Ubiquitin ligase SYVN1/HRD1 facilitates degradation of the SERPINA1 Z variant/α-1-antitrypsin Z variant via SQSTM1/p62-dependent selective autophagy

Abstract

SERPINA1/AAT/α-1-antitrypsin (serpin family A member 1) deficiency (SERPINA1/ AAT-D) is an autosomal recessive disorder characterized by the retention of misfolded SERPINA1/AAT in the endoplasmic reticulum (ER) of hepatocytes and a significant reduction of serum SERPINA1/AAT level. The Z variant of SERPINA1/AAT, containing a Glu342Lys (E342K) mutation (SERPINA1E342K/ATZ), the most common form of SERPINA1/AAT-D, is prone to misfolding and polymerization, which retains it in the ER of hepatocytes and leads to liver injury. Both proteasome and macroautophagy/autophagy pathways are responsible for disposal of SERPINA1E342K/ATZ after it accumulates in the ER. However, the mechanisms by which SERPINA1E342K/ATZ is selectively degraded by autophagy remain unknown. Here, we showed that ER membrane-spanning ubiquitin ligase (E3) SYVN1/HRD1 enhances the degradation of SERPINA1E342K/ATZ through the autophagy-lysosome pathway. We found that SYVN1 promoted SERPINA1E342K/ATZ, especially Triton X 100-insoluble SERPINA1E342K/ATZ clearance. However, the effect of SYVN1 in SERPINA1E342K/ATZ clearance was impaired after autophagy inhibition, as well as in autophagy-related 5 (atg5) knockout cells. On the contrary, autophagy induction enhanced SYVN1-mediated SERPINA1E342K/ATZ degradation. Further study showed that SYVN1 mediated SERPINA1E342K/ATZ ubiquitination, which is required for autophagic degradation of SERPINA1E342K/ATZ by promoting the interaction between SERPINA1E342K/ATZ and SQSTM1/p62 for formation of the autophagy complex. Interestingly, SYVN1-mediated lysine 48 (K48)-linked polyubiquitin chains that conjugated onto SERPINA1E342K/ATZ might predominantly bind to the ubiquitin-associated (UBA) domain of SQSTM1 and couple the ubiquitinated SERPINA1E342K/ATZ to the lysosome for degradation. In addition, autophagy inhibition attenuated the suppressive effect of SYVN1 on SERPINA1E342K/ATZ cytotoxicity, and the autophagy inducer rapamycin enhanced the suppressive effect of SYVN1 on SERPINA1E342K/ATZ-induced cell apoptosis. Therefore, this study proved that SYVN1 enhances SERPINA1E342K/ATZ degradation through SQSTM1-dependent autophagy and attenuates SERPINA1E342K/ATZ cytotoxicity.

Crosstalk and Interplay between the Ubiquitin-Proteasome System and Autophagy

“…Parkin-assembled Lys6 and Lys11 atypical linkages were observed on ubiquitinated mitochondria upon membrane depolarization ( Cunningham et al, 2015 ). Even Lys48 linkages can partially target α-1-antitrypsin mutant Z (ATZ), a pathologically aggregation-prone protein, for autophagy degradation ( Feng et al, 2017 ). Moreover, in parallel with Lys63, both Lys48 and Lys11 ubiquitin chains accumulate in Atg5- and Atg7 -knockout mice ( Riley et al, 2010 ).…”

Model Proposal for Development of a Passive Exoeskeleton for Lower Limb

“…The hip, like the ankle joint, has 3 DOFs: flexion or extension, abduction or adduction and, internal or external rotation. The human knee joint works combining rolling and sliding movements between the tibial condyle and the femoral condyle [1] [10]. In the ELL, however, was not considered all the DOFs of the human legs since the main objective was to assist the displacement in the in the sagittal direction with no lateral movement.…”

“…Joint range of motion is one of important parameters to be considered to design a ELL [10]. In the present work, the range of motion was defined by the angles listed in Table 1.…”

Alpha 1-Antitrypsin Deficiency: A Disorder of Proteostasis-Mediated Protein Folding and Trafficking Pathways

“…Thus, for instance, silencing the members of the ERAD pathway such as HRD1, HERP, or EDEM3 increase Z-AAT secretion in cellulo. HRD1 promotes degradation of Z-AAT and increases its solubility, and conversely HRD1 knockdown enhances Z-AAT accumulation and toxicity [40,41].…”