Protein disulfide isomerase (PDI) associates with NADPH oxidase and is required for phagocytosis of Leishmania chagasi promastigotes by macrophages

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.

Protein disulfide isomerase-mediated transcriptional upregulation of Nox1 contributes to vascular dysfunction in hypertension

Nox1 signaling is a causal key element in arterial hypertension. Recently, we identified protein disulfide isomerase A1 (PDI) as a novel regulatory protein that regulates Nox1 signaling in VSMCs. Spontaneously hypertensive rats (SHR) have increased levels of PDI in mesenteric resistance arteries compared with Wistar controls; however, its consequences remain unclear. Herein, we investigated the role of PDI in mediating Nox1 transcriptional upregulation and its effects on vascular dysfunction in hypertension. We demonstrate that PDI contributes to the development of hypertension via enhanced transcriptional upregulation of Nox1 in vascular smooth muscle cells (VSMCs). We show for the first time that PDI sulfenylation by hydrogen peroxide contributes to EGFR activation in hypertension via increased shedding of epidermal growth factor-like ligands. PDI also increases intracellular calcium levels, and contractile responses induced by ANG II. PDI silencing or pharmacological inhibition in VSMCs significantly decreases EGFR activation and Nox1 transcription. Overexpression of PDI in VSMCs enhances ANG II-induced EGFR activation and ATF1 translocation to the nucleus. Mechanistically, PDI increases ATF1-induced Nox1 transcription and enhances the contractile responses to ANG II. Herein we show that ATF1 binding to Nox1 transcription putative regulatory regions is augmented by PDI. Altogether, we provide evidence that HB-EGF in SHR resistance vessels promotes the nuclear translocation of ATF1, under the control of PDI, and thereby induces Nox1 gene expression and increases vascular reactivity. Thus, PDI acts as a thiol redox-dependent enhancer of vascular dysfunction in hypertension and could represent a novel therapeutic target for the treatment of this disease.

ROS signaling in innate immunity via oxidative protein modifications

The innate immune response represents the first-line of defense against invading pathogens. Reactive oxygen species (ROS) and reactive nitrogen species (RNS) have been implicated in various aspects of innate immune function, which involves respiratory bursts and inflammasome activation. These reactive species widely distributed within the cellular environment are short-lived intermediates that play a vital role in cellular signaling and proliferation and are likely to depend on their subcellular site of formation. NADPH oxidase complex of phagocytes is known to generate superoxide anion radical (O2 •-) that functions as a precursor for antimicrobial hydrogen peroxide (H2O2) production, and H2O2 is utilized by myeloperoxidase (MPO) to generate hypochlorous acid (HOCl) that mediates pathogen killing. H2O2 modulates the expression of redox-responsive transcriptional factors, namely NF-kB, NRF2, and HIF-1, thereby mediating redox-based epigenetic modification. Survival and function of immune cells are under redox control and depend on intracellular and extracellular levels of ROS/RNS. The current review focuses on redox factors involved in the activation of immune response and the role of ROS in oxidative modification of proteins in macrophage polarization and neutrophil function.

Recognition of Immunoreactive Proteins in Leishmania infantum Amastigote-Like and Promastigote Using Sera of Visceral Leishmaniasis Patients: a Preliminary Study

PURPOSE

Visceral leishmaniasis (VL) is a systemic and parasitic disease that is usually fatal if left untreated. VL is endemic in different parts of Iran and is caused mainly by Leishmania infantum. This study aimed to recognition immunoreactive proteins in amastigote-like and promastigote stages of L. infantum (Iranian strain) by antibodies present in the sera of VL patients.

METHODS

Total protein extract from amastigote-like and promastigote cells was separated by two-dimensional electrophoresis (2DE). To detect the immunoreactive proteins, 2DE immunoblotting method was performed using different pools of VL patients' sera.

RESULTS

Approximately 390 and 430 protein spots could be separated in 2DE profiles of L. infantum amastigote-like and promastigote stages, respectively. In immunoblotting method, approximately 295 and 135 immunoreactive proteins of amastigotes-like reacted with high antibody titer serum pool and low antibody titer serum pool, respectively. Approximately 120 and 85 immunoreactive proteins of promastigote extract were recognized using the high antibody titer sera pool and low antibody titer sera, respectively.

