Development of a sensor for disulfide bond formation in diverse bacteria

In bacteria, disulfide bonds contribute to the folding and stability of proteins important for processes in the cellular envelope. In Escherichia coli, disulfide bond formation is catalyzed by DsbA and DsbB enzymes. DsbA is a periplasmic protein that catalyzes disulfide bond formation in substrate proteins, while DsbB is an inner membrane protein that transfers electrons from DsbA to quinones, thereby regenerating the DsbA active state. Actinobacteria including mycobacteria use an alternative enzyme named VKOR, which performs the same function as DsbB. Disulfide bond formation enzymes, DsbA and DsbB/VKOR, represent novel drug targets because their inhibition could simultaneously affect the folding of several cell envelope proteins including virulence factors, proteins involved in outer membrane biogenesis, cell division, and antibiotic resistance. We have previously developed a cell-based and target-based assay to identify molecules that inhibit the DsbB and VKOR in pathogenic bacteria, using E. coli cells expressing a periplasmic β-Galactosidase sensor (β-Galdbs), which is only active when disulfide bond formation is inhibited. Here, we report the construction of plasmids that allows fine-tuning of the expression of the β-Galdbs sensor and can be mobilized into other gram-negative organisms. As an example, when expressed in Pseudomonas aeruginosa UCBPP-PA14, which harbors two DsbB homologs, β-Galdbs behaves similarly as in E. coli, and the biosensor responds to the inhibition of the two DsbB proteins. Thus, these β-Galdbs reporter plasmids provide a basis to identify novel inhibitors of DsbA and DsbB/VKOR in multidrug-resistant gram-negative pathogens and to further study oxidative protein folding in diverse gram-negative bacteria.

IMPORTANCE

Disulfide bonds contribute to the folding and stability of proteins in the bacterial cell envelope. Disulfide bond-forming enzymes represent new drug targets against multidrug-resistant bacteria because inactivation of this process would simultaneously affect several proteins in the cell envelope, including virulence factors, toxins, proteins involved in outer membrane biogenesis, cell division, and antibiotic resistance. Identifying the enzymes involved in disulfide bond formation in gram-negative pathogens as well as their inhibitors can contribute to the much-needed antibacterial innovation. In this work, we developed sensors of disulfide bond formation for gram-negative bacteria. These tools will enable the study of disulfide bond formation and the identification of inhibitors for this crucial process in diverse gram-negative pathogens.

Protein disulfide isomerase 1 is required for RodA assembling-based conidial hydrophobicity of Aspergillus fumigatus

The hydrophobic layer of Aspergillus conidia, composed of RodA, plays a crucial role in conidia transfer and immune evasion. It self-assembles into hydrophobic rodlets through intramolecular disulfide bonds. However, the secretory process of RodA and its regulatory elements remain unknown. Since protein disulfide isomerase (PDI) is essential for the secretion of many disulfide-bonded proteins, we investigated whether PDI is also involved in RodA secretion and assembly. By gene knockout and phenotypic analysis, we found that Pdi1, one of the four PDI-related proteins of Aspergillus fumigatus, determines the hydrophobicity and integrity of the rodlet layer of the conidia. Preservation of the thioredoxin-active domain of Pdi1 was sufficient to maintain conidial hydrophobicity, suggesting that Pdi1 mediates RodA assembly through its disulfide isomerase activity. In the absence of Pdi1, the disulfide mismatch of RodA in conidia may prevent its delivery from the inner to the outer layer of the cell wall for rodlet assembly. This was demonstrated using a strain expressing a key cysteine-mutated RodA. The dormant conidia of the Pdi1-deficient strain (Δpdi) elicited an immune response, suggesting that the defective conidia surface in the absence of Pdi1 exposes internal immunogenic sources. In conclusion, Pdi1 ensures the correct folding of RodA in the inner layer of conidia, facilitating its secretion into the outer layer of the cell wall and allowing self-assembly of the hydrophobic layer. This study has identified a regulatory element for conidia rodlet assembly.IMPORTANCEAspergillus fumigatus is the major cause of invasive aspergillosis, which is mainly transmitted by the inhalation of conidia. The spread of conidia is largely dependent on their hydrophobicity, which is primarily attributed to the self-assembly of the hydrophobic protein RodA on the cell wall. However, the mechanisms underlying RodA secretion and transport to the outermost layer of the cell wall are still unclear. Our study identified a critical role for Pdi1, a fungal protein disulfide isomerase found in regulating RodA secretion and assembly. Inhibition of Pdi1 prevents the formation of correct S-S bonds in the inner RodA, creating a barrier to RodA delivery and resulting in a defective hydrophobic layer. Our findings provided insight into the formation of the conidial hydrophobic layer and suggested potential drug targets to inhibit A. fumigatus infections by limiting conidial dispersal and altering their immune inertia.

Ultrafast Biomimetic Oxidative Folding of Cysteine-rich Peptides and Microproteins in Organic Solvents

Disulfides in peptides and proteins are essential for maintaining a properly folded structure. Their oxidative folding is invariably performed in an aqueous-buffered solution. However, this process is often slow and can lead to misfolded products. Here, we report a novel concept and strategy that is bio-inspired to mimic protein disulfide isomerase (PDI) by accelerating disulfide exchange rates many thousand-fold. The proposed strategy termed organic oxidative folding is performed under organic solvents to yield correctly folded cysteine-rich microproteins instantaneously without observable misfolded or dead-end products. Compared to conventional aqueous oxidative folding strategies, enormously large rate accelerations up to 113,200-fold were observed. The feasibility and generality of the organic oxidative folding strategy was successfully demonstrated on 15 cysteine-rich microproteins of different hydrophobicity, lengths (14 to 58 residues), and numbers of disulfides (2 to 5 disulfides), producing the native products in a second and in high yield.

The role and mechanism of TXNDC5 in disease progression

Thioredoxin domain containing protein-5 (TXNDC5), also known as endothelial protein-disulfide isomerase (Endo-PDI), is confined to the endoplasmic reticulum through the structural endoplasmic reticulum retention signal (KDEL), is a member of the PDI protein family and is highly expressed in the hypoxic state. TXNDC5 can regulate the rate of disulfide bond formation, isomerization and degradation of target proteins through its function as a protein disulfide isomerase (PDI), thereby altering protein conformation, activity and improving protein stability. Several studies have shown that there is a significant correlation between TXNDC5 gene polymorphisms and genetic susceptibility to inflammatory diseases such as rheumatoid, fibrosis and tumors. In this paper, we detail the expression characteristics of TXNDC5 in a variety of diseases, summarize the mechanisms by which TXNDC5 promotes malignant disease progression, and summarize potential therapeutic strategies to target TXNDC5 for disease treatment.

A novel PDIA3/FTO/USP20 positive feedback regulatory loop induces osteogenic differentiation of preosteoblast in osteoporosis

Osteoporosis is a chronic skeletal disease and the major source of risk for fractures in aged people. It is urgent to investigate the mechanism regulating osteoporosis for developing potential treatment and prevention strategies. Osteogenic differentiation of preosteoblast enhances bone formation, which might be a promising strategy for treatment and prevention of osteoporosis. Protein disulfide isomerase family A, member 3 (PDIA3) could induce bone formation, yet the role of PDIA3 in osteogenic differentiation of preosteoblast remains unknown. In this study, m6 A RNA methylation was detected by methylated RNA immunoprecipitation (MeRIP), while mRNA stability was identified by RNA decay assay. Besides, protein-protein interaction and protein phosphorylation were determined using co-immunoprecipitation (Co-IP). Herein, results revealed that PDIA3 promoted osteogenic differentiation of preosteoblast MC3T3-E1. Besides, PDIA3 mRNA methylation was suppressed by FTO alpha-ketoglutarate dependent dioxygenase (FTO) as RNA methylation reduced PDIA3 mRNA stability during osteogenic differentiation of MC3T3-E1 cells. Moreover, ubiquitin specific peptidase 20 (USP20) improved FTO level through inhibiting FTO degradation while PDIA3 increased FTO level by enhancing USP20 phosphorylation during osteogenic differentiation of MC3T3-E1 cells, suggesting a positive feedback regulatory loop between PDIA3 and FTO. In summary, these findings indicated the mechanism of PDIA3 regulating osteogenic differentiation of preosteoblast and provided potential therapeutic targets for osteoporosis.

Vascular protein disulfide isomerase A1 mediates endothelial dysfunction induced by angiotensin II in mice

AIM

Protein disulfide isomerases (PDIs) are involved in platelet aggregation and intravascular thrombosis, but their role in regulating endothelial function is unclear. Here, we characterized the involvement of vascular PDIA1 in angiotensin II (Ang II)-induced endothelial dysfunction in mice.

METHODS

Endothelial dysfunction was induced in C57BL/6JCmd male mice via Ang II subcutaneous infusion, and PDIA1 was inhibited with bepristat. Endothelial function was assessed in vivo with magnetic resonance imaging and ex vivo with a myography, while arterial stiffness was measured as pulse wave velocity. Nitric oxide (NO) bioavailability was measured in the aorta (spin-trapping electron paramagnetic resonance) and plasma (NO2 - and NO3 - levels). Oxidative stress, eNOS uncoupling (DHE-based aorta staining), and thrombin activity (thrombin-antithrombin complex; calibrated automated thrombography) were evaluated.

