Protein Disulfide Isomerase and Its Potential Function on Endoplasmic Reticulum Quality Control in Diatom Phaeodactylum tricornutum

PDI is a molecular chaperone and plays an important role in Endoplasmic Reticulum quality control (ERQC).PDI participates in the refolding of the misfolded/unfolded proteins to maintain cellular homeostasis under differentstresses. However, bioinformatic characteristics and potential functions of PDIs in diatom Phaeodactylumtricornutum (Pt) are still unknown so far. Hence, the genome-wide characteristics of PtPDI proteins in P. tricornutumwere first studied via bioinformatic and transcriptomic methods. 42 PtPDI genes were identified from thegenome of P. tricornutum. The motif, protein structure, classification, number of introns, phylogenetic relationship,and the expression level of 42 PtPDI genes under the tunicamycin stress were analyzed. A pair of tandemduplicated genes (PtPDI15 and PtPDI18) was observed in P. tricornutum. The 42 PtPDIs with different genecharacteristics were divided into three independent clades, indicating different evolutional relationships and functionsof these PtPDIs. The 14 up-regulated PtPDI genes under the tunicamycin treatment might have a positiveeffect on the ER quality control of the unfolded/misfolded proteins, while the 7 down-regulated PtPDIs mightnegatively affect the ERQC. The characteristics of all 42 PtPDIs and their proposed working model here providea comprehensive understanding of the PtPDIs gene family. The differential expression of 21 PtPDIs will be usefulfor further functional study in the ERQC.

Protein Disulfide Isomerase A2 Is Correlated with Immune Infiltrates and Is a Novel Prognostic Biomarker in Glioma Patients

Objective Protein disulfide isomerase A2(PDIA2),a member of the protein disulfide isomerase family,plays a key role in the folding of nascent proteins in the endoplasmic reticulum by forming disulfide bonds,together with enzymes such as thiol isomerase,oxidase,and reductase.This study investigated the clinical significance and potential functions of PDIA2 in glioma.Methods The expression of PDIA2 in gliomas was explored using The Cancer Genome Atlas and Gene Expression Omnibus databases.We analyzed the clinical characteristics of glioma patients and the prognostic and diagnostic value of PDIA2 expression.Kaplan-Meier and Cox regression analyses were used to examine the effect of PDIA2 expression on overall survival,progression-free interval,and disease-specific survival.Furthermore,we performed Gene Set Enrichment Analysis and immune infiltration analysis to investigate the functions of PDIA2.PDIA2 mRNA and protein expression was evaluated in cell lines and glioma tissues.Results PDIA2 was expressed at low levels in glioma patients.Kaplan-Meier survival analysis showed that glioma patients with low PDIA2 levels had a worse prognosis than those with high PDIA2 levels.Receiver operating characteristic curve analysis indicated the diagnostic and prognostic ability of PDIA2(area under the curve=0.918).Pathways associated with PD1,PI3K/AKT,cancer immunotherapy via PD1 blockade,Fceri-mediated NF-kB activation,FOXM1,and DNA repair were enriched in glioma patients with low levels of PDIA2.PDIA2 expression levels were negatively correlated with immune cell infiltrate levels.Conclusion PDIA2 levels are significantly downregulated in glioma.PDIA2 expression may be a potential biomarker for the diagnosis and prognosis of glioma patients.

Evidence That Protein Disulfide Isomerase in Yeast Saccharomyces cerevisiae Is Transported from the ER to the Golgi Apparatus

Newly synthesized membrane and secretory proteins in cells undergo folding in the endoplasmic reticulum with the introduction of disulfide bonds and acquire the correct three-dimensional structure. Disulfide bonds are especially important for protein folding. It has been thought that formation of protein disulfide bonds in eukaryotes is mainly carried out by an enzyme called protein disulfide isomerase. Proteins, bearing the C-terminus of amino acids sequences with His-Asp-Glu-Leu (HDEL) sequence in yeast, in the endoplasmic reticulum (ER), which is a eukaryotic cellular organelle involved in protein synthesis, processing, and transport, have been considered to recycle between ER and Golgi apparatus. The proposal for this recycling model derives from the study of an HDEL-tagged fusion protein. Here, the localization and oligosaccharide modification of protein disulfide isomerase were investigated in yeast, and showed the first direct evidence that this intrinsic ER protein transports from ER to Golgi. Results suggest that this native protein is also accessible to post-ER enzymes, and yet accumulates in the ER.