CONCLUSION

The present study has recognized a number of antigenic diversity proteins based on the molecular weight and pH in amastigote-like and promastigote stages of L. infantum. These results provide us a new concept for further analysis development in the field of diagnosis biomarkers and vaccine targets.

Leishmania infection upregulates and engages host macrophage Argonaute 1, and system-wide proteomics reveals Argonaute 1-dependent host response

Leishmania donovani, an intracellular protozoan parasite, is the causative agent of visceral leishmaniasis, the most severe form of leishmaniasis in humans. It is becoming increasingly clear that several intracellular pathogens target host cell RNA interference (RNAi) pathways to promote their survival. Complexes of Argonaute proteins with small RNAs are core components of the RNAi. In this study, we investigated the potential role of host macrophage Argonautes in Leishmania pathogenesis. Using Western blot analysis of Leishmania donovani-infected macrophages, we show here that Leishmania infection selectively increased the abundance of host Argonaute 1 (Ago1). This increased abundance of Ago1 in infected cells also resulted in higher levels of Ago1 in active Ago-complexes, suggesting the preferred use of Ago1 in RNAi in Leishmania-infected cells. This analysis used a short trinucleotide repeat containing 6 (TNRC6)/glycine-tryptophan repeat protein (GW182) protein-derived peptide fused to Glutathione S-transferase as an affinity matrix to capture mature Ago-small RNAs complexes from the cytosol of non-infected and Leishmania-infected cells. Furthermore, Ago1 silencing significantly reduced intracellular survival of Leishmania, demonstrating that Ago1 is essential for Leishmania pathogenesis. To investigate the role of host Ago1 in Leishmania pathogenesis, a quantitative whole proteome approach was employed, which showed that expression of several previously reported Leishmania pathogenesis-related proteins was dependent on the level of macrophage Ago1. Together, these findings identify Ago1 as the preferred Argonaute of RNAi machinery in infected cells and a novel and essential virulence factor by proxy that promotes Leishmania survival.

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.

Genomic Signatures of Coevolution between Nonmodel Mammals and Parasitic Roundworms

Antagonistic coevolution between host and parasite drives species evolution. However, most of the studies only focus on parasitism adaptation and do not explore the coevolution mechanisms from the perspective of both host and parasite. Here, through the de novo sequencing and assembly of the genomes of giant panda roundworm, red panda roundworm, and lion roundworm parasitic on tiger, we investigated the genomic mechanisms of coevolution between nonmodel mammals and their parasitic roundworms and those of roundworm parasitism in general. The genome-wide phylogeny revealed that these parasitic roundworms have not phylogenetically coevolved with their hosts. The CTSZ and prolyl 4-hydroxylase subunit beta (P4HB) immunoregulatory proteins played a central role in protein interaction between mammals and parasitic roundworms. The gene tree comparison identified that seven pairs of interactive proteins had consistent phylogenetic topology, suggesting their coevolution during host–parasite interaction. These coevolutionary proteins were particularly relevant to immune response. In addition, we found that the roundworms of both pandas exhibited higher proportions of metallopeptidase genes, and some positively selected genes were highly related to their larvae’s fast development. Our findings provide novel insights into the genetic mechanisms of coevolution between nonmodel mammals and parasites and offer the valuable genomic resources for scientific ascariasis prevention in both pandas.

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.

Effect of Reactive Oxygen Species on the Endoplasmic Reticulum and Mitochondria during Intracellular Pathogen Infection of Mammalian Cells

Oxidative stress, particularly reactive oxygen species (ROS), are important for innate immunity against pathogens. ROS directly attack pathogens, regulate and amplify immune signals, induce autophagy and activate inflammation. In addition, production of ROS by pathogens affects the endoplasmic reticulum (ER) and mitochondria, leading to cell death. However, it is unclear how ROS regulate host defense mechanisms. This review outlines the role of ROS during intracellular pathogen infection, mechanisms of ROS production and regulation of host defense mechanisms by ROS. Finally, the interaction between microbial pathogen-induced ROS and the ER and mitochondria is described.

