Glucosidase and Mannosidase Inhibitors Mediate Increased Secretion of Mutant α1 Antitrypsin Z

Nancy Y Marcus,David H Perlmutter

doi:10.1074/jbc.275.3.1987

Abstract

It is now well known that the addition and trimming of oligosaccharide side chains during post-translational modification play an important role in determining the fate of secretory, membrane, and lysosomal glycoproteins. Recent studies have suggested that trimming of oligosaccharide side chains also plays a role in the degradation of misfolded glycoproteins as a part of the quality control mechanism of the endoplasmic reticulum (ER). In this study, we examined the effect of several inhibitors of carbohydrate processing on the fate of the misfolded secretory protein alpha1 antitrypsin Z. Retention of this misfolded glycoprotein in the ER of liver cells in the classical form of alpha1 antitrypsin (alpha1-AT) deficiency is associated with severe liver injury and hepatocellular carcinoma and lack of its secretion is associated with destructive lung disease/emphysema. The results show marked alterations in the fate of alpha1 antitrypsin Z (alpha1-ATZ). Indeed, one glucosidase inhibitor, castanospermine (CST), and two mannosidase inhibitors, kifunensine (KIF) and deoxymannojirimycin (DMJ), mediate marked increases in secretion of alpha1-ATZ by distinct mechanisms. The effects of these inhibitors on secretion have interesting implications for our understanding of the quality control apparatus of the ER. These inhibitors may also constitute models for development of additional drugs for chemoprophylaxis of liver injury and emphysema in patients with alpha1-AT deficiency.

Highlights

Recent studies have provided further evidence that asparagine-linked oligosaccharide side chains play an important role in intracellular transport of glycoproteins
Effect of Glucosidase Inhibitors on the Fate of ␣1-ATZ—First, we examined the effect of several glucosidase inhibitors, CST and MDNJ, on the relative electrophoretic migration of ␣1-ATZ (Fig. 1A)
The results show that in the absence of CST, the 52-kDa ␣1-ATZ polypeptide is retained for 1 h but begins to disappear from IC between 2 and 4 h, with only trace amounts of the 55-kDa mature ␣1-AT polypeptide appearing in Extracellular fluid (EC)

Summary

Introduction

Recent studies have provided further evidence that asparagine-linked oligosaccharide side chains play an important role in intracellular transport of glycoproteins. Careful accounting for radioactivity in the pulse-chase experiments in intact cells in Fig. 1B suggests that there is no difference in the disappearance of ␣1-ATZ from IC in the presence of CST, we chose to determine the effect of CST on degradation of ␣1ATZ here using the cell-free microsomal translocation system.

Results

Conclusion