Role of extracellular molecular chaperones in the folding of oxidized proteins. Refolding of colloidal thyroglobulin by protein disulfide isomerase and immunoglobulin heavy chain-binding protein

Modulation of Protein Disulfide Isomerase Functions by Localization: The Example of the Anterior Gradient Family

Significance: Oxidative folding within the endoplasmic reticulum (ER) introduces disulfide bonds into nascent polypeptides, ensuring proteins' stability and proper functioning. Consequently, this process is critical for maintaining proteome integrity and overall health. The productive folding of thousands of secretory proteins requires stringent quality control measures, such as the unfolded protein response (UPR) and ER-Associated Degradation (ERAD), which contribute significantly to maintaining ER homeostasis. ER-localized protein disulfide isomerases (PDIs) play an essential role in each of these processes, thereby contributing to various aspects of ER homeostasis, including maintaining redox balance, proper protein folding, and signaling from the ER to the nucleus. Recent Advances: Over the years, there have been increasing reports of the (re)localization of PDI family members and other ER-localized proteins to various compartments. A prime example is the anterior gradient (AGR) family of PDI proteins, which have been reported to relocate to the cytosol or the extracellular environment, acquiring gain of functions that intersect with various cellular signaling pathways. Critical Issues: Here, we summarize the functions of PDIs and their gain or loss of functions in non-ER locations. We will focus on the activity, localization, and function of the AGR proteins: AGR1, AGR2, and AGR3. Future Directions: Targeting PDIs in general and AGRs in particular is a promising strategy in different human diseases. Thus, there is a need for innovative strategies and tools aimed at targeting PDIs; those strategies should integrate the specific localization and newly acquired functions of these PDIs rather than solely focusing on their canonical roles.

Integrative analysis of genomic and transcriptomic alterations of AGR2 and AGR3 in cancer

The AGR2 and AGR3 genes have been shown by numerous groups to be functionally associated with adenocarcinoma progression and metastasis. In this paper, we explore the data available in databases concerning genomic and transcriptomic features of these two genes: the NCBI dbSNP database was used to explore the presence and roles of constitutional SNPs, and the NCI, Cancer Cell Line Encyclopedia (CCLE) and TCGA databases were used to explore somatic mutations and copy number variations (CNVs), as well as mRNA expression of these genes in human cancer cell lines and tumours. Relationships of AGR2/3 expression with whole-genome mRNA expression and cancer features (i.e. mutations and CNVs of oncogenes and tumour suppressor genes (TSG)) were established using the CCLE and TCGA databases. In addition, the CCLE data concerning CRISPR gene extinction screens (Achilles project) of these two genes and a panel of oncogenes and TSG were explored. We observed that no functional polymorphism or recurrent mutation could be detected in AGR2 or AGR3. The expression of these genes was positively correlated with the expression of epithelial genes and inversely correlated with that of mesenchymal genes. It was also significantly associated with several cancer features, such as TP53 or SMAD4 mutations, depending on the gene and the cancer type. In addition, the CRISPR screens revealed the absence of cell fitness modification upon gene extinction, in contrast with oncogenes (cell fitness decrease) and TSG (cell fitness increase). Overall, these explorations revealed that AGR2 and AGR3 proteins appear as common non-genetic evolutionary factors in the process of human tumorigenesis.

Proteomic profiling of thyroid tissue in patients with obesity and benign diffuse goiter

Goiter is a term to describe the enlargement of the thyroid gland. The pathophysiology and molecular changes behind development of diffuse benign goiter remains unclear. The present study targeted to identify and describe the alterations in the thyroid tissue proteome from patients (obese euthyroid) with benign diffuse goiter (BDG) using proteomics approach. Thyroid tissue samples, from 7 age and sex matched, patients with BDG and 7 controls were obtained at the time of surgery. An untargeted proteomic analysis of the thyroid tissue was performed out utilizing two-dimensional difference (2D-DIGE) in gel electrophoresis followed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) for identification of the proteins. Progenesis software was used to identify changes in expression of tissue proteins and found statistically significant differences in abundance in a total of 90 proteins, 46 up and 44 down (1.5-fold change, ANOVA, p ≤ 0.05) in BDG compared to the control group. Bioinformatic analysis using Ingenuity Pathway Analysis (IPA) identified dysregulation of signalling pathways linked to ERK1/2, Glutathione peroxidase and NADPH oxidase associated to organismal injury and abnormalities, endocrine system disorders and cancer. The thyroid tissue proteome in patients with BDG revealed a significant decrease in thyroglobulin along with dysregulation of glycolysis and an increase in prooxidant peroxidase enzymes. Dysregulation of metabolic pathways related to glycolysis, redox proteins, and the proteins associated with maintaining the cytoskeletal structure of the thyrocytes was also identified.

The Anterior GRadient (AGR) family proteins in epithelial ovarian cancer

Epithelial ovarian cancer (EOC) is the most common gynecologic disorder. Even with the recent progresses made towards the use of new therapeutics, it still represents the most lethal gynecologic malignancy in women from developed countries.

The discovery of the anterior gradient proteins AGR2 and AGR3, which are highly related members belonging to the protein disulfide isomerase (PDI) family, attracted researchers’ attention due to their putative involvement in adenocarcinoma development. This review compiles the current knowledge on the role of the AGR family and the expression of its members in EOC and discusses the potential clinical relevance of AGR2 and AGR3 for EOC diagnosis, prognosis, and therapeutics.

A better understanding of the role of the AGR family may thus provide new handling avenues for EOC patients.

Pathophysiological roles of cell surface and extracellular protein disulfide isomerase and their molecular mechanisms

Protein disulfide isomerase (PDI) is the prototypic member of the thiol isomerase family that catalyses disulfide bond rearrangement. Initially identified in the endoplasmic reticulum as folding catalysts, PDI and other members in its family have also been widely reported to reside on the cell surface and in the extracellular matrix. Although how PDI is exported and retained on the cell surface remains a subject of debate, this unique pool of PDI is developing into an important mechanism underlying the redox regulation of protein sulfhydryls that are critical for the cellular activities under various disease conditions. This review aims to provide an overview of the pathophysiological roles of surface and extracellular PDI and their underlying molecular mechanisms. Understanding the involvement of extracellular PDI in these diseases will advance our knowledge in the molecular aetiology to facilitate the development of novel pharmacological strategies by specifically targeting PDI in extracellular compartments.