Potential Roles of Endoplasmic Reticulum Stress and Cellular Proteins Implicated in Diabesity

The role of the endoplasmic reticulum (ER) has evolved from protein synthesis, processing, and other secretory pathways to forming a foundation for lipid biosynthesis and other metabolic functions. Maintaining ER homeostasis is essential for normal cellular function and survival. An imbalance in the ER implied stressful conditions such as metabolic distress, which activates a protective process called unfolded protein response (UPR). This response is activated through some canonical branches of ER stress, i.e., the protein kinase RNA-like endoplasmic reticulum kinase (PERK), inositol-requiring enzyme 1α (IRE1α), and activating transcription factor 6 (ATF6). Therefore, chronic hyperglycemia, hyperinsulinemia, increased proinflammatory cytokines, and free fatty acids (FFAs) found in diabesity (a pathophysiological link between obesity and diabetes) could lead to ER stress. However, limited data exist regarding ER stress and its association with diabesity, particularly the implicated proteins and molecular mechanisms. Thus, this review highlights the role of ER stress in relation to some proteins involved in diabesity pathogenesis and provides insight into possible pathways that could serve as novel targets for therapeutic intervention.

PDIA1 acts as master organizer of NOX1/NOX4 balance and phenotype response in vascular smooth muscle

Changes in vascular smooth muscle cell (VSMC) phenotype underlie disease pathophysiology and are strongly regulated by NOX NADPH oxidases, with NOX1 favoring synthetic proliferative phenotype and NOX4 supporting differentiation. Growth factor-triggered NOX1 expression/activity strictly depends on the chaperone oxidoreductase protein disulfide isomerase-A1 (PDIA1). Intracellular PDIA1 is required for VSMC migration and cytoskeleton organization, while extracellular PDIA1 fine-tunes cytoskeletal mechanoadaptation and vascular remodeling. We hypothesized that PDIA1 orchestrates NOX1/NOX4 balance and VSMC phenotype. Using an inducible PDIA1 overexpression model in VSMC, we showed that early PDIA1 overexpression (for 24-48 h) increased NOX1 expression, hydrogen peroxide steady-state levels and spontaneous VSMC migration distances. Sustained PDIA1 overexpression for 72 h and 96 h supported high NOX1 levels while also increasing NOX4 expression and, remarkably, switched VSMC phenotype to differentiation. Differentiation was preceded by increased nuclear myocardin and serum response factor-response element activation, with no change in cell viability. Both NOX1 and hydrogen peroxide were necessary for later PDIA1-induced VSMC differentiation. In primary VSMC, PDIA1 knockdown decreased nuclear myocardin and increased the proliferating cell nuclear antigen expression. Newly-developed PDIA1-overexpressing mice (TgPDIA1) exhibited normal general and cardiovascular baseline phenotypes. However, in TgPDIA1 carotids, NOX1 was decreased while NOX4 and calponin expressions were enhanced, indicating overdifferentiation vs. normal carotids. Moreover, in a rabbit overdistension injury model during late vascular repair, PDIA1 silencing impaired VSMC redifferentiation and NOX1/NOX4 balance. Our results suggest a model in which PDIA1 acts as an upstream organizer of NOX1/NOX4 balance and related VSMC phenotype, accounting for baseline differentiation setpoint.

Protein Disulfide Isomerase 4 Drives Docetaxel Resistance in Prostate Cancer

BACKGROUND

Protein disulfide isomerase 4 (PDIA4) has been reported to be closely associated with chemoresistance in several types of malignancies. But the pathogenic mechanisms of PDIA4 involved in docetaxel (DTX) resistance in prostate cancer (PCa) are still unknown. Hence, this study was conducted to evaluate the potential effect of PDIA4 on chemoresistance to DTX in PCa cells and to investigate the underlying mechanisms.

