteins (C/EBP(alpha) and beta) are involved in multiple aspects of the nutritional, developmental and hormonal regulation of PEPCK gene expression. Previously, we have identified a thyroid hormone response element in the PEPCK promoter and demonstrated that C/EBP proteins bound to the P3(I) site are participants in the induction of PEPCK gene expression by thyroid hormone and cAMP. Here, we identify several peptide regions within the transactivation domain of C/EBP(alpha) that enhance the ability of T(3) to stimulate gene transcription. We also demonstrate that several conserved amino acids in the transactivation domain of C/EBP(alpha) and C/EBPbeta are required for the stimulation of basal gene expression and identify amino acids within C/EBPbeta that participate in the cAMP induction of the PEPCK gene. Finally, we show that the CREB-binding protein (CBP) enhanced the induction of PEPCK gene transcription by thyroid hormone and that CBP is associated with the PEPCK gene in vivo. Our results indicate that both C/EBP proteins and CBP participate in the regulation of PEPCK gene transcription by thyroid hormone.

Highlights

Transcription of the gene for phosphoenolpyruvate carboxykinase (PEPCK)1 is stimulated in various nutritional and pathologic states such as high protein diets, fasting, hyperthy
These results indicate that C/EBP can enhance the T3 induction through a thyroid hormone response element (TRE) and that this enhancement does not require it in the context of the PEPCK promoter
Our studies have focused on the role of C/EBP proteins in the cAMP and T3 induction of PEPCK gene expression

Summary

Introduction

Transcription of the gene for phosphoenolpyruvate carboxykinase (PEPCK) is stimulated in various nutritional and pathologic states such as high protein diets, fasting, hyperthy-. The full induction by these hormones requires accessory factors associated with the PEPCK promoter Our studies and those of others have shown that CCAAT enhancer-binding proteins (C/ EBP) are accessory factors required for the stimulation by cAMP, T3, and glucocorticoids [5,6,7,8]. A site called P3(I) (Ϫ250/Ϫ234) binds C/EBP␣ and C/EBP␤ [7] Both sites are required for T3 to stimulate PEPCK gene expression. Glucocorticoids induce PEPCK gene expression through two weak glucocorticoid response elements, but multiple accessory factors are involved in the glucocorticoid induction of the PEPCK gene including C/EBP␤ bound to the CRE [8, 11]. T3 is not required for DNA binding and in the absence of ligand the TR generally acts as a repressor of gene

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