Activating Transcription Factor-2 Regulates Phosphoenolpyruvate Carboxykinase Transcription through a Stress-inducible Mitogen-activated Protein Kinase Pathway

Jaehun Cheong,John E Coligan,Jon D Shuman

doi:10.1074/jbc.273.35.22714

Abstract

Several protein-nucleic acid complexes are observed when nuclear extracts from hepatoma cells are assayed for binding to the cAMP response element found in the phosphoenolpyruvate carboxykinase-cytosolic (PEPCK-C) promoter. Although cAMP response element-binding protein and CCAAT/enhancer binding proteins alpha and beta have been identified as liver factors that bind this motif, an uncharacterized, slower migrating complex was also observed. We identify activating transcription factor-2 (ATF-2) as the factor in this complex and show that ATF-2 stimulates expression from the PEPCK-C promoter. ATF-2 is a basic-leucine zipper transcription factor and a target for stress-activated protein kinases. We demonstrate that p38beta mitogen-activated protein (MAP) kinase augments ATF-2 transactivation activity on the PEPCK-C promoter, which is consistent with the interpretation that PEPCK-C promoter activity is maintained under stress through a p38 MAP kinase dependent pathway. In this regard, we show that treatment with sodium arsenite, a known activator of p38 MAP kinases, also stimulates expression from the PEPCK promoter. These results show that ATF-2 can stimulate transcription of the PEPCK-C promoter and support a role for stress inducible kinases in the maintenance of PEPCK-C expression.

Highlights

The minimal sequence of the phosphoenolpyruvate carboxykinase-cytosolic (PEPCK-C) promoter sufficient for reduplication of hormonal regulation in liver has been mapped to the region encompassing Ϫ460 to ϩ73 [7,8,9,10], and many of the transcription factors that bind elements in this region have been identified [2, 11]
Glucagon secretion leads to an increase in cAMP levels, which exerts effects by inducing factors that bind to the element denoted cyclic AMP response element I (CRE-1) and may induce factors that bind to the element denoted P3
Because PEPCK-C transcription increases after partial hepatectomy [19], a stress condition, we considered that activating transcription factor-2 (ATF-2) may contribute to regulation through the CRE-1 element

Summary

Introduction

The minimal sequence of the PEPCK-C promoter sufficient for reduplication of hormonal regulation in liver has been mapped to the region encompassing Ϫ460 to ϩ73 [7,8,9,10], and many of the transcription factors that bind elements in this region have been identified [2, 11]. Modulation of ATF-2 Expression Levels Correlates with Reporter Gene Activity—To determine what effect, if any, ATF-2 might have on PEPCK-C promoter activity, we transfected Fao hepatoma cells with a luciferase reporter construct encompassing Ϫ275 to ϩ73 of the PEPCK promoter (Fig. 1A) [27]. Given the level of induction observed, the results are consistent with the notion that ATF-2 functions in maintenance of PEPCK-C transcription, likely during conditions that activate a stress-inducible MAP kinase pathway(s).

Results

Conclusion