METHODS

Two types of DTX-resistant PCa cells, that is, DTX-resistant PC-3 cells (PC-3/DTXR) and C4-2B cells (C4-2B/DTXR) were developed, as well as the parental PC-3 and C4-2B cells were obtained to investigate these issues. Short hairpin RNAs targeting human PDIA4 to knockdown the expression of PDIA4 or PDIA4-expressing adenoviral vectors to overexpress the PDIA4 were transfected into PCa cells to study the underlying mechanisms of PDIA4 involving in PCa DTX resistance.

RESULTS

Results showed that PDIA4 exhibited a dramatic overexpression in PC-3/DTXR and C4-2B/DTXR cells. Down-regulation of PDIA4 by infecting PC-3/DTXR and C4-2B/DTXR cells with shPDIA4 lentivirus stimulated cell death by prompting apoptosis. Up-regulation of PDIA4 by infecting PC-3 and C4-2B cells with PDIA4-expressing adenovirus showed severer resistance to DTX. In addition, PDIA4 up-regulation induced phosphorylated protein kinase B (Akt) expression, while PDIA4 knockdown significantly inhibited the expression in PCa cells.

CONCLUSIONS

Our study indicates that PDIA4 is a negative regulator of PCa cell apoptosis and plays a critical role in PCa DTX resistance by activating the Akt-signaling pathway. Thereby, it implies that targeting PDIA4 could be a potential adjuvant therapeutic approach against DTX resistance in PCa.

Analysis of splice variants of the human protein disulfide isomerase (P4HB) gene

BACKGROUND

Protein Disulfide Isomerases are thiol oxidoreductase chaperones from thioredoxin superfamily with crucial roles in endoplasmic reticulum proteostasis, implicated in many diseases. The family prototype PDIA1 is also involved in vascular redox cell signaling. PDIA1 is coded by the P4HB gene. While forced changes in P4HB gene expression promote physiological effects, little is known about endogenous P4HB gene regulation and, in particular, gene modulation by alternative splicing. This study addressed the P4HB splice variant landscape.

RESULTS

Ten protein coding sequences (Ensembl) of the P4HB gene originating from alternative splicing were characterized. Structural features suggest that except for P4HB-021, other splice variants are unlikely to exert thiol isomerase activity at the endoplasmic reticulum. Extensive analyses using FANTOM5, ENCODE Consortium and GTEx project databases as RNA-seq data sources were performed. These indicated widespread expression but significant variability in the degree of isoform expression among distinct tissues and even among distinct locations of the same cell, e.g., vascular smooth muscle cells from different origins. P4HB-02, P4HB-027 and P4HB-021 were relatively more expressed across each database, the latter particularly in vascular smooth muscle. Expression of such variants was validated by qRT-PCR in some cell types. The most consistently expressed splice variant was P4HB-021 in human mammary artery vascular smooth muscle which, together with canonical P4HB gene, had its expression enhanced by serum starvation.

CONCLUSIONS

Our study details the splice variant landscape of the P4HB gene, indicating their potential role to diversify the functional reach of this crucial gene. P4HB-021 splice variant deserves further investigation in vascular smooth muscle cells.

Ehrlichia chaffeensis EplA Interaction With Host Cell Protein Disulfide Isomerase Promotes Infection