In silico approach to predict pancreatic β-cells classically secreted proteins

Pancreatic β-cells, residents of the islets of Langerhans, are the unique insulin-producers in the body. Their physiology is a topic of intensive studies aiming to understand the biology of insulin production and its role in diabetes pathology. However, investigations about these cells' subset of secreted proteins, the secretome, are surprisingly scarce and a list describing islet/β-cell secretome upon glucose-stimulation is not yet available. In silico predictions of secretomes are an interesting approach that can be employed to forecast proteins likely to be secreted. In this context, using the rationale behind classical secretion of proteins through the secretory pathway, a Python tool capable of predicting classically secreted proteins was developed. This tool was applied to different available proteomic data (human and rodent islets, isolated β-cells, β-cell secretory granules, and β-cells supernatant), filtering them in order to selectively list only classically secreted proteins. The method presented here can retrieve, organize, search and filter proteomic lists using UniProtKB as a central database. It provides analysis by overlaying different sets of information, filtering out potential contaminants and clustering the identified proteins into functional groups. A range of 70-92% of the original proteomes analyzed was reduced generating predicted secretomes. Islet and β-cell signal peptide-containing proteins, and endoplasmic reticulum-resident proteins were identified and quantified. From the predicted secretomes, exemplary conservational patterns were inferred, as well as the signaling pathways enriched within them. Such a technique proves to be an effective approach to reduce the horizon of plausible targets for drug development or biomarkers identification.

Protein Disulfide Isomerases Regulate IgE-Mediated Mast Cell Responses and Their Inhibition Confers Protective Effects During Food Allergy

The thiol isomerase, protein disulfide isomerase (PDI), plays important intracellular roles during protein folding, maintaining cellular function and viability. Recent studies suggest novel roles for extracellular cell surface PDI in enhancing cellular activation and promoting their function. Moreover, a number of food-derived substances have been shown to regulate cellular PDI activity and alter disease progression. We hypothesized that PDI may have similar roles during mast cell-mediated allergic responses and examined its effects on IgE-induced mast cell activity during cell culture and food allergy. Mast cells were activated via IgE and antigen and the effects of PDI inhibition on mast cell activation were assessed. The effects of PDI blockade in vivo were examined by treating mice with the irreversible PDI inhibitor, PACMA-31, in an ovalbumin-induced model of food allergy. The role of dietary PDI modulators was investigated using various dietary compounds including curcumin and quercetin-3-rutinoside (rutin). PDI expression was observed on resting mast cell surfaces, intracellularly, and in the intestines of allergic mice. Furthermore, enhanced secretion of extracellular PDI was observed on mast cell membranes during IgE and antigen activation. Insulin turbidimetric assays demonstrated that curcumin is a potent PDI inhibitor and pre-treatment of mast cells with curcumin or established PDI inhibitors such as bacitracin, rutin or PACMA-31, resulted in the suppression of IgE-mediated activation and the secretion of various cytokines. This was accompanied by decreased mast cell proliferation, FcεRI expression, and mast cell degranulation. Similarly, treatment of allergic BALB/c mice with PACMA-31 attenuated the development of food allergy resulting in decreased allergic diarrhea, mast cell activation, and fewer intestinal mast cells. The production of TH2-specific cytokines was also suppressed. Our observations suggest that PDI catalytic activity is essential in the regulation of mast cell activation, and that its blockade may benefit patients with allergic inflammation.

Extracellular AGR2 triggers lung tumour cell proliferation through repression of p21CIP1

The human Anterior GRadient 2 (AGR2) protein is an Endoplasmic Reticulum (ER)-resident protein which belongs to the Protein-Disulfide Isomerase (PDI) superfamily and is involved to productive protein folding in the ER. As such AGR2, often found overexpressed in adenocarcinomas, contributes to tumour development by enhancing ER proteostasis. We previously demonstrated that AGR2 is secreted (extracellular AGR2 (eAGR2)) in the tumour microenvironment and plays extracellular roles independent of its ER functions. Herein, we show that eAGR2 triggers cell proliferation and characterize the underlying molecular mechanisms. We demonstrate that eAGR2 enhances tumour cell growth by repressing the tumour suppressor p21^CIP1. Our findings shed light on a novel mechanism through which eAGR2 behaves as a growth factor in the tumour microenvironment, independently of its ER function, thus promoting tumour cell growth through repression of p21^CIP1. Our results provide a rationale for targeting eAGR2/p21^CIP1-based signalling as a potential therapeutic target to impede tumour growth.

Cross-Reactivity between Chemical Antibodies Formed to Serum Proteins and Thyroid Axis Target Sites

In some instances, when chemicals bind to proteins, they have the potential to induce a conformational change in the macromolecule that may misfold in such a way that makes it similar to the various target sites or act as a neoantigen without conformational change. Cross-reactivity then can occur if epitopes of the protein share surface topology to similar binding sites. Alteration of peptides that share topological equivalence with alternating side chains can lead to the formation of binding surfaces that may mimic the antigenic structure of a variant peptide or protein. We investigated how antibodies made against thyroid target sites may bind to various chemical–albumin compounds where binding of the chemical has induced human serum albumin (HSA) misfolding. We found that specific monoclonal or polyclonal antibodies developed against thyroid-stimulating hormone (TSH) receptor, 5′-deiodinase, thyroid peroxidase, thyroglobulin, thyroxine-binding globulin (TBG), thyroxine (T4), and triiodothyronine (T3) bound to various chemical HSA compounds. Our study identified a new mechanism through which chemicals bound to circulating serum proteins lead to structural protein misfolding that creates neoantigens, resulting in the development of antibodies that bind to key target proteins of the thyroid axis through protein misfolding. For demonstration of specificity of thyroid antibody binding to various haptenic chemicals bound to HSA, both serial dilution and inhibition studies were performed and proportioned to the dilution. A significant decline in these reactions was observed. This laboratory analysis of immune reactivity between thyroid target sites and chemicals bound to HSA antibodies identifies a new mechanism by which chemicals can disrupt thyroid function.

The role of thyroglobulin in thyroid hormonogenesis

In humans, the thyroid hormones T₃ and T₄ are synthesized in the thyroid gland in a process that crucially involves the iodoglycoprotein thyroglobulin. The overall structure of thyroglobulin is conserved in all vertebrates. Upon thyroglobulin delivery from thyrocytes to the follicular lumen of the thyroid gland via the secretory pathway, multiple tyrosine residues can become iodinated to form mono-iodotyrosine (MIT) and/or di-iodotyrosine (DIT); however, selective tyrosine residues lead to preferential formation of T₄ and T₃ at distinct sites. T₄ formation involves oxidative coupling between two DIT side chains, and de novo T₃ formation involves coupling between an MIT donor and a DIT acceptor. Thyroid hormone synthesis is stimulated by TSH activating its receptor (TSHR), which upregulates the activity of many thyroid gene products involved in hormonogenesis. Additionally, TSH regulates post-translational changes in thyroglobulin that selectively enhance its capacity for T₃ formation - this process is important in iodide deficiency and in Graves disease. 167 different mutations, many of which are newly discovered, are now known to exist in TG (encoding human thyroglobulin) that can lead to defective thyroid hormone synthesis, resulting in congenital hypothyroidism.

