ERp57 as a novel cellular factor controlling prion protein biosynthesis: Therapeutic potential of protein disulfide isomerases

PDIA3 Expression Is Altered in the Limbic Brain Regions of Triple-Transgenic Mouse Model of Alzheimer's Disease

In the present study, we used a mouse model of Alzheimer's disease (AD) (3×Tg-AD mice) to longitudinally analyse the expression level of PDIA3, a protein disulfide isomerase and endoplasmic reticulum (ER) chaperone, in selected brain limbic areas strongly affected by AD-pathology (amygdala, entorhinal cortex, dorsal and ventral hippocampus). Our results suggest that, while in Non-Tg mice PDIA3 levels gradually reduce with aging in all brain regions analyzed, 3×Tg-AD mice showed an age-dependent increase in PDIA3 levels in the amygdala, entorhinal cortex, and ventral hippocampus. A significant reduction of PDIA3 was observed in 3×Tg-AD mice already at 6 months of age, as compared to age-matched Non-Tg mice. A comparative immunohistochemistry analysis performed on 3×Tg-AD mice at 6 (mild AD-like pathology) and 18 (severe AD-like pathology) months of age showed a direct correlation between the cellular level of Aβ and PDIA3 proteins in all the brain regions analysed, even if with different magnitudes. Additionally, an immunohistochemistry analysis showed the presence of PDIA3 in all post-mitotic neurons and astrocytes. Overall, altered PDIA3 levels appear to be age- and/or pathology-dependent, corroborating the ER chaperone's involvement in AD pathology, and supporting the PDIA3 protein as a potential novel therapeutic target for the treatment of AD.

ERp57/PDIA3: new insight

The ERp57/PDIA3 protein is a pleiotropic member of the PDIs family and, although predominantly located in the endoplasmic reticulum (ER), has indeed been found in other cellular compartments, such as the nucleus or the cell membrane. ERp57/PDIA3 is an important research target considering it can be found in various subcellular locations. This protein is involved in many different physiological and pathological processes, and our review describes new data on its functions and summarizes some ligands identified as PDIA3-specific inhibitors.

Role and mechanism of chaperones calreticulin and ERP57 in restoring trafficking to mutant HERG‑A561V protein

Long QT syndrome type 2 is caused by a mutation in the human‑ether‑a‑go‑go‑related gene (HERG) gene encoding the rapidly activating delayed rectifier K‑current. HERG is a key cell membrane glycoprotein; however, whether the maturation process of HERG protein involves key molecules derived from the calnexin (CNX)/calreticulin (CRT) cycle and how these molecules work remains unknown. Using western blotting, the present study screened the key molecules CNX/CRT/endoplasmic reticulum protein 57 (ERP57) involved in this cycle, and it was revealed that the protein expression levels of CNX/CRT/ERP57 in wild‑type (WT)/A561V cells were increased compared with those in WT cells (n=3; P<0.05). Additionally, a co‑immunoprecipitation experiment was used to reveal that the ability of CNX/ERP57/CRT to interact with HERG was significantly increased in A561V and WT/A561V cells (n=3; P<0.05). A plasmid lacking the bb' domain of ERP57 was constructed and it was demonstrated that the key site of ERP57 binding to CRT and immature HERG protein is the bb' domain. The whole‑cell patch‑clamp technique detected that the tail current density increased by 46% following overexpression of CRT and by 53% following overexpression of ERP57 in WT/A561V cells. Overexpression of CRT and ERP57 could increased HERG protein levels on the membrane detected by confocal imaging. Furthermore, overexpression of ERP57 and CRT proteins could restore the HERG‑A561V mutant protein trafficking process and rescue the dominant‑negative suppression of WT. Overall, ERP57/CRT served a crucial role in the HERG‑A561V mutant protein trafficking deficiency and degradation process.

Phenotypic Discovery of Neuroprotective Agents by Regulation of Tau Proteostasis via Stress-Responsive Activation of PERK Signaling

Tau protein aggregates are a recognized neuropathological feature in Alzheimer's disease as well as many other neurodegenerative disorders, known as tauopathies. The development of tau-targeting therapies is therefore extremely important but efficient strategies or protein targets are still unclear. Here, we performed a cell-based phenotypic screening under endoplasmic reticulum (ER) stress conditions and identified a small molecule, SB1617, capable of suppressing abnormal tau protein aggregation. By applying label-free target identification technology, we revealed that the transient enhancement of protein kinase-like endoplasmic reticulum kinase (PERK) signaling pathway through the inhibition of stress-responsive SB1617 targets, PDIA3 and DNAJC3, is an effective strategy for regulating proteostasis in tauopathies. The molecular mechanism and the promising efficacy of SB1617 were demonstrated in neuronal cells and a mouse model with traumatic brain injury, a tauopathy known to involve ER stress.

Multifunctional molecule ERp57: From cancer to neurodegenerative diseases

The protein disulfide isomerase (PDI) gene family is a protein family classically characterized by endoplasmic reticulum (ER) localization and isomerase and redox activity. ERp57, a prominent multifunctional member of the PDI family, is detected at various levels in multiple cellular localizations outside of the ER. ERp57 has been functionally linked to a host of physiological processes and numerous studies have demonstrated altered expression and aberrant functionality of ERp57 in association with diverse pathological states. Here, we summarize available knowledge of ERp57's functions in subcellular compartments and the roles of dysregulated ERp57 in various diseases toward an emphasis on the potential utility of therapeutic development of ERp57.