Ehrlichia chaffeensis is an obligate intracellular bacterium that invades monocytes to cause the emerging and potentially severe disease, monocytic ehrlichiosis. Ehrlichial invasion of host cells, a process that is essential for the bacterium's survival and pathogenesis, is incompletely understood. In this study, we identified ECH_0377, henceforth designated as EplA (E. chaffeensis PDI ligand A) as an E. chaffeensis adhesin that interacts with host cell protein disulfide isomerase (PDI) to mediate bacterial entry into host cells. EplA is an outer membrane protein that E. chaffeensis expresses during growth in THP-1 monocytic cells. Canine sera confirmed to be positive for exposure to Ehrlichia spp. recognized recombinant EplA, indicating that it is expressed during infection in vivo. EplA antiserum inhibited the bacterium's ability to infect monocytic cells. The EplA-PDI interaction was confirmed via co-immunoprecipitation. Treating host cell surfaces with antibodies that inhibit PDI and/or thioredoxin-1 thiol reductase activity impaired E. chaffeensis infection. Chemical reduction of host cell surfaces, but not bacterial surfaces with tris(2-carboxyethyl)phosphine (TCEP) restored ehrlichial infectivity in the presence of the PDI-neutralizing antibody. Antisera specific for EplA C-terminal residues 95-104 (EplA₉₅₋₁₀₄) or outer membrane protein A amino acids 53-68 (OmpA₅₃₋₆₈) reduced E. chaffeensis infection of THP-1 cells. Notably, TCEP rescued ehrlichial infectivity of bacteria that had been treated with anti-EplA₉₅₋₁₀₄, but not anti-EcOmpA₅₃₋₆₈. These results demonstrate that EplA contributes to E. chaffeensis infection of monocytic cells by engaging PDI and exploiting the enzyme's reduction of host cell surface disulfide bonds in an EplA C-terminus-dependent manner and identify EplA₉₅₋₁₀₄ and EcOmpA₅₃₋₆₈ as novel ehrlichial receptor binding domains.

Endoplasmic Reticulum Stress Induced by Toxic Elements-a Review of Recent Developments

Endoplasmic reticulum of all eukaryotic cells is a membrane-bound organelle. Under electron microscope it appears as parallel arrays of "rough membranes" and a maze of "smooth vesicles" respectively. It performs various functions in cell, i.e., synthesis of proteins to degradation of xenobiotics. Bioaccumulation of drugs/chemicals/xenobiotics in the cytosol can trigger ER stress. It is recognized by the accumulation of unfolded or misfolded proteins in the lumen of ER. Present review summarizes the present status of knowledge on ER stress caused by toxic elements, viz arsenic, cadmium, lead, mercury, copper, chromium, and nickel. While inorganic arsenic may induce various glucose-related proteins, i.e., GRP78, GRP94 and CHOP, XBP1, and calpains, cadmium upregulates GRP78. Antioxidants like ascorbic acid, NAC, and Se inhibit the expression of UPR. Exposure to lead also changes ER stress related genes, i.e., GRP 78, GRP 94, ATF4, and ATF6. Mercury too upregulates these genes. Nickel, a carcinogenic element upregulates the expression of Bak, cytochrome C, caspase-3, caspase-9, caspase-12, and GADD 153. Much is not known on ER stress caused by nanoparticles. The review describes inter-organelle association between mitochondria and ER. It also discusses the interdependence between oxidative stress and ER stress. A cross talk amongst different cellular components appears essential to disturb pathways leading to cell death. However, these molecular switches within the signaling network used by toxic elements need to be identified. Nevertheless, ER stress especially caused by toxic elements still remains to be an engaging issue.

Role of the ERO1-PDI interaction in oxidative protein folding and disease

Protein folding in the endoplasmic reticulum is an oxidative process that relies on protein disulfide isomerase (PDI) and endoplasmic reticulum oxidase 1 (ERO1). Over 30% of proteins require the chaperone PDI to promote disulfide bond formation. PDI oxidizes cysteines in nascent polypeptides to form disulfide bonds and can also reduce and isomerize disulfide bonds. ERO1 recycles reduced PDI family member PDIA1 using a FAD cofactor to transfer electrons to oxygen. ERO1 dysfunction critically affects several diseases states. Both ERO1 and PDIA1 are overexpressed in cancers and implicated in diabetes and neurodegenerative diseases. Cancer-associated ERO1 promotes cell migration and invasion. Furthermore, the ERO1-PDIA1 interaction is critical for epithelial-to-mesenchymal transition. Co-expression analysis of ERO1A gene expression in cancer patients demonstrated that ERO1A is significantly upregulated in lung adenocarcinoma (LUAD), glioblastoma and low-grade glioma (GBMLGG), pancreatic ductal adenocarcinoma (PAAD), and kidney renal papillary cell carcinoma (KIRP) cancers. ERO1Α knockdown gene signature correlates with knockdown of cancer signaling proteins including IGF1R, supporting the search for novel, selective ERO1 inhibitors for the treatment of cancer. In this review, we explore the functions of ERO1 and PDI to support inhibition of this interaction in cancer and other diseases.