Secretion of protein disulphide isomerase AGR2 confers tumorigenic properties

The extracellular matrix (ECM) plays an instrumental role in determining the spatial orientation of epithelial polarity and the formation of lumens in glandular tissues during morphogenesis. Here, we show that the Endoplasmic Reticulum (ER)-resident protein anterior gradient-2 (AGR2), a soluble protein-disulfide isomerase involved in ER protein folding and quality control, is secreted and interacts with the ECM. Extracellular AGR2 (eAGR2) is a microenvironmental regulator of epithelial tissue architecture, which plays a role in the preneoplastic phenotype and contributes to epithelial tumorigenicity. Indeed, eAGR2, is secreted as a functionally active protein independently of its thioredoxin-like domain (CXXS) and of its ER-retention domain (KTEL), and is sufficient, by itself, to promote the acquisition of invasive and metastatic features. Therefore, we conclude that eAGR2 plays an extracellular role independent of its ER function and we elucidate this gain-of-function as a novel and unexpected critical ECM microenvironmental pro-oncogenic regulator of epithelial morphogenesis and tumorigenesis.

DOI:http://dx.doi.org/10.7554/eLife.13887.001

Cancer cells multiply abnormally fast and therefore produce protein molecules faster than normal cells. To avoid becoming stressed by this overproduction, cancer cells make use of proteins that fold the new proteins inside the cell. One of these protein folders is called anterior gradient-2 (or AGR2 for short) and is produced at high levels in so-called epithelial cancers, such as breast and lung cancer.

Previous research has shown that AGR2 inside cancer cells can help them grow and survive and AGR2 can also be found outside cells, such as in the blood or the urine of cancer patients. Therefore some researchers have suggested that measuring the levels of AGR2 in bodily fluids may be a useful marker for detecting cancers. Fessart et al. hypothesized that – apart from becoming a promising diagnostic tool – the AGR2 protein itself, specifically when found outside cells, might make cancer cells more aggressive.

Fessart et al. used a range of techniques to test this hypothesis. For example, healthy lung cells and lung cancer cells were grown into miniature replicas of lung organs in the laboratory, and in a key experiment, AGR2 was added to the lung organoids grown from the healthy cells. The addition of AGR2 protein was enough to change the non-tumor organoids into tumor organoids and boosted their growth about ten-fold. Further experiments then revealed that AGR2 also makes cells more invasive and capable of moving, both important features of aggressive cancer cells.

Overall, Fessart et al. have proven that AGR2 is a signalling molecule found outside cancer cells that makes them more aggressive. In future, more research addressing how AGR2 achieves this may lead to new therapeutic strategies against some forms of cancer.

DOI:http://dx.doi.org/10.7554/eLife.13887.002

Heat shock protein 70 regulates platelet integrin activation, granule secretion and aggregation

Molecular chaperones that support protein quality control, including heat shock protein 70 (Hsp70), participate in diverse aspects of cellular and physiological function. Recent studies have reported roles for specific chaperone activities in blood platelets in maintaining hemostasis; however, the functions of Hsp70 in platelet physiology remain uninvestigated. Here we characterize roles for Hsp70 activity in platelet activation and function. In vitro biochemical, microscopy, flow cytometry, and aggregometry assays of platelet function, as well as ex vivo analyses of platelet aggregate formation in whole blood under shear, were carried out under Hsp70-inhibited conditions. Inhibition of platelet Hsp70 blocked platelet aggregation and granule secretion in response to collagen-related peptide (CRP), which engages the immunoreceptor tyrosine-based activation motif-bearing collagen receptor glycoprotein VI (GPVI)-Fc receptor-γ chain complex. Hsp70 inhibition also reduced platelet integrin-αIIbβ3 activation downstream of GPVI, as Hsp70-inhibited platelets showed reduced PAC-1 and fibrinogen binding. Ex vivo, pharmacological inhibition of Hsp70 in human whole blood prevented the formation of platelet aggregates on collagen under shear. Biochemical studies supported a role for Hsp70 in maintaining the assembly of the linker for activation of T cells signalosome, which couples GPVI-initiated signaling to integrin activation, secretion, and platelet function. Together, our results suggest that Hsp70 regulates platelet activation and function by supporting linker for activation of T cells-associated signaling events downstream of platelet GPVI engagement, suggesting a role for Hsp70 in the intracellular organization of signaling systems that mediate platelet secretion, "inside-out" activation of platelet integrin-αIIbβ3, platelet-platelet aggregation, and, ultimately, hemostatic plug and thrombus formation.

Novel roles for protein disulphide isomerase in disease states: a double edged sword?

Protein disulphide isomerase (PDI) is a multifunctional redox chaperone of the endoplasmic reticulum (ER). Since it was first discovered 40 years ago the functions ascribed to PDI have evolved significantly and recent studies have recognized its distinct functions, with adverse as well as protective effects in disease. Furthermore, post translational modifications of PDI abrogate its normal functional roles in specific disease states. This review focusses on recent studies that have identified novel functions for PDI relevant to specific diseases.

