Activation of inflammation and cholestasis by Egr-1 is linked to liver regeneration by regulating ALR expression

Introduction: cholestasis is defined as the impairment of bile flow in the liver leading to bile acids accumulation within the liver, promoting inflammation and therefore causing liver injury. Previous studies indicated the role of bile acids in the up-regulation of early growth response fator-1 (Egr-1) which initiates the inflammation through up-regulating several pro-inflammatory genes. The hepatotrophic factor Augmenter of liver regeneration (ALR), with anti-oxidative and anti-apoptotic properties, was demonstrated to support liver regeneration after hepatic injury. Nevertheless, little is known about the impact of ALR in cholestasis. Therefore, the aim of our study was to investigate the potential role of key bile acids and Egr-1 in regulating ALR expression, and to determine a potential role of Egr-1 in the regeneration process mediated by ALR.

Results: Analysis of ALR promoter showed three potential response elements for Egr 1. Reporter-gene assays, using two different constructs of ALR promoter demonstrated increased promoter activity upon treatment with various bile acids or co transfection with Egr-1 in hepatoma cells compared to control. Nevertheless, co transfection with dn-Egr-1 diminished the induced promoter activity. Furthermore, we found induced levels of ALR protein in bile acid-treated HepG2 cells and Egr-1-overexpressing HepG2 cells compared to control.

We further performed EMSA technique and demonstrated the specific binding of Egr 1 to its response element within ALR promoter in liver cells.

Conclusion: Our data indicate that bile acids-induced Egr-1 regulates ALR as a marker of liver regeneration in cholestasis.