Binding of Host Cell Surface Protein Disulfide Isomerase by Anaplasma phagocytophilum Asp14 Enables Pathogen Infection

Diverse intracellular pathogens rely on eukaryotic cell surface disulfide reductases to invade host cells. Pharmacologic inhibition of these enzymes is cytotoxic, making it impractical for treatment. Identifying and mechanistically dissecting microbial proteins that co-opt surface reductases could reveal novel targets for disrupting this common infection strategy. Anaplasma phagocytophilum invades neutrophils by an incompletely defined mechanism to cause the potentially fatal disease granulocytic anaplasmosis. The bacterium's adhesin, Asp14, contributes to invasion by virtue of its C terminus engaging an unknown receptor. Yeast-two hybrid analysis identified protein disulfide isomerase (PDI) as an Asp14 binding partner. Coimmunoprecipitation confirmed the interaction and validated it to be Asp14 C terminus dependent. PDI knockdown and antibody-mediated inhibition of PDI reductase activity impaired A. phagocytophilum infection of but not binding to host cells. Infection during PDI inhibition was rescued when the bacterial but not host cell surface disulfide bonds were chemically reduced with tris(2-carboxyethyl)phosphine-HCl (TCEP). TCEP also restored bacterial infectivity in the presence of an Asp14 C terminus blocking antibody that otherwise inhibits infection. A. phagocytophilum failed to productively infect myeloid-specific-PDI conditional-knockout mice, marking the first demonstration of in vivo microbial dependency on PDI for infection. Mutational analyses identified the Asp14 C-terminal residues that are critical for binding PDI. Thus, Asp14 binds and brings PDI proximal to A. phagocytophilum surface disulfide bonds that it reduces, which enables cellular and in vivo infection.IMPORTANCEAnaplasma phagocytophilum infects neutrophils to cause granulocytic anaplasmosis, an emerging potentially fatal disease and the second-most common tick-borne illness in the United States. Treatment options are limited, and no vaccine exists. Due to the bacterium's obligatory intracellular lifestyle, A. phagocytophilum survival and pathogenesis are predicated on its ability to enter host cells. Understanding its invasion mechanism will yield new targets for preventing bacterial entry and, hence, disease. We report a novel entry pathway in which the A. phagocytophilum outer membrane protein Asp14 binds host cell surface protein disulfide isomerase via specific C-terminal residues to promote reduction of bacterial surface disulfide bonds, which is critical for cellular invasion and productive infection in vivo Targeting the Asp14 C terminus could be used to prevent/treat granulocytic anaplasmosis. Our findings have broad implications, as a thematically similar approach could be applied to block infection by other intracellular microbes that exploit cell surface reductases.

SILAC-based quantitative proteomics reveals pleiotropic, phenotypic modulation in primary murine macrophages infected with the protozoan pathogen Leishmania donovani

Leishmaniases are major vector-borne tropical diseases responsible for great human morbidity and mortality, caused by protozoan, trypanosomatid parasites of the genus Leishmania. In the mammalian host, parasites survive and multiply within mononuclear phagocytes, especially macrophages. However, the underlying mechanisms by which Leishmania spp. affect their host are not fully understood. Herein, proteomic alterations of primary, bone marrow-derived BALB/c macrophages are documented after 72 h of infection with Leishmania donovani insect-stage promastigotes, applying a SILAC-based, quantitative proteomics approach. The protocol was optimised by combining strong anion exchange and gel electrophoresis fractionation that displayed similar depth of analysis (combined total of 6189 mouse proteins). Our analyses revealed 86 differentially modulated proteins (35 showing increased and 51 decreased abundance) in response to Leishmania donovani infection. The proteomics results were validated by analysing the abundance of selected proteins. Intracellular Leishmania donovani infection led to changes in various host cell biological processes, including primary metabolism and catabolic process, with a significant enrichment in lysosomal organisation. Overall, our analysis establishes the first proteome of bona fide primary macrophages infected ex vivo with Leishmania donovani, revealing new mechanisms acting at the host/pathogen interface. SIGNIFICANCE: Little is known on proteome changes that occur in primary macrophages after Leishmania donovani infection. This study describes a SILAC-based quantitative proteomics approach to characterise changes of bone marrow-derived macrophages infected with L. donovani promastigotes for 72 h. With the application of SILAC and the use of SAX and GEL fractionation methods, we have tested new routes for proteome quantification of primary macrophages. The protocols developed here can be applicable to other diseases and pathologies. Moreover, this study sheds important new light on the "proteomic reprogramming" of infected macrophages in response to L. donovani promastigotes that affects primary metabolism, cellular catabolic processes, and lysosomal/vacuole organisation. Thus, our study reveals key molecules and processes that act at the host/pathogen interface that may inform on new immuno- or chemotherapeutic interventions to combat leishmaniasis.