RESULTS

The inhibition of PDIA1 by bepristat in Ang II-treated mice prevented the impairment of NO-dependent vasodilation in the aorta as evidenced by the response to acetylcholine in vivo, increased systemic NO bioavailability and the aortic NO production, and decreased vascular stiffness. Bepristat's effect on NO-dependent function was recapitulated ex vivo in Ang II-induced endothelial dysfunction in isolated aorta. Furthermore, bepristat diminished the Ang II-induced eNOS uncoupling and overproduction of ROS without affecting thrombin activity.

CONCLUSION

In Ang II-treated mice, the inhibition of PDIA1 normalized the NO-ROS balance, prevented endothelial eNOS uncoupling, and, thereby, improved vascular function. These results indicate the importance of vascular PDIA1 in regulating endothelial function, but further studies are needed to elucidate the details of the mechanisms involved.

Downregulation of PDIA3 inhibits gastric cancer cell growth through cell cycle regulation

OBJECTIVE

Protein disulfide isomerase A3 (PDIA3) promotes the correct folding of newly synthesized glycoproteins in the endoplasmic reticulum. PDIA3 is overexpressed in most tumors, and it may become a biomarker of cancer prognosis and immunotherapy. Our study aims to detect the expression level of PDIA3 in gastric cancer (GC) and its association with GC development as wells as the underlying mechanisms.

METHODS

GC cell lines with PDIA3 knockdown by siRNA, CRISPR-cas9 sgRNAs or a pharmacological inhibitor of LOC14 were prepared and used. PDIA3 knockout GC cells were established by CRISPR-cas9-PDIA3 system. The proliferation, migration, invasion and cell cycle of GC cells were analyzed by cell counting kit-8 assay, wound healing assay, transwell assay and flow cytometry, respectively. Immunodeficient nude mice was used to evaluate the role of PDIA3 in tumor formation. Quantitative PCR and western blot were used for examining gene and protein expressions. RNA sequencing was performed to see the altered gene expression.

RESULTS

The expressions of PDIA3 in GC tissues and cells were increased significantly, and its expression was negatively correlated with the three-year survival rate of GC patients. Down-regulation of PDIA3 by siRNA, LOC14 or CRISPR-cas9 significantly inhibited proliferation, invasion and migration of GC cells TMK1 and AGS, with cell cycle arrested at G2/M phase. Meanwhile, decreased PDIA3 significantly inhibited growth of tumor xenograft in vivo. It was found that cyclin G1 (encoded by CCNG1 gene) expression was decreased by downregulation of PDIA3 in GC cells both in vitro and in vivo. In addition, protein levels of other cell cycle related factors including cyclin D1, CDK2, and CDK6 were also significantly decreased. Further study showed that STAT3 was associated with PDIA3-mediated cyclin G1 regulation.

CONCLUSION

PDIA3 plays an oncogenic role in GC. Our findings unfolded the functional role of PDIA3 in GC development and highlighted a novel target for cancer therapeutic strategy.

CdbC: a disulfide bond isomerase involved in the refolding of mycoloyltransferases in Corynebacterium glutamicum cells exposed to oxidative conditions

In Corynebacterium glutamicum cells, cdbC, which encodes a protein containing the CysXXCys motif, is regulated by the global redox-responsive regulator OsnR. In this study, we assessed the role of the periplasmic protein CdbC in disulfide bond formation and its involvement in mycomembrane biosynthesis. Purified CdbC efficiently refolded scrambled RNaseA, exhibiting prominent disulfide bond isomerase activity. The transcription of cdbC was decreased in cells grown in the presence of the reductant dithiothreitol (DTT). Moreover, unlike wild-type and cdbC-deleted cells, cdbC-overexpressing (P180-cdbC) cells grown in the presence of DTT exhibited retarded growth, abnormal cell morphology, increased cell surface hydrophobicity and altered mycolic acid composition. P180-cdbC cells cultured in a reducing environment accumulated trehalose monocorynomycolate, indicating mycomembrane deformation. Similarly, a two-hybrid analysis demonstrated the interaction of CdbC with the mycoloyltransferases MytA and MytB. Collectively, our findings suggest that CdbC, a periplasmic disulfide bond isomerase, refolds misfolded MytA and MytB and thereby assists in mycomembrane biosynthesis in cells exposed to oxidative conditions.

Komagataella phaffii Erp41 is a protein disulfide isomerase with unprecedented disulfide bond catalyzing activity when coupled to glutathione

In the methylotrophic yeast Komagataella phaffii, we identified an endoplasmic reticulum-resident protein disulfide isomerase (PDI) family member, Erp41, with a peculiar combination of active site motifs. Like fungal ERp38, it has two thioredoxin-like domains which contain active site motifs (a and a'), followed by an alpha-helical ERp29c C-terminal domain (c domain). However, while the a domain has a typical PDI-like active site motif (CGHC), the a' domain instead has CGYC, a glutaredoxin-like motif which confers to the protein an exceptional affinity for GSH/GSSG. This combination of active site motifs has so far been unreported in PDI-family members. Homology searches revealed ERp41 is present in the genome of some plants, fungal parasites, and a few nonconventional yeasts, among which are Komagataella spp. and Yarrowia lipolytica. These yeasts are both used for the production of secreted recombinant proteins. Here, we analyzed the activity of K. phaffii Erp41. We report that it is nonessential in K. phaffii, and that it can catalyze disulfide bond formation in partnership with the sulfhydryl oxidase Ero1 in vitro with higher turnover rates than the canonical PDI from K. phaffii, Pdi1, but slower activation times. We show how Erp41 has unusually fast glutathione-coupled oxidation activity and relate it to its unusual combination of active sites in its thioredoxin-like domains. We further describe how this determines its unusually efficient catalysis of dithiol oxidation in peptide and protein substrates.

Exploring the Influence of Zinc Ions on the Conformational Stability and Activity of Protein Disulfide Isomerase

The interplay between metal ion binding and the activity of thiol proteins, particularly within the protein disulfide isomerase family, remains an area of active investigation due to the critical role that these proteins play in many vital processes. This research investigates the interaction between recombinant human PDIA1 and zinc ions, focusing on the subsequent implications for PDIA1's conformational stability and enzymatic activity. Employing isothermal titration calorimetry and differential scanning calorimetry, we systematically compared the zinc binding capabilities of both oxidized and reduced forms of PDIA1 and assessed the structural consequences of this interaction. Our results demonstrate that PDIA1 can bind zinc both in reduced and oxidized states, but with significantly different stoichiometry and more pronounced conformational effects in the reduced form of PDIA1. Furthermore, zinc binding was observed to inhibit the catalytic activity of reduced-PDIA1, likely due to induced alterations in its conformation. These findings unveil a potential regulatory mechanism in PDIA1, wherein metal ion binding under reductive conditions modulates its activity. Our study highlights the potential role of zinc in regulating the catalytic function of PDIA1 through conformational modulation, suggesting a nuanced interplay between metal binding and protein stability in the broader context of cellular redox regulation.

Protein disulfide isomerase family member 4 promotes triple-negative breast cancer tumorigenesis and radiotherapy resistance through JNK pathway

BACKGROUND

Despite radiotherapy ability to significantly improve treatment outcomes and survival in triple-negative breast cancer (TNBC) patients, acquired resistance to radiotherapy poses a serious clinical challenge. Protein disulfide isomerase exists in endoplasmic reticulum and plays an important role in promoting protein folding and post-translational modification. However, little is known about the role of protein disulfide isomerase family member 4 (PDIA4) in TNBC, especially in the context of radiotherapy resistance.

METHODS

We detected the presence of PDIA4 in TNBC tissues and paracancerous tissues, then examined the proliferation and apoptosis of TNBC cells with/without radiotherapy. As part of the validation process, xenograft tumor mouse model was used. Mass spectrometry and western blot analysis were used to identify PDIA4-mediated molecular signaling pathway.

RESULTS

Based on paired clinical specimens of TNBC patients, we found that PDIA4 expression was significantly higher in tumor tissues compared to adjacent normal tissues. In vitro, PDIA4 knockdown not only increased apoptosis of tumor cells with/without radiotherapy, but also decreased the ability of proliferation. In contrast, overexpression of PDIA4 induced the opposite effects on apoptosis and proliferation. According to Co-IP/MS results, PDIA4 prevented Tax1 binding protein 1 (TAX1BP1) degradation by binding to TAX1BP1, which inhibited c-Jun N-terminal kinase (JNK) activation. Moreover, PDIA4 knockdown suppressed tumor growth xenograft model in vivo, which was accompanied by an increase in apoptosis and promoted tumor growth inhibition after radiotherapy.

CONCLUSIONS

The results of this study indicate that PDIA4 is an oncoprotein that promotes TNBC progression, and targeted therapy may represent a new and effective anti-tumor strategy, especially for patients with radiotherapy resistance.

