Post-Transcriptional Regulation of Alpha One Antitrypsin by a Proteasome Inhibitor.

Lang Rao,Lucas Charles Reineke,Jin Na Shin,Alexey Tyryshkin,Abhisek Bhattacharya,Yi Xu,N Tony Eissa

doi:10.3390/ijms21124318

Abstract

Alpha one antitrypsin (α1AT), a serine proteinase inhibitor primarily produced by the liver, protects pulmonary tissue from neutrophil elastase digestion. Mutations of the SERPINA1 gene results in a misfolded α1AT protein which aggregates inside hepatocytes causing cellular damage. Therefore, inhibition of mutant α1AT production is one practical strategy to alleviate liver damage. Here we show that proteasome inhibitors can selectively downregulate α1AT expression in human hepatocytes by suppressing the translation of α1AT. Translational suppression of α1AT is mediated by phosphorylation of eukaryotic translation initiation factor 2α and increased association of RNA binding proteins, especially stress granule protein Ras GAP SH3 binding protein (G3BP1), with α1AT mRNA. Treatment of human-induced pluripotent stem cell-derived hepatocytes with a proteasome inhibitor also results in translational inhibition of mutant α1AT in a similar manner. Together we revealed a previously undocumented role of proteasome inhibitors in the regulation of α1AT translation.

Highlights

Alpha one antitrypsin deficiency (α1ATD), a protein misfolding disorder characterized by aggregation of a misfolded alpha one antitrypsin (α1AT) protein in the hepatocytes and decreased circulating levels of α1AT, is caused by mutations of the SERPINA1 gene [1,2]
Our initial screening showed that many proteasome inhibitors substantially reduced the amount of α1AT protein and increased GADD34 in human hepatocyte cell line C3A
To rule out the possibility that the reduction of α1AT protein levels resulted from the protease inhibitory activity reported for several proteasome inhibitors, including MG32 [13], we treated hepatocytes with a protease inhibitor cocktail containing E-64 and Calpastatin

Summary

Introduction

Alpha one antitrypsin deficiency (α1ATD), a protein misfolding disorder characterized by aggregation of a misfolded alpha one antitrypsin (α1AT) protein in the hepatocytes and decreased circulating levels of α1AT, is caused by mutations of the SERPINA1 gene [1,2]. Researchers have investigated several methods to reduce liver damage caused by the misfolding and aggregation of α1ATZ These methods include gene therapy with artificial microRNA to suppress transcription of α1ATZ [7,8], induction of autophagy to remove aggregated proteins [9,10] and use of small molecules to block the polymerization of the mutant protein [11,12]. Another interesting strategy to reduce liver toxicity is to reduce the synthesis of α1ATZ by inhibiting its translation, though there has been little focus on utilizing this approach

Methods

Results

Conclusion