Male-Specific Protein Disulphide Isomerase Function is Essential for Plasmodium Transmission and a Vulnerable Target for Intervention

Inhibiting transmission of Plasmodium is an essential strategy in malaria eradication, and the biological process of gamete fusion during fertilization is a proven target for this approach. Lack of knowledge of the mechanisms underlying fertilization have been a hindrance in the development of transmission-blocking interventions. Here we describe a protein disulphide isomerase essential for malarial transmission (PDI-Trans/PBANKA_0820300) to the mosquito. We show that PDI-Trans activity is male-specific, surface-expressed, essential for fertilization/transmission, and exhibits disulphide isomerase activity which is up-regulated post-gamete activation. We demonstrate that PDI-Trans is a viable anti-malarial drug and vaccine target blocking malarial transmission with the use of PDI inhibitor bacitracin (98.21%/92.48% reduction in intensity/prevalence), and anti-PDI-Trans antibodies (66.22%/33.16% reduction in intensity/prevalence). To our knowledge, these results provide the first evidence that PDI function is essential for malarial transmission, and emphasize the potential of anti-PDI agents to act as anti-malarials, facilitating the future development of novel transmission-blocking interventions.

Role of Platelet Activation and Oxidative Stress in the Evolution of Myocardial Infarction

Myocardial infarction, commonly known as heart attack, evolves from the rupture of unstable atherosclerotic plaques to coronary thrombosis and myocardial ischemia–reperfusion injury. A body of evidence supports a close relationship between the alterations following an ischemia–reperfusion injury-induced oxidative stress and platelet activity. Through their critical role in thrombogenesis and inflammatory responses, platelets are fully (totally) implicated from atherothrombotic plaque formation to myocardial infarction onset and expansion. However, mere platelet aggregation prevention does not offer full protection, suggesting that other antiplatelet therapy mechanisms may also be involved. Thus, the present review discusses the integrative role of platelets, oxidative stress, and antiplatelet therapy in triggering myocardial infarction pathophysiology.

A comparative analysis of secreted protein disulfide isomerases from the tropical co-endemic parasites Schistosoma mansoni and Leishmania major

The human parasites Schistosoma mansoni and Leishmania major are co-endemic and a major threat to human health. Though displaying different tissue tropisms, they excrete/secrete similar subsets of intracellular proteins that, interacting with the host extracellular matrix (ECM), help the parasites invading the host. We selected one of the most abundant proteins found in the secretomes of both parasites, protein disulfide isomerase (PDI), and performed a comparative screening with surface plasmon resonance imaging (SPRi), looking for ECM binding partners. Both PDIs bind heparan sulfate; none of them binds collagens; each of them binds further ECM components, possibly linked to the different tropisms. We investigated by small-angle X-ray scattering both PDIs structures and those of a few complexes with host partners, in order to better understand the differences within this conserved family fold. Furthermore, we highlighted a previously undisclosed moonlighting behaviour of both PDIs, namely a concentration-dependent switch of function from thiol-oxidoreductase to holdase. Finally, we have tried to exploit the differences to look for possible compounds able to interfere with the redox activity of both PDI.