Genome-wide analysis and expression divergence of protein disulfide isomerase (PDI) gene family members in chickpea (Cicer arietinum) under salt stress

Chickpea (Cicer arietinum ) is a grain crop that is an important source of protein, vitamins, carbohydrates and minerals. It is highly sensitive to salt stress, and salt damage to cellular homeostasis and protein folding affects production. Plants have several mechanisms to prevent cellular damages under abiotic stresses, such as proteins in the endoplasmic reticulum (protein isulfide somerases (PDIs) and PDI-like proteins), which help prevent the build-up of mis-folded proteins that are damaged under abiotic stresses. In this study, we completed initial comprehensive genome-wide analysis of the chickpea PDI gene family. We found eight PDI genes are distributed on six out of eight chromosomes. Two pairs of paralogous genes were found to have segmental duplications. The phylogenetic analysis showed that the PDI s have a high degree of homology in C. arietinum, Cicer reticulatum, Lens culinaris, Phaseolus acutifolius, Pisum sativum and Oryza sativa . The gene structure analysis displayed that CaPDI1-CaPDI8 have 9-12 exons except for CaPDI5 , which has 25 exons. Subcellular localisation indicated accumulation of CaPDIs in endoplasmic reticulum. Protein-conserved motifs and domain analysis demonstrated that thioredoxin domains of PDI family is present in all CaPDIs. CaPDI proteins have strong protein-protein interaction. In silico expression analysis showed that four out of eight PDI genes (CPDI2, CaPDI6, CaPDI7 and CaPDI8 ) were expressed under salt stress. Of these, expression of CaPDI2 and CaPDI8 was the highest. This work indicated that PDI genes are involved in salt stress tolerance in chickpea and the CaPDIs may be further studied for their role of inducing salt tolerance.

[Redox Biology Involved in the Toxicity of Enterohemorrhagic Escherichia coli Toxin SubAB]

AB5 toxins of pathogenic bacteria enter host cells and utilize the retrograde trafficking pathway to translocate to the cytoplasm and exert its pathogenesis. Cholera toxin and Shiga toxin reach the endoplasmic reticulum (ER), and the A subunit undergoes redox regulation by ER proteins to become active fragments, which pass through the ER membrane and translocate to the cytoplasm. By acting on molecular targets in the cytoplasm, the normal function of host cells are disrupted, causing diseases. ER chaperone proteins such as protein disulfide isomerase (PDI) and binding immunoglobulin protein (BiP) induce conformational changes triggered by the reduction of disulfide bonds in the A subunit. This is thought to be dependent on cysteine thiol-mediated redox regulation, but the detailed mechanism remains unclear. On the other hand, subtilase cytotoxin (SubAB), produced by enterohemorrhagic Escherichia coli (EHEC), localizes to the ER without translocating to the cytoplasm and cleaves BiP as a substrate. Therefore, it is thought that ER stress-based cytotoxicity and intestinal bleeding occur without translocating to the cytoplasm. We reported that PDI is involved in BiP cleavage through SubAB localization to the ER. Like other AB5 toxins, this indicates the involvement of redox regulation via chaperone proteins in the ER, but also suggests that SubAB does not translocate to the cytoplasm because it cleaves BiP. Although there are few reports on the redox state of ER protein thiols, it is suggested that polysulfidation, which is discussed in this symposium, may be involved.

PDIA6, which is regulated by TRPM2-AS/miR-424-5p axis, promotes endometrial cancer progression via TGF-beta pathway

PDIA6 have been reported to be involved in a variety of cancers, however, the underlying role in endometrial cancer is still unclear. In this study, we aimed to study the function of PDIA6 in endometrial cancer. Firstly, we verified that PDIA6 was significantly upregulated in endometrial cancer, which was correlated with the progression of endometrial cancer patients. Furthermore, we identified PDIA6 significantly altered the ability of endometrial cancer cells to proliferate and metastasize. In addition, our result illustrated the oncogene effects of PDIA6 in promoting malignant biological behavior of endometrial cancer cells by regulating TGF-β pathway and being modulated by TRPM2-AS/miR-424-5p axis for the first time. Taken together, this study suggested that PDIA6 may be a new candidate target for endometrial cancer therapy.

Endoplasmic Reticulum Protein TXNDC5 Interacts with PRDX6 and HSPA9 to Regulate Glutathione Metabolism and Lipid Peroxidation in the Hepatic AML12 Cell Line

Non-alcoholic fatty liver disease or steatosis is an accumulation of fat in the liver. Increased amounts of non-esterified fatty acids, calcium deficiency, or insulin resistance may disturb endoplasmic reticulum (ER) homeostasis, which leads to the abnormal accumulation of misfolded proteins, activating the unfolded protein response. The ER is the primary location site for chaperones like thioredoxin domain-containing 5 (TXNDC5). Glutathione participates in cellular oxidative stress, and its interaction with TXNDC5 in the ER may decrease the disulfide bonds of this protein. In addition, glutathione is utilized by glutathione peroxidases to inactivate oxidized lipids. To characterize proteins interacting with TXNDC5, immunoprecipitation and liquid chromatography-mass spectrometry were used. Lipid peroxidation, reduced glutathione, inducible phospholipase A2 (iPLA2) and hepatic transcriptome were assessed in the AML12 and TXNDC5-deficient AML12 cell lines. The results showed that HSPA9 and PRDX6 interact with TXNDC5 in AML12 cells. In addition, TXNDC5 deficiency reduced the protein levels of PRDX6 and HSPA9 in AML12. Moreover, lipid peroxidation, glutathione and iPLA2 activities were significantly decreased in TXNDC5-deficient cells, and to find the cause of the PRDX6 protein reduction, proteasome suppression revealed no considerable effect on it. Finally, hepatic transcripts connected to PRDX6 and HSPA9 indicated an increase in the Dnaja3, Mfn2 and Prdx5 and a decrease in Npm1, Oplah, Gstp3, Gstm6, Gstt1, Serpina1a, Serpina1b, Serpina3m, Hsp90aa1 and Rps14 mRNA levels in AML12 KO cells. In conclusion, the lipid peroxidation system and glutathione mechanism in AML12 cells may be disrupted by the absence of TXNDC5, a novel protein-protein interacting partner of PRDX6 and HSPA9.

Naringin binds to protein disulfide isomerase to inhibit its activity and modulate the blood coagulation rates: Implications in controlling thrombosis

Currently used antithrombotic drugs are beset with several drawbacks which necessitates the need for new and cheaper alternatives. Protein disulfide isomerase (PDI) is secreted in the blood plasma in cellular stress conditions and initiates the thrombus formation. A screening of library of natural compounds revealed that naringin had a high binding affinity for the PDI (-8.2 kcal/mol). Recombinant PDI was purified using the affinity chromatography. Incubation of purified PDI (3 μM) with naringin (0-100 μM, pH 7.4, 25 °C) partially modulated its conformation. Consequently, the fluorescence emission spectra of the PDI binding to naringin were assessed using the Stern-Volmer equation, which indicated an association constant of 2.78 × 104 M-1 suggesting an appreciable affinity for the naringin, with a unique binding site. An insulin turbidity assay showed that PDI activity is decreased in the presence of naringin indicating inhibition. Molecular dynamic simulation studies showed the changes in the PDI structure on binding to the naringin. Incubation of naringin (80 μM) in fresh human plasma along with exogenous PDI (175 nM) showed a significant delay in the intrinsic and extrinsic coagulation pathways. We show that naringin is able to modulate the PDI conformation and activity resulting in altered blood coagulation rates.

Optimization of Protein Folding for Improved Secretion of Human Serum Albumin Fusion Proteins in Saccharomyces cerevisiae

The successful expression and secretion of recombinant proteins in cell factories significantly depend on the correct folding of nascent peptides, primarily achieved through disulfide bond formation. Thus, optimizing cellular protein folding is crucial, especially for proteins with complex spatial structures. In this study, protein disulfide isomerases (PDIs) from various species were introduced into Saccharomyces cerevisiae to facilitate proper disulfide bond formation and enhance recombinant protein secretion. The impacts of these PDIs on recombinant protein production and yeast growth metabolism were evaluated by substituting the endogenous PDI1. Heterologous PDIs cannot fully compensate the endogenous PDI. Furthermore, protein folding mediators, PDI and ER oxidoreductase 1 (Ero1), from different species were used to increase the production of complex human serum albumin (HSA) fusion proteins. The validated folding mediators were then introduced into unfolded protein response (UPR)-optimized strains, resulting in a 7.8-fold increase in amylase-HSA and an 18.2-fold increase in albiglutide compared with the control strain. These findings provide valuable insights for optimizing protein folding and expressing HSA-based drugs.

Reduction is sufficient for the disassembly of ricin and Shiga toxin 1 but not Escherichia coli heat-labile enterotoxin

Many AB toxins contain an enzymatic A moiety that is anchored to a cell-binding B moiety by a disulfide bridge. After receptor-mediated endocytosis, some AB toxins undergo retrograde transport to the endoplasmic reticulum (ER) where reduction of the disulfide bond occurs. The reduced A subunit then dissociates from the holotoxin and enters the cytosol to alter its cellular target. Intoxication requires A chain separation from the holotoxin, but, for many toxins, it is unclear if reduction alone is sufficient for toxin disassembly. Here, we examined the link between reduction and disassembly for several ER-translocating toxins. We found disassembly of the reduced Escherichia coli heat-labile enterotoxin (Ltx) required an interaction with one specific ER-localized oxidoreductase: protein disulfide isomerase (PDI). In contrast, the reduction and disassembly of ricin toxin (Rtx) and Shiga toxin 1 (Stx1) were coupled events that did not require PDI and could be triggered by reductant alone. PDI-deficient cells accordingly exhibited high resistance to Ltx with continued sensitivity to Rtx and Stx1. The distinct structural organization of each AB toxin thus appears to determine whether holotoxin disassembly occurs spontaneously upon disulfide reduction or requires the additional input of PDI.