Protein disulfide isomerase is required for platelet-derived growth factor-induced vascular smooth muscle cell migration, Nox1 NADPH oxidase expression, and RhoGTPase activation

Vascular Smooth Muscle Cell (VSMC) migration into vessel neointima is a therapeutic target for atherosclerosis and postinjury restenosis. Nox1 NADPH oxidase-derived oxidants synergize with growth factors to support VSMC migration. We previously described the interaction between NADPH oxidases and the endoplasmic reticulum redox chaperone protein disulfide isomerase (PDI) in many cell types. However, physiological implications, as well as mechanisms of such association, are yet unclear. We show here that platelet-derived growth factor (PDGF) promoted subcellular redistribution of PDI concomitant to Nox1-dependent reactive oxygen species production and that siRNA-mediated PDI silencing inhibited such reactive oxygen species production, while nearly totally suppressing the increase in Nox1 expression, with no change in Nox4. Furthermore, PDI silencing inhibited PDGF-induced VSMC migration assessed by distinct methods, whereas PDI overexpression increased spontaneous basal VSMC migration. To address possible mechanisms of PDI effects, we searched for PDI interactome by systems biology analysis of physical protein-protein interaction networks, which indicated convergence with small GTPases and their regulator RhoGDI. PDI silencing decreased PDGF-induced Rac1 and RhoA activities, without changing their expression. PDI co-immunoprecipitated with RhoGDI at base line, whereas such association was decreased after PDGF. Also, PDI co-immunoprecipitated with Rac1 and RhoA in a PDGF-independent way and displayed detectable spots of perinuclear co-localization with Rac1 and RhoGDI. Moreover, PDI silencing promoted strong cytoskeletal changes: disorganization of stress fibers, decreased number of focal adhesions, and reduced number of RhoGDI-containing vesicular recycling adhesion structures. Overall, these data suggest that PDI is required to support Nox1/redox and GTPase-dependent VSMC migration.

Protein disulfide isomerase in redox cell signaling and homeostasis

Thiol proteins may potentially act as redox signaling adaptor proteins, adjusting reactive oxygen species intermediates to specific signals and redox signals to cell homeostasis. In this review, we discuss redox effects of protein disulfide isomerase (PDI), a thioredoxin superfamily oxidoreductase from the endoplasmic reticulum (ER). Abundantly expressed PDI displays ubiquity, interactions with redox and nonredox proteins, versatile effects, and several posttranslational modifications. The PDI family contains >20 members with at least some apparent complementary actions. PDI has oxidoreductase, isomerase, and chaperone effects, the last not directly dependent on its thiols. PDI is a converging hub for pathways of disulfide bond introduction into ER-processed proteins, via hydrogen peroxide-generating mechanisms involving the oxidase Ero1α, as well as hydrogen peroxide-consuming reactions involving peroxiredoxin IV and the novel peroxidases Gpx7/8. PDI is a candidate pathway for coupling ER stress to oxidant generation. Emerging information suggests a convergence between PDI and Nox family NADPH oxidases. PDI silencing prevents Nox responses to angiotensin II and inhibits Akt phosphorylation in vascular cells and parasite phagocytosis in macrophages. PDI overexpression spontaneously enhances Nox activation and expression. In neutrophils, PDI redox-dependently associates with p47phox and supports the respiratory burst. At the cell surface, PDI exerts transnitrosation, thiol reductase, and apparent isomerase activities toward targets including adhesion and matrix proteins and proteases. Such effects mediate redox-dependent adhesion, coagulation/thrombosis, immune functions, and virus internalization. The route of PDI externalization remains elusive. Such multiple redox effects of PDI may contribute to its conspicuous expression and functional role in disease, rendering PDI family members putative redox cell signaling adaptors.

Phylogenetic analysis of the human thyroglobulin regions

Thyroglobulin is a large protein present in all vertebrates. It is synthesized in the thyrocytes and exported to lumen of the thyroid follicle, where its tyrosine residues are iodinated . The iodinated thyroglobulin is reintegrated into the cell and processed (cleaved to free its two extremities) for thyroid hormone synthesis. Thyroglobulin sequence analysis has identified four regions of the molecule: Tg1, Tg2, Tg3 and ChEL. Structural abnormalities and mutations result in different pathological consequences, depending on the thyroglobulin region affected. We carried out a bioinformatic analysis of thyroglobulin, determining the origin and the function of each region. Our results suggest that the Tg1 region acts as a binding protein on the apical membrane, the Tg2 region is involved in protein adhesion and the Tg3 region is involved in determining the three-dimensional structure of the protein. The ChEL domain is involved in thyroglobulin transport, dimerization and adhesion. The presence of repetitive domains in the Tg1, Tg2 and Tg3 regions suggests that these domains may have arisen through duplication.

Mechanisms of neuroprotection by protein disulphide isomerase in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease characterised by the progressive loss of motor neurons, leading to paralysis and death within several years of onset. Although protein misfolding is a key feature of ALS, the upstream triggers of disease remain elusive. Recently, endoplasmic reticulum (ER) stress was identified as an early and central feature in ALS disease models as well as in human patient tissues, indicating that ER stress could be an important process in disease pathogenesis. One important chaperone induced by ER stress is protein disulphide isomerase (PDI), which is both upregulated and posttranslationally inhibited by S-nitrosylation in ALS. In this paper, we present evidence from studies of genetics, model organisms, and patient tissues which indicate an active role for PDI and ER stress in ALS disease processes.

Glucose-regulated protein 78 (Grp78/BiP) is secreted by human oviduct epithelial cells and the recombinant protein modulates sperm-zona pellucida binding

OBJECTIVE

To determine the secretion of Grp78 by human oviduct epithelial cells, its association to spermatozoa, and its involvement in gamete interaction.

DESIGN

Prospective study.

SETTING

Basic research laboratory.

SUBJECT(S)

Semen samples obtained from normozoospermic volunteers. Tubal tissue provided by patients undergoing hysterectomies. Oocytes collected from women undergoing IVF-ET.

INTERVENTION(S)

Analysis of Grp78 expression and secretion by oviductal tissue. Gamete incubation with recombinant Grp78 (rec-Grp78).

MAIN OUTCOME MEASURE(S)

Assessment of protein expression and secretion by immunohistochemistry and Western immunoblotting, respectively. Evaluation of rec-Grp78 binding to human spermatozoa by immunocytochemistry, and analysis of its effect upon gamete interaction using the hemizona assay.

RESULT(S)

Grp78 was found in the surface of oviduct epithelial cells. Soluble Grp78 was detected in oviductal fluids from women in the periovulatory period and in oviductal tissue conditioned medium. Rec-Grp78 was able to bind to the sperm acrosomal cap, and its presence during gamete interaction led to a decrease in the number of spermatozoa bound to the zona pellucida (ZP). When calcium ions from the incubation medium were replaced by strontium, rec-Grp78 enhanced sperm-ZP interaction.

CONCLUSION(S)

Grp78 is expressed and secreted by oviduct epithelial cells. The protein would bind to the gametes and may modulate their interaction in a calcium-dependent manner.

