Accumulation of Mutant α1-Antitrypsin Z in the Endoplasmic Reticulum Activates Caspases-4 and -12, NFκB, and BAP31 but Not the Unfolded Protein Response

Tunda Hidvegi,Bela Z Schmidt,Pamela Hale,David H Perlmutter

doi:10.1074/jbc.m508652200

Tunda Hidvegi, Bela Z Schmidt + Show 2 more

Open Access

https://doi.org/10.1074/jbc.m508652200

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Abstract

In alpha(1)-antitrypsin (alpha1AT) deficiency, a polymerogenic mutant form of the secretory glycoprotein alpha1AT, alpha1ATZ, is retained in the endoplasmic reticulum (ER) of liver cells. It is not yet known how this results in liver injury in a subgroup of deficient individuals and how the remainder of deficient individuals escapes liver disease. One possible explanation is that the "susceptible" subgroup is unable to mount the appropriate protective cellular responses. Here we examined the effect of mutant alpha1ATZ on several potential protective signaling pathways by using cell lines with inducible expression of mutant alpha1AT as well as liver from transgenic mice with liver-specific inducible expression of mutant alpha1AT. The results show that ER retention of polymerogenic mutant alpha1ATZ does not result in an unfolded protein response (UPR). The UPR can be induced in the presence of alpha1ATZ by tunicamycin excluding the possibility that the pathway has been disabled. In striking contrast, ER retention of nonpolymerogenic alpha1AT mutants does induce the UPR. These results indicate that the machinery responsible for activation of the UPR can distinguish the physical characteristics of proteins that accumulate in the ER in such a way that it can respond to misfolded but not relatively ordered polymeric structures. Accumulation of mutant alpha1ATZ does activate specific signaling pathways, including caspase-12 in mouse, caspase-4 in human, NFkappaB, and BAP31, a profile that was distinct from that activated by nonpolymerogenic alpha1AT mutants.

Highlights

Proteolytic destruction of the connective tissue matrix
HeLa Tet-Off cells (HTO)/Z cells that had been maintained in the absence of dox were incubated for 3 days in medium supplemented with several doses of dox and were pulselabeled (Fig. 1a)
Studies of Pelizaeus-Merzbacher disease [24] and diabetes in the Akita mouse model [25] have provided evidence that cellular responses to mutant proteins that accumulate in the endoplasmic reticulum (ER) can modulate the severity of those diseases

Summary

Introduction

Proteolytic destruction of the connective tissue matrix. In contrast, liver injury appears to involve a gain-of-toxic-function mechanism whereby the accumulation of mutant ␣1ATZ in the ER damages liver cells [1]. Western blot analysis did not detect phosphorylation of IRE1 or PERK or cleavage of ATF-6 when dox was removed from, and ␣1ATZ expressed in, the HTO/Z2 cell line (data not shown).

Results

Conclusion