Adsorption and Molecular Display of a Redox-Active Protein on Gold Nanoparticle Surfaces

Engineered gold nanoparticles (AuNPs) have great potential in many applications due to their tunable optical properties, facile synthesis, and surface functionalization via thiol chemistry. When exposed to a biological environment, NPs are coated with a protein corona that can alter the NPs' biological identity but can also affect the proteins' structures and functions. Protein disulfide isomerase (PDI) is an abundant protein responsible for the disulfide formation and isomerization that contribute to overall cell redox homeostasis and signaling. Given that AuNPs are widely employed in nanomedicine and PDI plays a functional role in various diseases, the interactions between oxidized (oPDI) and reduced (rPDI) with 50 nm citrate-coated AuNPs (AuNPs) are examined in this study using various techniques. Upon incubation, PDI adsorbs to the AuNP surface, which leads to a reduction in its enzymatic activity despite limited changes in secondary structures. Partial enzymatic digestion followed by mass spectrometry analysis shows that orientation of PDI on the NP surface is dependent on both its oxidation state and the PDI:AuNP incubation ratios.

PDIA3 modulates genomic response to 1,25-dihydroxyvitamin D3 in squamous cell carcinoma of the skin

An active form of vitamin D3 (1,25-dihydroxyvitamin D3) acts through vitamin D receptor (VDR) initiating genomic response, but several studies described also non-genomic actions of 1,25-dihydroxyvitamin D3, implying the role of PDIA3 in the process. PDIA3 is a membrane-associated disulfide isomerase involved in disulfide bond formation, protein folding, and remodeling. Here, we used a transcriptome-based approach to identify changes in expression profiles in PDIA3-deficient squamous cell carcinoma line A431 after 1,25-dihydroxyvitamin D3 treatment. PDIA3 knockout led to changes in the expression of more than 2000 genes and modulated proliferation, cell cycle, and mobility of cells; suggesting an important regulatory role of PDIA3. PDIA3-deficient cells showed increased sensitivity to 1,25-dihydroxyvitamin D3, which led to decrease migration. 1,25-dihydroxyvitamin D3 treatment altered also genes expression profile of A431ΔPDIA3 in comparison to A431WT cells, indicating the existence of PDIA3-dependent genes. Interestingly, classic targets of VDR, including CAMP (Cathelicidin Antimicrobial Peptide), TRPV6 (Transient Receptor Potential Cation Channel Subfamily V Member 6), were regulated differently by 1,25-dihydroxyvitamin D3, in A431ΔPDIA3. Deletion of PDIA3 impaired 1,25-dihydroxyvitamin D3-response of genes, such as PTGS2, MMP12, and FOCAD, which were identified as PDIA3-dependent. Additionally, response to 1,25-dihydroxyvitamin D3 in cancerous A431 cells differed from immortalized HaCaT keratinocytes, used as non-cancerous control. Finally, silencing of PDIA3 and 1,25-dihydroxyvitamin D3, at least partially reverse the expression of cancer-related genes in A431 cells, thus targeting PDIA3 and use of 1,25-dihydroxyvitamin D3 could be considered in a prevention and therapy of the skin cancer. Taken together, PDIA3 has a strong impact on gene expression and physiology, including genomic response to 1,25-dihydroxyvitamin D3.

Protein Disulfide Isomerase Family A Member 3 Knockout Abrogate Effects of Vitamin D on Cellular Respiration and Glycolysis in Squamous Cell Carcinoma

PDIA3 is an endoplasmic reticulum disulfide isomerase, which is involved in the folding and trafficking of newly synthesized proteins. PDIA3 was also described as an alternative receptor for the active form of vitamin D (1,25(OH)2D3). Here, we investigated an impact of PDIA3 in mitochondrial morphology and bioenergetics in squamous cell carcinoma line A431 treated with 1,25(OH)2D3. It was observed that PDIA3 deletion resulted in changes in the morphology of mitochondria including a decrease in the percentage of mitochondrial section area, maximal diameter, and perimeter. The 1,25(OH)2D3 treatment of A431∆PDIA3 cells partially reversed the effect of PDIA3 deletion increasing aforementioned parameters; meanwhile, in A431WT cells, only an increase in mitochondrial section area was observed. Moreover, PDIA3 knockout affected mitochondrial bioenergetics and modulated STAT3 signaling. Oxygen consumption rate (OCR) was significantly increased, with no visible effect of 1,25(OH)2D3 treatment in A431∆PDIA3 cells. In the case of Extracellular Acidification Rate (ECAR), an increase was observed for glycolysis and glycolytic capacity parameters in the case of non-treated A431WT cells versus A431∆PDIA3 cells. The 1,25(OH)2D3 treatment had no significant effect on glycolytic parameters. Taken together, the presented results suggest that PDIA3 is strongly involved in the regulation of mitochondrial bioenergetics in cancerous cells and modulation of its response to 1,25(OH)2D3, possibly through STAT3.

Circular RNA P4HB promotes glycolysis and tumor progression by binding with PKM2 in lung adenocarcinoma

BACKGROUND

Emerging evidence indicates that circular RNAs (circRNAs) play vital roles in tumor progression, including lung adenocarcinomas (LUAD). However, the mechanisms by which circRNAs promote the progression of LUAD still require further investigation.

METHODS

Quantitative real-time PCR was performed to detect the expression of circP4HB in LUAD tissues and cells. Then, Kaplan-Meier analysis was used to determine the prognostic value of circP4HB expression. We employed RNA pull-down, RNA immunoprecipitation, mass spectrometry, cells fraction, glucose consumption, lactate production, pyruvate kinase M2 (PKM2) activity, and macrophage polarization assays to uncover the underlying mechanisms of circP4HB in LUAD.

RESULTS

We found that circP4HB is upregulated in LUAD tissues and correlated with advanced TNM stages and lymph node metastasis. LUAD patients with high circP4HB expression had poor prognoses. Functionally, circP4HB promoted LUAD progression in vivo and in vitro. Upregulated circP4HB increased glucose consumption, lactate production and accelerated aerobic glycolysis in LUAD cells. Mechanically, circP4HB mainly accumulated in the cytoplasm of LUAD cells and bound with PKM2 and subsequently upregulating PKM2 enzymatic activity by increasing its tetramer formation. Additionally, circP4HB promoted M2 macrophage phenotype shift via targeting PKM2. Finally, rescue assays further confirmed that circP4HB could promote LUAD cell progression through its interaction with PKM2.

CONCLUSION

These results demonstrate that circP4HB could promote LUAD progression, indicating circP4HB might be a potential therapeutic target of LUAD.

Divergent Proteome Reactivity Influences Arm-Selective Activation of the Unfolded Protein Response by Pharmacological Endoplasmic Reticulum Proteostasis Regulators

Pharmacological activation of the activating transcription factor 6 (ATF6) arm of the unfolded protein response (UPR) has proven useful for ameliorating proteostasis deficiencies in cellular and mouse models of numerous etiologically diverse diseases. Previous high-throughput screening efforts identified the small molecule AA147 as a potent and selective ATF6 activating compound that operates through a mechanism involving metabolic activation of its 2-amino-p-cresol substructure affording a quinone methide, which then covalently modifies a subset of endoplasmic reticulum (ER) protein disulfide isomerases (PDIs). Another compound identified in this screen, AA132, also contains a 2-amino-p-cresol moiety; however, this compound showed less transcriptional selectivity, instead globally activating all three arms of the UPR. Here, we show that AA132 activates global UPR signaling through a mechanism analogous to that of AA147, involving metabolic activation and covalent modification of proteins including multiple PDIs. Chemoproteomic-enabled analyses show that AA132 covalently modifies PDIs to a greater extent than AA147. However, the extent of PDI labeling by AA147 approaches a plateau more rapidly than PDI labeling by AA132. These observations together suggest that AA132 can access a larger pool of proteins for covalent modification, possibly because its activated form is less susceptible to quenching than activated AA147. In other words, the lower reactivity of activated AA132 allows it to persist longer and modify more PDIs in the cellular environment. Collectively, these results suggest that AA132 globally activates the UPR through increased engagement of ER PDIs. Consistent with this, reducing the cellular concentration of AA132 decreases PDI modifications and enables selective ATF6 activation. Our results highlight the relationship between metabolically activatable-electrophile stability, ER proteome reactivity, and the transcriptional response observed with the enaminone chemotype of ER proteostasis regulators, enabling continued development of next-generation ATF6 activating compounds.

Sulfenylation links oxidative stress to protein disulfide isomerase oxidase activity and thrombus formation

BACKGROUND

Oxidative stress contributes to thrombosis in atherosclerosis, inflammation, infection, aging, and malignancy. Oxidant-induced cysteine modifications, including sulfenylation, can act as a redox-sensitive switch that controls protein function. Protein disulfide isomerase (PDI) is a prothrombotic enzyme with exquisitely redox-sensitive active-site cysteines.

OBJECTIVES

We hypothesized that PDI is sulfenylated during oxidative stress, contributing to the prothrombotic potential of PDI.

METHODS

Biochemical and enzymatic assays using purified proteins, platelet and endothelial cell assays, and in vivo murine thrombosis studies were used to evaluate the role of oxidative stress in PDI sulfenylation and prothrombotic activity.

RESULTS

PDI exposure to oxidants resulted in the loss of PDI reductase activity and simultaneously promoted sulfenylated PDI generation. Following exposure to oxidants, sulfenylated PDI spontaneously converted to disulfided PDI. PDI oxidized in this manner was able to transfer disulfides to protein substrates. Inhibition of sulfenylation impaired disulfide formation by oxidants, indicating that sulfenylation is an intermediate during PDI oxidation. Agonist-induced activation of platelets and endothelium resulted in the release of sulfenylated PDI. PDI was also sulfenylated by oxidized low-density lipoprotein (oxLDL). In an in vivo model of thrombus formation, oxLDL markedly promoted platelet accumulation following an arteriolar injury. PDI oxidoreductase inhibition blocked oxLDL-mediated augmentation of thrombosis.