Proliferative effects of bovine and porcine thyroglobulins on thyroid epithelial cells

Thyroglobulin is the precursor of the thyroid hormones, triiodothyronine and thyroxine. Because the molecular size of thyroglobulin is relatively large (660 kDa), it could have other additional functions besides serving as the precursor of the thyroid hormones. In this report, we examined the proliferative effects of thyroglobulins purified from bovine and porcine thyroid tissues on the growth of a rat thyroid follicular cell line, FRTL-5, as well as the primary culture of porcine thyroid epithelial cells. Bovine and porcine thyroglobulins stimulated the proliferation of not only FRTL-5 cells but also porcine thyroid epithelial cells in a dose-dependent manner. The proliferative effect of thyroglobulin was neutralized by an anti-thyroglobulin monoclonal antibody but not by two different anti-fibroblast growth factor antibodies. The stimulatory signal of thyroglobulin was transmitted via the phosphatidylinositol 3-kinase pathway. Also, removal of the N-linked oligosaccharides on thyroglobulin reduced the proliferative activity of porcine thyroglobulin, suggesting that the proliferative effect of thyroglobulin is in part exerted by its carbohydrate moiety. Taken together, we have demonstrated for the first time that thyroglobulin possesses proliferative effect on thyroid epithelial cells in addition to being the precursor of the thyroid hormones.

Downregulation of protein disulfide isomerase in sepsis and its role in tumor necrosis factor-alpha release

Introduction

Protein disulfide isomerase (PDI) is an important factor for the protein modification step in the post-translational event. PDI plays an essential role in cell survival under various stress conditions. It has been reported that PDI can serve as a negative regulator of nuclear factor-kappa-B (NF-κB) and that it can inhibit lipopolysaccharide (LPS)-induced proinflammatory cytokine production in macrophages. Thus, PDI may be an intracellular anti-inflammatory molecule. Although we have previously shown that Kupffer cell-derived proinflammatory cytokines cause liver injury in sepsis, the effect of sepsis on PDI expression as well as the effect of PDI inhibition on cytokine production have not been investigated. We therefore hypothesized that sepsis downregulates PDI expression and that the inhibition of PDI promotes proinflammatory cytokine production.

Method

Adult male rats were subjected to sepsis by cecal ligation and puncture (CLP) or endotoxemia (continuous infusion of 1 μg/kg body weight LPS by an osmotic pump) for 20 hours. Hepatic tissues were collected and PDI gene expression was determined. In additional experiments, cells from a macrophage-like cell line, RAW 264.7, were treated with 100 ng/mL LPS for 4 hours and protein expressions were measured. RAW 264.7 cells were also treated with bacitracin, a specific PDI inhibitor, for 24 hours, and tumor necrosis factor-alpha (TNF-α) gene and protein expression as well as its release in the cell supernatant were determined. To further confirm the beneficial effect of PDI in sepsis, RAW 264.7 cells were transfected with PDI short interfering RNA (siRNA) and PDI gene expression and TNF-α release were measured by quantitative polymerase chain reaction and enzyme-linked immunosorbent assay, respectively.

Results

PDI gene expression was significantly decreased by 28% and 69% at 20 hours after CLP or LPS infusion, respectively. LPS also decreased PDI protein expression by 33% in RAW 264.7 cells. Incubation of RAW 264.7 cells with bacitracin significantly increased TNF-α gene expression and TNF-α release as well as its cellular levels in a dose-dependent manner. Transfection of RAW 264.7 cells with PDI siRNA produced an average 36.8% inhibition of the PDI gene expression. This downregulation was correlated with a 3.19-fold increase in TNF-α release into the cell supernatant.

Conclusion

Taken together, these results suggest that downregulation of PDI by sepsis significantly increases proinflammatory cytokine production. Thus, prevention of PDI downregulation in sepsis may be a novel approach to attenuate hyperinflammation and to reduce tissue injury under such conditions.

Novel role of protein disulfide isomerase in the regulation of NADPH oxidase activity: pathophysiological implications in vascular diseases

Vascular cell NADPH oxidase complexes are key sources of signaling reactive oxygen species (ROS) and contribute to disease pathophysiology. However, mechanisms that fine-tune oxidase-mediated ROS generation are incompletely understood. Besides known regulatory subunits, upstream mediators and scaffold platforms reportedly control and localize ROS generation. Some evidence suggest that thiol redox processes may coordinate oxidase regulation. We hypothesized that thiol oxidoreductases are involved in this process. We focused on protein disulfide isomerase (PDI), a ubiquitous dithiol disulfide oxidoreductase chaperone from the endoplasmic reticulum, given PDI's unique versatile role as oxidase/isomerase. PDI is also involved in protein traffic and can translocate to the cell surface, where it participates in cell adhesion and nitric oxide internalization. We recently provided evidence that PDI exerts functionally relevant regulation of NADPH oxidase activity in vascular smooth muscle and endothelial cells, in a thiol redox-dependent manner. Loss-of-function experiments indicate that PDI supports angiotensin II-mediated ROS generation and Akt phosphorylation. In addition, PDI displays confocal co-localization and co-immunoprecipitates with oxidase subunits, indicating close association. The mechanisms of such interaction are yet obscure, but may involve subunit assembling stabilization, assistance with traffic, and subunit disposal. These data may clarify an integrative view of oxidase activation in disease conditions, including stress responses.

Identification of three protein disulfide isomerase members from Haemaphysalis longicornis tick

Three genes encoding putative protein disulfide isomerase (PDI) were isolated from the Haemaphysalis longicornis EST database and designed as HlPDI-1, HlPDI-2, and HlPDI-3. All three PDI genes contain two typical PDI active sites CXXC and encode putative 435, 499, and 488 amino acids, respectively. The recombinant proteins expressed in Escherichia coli all show PDI activities, and the activities were inhibited by a PDI-specific inhibitor, zinc bacitracin. Western blot analysis and real-time PCR revealed that three HlPDIs were present in all the developmental stages of the tick as well as in the midgut, salivary glands, ovary, hemolymph, and fatbody of adult female ticks, but the three genes were expressed at the highest level in the egg stage. HlPDI-1 is expressed primarily in the ovary and secondarily in the salivary glands. HlPDI-2 and HlPDI-3 are expressed primarily in the salivary gland, suggesting that the PDI genes are important for tick biology, especially for egg development, and that they play distinct roles in different tissues. Blood feeding induced significantly increased expression of HlPDI-1 and HlPDI-3 in both partially fed nymphs and adults. Babesia gibsoni-infected larval ticks expressed HlPDI-1 and HlPDI-3 2.0 and 4.0 times higher than uninfected normal larval ticks, respectively. The results indicate that HlPDI-1 and HlPDI-3 might be involved in tick blood feeding and Babesia parasite infection in ticks.

