Retention of mutant α1-antitrypsin Z in endoplasmic reticulum is associated with an autophagic response

Abstract

Although there is evidence for specific subcellular morphological alterations in response to accumulation of misfolded proteins in the endoplasmic reticulum (ER), it is not clear whether these morphological changes are stereotypical or if they depend on the specific misfolded protein retained. This issue may be particularly important for mutant secretory protein α 1-antitrypsin (α 1 AT) Z because retention of this mutant protein in the ER can cause severe target organ injury, the chronic hepatitis/hepatocellular carcinoma associated with α 1 AT deficiency. Here we examined the morphological changes that occur in human fibroblasts engineered for expression and ER retention of mutant α 1 ATZ and in human liver from three α 1 AT-deficient patients. In addition to marked expansion and dilatation of ER, there was an intense autophagic response. Mutant α 1 ATZ molecules were detected in autophagosomes by immune electron microscopy, and intracellular degradation of α 1 ATZ was partially reduced by chemical inhibitors of autophagy. In contrast to mutant CFTRΔF508, expression of mutant α 1 ATZ in heterologous cells did not result in the formation of aggresomes. These results show that ER retention of mutant α 1 ATZ is associated with a marked autophagic response and raise the possibility that autophagy represents a mechanism by which liver of α 1 AT-deficient patients attempts to protect itself from injury and carcinogenesis.