CONCLUSION

PDI sulfenylation is a critical posttranslational modification that is an intermediate during disulfide PDI formation in the setting of oxidative stress. Oxidants generated by vascular cells during activation promote PDI sulfenylation, and interference with PDI during oxidative stress impairs thrombus formation.

Protein disulfide isomerases - a way to tackle malaria

Protein disulfide isomerases (PDIs) ensure that specific substrate proteins are correctly folded. PDI activity plays an essential role in malaria transmission. Here we provide an overview of the role of PDIs in malaria-causing Plasmodium parasites and outline why PDI inhibition could be a novel way to treat malaria and prevent transmission.

High-resolution structural-omics of human liver enzymes

We applied raw human liver microsome lysate to a holey carbon grid and used cryo-electron microscopy (cryo-EM) to define its composition. From this sample we identified and simultaneously determined high-resolution structural information for ten unique human liver enzymes involved in diverse cellular processes. Notably, we determined the structure of the endoplasmic bifunctional protein H6PD, where the N- and C-terminal domains independently possess glucose-6-phosphate dehydrogenase and 6-phosphogluconolactonase enzymatic activity, respectively. We also obtained the structure of heterodimeric human GANAB, an ER glycoprotein quality-control machinery that contains a catalytic α subunit and a noncatalytic β subunit. In addition, we observed a decameric peroxidase, PRDX4, which directly contacts a disulfide isomerase-related protein, ERp46. Structural data suggest that several glycosylations, bound endogenous compounds, and ions associate with these human liver enzymes. These results highlight the importance of cryo-EM in facilitating the elucidation of human organ proteomics at the atomic level.

Protein Disulfide Isomerase and Extracellular Adherence Protein Cooperatively Potentiate Staphylococcal Invasion into Endothelial Cells

Invasion of host cells is an important feature of Staphylococcus aureus. The main internalization pathway involves binding of the bacteria to host cells, e.g., endothelial cells, via a fibronectin (Fn) bridge between S. aureus Fn binding proteins and α5β1-integrin, followed by phagocytosis. The secreted extracellular adherence protein (Eap) has been shown to promote this cellular uptake pathway of not only S. aureus, but also of bacteria otherwise poorly taken up by host cells, such as Staphylococcus carnosus. The exact mechanisms are still unknown. Previously, we demonstrated that Eap induces platelet activation by stimulation of the protein disulfide isomerase (PDI), a catalyst of thiol-disulfide exchange reactions. Here, we show that Eap promotes PDI activity on the surface of endothelial cells, and that this contributes critically to Eap-driven staphylococcal invasion. PDI-stimulated β1-integrin activation followed by increased Fn binding to host cells likely accounts for the Eap-enhanced uptake of S. aureus into non-professional phagocytes. Additionally, Eap supports the binding of S. carnosus to Fn-α5β1 integrin, thereby allowing its uptake into endothelial cells. To our knowledge, this is the first demonstration that PDI is crucial for the uptake of bacteria into host cells. We describe a hitherto unknown function of Eap-the promotion of an enzymatic activity with subsequent enhancement of bacterial uptake-and thus broaden mechanistic insights into its importance as a driver of bacterial pathogenicity. IMPORTANCE Staphylococcus aureus can invade and persist in non-professional phagocytes, thereby escaping host defense mechanisms and antibiotic treatment. The intracellular lifestyle of S. aureus contributes to the development of infection, e.g., in infective endocarditis or chronic osteomyelitis. The extracellular adherence protein secreted by S. aureus promotes its own internalization as well as that of bacteria that are otherwise poorly taken up by host cells, such as Staphylococcus carnosus. In our study, we demonstrate that staphylococcal uptake by endothelial cells requires catalytic disulfide exchange activity by the cell-surface protein disulfide isomerase, and that this critical enzymatic function is enhanced by Eap. The therapeutic application of PDI inhibitors has previously been investigated in the context of thrombosis and hypercoagulability. Our results add another intriguing possibility: therapeutically targeting PDI, i.e., as a candidate approach to modulate the initiation and/or course of S. aureus infectious diseases.

Interaction with ERp57 is required for progranulin protection against Type 2 Gaucher disease

Gaucher disease (GD), one of the most common lysosomal storage diseases, is caused by GBA1 mutations resulting in defective glucocerebrosidase (GCase) and consequent accumulation of its substrates β-glucosylceramide (β-GlcCer). We reported progranulin (PGRN), a secretary growth factor-like molecule and an intracellular lysosomal protein was a crucial co-factor of GCase. PGRN binds to GCase and recruits Heat Shock Protein 70 (Hsp70) to GCase through its C-terminal Granulin (Grn) E domain, termed as ND7. In addition, both PGRN and ND7 are therapeutic against GD. Herein we found that both PGRN and its derived ND7 still displayed significant protective effects against GD in Hsp70 deficient cells. To delineate the molecular mechanisms underlying PGRN's Hsp70-independent regulation of GD, we performed a biochemical co-purification and mass spectrometry with His-tagged PGRN and His-tagged ND7 in Hsp70 deficient cells, which led to the identification of ERp57, also referred to as protein disulfide isomerase A3 (PDIA3), as a protein that binds to both PGRN and ND7. Within type 2 neuropathic GD patient fibroblasts L444P, bearing GBA1 L444P mutation, deletion of ERp57 largely abolished the therapeutic effects of PGRN and ND7, as manifested by loss of effects on lysosomal storage, GCase activity, and β-GlcCer accumulation. Additionally, recombinant ERp57 effectively restored the therapeutic effects of PGRN and ND7 in ERp57 knockout L444P fibroblasts. Collectively, this study reports ERp57 as a previously unrecognized binding partner of PGRN that contributes to PGRN regulation of GD.

Targeting unfolded protein response using albumin-encapsulated nanoparticles attenuates temozolomide resistance in glioblastoma

BACKGROUND

Chemoresistant cancer cells frequently exhibit a state of chronically activated endoplasmic reticulum (ER) stress. Engaged with ER stress, the unfolded protein response (UPR) is an adaptive reaction initiated by the accumulation of misfolded proteins. Protein disulfide isomerase (PDI) is a molecular chaperone known to be highly expressed in glioblastomas with acquired resistance to temozolomide (TMZ). We investigate whether therapeutic targeting of PDI provides a rationale to overcome chemoresistance.

METHODS

The activity of PDI was suppressed in glioblastoma cells using a small molecule inhibitor CCF642. Either single or combination treatment with TMZ was used. We prepared nanoformulation of CCF642 loaded in albumin as a drug carrier for orthotopic tumour model.

RESULTS

Inhibition of PDI significantly enhances the cytotoxic effect of TMZ on glioblastoma cells. More importantly, inhibition of PDI is able to sensitise glioblastoma cells that are initially resistant to TMZ treatment. Nanoformulation of CCF642 is well-tolerated and effective in suppressing tumour growth. It activates cell death-triggering UPR beyond repair and induces ER perturbations through the downregulation of PERK signalling. Combination treatment of TMZ with CCF642 significantly reduces tumour growth compared with either modality alone.

CONCLUSION

Our study demonstrates modulation of ER stress by targeting PDI as a promising therapeutic rationale to overcome chemoresistance.

Pharmacological and mechanistic study of PS1, a Pdia4 inhibitor, in β-cell pathogenesis and diabetes in db/db mice

Pdia4 has been characterized as a key protein that positively regulates β-cell failure and diabetes via ROS regulation. Here, we investigated the function and mechanism of PS1, a Pdia4 inhibitor, in β-cells and diabetes. We found that PS1 had an IC₅₀ of 4 μM for Pdia4. Furthermore, PS1 alone and in combination with metformin significantly reversed diabetes in db/db mice, 6 to 7 mice per group, as evidenced by blood glucose, glycosylated hemoglobin A1c (Hb_A1c), glucose tolerance test, diabetic incidence, survival and longevity (P < 0.05 or less). Accordingly, PS1 reduced cell death and dysfunction in the pancreatic β-islets of db/db mice as exemplified by serum insulin, serum c-peptide, reactive oxygen species (ROS), islet atrophy, and homeostatic model assessment (HOMA) indices (P < 0.05 or less). Moreover, PS1 decreased cell death in the β-islets of db/db mice. Mechanistic studies showed that PS1 significantly increased cell survival and insulin secretion in Min6 cells in response to high glucose (P < 0.05 or less). This increase could be attributed to a reduction in ROS production and the activity of electron transport chain complex 1 (ETC C1) and Nox in Min6 cells by PS1. Further, we found that PS1 inhibited the enzymatic activity of Pdia4 and mitigated the interaction between Pdia4 and Ndufs3 or p22 in Min6 cells (P < 0.01 or less). Taken together, this work demonstrates that PS1 negatively regulated β-cell pathogenesis and diabetes via reduction of ROS production involving the Pdia4/Ndufs3 and Pdia4/p22 cascades.

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.