Catalysis of Covalent Lp(a) Assembly: Evidence for an Extracellular Enzyme Activity that Enhances Disulfide Bond Formation

The assembly of lipoprotein(a) (Lp(a)) particles occurs via a two-step mechanism in which noncovalent interactions between apolipoprotein(a) (apo(a)) and the apolipoproteinB-100 component of low density lipoprotein precede the formation of a single disulfide bond. Although we have previously demonstrated that the rate constant for the covalent step of Lp(a) assembly can be enhanced by altering the conformational status of apo(a), the resultant rates of covalent Lp(a) particle formation measured in vitro are relatively slow. The large excess of Lp(a) (over apo(a)) observed in vivo can be accounted for by a preferential clearance of apo(a) over Lp(a) and/or a sufficiently high rate of covalent Lp(a) assembly. In the present study, we report that cultured human hepatoma cells secrete an oxidase activity that dramatically enhances the rate of covalent Lp(a) assembly. This activity is likely possessed by a protein because it is heat-sensitive and is retained in the concentrate following ultrafiltration through a 5 kDa cutoff filter. However, a small molecule cofactor for the activity is suggested by the observation that the activity is lost upon dialysis. Plots of Lp(a) assembly rate versus input apo(a) concentration gave rectangular hyperbolae; the reaction displayed an unusual dependence on the concentration of apoB-100, with increasing concentrations of apoB-100 resulting in slower rates of Lp(a) assembly at low concentrations of apo(a), an effect that was alleviated by higher apo(a) concentrations. Interestingly, V(max(app))/K(m(app)) ratios were insensitive to apoB-100 concentration, which is diagnostic of a ping-pong reaction mechanism. In this way, the putative Lp(a) oxidase may be functionally analogous to protein disulfide isomerase, which exhibits a similar mechanism during the catalysis of disulfide bond formation during protein folding, although we have ruled out a role for this enzyme in Lp(a) assembly.

Bisphenol A binds to protein disulfide isomerase and inhibits its enzymatic and hormone-binding activities

Bisphenol A [2,2-bis-(4-hydroxyphenyl) propane; BPA] is a versatile industrial material for plastic products, but is increasingly being recognized as a pervasive industrial pollutant as well. Accumulating evidence indicates that the environmental contaminant BPA is one of the endocrine-disrupting chemicals that potentially can adversely affect humans as well as wildlife. To define the molecular aspects of BPA action, we first investigated the molecules with which it physically interacts. High BPA-binding activity was detected in the P2 membrane fraction prepared from rat brains. As determined by SDS-PAGE analysis, the molecular mass of a BPA-binding protein purified from the rat brain P2 fraction was 53 kDa. The N-terminal amino acid sequence of the purified BPA-binding protein was identical with that of the rat protein disulfide isomerase (PDI), which is a multifunctional protein that is critically involved in the folding, assembly, and shedding of many cellular proteins via its isomerase activity in addition to being considered to function as an intracellular hormone reservoir. The Kd value of BPA binding to recombinant rat PDI was 22.6 +/- 6.6 microm. Importantly, the binding activity of L-T3 and 17beta-estradiol hormones to PDI was competitively inhibited by BPA in addition to abolishing its isomerase activities. In this paper we report that the ubiquitous and multifunctional protein PDI is a target of BPA and propose that binding to PDI and subsequent inhibition of PDI activity might be mechanistically responsible for various actions of BPA.

Defective thyroglobulin storage in LDL receptor-associated protein-deficient mice

The molecular chaperone receptor-associated protein (RAP) is required for biosynthesis of megalin, an endocytic receptor for follicular thyroglobulin (Tg), the thyroid hormone precursor. RAP also binds to Tg itself, suggesting that it may affect Tg trafficking in various manners. To elucidate RAP function, we have studied the thyroid phenotype in RAP-knockout (RAP-KO) mice and found a reduction of Tg aggregates into thyroid follicles. Serum Tg levels were significantly increased compared with those of wild-type (WT) mice, suggesting a directional alteration of Tg secretion. In spite of these abnormalities, hormone secretion was maintained as indicated by normal serum thyroxine levels. Because Tg in thyroid extracts from RAP-KO mice contained thyroxine residues as in WT mice, we concluded that in RAP-KO mice, follicular Tg, although reduced, was nevertheless sufficient to provide normal hormone secretion. Serum TSH was increased in RAP-KO mice, and although no thyroid enlargement was observed, some histological features resembling early goiter were present. Megalin was decreased in RAP-KO mice, but this did not affect thyroid function, probably because of the concomitant reduction of follicular Tg. In conclusion, RAP is required for the establishment of Tg reservoirs, but its absence does not affect hormone secretion.

Identification of a protein disulfide isomerase of Neospora caninum in excretory-secretory products and its IgA binding and enzymatic activities

A protein disulfide isomerase of Neospora caninum (NcPDI) with a molecular weight of 50kDa was identified in tachyzoite lysate and excretory-secretory (ES) products. The IgA antibody in 58.0% of the individual cattle tear samples recognized the NcPDI, which suggests that the PDI-specific antibody may be involved in defense against parasites. In addition, PDI-specific inhibitors and NcPDI antiserum showed inhibitory effects on the growth of N. caninum tachyzoites. Furthermore, the purified recombinant NcPDI demonstrated biological activities in vitro by catalysis and refolding of reduced RNase A and assisted in the recovery of native lysozyme. These findings indicate that NcPDI possesses PDI-specific enzymatic activity and could be a putative target for chemotherapy for neosporosis.

Heat-enhanced production of chitosanase from Streptomyces griseus in the presence of liposome

The effects of heat stress and liposome treatment on the growth of Streptomyces griseus cells and chitosanase production were investigated on the basis of using the designed strategy of a stress-mediated bioprocess. The effective conditions for increasing the interaction between chitosanase and the 1-palmitoyl-2-oleoyl-3-phosphocholine (POPC) liposome under heat stress condition were determined on the basis of the results of circular dichroism (CD) and dielectric dispersion analysis (DDA). Under these effective conditions, S. griseus cells were cultivated for the effective production of chitosanase. The results obtained from both CD spectra and DDA showed that heat stress enhances the interaction of the POPC liposomes and chitosanase. The strongest interaction between them could be obtained in the specific temperature range of 40-45 degrees C. The enhancement of the target chitosanase production was conducted under heat stress at 41 degrees C in the presence and absence of the POPC liposomes. The growth rates of S. griseus cells in the cases of heat (41 degrees C) and heat (41 degrees C)/POPC treatments were respectively 1.2 and 1.4 times higher than that obtained under the control condition. In the heat (41 degrees C) and heat (41 degrees C)/POPC treatments, chitosanase activity increased to 1.8 and 2 times, respectively, higher than that obtained under the control condition. Heat stress and the addition of the POPC liposomes could therefore be utilized to induce the potential functions of bacterial cells for the enhancement of the final target production.

