Erdj3 Has an Essential Role for Z Variant Alpha‐1‐Antitrypsin Degradation

Abstract

Alpha‐1‐antitrypsin deficiency (AATD) is an inherited disease characterized by emphysema and liver disease. AATD is most often caused by a single amino acid substitution at amino acid 342 in the mature protein, resulting in the Z mutation of the alpha‐1‐antitrypsin gene (ZAAT). This substitution is associated with misfolding and accumulation of ZAAT in the endoplasmic reticulum (ER) of hepatocytes and monocytes, causing a toxic gain of function. Retained ZAAT is eliminated by ER‐associated degradation and autophagy. We hypothesized that alpha‐1‐antitrypsin (AAT)‐interacting proteins play critical roles in quality control of human AAT. Using co‐immunoprecipitation, we identified ERdj3, an ER‐resident Hsp40 family member, as a part of the AAT trafficking network. Depleting ERdj3 increased the rate of ZAAT degradation in hepatocytes by redirecting ZAAT to the ER calreticulin‐EDEM1 pathway, followed by autophagosome formation. In the Huh7.5 cell line, ZAAT ER clearance resulted from enhancing ERdj3‐mediated ZAAT degradation by silencing ERdj3 while simultaneously enhancing autophagy. In this context, ERdj3 suppression may eliminate the toxic gain of function associated with polymerization of ZAAT, thus providing a potential new therapeutic approach to the treatment of AATD‐related liver disease. J. Cell. Biochem. 118: 3090–3101, 2017. © 2017 The Authors. Journal of Cellular Biochemistry Published by Wiley Periodicals Inc.

Modulation of calreticulin expression reveals a novel exosome-mediated mechanism of Z variant α1-antitrypsin disposal

“…ERdj3, a canonical co-chaperone, is known to efficiently secrete to the extracellular space because of ER stress and seems to protect the extracellular environment from potentially toxic (29). ERdj3 binds misfolded proteins such as ZAAT in the ER of hepatocytes (6,30). We showed that ERdj3 also binds to calreticulin, the ER-resident lectin chaperone, with the capacity for binding to ZAAT within the ER of hepatocytes (6).…”

“…Secreted ERdj3 can bind misfolded substrates and prevent their extracellular aggregation (17). Our previous studies revealed that ERdj3 competes with calreticulin when binding to ZAAT and delays ZAAT degradation (6). We extended these experiments using small interfering RNA against calreticulin (siCALR) to follow the ZAAT trafficking pathway.…”

“…Recently we have shown that ERdj3, along with calreticulin, is a part of the ZAAT trafficking network. We reported that depleting ERdj3 increased the rate of ZAAT degradation in hepatocytes by redirecting ZAAT proteasome-dependent degradation by autophagosome formation (6).…”

“…The most prevalent disease-related mutation is the Z form, which results in misfolding and accumulation of AAT within the ER of hepatocytes, causing a toxic gain of function (4). Chaperones involved in ZAAT degradation include calnexin, calreticulin (CALR), PDI, ERdj3, GRP78/BiP, and EDEM1 (5,6). ERdj3 is one of the soluble ER-associated Hsp40 families, which is highly expressed in the liver.…”

“…ERdj3 may regulate ZAAT cellular trafficking through a direct interaction (6). To test for a possible interaction between ZAAT and ERdj3 in the media, a co-immunoprecipitation study was performed on the conditioned media, as well as the cell lysate in NT siRNA-and siCALR-treated Huh 7.5 cells transfected with ZAAT or MAAT expression plasmids (Fig.…”