Protein disulfide isomerase A1 as a novel redox sensor in VEGFR2 signaling and angiogenesis

VEGFR2 signaling in endothelial cells (ECs) is regulated by reactive oxygen species (ROS) derived from NADPH oxidases (NOXs) and mitochondria, which plays an important role in postnatal angiogenesis. However, it remains unclear how highly diffusible ROS signal enhances VEGFR2 signaling and reparative angiogenesis. Protein disulfide isomerase A1 (PDIA1) functions as an oxidoreductase depending on the redox environment. We hypothesized that PDIA1 functions as a redox sensor to enhance angiogenesis. Here we showed that PDIA1 co-immunoprecipitated with VEGFR2 or colocalized with either VEGFR2 or an early endosome marker Rab5 at the perinuclear region upon stimulation of human ECs with VEGF. PDIA1 silencing significantly reduced VEGF-induced EC migration, proliferation and spheroid sprouting via inhibiting VEGFR2 signaling. Mechanistically, VEGF stimulation rapidly increased Cys-OH formation of PDIA1 via the NOX4-mitochondrial ROS axis. Overexpression of "redox-dead" mutant PDIA1 with replacement of the active four Cys residues with Ser significantly inhibited VEGF-induced PDIA1-CysOH formation and angiogenic responses via reducing VEGFR2 phosphorylation. Pdia1+/- mice showed impaired angiogenesis in developmental retina and Matrigel plug models as well as ex vivo aortic ring sprouting model. Study using hindlimb ischemia model revealed that PDIA1 expression was markedly increased in angiogenic ECs of ischemic muscles, and that ischemia-induced limb perfusion recovery and neovascularization were impaired in EC-specific Pdia1 conditional knockout mice. These results suggest that PDIA1 can sense VEGF-induced H2O2 signal via CysOH formation to promote VEGFR2 signaling and angiogenesis in ECs, thereby enhancing postnatal angiogenesis. The oxidized PDIA1 is a potential therapeutic target for treatment of ischemic vascular diseases.

The potential role of protein disulfide isomerases (PDIs) during parasitic infections: a focus on Leishmania spp

Leishmaniasis is a group of vector-borne diseases caused by intracellular protozoan parasites belonging to the genus Leishmania. Leishmania parasites can employ different and numerous sophisticated strategies, including modulating host proteins, cell signaling, and cell responses by parasite proteins, to change the infected host conditions to favor the parasite persistence and induce pathogenesis. In this sense, protein disulfide isomerases (PDIs) have been described as crucial proteins that can be modulated during leishmaniasis and affect the pathogenesis process. The effect of modulated PDIs can be investigated in both aspects, parasite PDIs and infected host cell PDIs, during infection. The information concerning PDIs is not sufficient in parasitology; however, this study aimed to provide data regarding the biological functions of such crucial proteins in parasites with a focus on Leishmania spp. and their relevant effects on the pathogenesis process. Although there are no clinical trial vaccines and therapeutic approaches, highlighting this information might be fruitful for the development of novel strategies based on PDIs for the management of parasitic diseases, especially leishmaniasis.

Sublethal and lethal Cd toxicity in soybean roots specifically affects the metabolome, Cd binding to proteins and cellular distribution of Cd

Soybean (Glycine max (L.) Merr.) plants were exposed to various Cd concentrations from background and low non-toxic (0.5-50 nM) via sublethally toxic (< 550 nM) to highly, ultimately lethally toxic (3 µM) concentrations. Plants were cultivated hydroponically for 10 weeks until pod development stage of the control plants. The threshold and mechanism of sublethal Cd toxicity was investigated by metabolomics and metalloproteomics (HPLC-ICP-MS) measuring metal binding to proteins in the harvested roots. Spatial distribution of Cd was revealed by µXRF-CT. Specific binding of Cd to proteins already at 50 nM Cd revealed the likely high-affinity protein binding targets in roots, identified by protein purification from natural abundance. This revealed allantoinase, aquaporins, peroxidases and protein disulfide isomerase as the most likely high-affinity targets of Cd binding. Cd was deposited in cortex cell vacuoles at sublethal and bound to the cell walls of the outer cortex and the vascular bundle at lethal Cd. Cd binding to proteins likely inhibits them, and possibly induces detoxification mechanisms, as verified by metabolomics: allantoic acid and allantoate increased due to sublethal Cd toxicity. Changes of the Cd binding pattern indicated a detoxification strategy at lower Cd, but saturated binding sites at higher Cd concentrations.

A discovery-based proteomics approach identifies protein disulphide isomerase (PDIA1) as a biomarker of β cell stress in type 1 diabetes

BACKGROUND

Stress responses within the β cell have been linked with both increased β cell death and accelerated immune activation in type 1 diabetes (T1D). At present, information on the timing and scope of these responses as well as disease-related changes in islet β cell protein expression during T1D development is lacking.

METHODS

Data independent acquisition-mass spectrometry was performed on islets collected longitudinally from NOD mice and NOD-SCID mice rendered diabetic through T cell adoptive transfer.

FINDINGS

In islets collected from female NOD mice at 10, 12, and 14 weeks of age, we found a time-restricted upregulation of proteins involved in stress mitigation and maintenance of β cell function, followed by loss of expression of protective proteins that heralded diabetes onset. EIF2 signalling and the unfolded protein response, mTOR signalling, mitochondrial function, and oxidative phosphorylation were commonly modulated pathways in both NOD mice and NOD-SCID mice rendered acutely diabetic by T cell adoptive transfer. Protein disulphide isomerase A1 (PDIA1) was upregulated in NOD islets and pancreatic sections from human organ donors with autoantibody positivity or T1D. Moreover, PDIA1 plasma levels were increased in pre-diabetic NOD mice and in the serum of children with recent-onset T1D compared to non-diabetic controls.

INTERPRETATION

We identified a core set of modulated pathways across distinct mouse models of T1D and identified PDIA1 as a potential human biomarker of β cell stress in T1D.

FUNDING

NIH (R01DK093954, DK127308, U01DK127786, UC4DK104166, R01DK060581, R01GM118470, and 5T32DK101001-09). VA Merit Award I01BX001733. JDRF (2-SRA-2019-834-S-B, 2-SRA-2018-493-A-B, 3-PDF-20016-199-A-N, 5-CDA-2022-1176-A-N, and 3-PDF-2017-385-A-N).

Mutation in protein disulfide isomerase A3 causes neurodevelopmental defects by disturbing endoplasmic reticulum proteostasis

Recessive gene mutations underlie many developmental disorders and often lead to disabling neurological problems. Here, we report identification of a homozygous c.170G>A (p.Cys57Tyr or C57Y) mutation in the gene coding for protein disulfide isomerase A3 (PDIA3, also known as ERp57), an enzyme that catalyzes formation of disulfide bonds in the endoplasmic reticulum, to be associated with syndromic intellectual disability. Experiments in zebrafish embryos show that PDIA3C57Y expression is pathogenic and causes developmental defects such as axonal disorganization as well as skeletal abnormalities. Expression of PDIA3C57Y in the mouse hippocampus results in impaired synaptic plasticity and memory consolidation. Proteomic and functional analyses reveal that PDIA3C57Y expression leads to dysregulation of cell adhesion and actin cytoskeleton dynamics, associated with altered integrin biogenesis and reduced neuritogenesis. Biochemical studies show that PDIA3C57Y has decreased catalytic activity and forms disulfide-crosslinked aggregates that abnormally interact with chaperones in the endoplasmic reticulum. Thus, rare disease gene variant can provide insight into how perturbations of neuronal proteostasis can affect the function of the nervous system.

Protein disulfide isomerases (PDIs) negatively regulate ebolavirus structural glycoprotein expression in the endoplasmic reticulum (ER) via the autophagy-lysosomal pathway

Zaire ebolavirus (EBOV) causes a severe hemorrhagic fever in humans and non-human primates with high morbidity and mortality. EBOV infection is dependent on its structural glycoprotein (GP), but high levels of GP expression also trigger cell rounding, detachment, and downregulation of many surface molecules that is thought to contribute to its high pathogenicity. Thus, EBOV has evolved an RNA editing mechanism to reduce its GP expression and increase its fitness. We now report that the GP expression is also suppressed at the protein level in cells by protein disulfide isomerases (PDIs). Although PDIs promote oxidative protein folding by catalyzing correct disulfide formation in the endoplasmic reticulum (ER), PDIA3/ERp57 adversely triggered the GP misfolding by targeting GP cysteine residues and activated the unfolded protein response (UPR). Abnormally folded GP was targeted by ER-associated protein degradation (ERAD) machinery and, unexpectedly, was degraded via the macroautophagy/autophagy-lysosomal pathway, but not the proteasomal pathway. PDIA3 also decreased the GP expression from other ebolavirus species but increased the GP expression from Marburg virus (MARV), which is consistent with the observation that MARV-GP does not cause cell rounding and detachment, and MARV does not regulate its GP expression via RNA editing during infection. Furthermore, five other PDIs also had a similar inhibitory activity to EBOV-GP. Thus, PDIs negatively regulate ebolavirus glycoprotein expression, which balances the viral life cycle by maximizing their infection but minimizing their cellular effect. We suggest that ebolaviruses hijack the host protein folding and ERAD machinery to increase their fitness via reticulophagy during infection.Abbreviations: 3-MA: 3-methyladenine; 4-PBA: 4-phenylbutyrate; ACTB: β-actin; ATF: activating transcription factor; ATG: autophagy-related; BafA1: bafilomycin A1; BDBV: Bundibugyo ebolavirus; CALR: calreticulin; CANX: calnexin; CHX: cycloheximide; CMA: chaperone-mediated autophagy; ConA: concanamycin A; CRISPR: clusters of regularly interspaced short palindromic repeats; Cas9: CRISPR-associated protein 9; dsRNA: double-stranded RNA; EBOV: Zaire ebolavirus; EDEM: ER degradation enhancing alpha-mannosidase like protein; EIF2AK3/PERK: eukaryotic translation initiation factor 2 alpha kinase 3; Env: envelope glycoprotein; ER: endoplasmic reticulum; ERAD: ER-associated protein degradation; ERN1/IRE1: endoplasmic reticulum to nucleus signaling 1; GP: glycoprotein; HA: hemagglutinin; HDAC6: histone deacetylase 6; HMM: high-molecular-mass; HIV-1: human immunodeficiency virus type 1; HSPA5/BiP: heat shock protein family A (Hsp70) member 5; IAV: influenza A virus; IP: immunoprecipitation; KIF: kifenesine; Lac: lactacystin; LAMP: lysosomal associated membrane protein; MAN1B1/ERManI: mannosidase alpha class 1B member 1; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MARV: Marburg virus; MLD: mucin-like domain; NHK/SERPINA1: alpha1-antitrypsin variant null (Hong Kong); NTZ: nitazoxanide; PDI: protein disulfide isomerase; RAVV: Ravn virus; RESTV: Reston ebolavirus; SARS-CoV: severe acute respiratory syndrome coronavirus; SBOV: Sudan ebolavirus; sGP: soluble GP; SQSTM1/p62: sequestosome 1; ssGP: small soluble GP; TAFV: Taï Forest ebolavirus; TIZ: tizoxanide; TGN: thapsigargin; TLD: TXN (thioredoxin)-like domain; Ub: ubiquitin; UPR: unfolded protein response; VLP: virus-like particle; VSV: vesicular stomatitis virus; WB: Western blotting; WT: wild-type; XBP1: X-box binding protein 1.