Regulation of NAD(P)H oxidase by associated protein disulfide isomerase in vascular smooth muscle cells

NAD(P)H oxidase, the main source of reactive oxygen species in vascular cells, is known to be regulated by redox processes and thiols. However, the nature of thiol-dependent regulation has not been established. Protein disulfide isomerase (PDI) is a dithiol/disulfide oxidoreductase chaperone of the thioredoxin superfamily involved in protein processing and translocation. We postulated that PDI regulates NAD(P)H oxidase activity of rabbit aortic smooth muscle cells (VSMCs). Western blotting confirmed robust PDI expression and shift to membrane fraction after incubation with angiotensin II (AII, 100 nm, 6 h). In VSMC membrane fraction, PDI antagonism with bacitracin, scrambled RNase, or neutralizing antibody led to 26-83% inhibition (p < 0.05) of oxidase activity. AII incubation led to significant increase in oxidase activity, accompanied by a 6-fold increase in PDI refolding isomerase activity. AII-induced NAD(P)H oxidase activation was inhibited by 57-71% with antisense oligonucleotide against PDI (PDIasODN). Dihydroethidium fluorescence showed decreased superoxide generation due to PDIasODN. Confocal microscopy showed co-localization between PDI and the oxidase subunits p22(phox), Nox1, and Nox4. Co-immunoprecipitation assays supported spatial association between PDI and oxidase subunits p22(phox), Nox1, and Nox4 in VSMCs. Moreover, in HEK293 cells transfected with green fluorescent protein constructs for Nox1, Nox2, and Nox4, each of these subunits co-immunoprecipitated with PDI. Akt phosphorylation, a known downstream pathway of AII-driven oxidase activation, was significantly reduced by PDIasODN. These results suggest that PDI closely associates with NAD(P)H oxidase and acts as a novel redox-sensitive regulatory protein of such enzyme complex, potentially affecting subunit traffic/assembling.

Neospora caninum protein disulfide isomerase is involved in tachyzoite-host cell interaction

We have previously shown that treatment of Neospora caninum tachyzoites with the aspartyl protease inhibitor pepstatin A reduces host cell invasion [Naguleswaran, A., Muller, N., Hemphill, A., 2003. Neospora caninum and Toxoplasma gondii: a novel adhesion/invasion assay reveals distinct differences in tachyzoite-host cell interactions. Exp. Parasitol. 104, 149-158]. Pepstatin A-affinity-chromatography led to the isolation of a major band of approximately 52 kDa which was identified as a homologue of a previously described Toxoplasma gondii putative protein disulfide isomerase (TgPDI) through tandem mass spectrometry. A BLAST search against N. caninum expressed sequence tags (ESTs) on the ApiDots server using TgPDI cDNA as query sequence revealed a 2251 bp PDI-like consensus (NcPDI), which shows 94% identity to the T. gondii homologue. In N. caninum tachyzoites, NcPDI was found mainly in the soluble hydrophilic fraction. Immunofluorescence showed that expression of NcPDI was dramatically down-regulated in the bradyzoite stage, and immunogold-EM on tachyzoites localised the protein to the cytoplasm, mostly in close vicinity to the nuclear membrane, to the micronemes, and to the parasite cell surface. However, NcPDI was absent in rhoptries and dense granules. Preincubation of tachyzoites with the sulfhydryl blocker 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB), p-chloromercuribenzoic acid (pCMBA), and with the PDI inhibitor bacitracin reduced adhesion of parasites to host cells. In addition, incubation of N. caninum tachyzoites with affinity-purified anti-NcPDI antibodies reduced host cell adhesion. PDIs catalyse the formation, reduction or isomerisation of disulfide bonds. Many major components of the adhesion and invasion machinery of apicomplexan parasites are cysteine-rich and dependent on correct folding via disulfide bond formation. Thus, our data points towards an important role for surface-associated NcPDI in Neospora-host cell interaction.

ERp57 binds competitively to protein disulfide isomerase and calreticulin

In this study, we screened for protein disulfide isomerase (PDI)-binding proteins in bovine liver microsomes under strict salt concentrations, using affinity column chromatography. One main band observed using SDS-PAGE was identified as ERp57 (one of the PDI family proteins) by LC-MS/MS analysis. The K(D) value of PDI binding to ERp57 was calculated as 5.46x10(-6)M with the BIACORE system. The interactions between PDI and ERp57 occurred specifically at their a and b domains, respectively. Interestingly, low concentrations of ERp57 enhanced the chaperone activity of PDI, while high concentrations interfered with chaperone activity. On the other hand, ERp57 did not affect the isomerase activity of PDI. Additionally, following pre-incubation of ERp57 with calreticulin (CRT), decreased interactions were observed between ERp57 and PDI, and vice versa. Based on the data, we propose that once ERp57 binds to PDI or CRT, the resultant complex inhibits further interactions. Therefore, ERp57 selectively forms a protein-folding complex with PDI or CRT in ER.

Multimerization of bovine Thyroglobulin, partially unfolded or partially unfolded/reduced; Involvement of protein disulfide isomerase and glutathionylated disulfide linkage

Fate of the nascent thyrolglobulin (Tg) molecule is characterized by multimerization. To establish the formation of Tg multimers, the partially unfolded/reduced Tg or deoxycholate-treated/ reduced Tg was subjected to protein disulfide isomerase (PDI)-mediated multimerization. Oxidized glutathione/PDI-mediated formation of multimeric Tg forms, requiring at least an equivalent molar ratio of PDI/Tg monomer, decreased with increasing concentration of reduced glutathione (GSH), suggesting the oxidizing role of PDI. Additional support was obtained when PDI alone, at a PDI/Tg molar ratio of 0.3, expressed a rapid multimerization. Independently, the exposure of partially unfolded Tg to GSH resulted in Tg multimerization, enhanced by PDI, according to thiol-disulfide exchange. Though to a lower extent, a similar result was observed with the dimerization of deoxycholate-pretreated Tg monomer. Consequently, it is implied that intermolecular disulfide linkage may be facilitated at a limited region of unfolded Tg. In an attempt to examine the multimerization site, the cysteine residue-rich fragments of the Tg were subjected to GSH-induced multimerization; a 50 kDa fragment, containing three vicinal dithiols, was multimerized, while an N-terminal domain was not. Present results suggest that the oxidase as well as isomerase function of PDI may be involved in the multimerization of partially unfolded Tg or deoxycholate-treated Tg.