Protein Disulfide Isomerase 2 of Chlamydomonas reinhardtii Is Involved in Circadian Rhythm Regulation

Protein disulfide isomerases （PDIs） are known to play important roles in the folding of nascent proteins and in the formation of disulfide bonds. Recently, we identified a PDI from Chlamydomonas reinhardtii （CrPDI2） by a mass spectrometry approach that is specifically enriched by heparin affinity chromatography in samples taken during the night phase. Here, we show that the recombinant CrPDI2 is a redox-active protein. It is reduced by thioredoxin reductase and catalyzes itself the reduction of insulin chains and the oxidative refolding of scrambled RNase A. By immunoblots, we confirm a high-amplitude change in abundance of the heparin-bound CrPDI2 during subjective night. Interestingly, we find that CrPDI2 is present in protein complexes of different sizes at both day and night. Among three identified interac- tion partners, one （a 2-cys peroxiredoxin） is present only during the night phase. To study a potential function of CrPDI2 within the circadian system, we have overexpressed its gene. Two transgenic lines were used to measure the rhythm of phototaxis~ In the transgenic strains, a change in the acrophase was observed. This indicates that CrPDI2 is involved in the circadian signaling pathway and, together with the night phase-specific interaction of CrPDI2 and a peroxiredoxin, these findings suggest a close coupling of redox processes and the circadian clock in C. reinhardtii.

Stress protein expression in early phase spinal cord ischemia/reperfusion injury

Spinal cord ischemia/reperfusion injury is a stress injury to the spinal cord. Our previous studies using differential proteomics identified 21 differentially expressed proteins （n 〉 2） in rabbits with spinal cord ischemia/reperfusion injury. Of these proteins, stress-related proteins included protein disulfide isomerase A3, stress-induced-phosphoprotein 1 and heat shock cognate protein 70. In this study, we established New Zealand rabbit models of spinal cord ischemia/reperfusion injury by abdominal aorta occlusion. Results demonstrated that hind limb function initially improved after spinal cord ischemia/reperfusion injury, but then deteriorated. The pathological morphology of the spinal cord became aggravated, but lessened 24 hours after reperfusion. However, the numbers of motor neurons and interneurons in the spinal cord gradually decreased. The expression of protein disulfide isomerase A3, stress-induced-phosphoprotein 1 and heat shock cognate protein 70 was induced by ischemia/reperfusion injury. The expression of these proteins increased within 12 hours after reperfusion, and then decreased, reached a minimum at 24 hours, but subsequently increased again to similar levels seen at 6-12 hours, showing a characterization of induction-inhibition-induc- tion. These three proteins were expressed only in cytoplasm but not in the nuclei. Moreover, the expression was higher in interneurons than in motor neurons, and the survival rate of interneurons was greater than that of motor neurons. It is assumed that the expression of stress-related proteins exhibited a protective effect on neurons.

A critical role of the thioredoxin domain containing protein 5(TXNDC5) in redox homeostasis and cancer development

Correct folding of nascent peptides occurs in the endoplasmic reticulum(ER).It is a complicate process primarily accomplished by the coordination of multiple redox proteins including members of the protein disulfide isomerase(PDI)family.As a critical member of the PDI family,thioredoxin domain containing protein 5(TXNDC5)assists the folding of newly synthesized peptides to their mature form through series of disulfide bond exchange reactions.Interestingly,TXNDC5 is frequently found overexpressed in specimens of many human diseases including various types of cancer.In this review,we summarized the biochemical function of TXNDC5 in mammalian cells and the recent progress on the understanding of its role and molecular mechanisms in cancer development.Findings of TXNDC5 in the activation of intracellular signaling pathways,stimulation of cell growth&proliferation,facilitation of cell survival and modulation of extracellular matrix to affect cancer cell invasion and metastasis are reviewed.These published studies suggest that strategies of targeting TXNDC5 can be developed as potentially valuable methods for the treatment of certain types of cancer in patients.