Protection against glutathione depletion-associated oxidative neuronal death by neurotransmitters norepinephrine and dopamine: Protein disulfide isomerase as a mechanistic target for neuroprotection

Oxidative stress is extensively involved in neurodegeneration. Clinical evidence shows that keeping the mind active through mentally-stimulating physical activities can effectively slow down the progression of neurodegeneration. With increased physical activities, more neurotransmitters would be released in the brain. In the present study, we investigated whether some of the released neurotransmitters might have a beneficial effect against oxidative neurodegeneration in vitro. Glutamate-induced, glutathione depletion-associated oxidative cytotoxicity in HT22 mouse hippocampal neuronal cells was used as an experimental model. We showed that norepinephrine (NE, 50 µM) or dopamine (DA, 50 µM) exerted potent protective effect against glutamate-induced cytotoxicity, but this effect was not observed when other neurotransmitters such as histamine, γ-aminobutyric acid, serotonin, glycine and acetylcholine were tested. In glutamate-treated HT22 cells, both NE and DA significantly suppressed glutathione depletion-associated mitochondrial dysfunction including mitochondrial superoxide accumulation, ATP depletion and mitochondrial AIF release. Moreover, both NE and DA inhibited glutathione depletion-associated MAPKs activation, p53 phosphorylation and GADD45α activation. Molecular docking analysis revealed that NE and DA could bind to protein disulfide isomerase (PDI). In biochemical enzymatic assay in vitro, NE and DA dose-dependently inhibited the reductive activity of PDI. We further revealed that the protective effect of NE and DA against glutamate-induced oxidative cytotoxicity was mediated through inhibition of PDI-catalyzed dimerization of the neuronal nitric oxide synthase. Collectively, the results of this study suggest that NE and DA may have a protective effect against oxidative neurodegeneration through inhibition of protein disulfide isomerase and the subsequent activation of the MAPKs‒p53‒GADD45α oxidative cascade.

Endoplasmic reticulum oxidoreductin provides resilience against reductive stress and hypoxic conditions by mediating luminal redox dynamics

Oxidative protein folding in the endoplasmic reticulum (ER) depends on the coordinated action of protein disulfide isomerases and ER oxidoreductins (EROs). Strict dependence of ERO activity on molecular oxygen as the final electron acceptor implies that oxidative protein folding and other ER processes are severely compromised under hypoxia. Here, we isolated viable Arabidopsis thaliana ero1 ero2 double mutants that are highly sensitive to reductive stress and hypoxia. To elucidate the specific redox dynamics in the ER in vivo, we expressed the glutathione redox potential (EGSH) sensor Grx1-roGFP2iL-HDEL with a midpoint potential of -240 mV in the ER of Arabidopsis plants. We found EGSH values of -241 mV in wild-type plants, which is less oxidizing than previously estimated. In the ero1 ero2 mutants, luminal EGSH was reduced further to -253 mV. Recovery to reductive ER stress induced by dithiothreitol was delayed in ero1 ero2. The characteristic signature of EGSH dynamics in the ER lumen triggered by hypoxia was affected in ero1 ero2 reflecting a disrupted balance of reductive and oxidizing inputs, including nascent polypeptides and glutathione entry. The ER redox dynamics can now be dissected in vivo, revealing a central role of EROs as major redox integrators to promote luminal redox homeostasis.

PDIA4, a novel ER stress chaperone, modulates adiponectin expression and inflammation in adipose tissue

Increasing evidence supporting a causal link between obesity and endoplasmic reticulum (ER) stress in adipose tissue is being reported. Protein disulfide isomerase 4 (PDIA4) is a novel ER chaperone involved in the pancreatic β-cells pathogenesis in diabetes. However, the role of PDIA4 in obesity progression remains poorly understood. To assess the relationship between PDIA4, adiponectin, and metformin, we used the palmitate-induced inflammation in hypertrophic adipocytes and the high-fat diet-induced obesity mouse model. Our results revealed that palmitate-induced hypertrophic adipocytes exhibit obesity-associated conditions such as increased lipid accumulation, inflammation, and reduced glucose uptake. Pharmacological and genetic inhibition of PDIA4 significantly reverses these obesity-associated conditions in adipocytes. PDIA4 mechanistically promotes obesity progression via adiponectin downregulation. Furthermore, metformin modulates PDIA4 and adiponectin expression and improves obesity-associated conditions in both in vitro adipocytes and in vivo mouse models. Serum PDIA4 concentrations are also associated with body mass index, adiponectin, triglycerides, and inflammatory cytokines in humans. This is the first study demonstrating that PDIA4 modulates adipocytes by downregulating adiponectin. Moreover, metformin may serve as a potential therapeutic for preventing obesity via PDIA4-targeting.

P4HB UFMylation regulates mitochondrial function and oxidative stress

UFMylation is a ubiquitin-like modification which attaches the ubiquitin-fold modifier 1 to target proteins. To date, only a few UFMylation targets have been identified. In the current study, we demonstrated that P4HB is a new target protein for UFMylation and it can be UFMylated at three lysine residues in the form of mono-UFMylation. P4HB has oxidoreductase, chaperone and isomerase effects. It presents in the endoplasmic reticulum, mitochondria and cytosol. Next, we generated a stable HepG2 cell line, the hepatocellular cells, with defective P4HB UFMylation. Our data show that P4HB UFMylation defect promotes P4HB protein degradation via the ubiquitin-proteasome pathway. Defective P4HB UFMylation causes mitochondrial function damage, oxidative stress, and endoplasmic reticulum stress in HepG2 cells. These effects are more obvious when treating HepG2 cells with palmitic acid, which is frequently used as one of the cell models of non-alcoholic fatty liver disease (NAFLD). Our results identify UFMylation as a key post-translational modification for the maintenance of P4HB stability and biological functions in HepG2 cells, and point to P4HB UFMylation as a potential direction in the study of NAFLD.

Identification of Antithrombotic Natural Products Targeting the Major Substrate Binding Pocket of Protein Disulfide Isomerase

Protein disulfide isomerase (PDI) is a vital oxidoreductase. Extracellular PDI promotes thrombus formation but does not affect physiological blood hemostasis. Inhibition of extracellular PDI has been demonstrated as a promising strategy for antithrombotic treatment. Herein, we focused on the major substrate binding site, a unique pocket in the PDI b' domain, and identified four natural products binding to PDI by combining virtual screening with tryptophan fluorescence-based assays against a customized natural product library. These hits all directly bound to the PDI-b' domain and inhibited the reductase activity of PDI. Among them, galangin showed the most prominent potency (5.9 μM) against PDI and as a broad-spectrum inhibitor for vascular thiol isomerases. In vivo studies manifested that galangin delayed the time of blood vessel occlusion in an electricity-induced mouse thrombosis model. Molecular docking and dynamics simulation further revealed that the hydroxyl-substituted benzopyrone moiety of galangin deeply inserted into the interface between the PDI-b' substrate-binding pocket and the a' domain. Together, these findings provide a potential antithrombotic drug candidate and demonstrate that the PDI b' domain is a critical domain for inhibitor development. Besides, we also report an innovative high-throughput screening method for the rapid discovery of PDI b' targeted inhibitors.

Protein disulfide isomerase modulation of TRPV1 controls heat hyperalgesia in chronic pain

Protein disulfide isomerase (PDI) plays a key role in maintaining cellular homeostasis by mediating protein folding via catalyzing disulfide bond formation, breakage, and rearrangement in the endoplasmic reticulum. Increasing evidence suggests that PDI can be a potential treatment target for several diseases. However, the function of PDI in the peripheral sensory nervous system is unclear. Here we report the expression and secretion of PDI from primary sensory neurons is upregulated in inflammatory and neuropathic pain models. Deletion of PDI in nociceptive DRG neurons results in a reduction in inflammatory and neuropathic heat hyperalgesia. We demonstrate that secreted PDI activates TRPV1 channels through oxidative modification of extracellular cysteines of the channel, indicating that PDI acts as an unconventional positive modulator of TRPV1. These findings suggest that PDI in primary sensory neurons plays an important role in development of heat hyperalgesia and can be a potential therapeutic target for chronic pain.