Differential protein synthesis and expression levels in normal and neoplastic human prostate cells and their regulation by type I and II interferons

Protein expression and de novo synthesis in normal and prostate cancer cell lines derived from the same patient were compared by proteomic analysis, and the effects of INFalpha and INFgamma (INF=interferon) determined. The expressions of several INF-inducible proteins, including MxA, Nmi, PA28a and IFP53, were downregulated in the cancer cells. INFgamma induced a more than twofold increase or decrease in the synthesis rates of almost twice as many proteins in the cancer cell line. The positive regulator of INF-induced transcription ISGF3gamma was upregulated in the cancer cells and inversely regulated by INFalpha and INFgamma in the normal and cancer cells. Moreover, ISGF3gamma's induction by INFgamma in the cancer cells was more enhanced by simultaneous stimulation with EGF, than its induction in the normal cells. In all, 31 differentially regulated proteins were identified by mass spectrometry analysis, several of which are involved in chaperone-assisted protein folding in the endoplasmic reticulum (ER) or in regulated protein degradation. Our results suggest that the exclusion of proteins by the ER quality control system, crosstalk between the EGF- and INF-induced signalling pathways and the regulation of INF-inducible genes are all altered in the prostate cancer cells. The combination of upregulated activity in the growth-promoting PI3K/Akt pathway, suppression of Nmi and overexpression of hnRNP-K and c-myc proteins may explain why the prostate cancer cells were found to be more resistant to the growth inhibitory effects of INFgamma.

Complement activation by direct C4 binding to thyroperoxidase in Hashimoto's thyroiditis

Biosynthesis of thyroid hormones is an oxidative process that generates reactive oxygen species (ROS) and involves thyroperoxidase (TPO) that is one of the main autoantigens involved in autoimmune thyroid diseases. The ectodomain of TPO consists of a large N-terminal myeloperoxidase-like module followed by a complement control protein (CCP)-like module and an epidermal growth factor-like module. The presence of these two additional gene modules suggests that they may play some crucial, hitherto unsuspected role associated with thyroid function. Because the CCP module is a constituent of the molecules involved in the activation of C4 complement component, we investigated the possibility that C4 may bind to TPO and activate the complement pathway in autoimmune conditions. We showed that TPO via its CCP module directly activated complement without any mediation by Ig. We suggested that this additional complement pathway requires the production of ROS and specially hydroxyl radicals that aggregate TPO and oxidize methionines of C4. Moreover, we found, in patients with Hashimoto's thyroiditis, that thyrocytes overexpress C4 and all the downstream components of the complement pathway. These results indicate that TPO has some as yet unknown function, which may contribute along with other mechanisms to the massive cell destruction observed in Hashimoto's thyroiditis. Investigating this complement pathway, therefore, would provide an excellent means of reaching a better understanding of the etiology of other degenerative diseases.

Molecular chaperones, stress proteins and redox homeostasis

Protection against oxidative stress is highly interrelated with the function of the most ancient cellular defense system, the network of molecular chaperones, heat shock, or stress-proteins. These ubiquitous, conserved proteins help other proteins and macromolecules to fold or re-fold and reach their final, native conformation. Redox regulation of protein folding becomes especially important during the preparation of extracellular proteins to the outside oxidative milieu, which should take place in a gradual and step-by-step controlled manner in the endoplasmic reticulum or in the periplasm. Several chaperones, such as members of the Hsp33 family in yeast and the plethora of small heat shock proteins as well as one of the major chaperones, Hsp70 are able to act against cytoplasmic oxidative damage. Abrupt changes of cellular redox status lead to chaperone induction. The function of several chaperones is tightly regulated by the surrounding redox conditions. Moreover, our recent data suggest that chaperones may act as a central switchboard for the transmission of redox changes in the life of the cell.

Proteins of the PDI family: unpredicted non-ER locations and functions

Protein disulfide isomerases (PDIs) constitute a family of structurally related enzymes which catalyze disulfide bonds formation, reduction, or isomerization of newly synthesized proteins in the lumen of the endoplasmic reticulum (ER). They act also as chaperones, and are, therefore, part of a quality-control system for the correct folding of the proteins in the same subcellular compartment. While their functions in the ER have been thoroughly studied, much less is known about their roles in non-ER locations, where, however, they have been shown to be involved in important biological processes. At least three proteins of this family from higher vertebrates have been found in unusual locations (i.e., the cell surface, the extracellular space, the cytosol, and the nucleus), reached through an export mechanism which has not yet been understood. In some cases their function in the non-ER location is clearly related to their redox properties, but in most cases their mechanism of action has still to be disclosed, although their propensity to associate with other proteins or even with DNA might be the main factor responsible for their activities.

Role of protein disulfide isomerase in molecular fate of thyroglobulin and its regulation by endogenous oxidants and reductants

The molecular fate of thyroglobulin (Tg) is controlled by oligomerization, a means of storing Tg at high concentrations, and deoligomerization. The oligomerization of bovine Tg are intermolecular reactions that occur through oxidative processes, such as disulfide and dityrosine formation, as well as isopeptide formation; disulfide formation is primarily responsible for Tg oligomerization. Here, the protein disulfide isomerase (PDI) and/or peroxidase-induced oligomerization of unfolded thyroglobulins, which were prepared by treating bovine Tg with heat, urea or thiol/urea, was investigated using SDS-PAGE analyses. In addition, the enzymatic oligomerization was compared with non-enzymatic oligomerization. The thermally-induced oilgomerization of Tg, dependent on glutathione redox state, was affected by the ionic strength or the presence of a surfactant. Meanwhile, PDI-catalyzed oligomerization, time and pH-dependent, was the most remarkable with unfolded/reduced Tg, which was prepared from a treatment with urea/DTT, while the thermally-unfolded Tg was less sensitive. Similarly, the oligomerization of unfolded/reduced Tg was also mediated by peroxidase. However, PDI showed no remarkable effect on the peroxidase-mediated oligomerization of either the unfolded or unfolded/reduced Tg. Additionally, the reductive deoligomerization of oligomeric Tg was exerted by PDI in an excessively reducing state. Based on these results, it is proposed that PDI catalyzes the oligomerization of Tg through the disulfide linkage and its deoligomerization in the molecular fate, and this process may require a specific molecular form of Tg, optimally unfolded/reduced, in a proper redox state.