Correlation between low expression of protein disulfide isomerase A3 and lymph node metastasis in papillary thyroid carcinoma and poor prognosis: a clinicopathological study of 1,139 cases with long-term follow-up

The incidence of papillary thyroid carcinoma (PTC) is increasing worldwide. The biomarkers to identify aggressive types of PTC are limited, illustrating the need to establish reliable novel biomarkers. Protein disulfide isomerase A3 (PDIA3) is a chaperone protein that modulates the folding of newly synthesized glycoproteins and stress-responsive proteins in the endoplasmic reticulum. Although the role of PDIA3 in various cancers such as breast, uterine cervix, head and neck, and gastrointestinal tract has been examined, its expression in thyroid cancer has not been reported. We retrospectively reviewed accumulated data with long-term follow-up of 1,139 PTC patients, and investigated the correlation between immunohistochemical expression of PDIA3 in PTC patients and clinicopathological features and prognosis. PDIA3 expression was significantly lower in PTCs compared to normal thyroid tissues (NTT; n = 80, p = 0.002). In PTCs, correlation between low PDIA3 expression and lymph node metastasis (p = 0.018) and the number of positive nodes (p = 0.004) was observed. Patients with low PDIA3 expression exhibited worse cause-specific survival compared to those with high PDIA3 expression (p = 0.013). Our findings indicate that low PDIA3 expression is related to poor clinical outcome in PTC patients, and that PDIA3 may potentially be a novel ancillary biomarker. Further clarification of the biological role of PDIA3 in PTC is warranted for the future clinical application.

One-Pot Chemical Protein Synthesis Utilizing Fmoc-Masked Selenazolidine to Address the Redox Functionality of Human Selenoprotein F

Human SELENOF is an endoplasmic reticulum (ER) selenoprotein that contains the redox active motif CXU (C is cysteine and U is selenocysteine), resembling the redox motif of thiol-disulfide oxidoreductases (CXXC). Like other selenoproteins, the challenge in accessing SELENOF has somewhat limited its full biological characterization thus far. Here we present the one-pot chemical synthesis of the thioredoxin-like domain of SELENOF, highlighted by the use of Fmoc-protected selenazolidine, native chemical ligations and deselenization reactions. The redox potential of the CXU motif, together with insulin turbidimetric assay suggested that SELENOF may catalyze the reduction of disulfides in misfolded proteins. Furthermore, we demonstrate that SELENOF is not a protein disulfide isomerase (PDI)-like enzyme, as it did not enhance the folding of the two protein models; bovine pancreatic trypsin inhibitor and hirudin. These studies suggest that SELENOF may be responsible for reducing the non-native disulfide bonds of misfolded glycoproteins as part of the quality control system in the ER.

Inhibitors of ERp44, PDIA1, and AGR2 induce disulfide-mediated oligomerization of Death Receptors 4 and 5 and cancer cell death

Breast cancer mortality remains unacceptably high, indicating a need for safer and more effective therapeutic agents. Disulfide bond Disrupting Agents (DDAs) were previously identified as a novel class of anticancer compounds that selectively kill cancers that overexpress the Epidermal Growth Factor Receptor (EGFR) or its family member HER2. DDAs kill EGFR+ and HER2+ cancer cells via the parallel downregulation of EGFR, HER2, and HER3 and activation/oligomerization of Death Receptors 4 and 5 (DR4/5). However, the mechanisms by which DDAs mediate these effects are unknown. Affinity purification analyses employing biotinylated-DDAs reveal that the Protein Disulfide Isomerase (PDI) family members AGR2, PDIA1, and ERp44 are DDA target proteins. Further analyses demonstrate that shRNA-mediated knockdown of AGR2 and ERp44, or expression of ERp44 mutants, enhance basal DR5 oligomerization. DDA treatment of breast cancer cells disrupts PDIA1 and ERp44 mixed disulfide bonds with their client proteins. Together, the results herein reveal DDAs as the first small molecule, active site inhibitors of AGR2 and ERp44, and demonstrate roles for AGR2 and ERp44 in regulating the activity, stability, and localization of DR4 and DR5, and activation of Caspase 8.

Tissue Transglutaminase but Not Microbial Transglutaminase Is Inhibited by Exogenous Oxidative Substances in Celiac Disease

Enzymatic modification of gliadin peptides by human transglutaminase 2 (TG2) is a central step in celiac disease (CD) pathogenesis. Microbial transglutaminase (mTG) mimics the enzymatic function of TG2 and might play a role in CD. TG2 is inhibited by endogenous oxidative endoplasmic reticulum-resident protein 57 (ERp57), but data about mTG are lacking. We investigated the localization of ERp57 in duodenal biopsies and examined inhibition of TG2, and mTG by competitive, and oxidative molecules. Localization of ERp57 was investigated in duodenal biopsies from CD, and control patients by electron microcopy. Inhibition of TG2 and mTG was analyzed on an in vitro level using a photometric assay. ERp57 was observed within the lamina propria and its abundance within the endoplasmic reticulum (ER) was reduced in CD patients. TG2 was oxidatively inhibited by up to 95% by PX12 (p < 0.001) and L-cystine (p < 0.001), whereas mTG remained unaffected. The reduced presence of ERp57 within the ER of CD biopsies suggests a regulatory function of this protein within CD pathogenesis. PX12 and L-cystine oxidatively inhibit TG2 and might serve as treatment options in CD. mTG is poorly regulated and could contribute to the accumulation of immunogenic peptides within the gut with potential pathogenic effects.

Roles of the protein disulphide isomerases AccPDIA1 and AccPDIA3 in response to oxidant stress in Apis cerana cerana

Protein disulphide isomerase (PDI) plays an important role in a variety of physiological processes through its oxidoreductase activity and molecular chaperone activity. In this study, we cloned two PDI family members, AccPDIA1 and AccPDIA3, from Apis cerana cerana. AccPDIA1 and AccPDIA3 had typical sequence features of PDI family members and were constitutively expressed in A. cerana cerana. The expression levels of AccPDIA1 and AccPDIA3 were generally upregulated after treatment with a variety of environmental stress factors. Inhibition assays showed that E. coli expressing recombinant AccPDIA1 and AccPDIA3 proteins was more resistant to oxidative stress than control E. coli. In addition, silencing AccPDIA1 or AccPDIA3 in A. cerana cerana resulted in significant changes in the expression levels of several antioxidant-related genes as well as the enzymatic activities of peroxidase (POD), superoxide dismutase (SOD) and catalase (CAT) and reduced the survival rate of A. cerana cerana under oxidative stress caused by high temperature. In conclusion, our results suggest that AccPDIA1 and AccPDIA3 may play important roles in the antioxidant activities of A. cerana cerana.

Two protein disulfide isomerase subgroups work synergistically in catalyzing oxidative protein folding

Disulfide bonds play essential roles in the folding of secretory and plasma membrane proteins in the endoplasmic reticulum (ER). In eukaryotes, protein disulfide isomerase (PDI) is an enzyme catalyzing the disulfide bond formation and isomerization in substrates. The Arabidopsis (Arabidopsis thaliana) genome encodes diverse PDIs including structurally distinct subgroups PDI-L and PDI-M/S. It remains unclear how these AtPDIs function to catalyze the correct disulfide formation. We found that one Arabidopsis ER oxidoreductin-1 (Ero1), AtERO1, can interact with multiple PDIs. PDI-L members AtPDI2/5/6 mainly serve as an isomerase, while PDI-M/S members AtPDI9/10/11 are more efficient in accepting oxidizing equivalents from AtERO1 and catalyzing disulfide bond formation. Accordingly, the pdi9/10/11 triple mutant exhibited much stronger inhibition than pdi1/2/5/6 quadruple mutant under dithiothreitol treatment, which caused disruption of disulfide bonds in plant proteins. Furthermore, AtPDI2/5 work synergistically with PDI-M/S members in relaying disulfide bonds from AtERO1 to substrates. Our findings reveal the distinct but overlapping roles played by two structurally different AtPDI subgroups in oxidative protein folding in the ER.

Calreticulin and PDIA3, two markers of endoplasmic reticulum stress, are associated with metabolic alterations and insulin resistance in pediatric obesity: A pilot study

Our aim was to evaluate the markers of endoplasmic reticulum (ER) stress among children and adolescents with obesity in relation to metabolic alterations. Calreticulin (CALR) and PDIA3 circulating levels were assessed on 52 pediatric subjects-26 patients with obesity and 26 normal weight controls (4-18 years)-enrolled in a pilot study. Clinical and metabolic evaluations were performed (BMI-SDS, insulin, and glucose at fasting and during an oral glucose tolerance test, lipid profile, blood pressure), and metabolic syndrome was detected. PDIA3 was higher (p < 0.02) and CALR slightly higher in children with obesity than in controls. PDIA3 was related positively to the Tanner stages. Both PDIA3 and CALR were positively associated with insulin resistance, cholesterol, and triglycerides and the number of criteria identifying metabolic syndrome and negatively with fasting and post-challenge insulin sensitivity. Our preliminary findings suggest the existence of a link between ER stress and metabolic changes behind obesity complications even at the pediatric age. CALR and PDIA3 could be early markers of insulin resistance and dyslipidemia-related ER stress useful to stratify patients at high risk of further complications.