Bioinformatics analysis of four proteins of Leishmania donovani to guide epitopes vaccine design and drug targets selection

Visceral leishmaniasis (VL) is a serious and widespread parasitic disease caused by Leishmania donovani complex. The threat of this fatal disease continues due to the lack of ideal drugs or vaccines. In this study, we selected Amastin, CaNA2, Kmp-11 and PDI proteins of Leishmania donovani for study, which are VL vaccine candidates or possible drug targets. Eleven bioinformatics tools were used to analyze different aspects of these proteins, including amino acid composition, topology, signal peptide, secondary structure, surface properties, phosphorylation sites and kinases, protein binding sites, 3D homology modeling, B cell epitopes, MHC class Ⅰ and Ⅱ epitopes and protein-protein interactions. Finally, the functionally related amino acid sites and dominant epitopes of these proteins were founded. Some possible relationships between protein structure, phosphorylation sites, protein binding sites and epitopes were also discovered. High flexibility and random coils regions of protein have a tendency to be phosphorylated, bind proteins and present epitopes. Since some phosphorylation sites and their kinases are involved in Leishmania invasion and survival in host cells, they may be potential drug targets. Bioinformatics analysis helps us better understand protein function and find dominant epitopes to guide drug design and vaccine development.

Subverted regulation of Nox1 NADPH oxidase-dependent oxidant generation by protein disulfide isomerase A1 in colon carcinoma cells with overactivated KRas

Protein disulfide isomerases including PDIA1 are implicated in cancer progression, but underlying mechanisms are unclear. PDIA1 is known to support vascular Nox1 NADPH oxidase expression/activation. Since deregulated reactive oxygen species (ROS) production underlies tumor growth, we proposed that PDIA1 is an upstream regulator of tumor-associated ROS. We focused on colorectal cancer (CRC) with distinct KRas activation levels. Analysis of RNAseq databanks and direct validation indicated enhanced PDIA1 expression in CRC with constitutive high (HCT116) vs. moderate (HKE3) and basal (Caco2) Ras activity. PDIA1 supported Nox1-dependent superoxide production in CRC; however, we first reported a dual effect correlated with Ras-level activity: in Caco2 and HKE3 cells, loss-of-function experiments indicate that PDIA1 sustains Nox1-dependent superoxide production, while in HCT116 cells PDIA1 restricted superoxide production, a behavior associated with increased Rac1 expression/activity. Transfection of Rac1G12V active mutant into HKE3 cells induced PDIA1 to become restrictive of Nox1-dependent superoxide, while in HCT116 cells treated with Rac1 inhibitor, PDIA1 became supportive of superoxide. PDIA1 silencing promoted diminished cell proliferation and migration in HKE3, not detectable in HCT116 cells. Screening of cell signaling routes affected by PDIA1 silencing highlighted GSK3β and Stat3. Also, E-cadherin expression after PDIA1 silencing was decreased in HCT116, consistent with PDIA1 support of epithelial-mesenchymal transition. Thus, Ras overactivation switches the pattern of PDIA1-dependent Rac1/Nox1 regulation, so that Ras-induced PDIA1 bypass can directly activate Rac1. PDIA1 may be a crucial regulator of redox-dependent adaptive processes related to cancer progression.

Analysis of Predicted Host-Parasite Interactomes Reveals Commonalities and Specificities Related to Parasitic Lifestyle and Tissues Tropism

The study of molecular host–parasite interactions is essential to understand parasitic infection and adaptation within the host system. As well, prevention and treatment of infectious diseases require a clear understanding of the molecular crosstalk between parasites and their hosts. Yet, large-scale experimental identification of host–parasite molecular interactions remains challenging, and the use of computational predictions becomes then necessary. Here, we propose a computational integrative approach to predict host—parasite protein—protein interaction (PPI) networks resulting from the human infection by 15 different eukaryotic parasites. We used an orthology-based approach to transfer high-confidence intraspecies interactions obtained from the STRING database to the corresponding interspecies homolog protein pairs in the host–parasite system. Our approach uses either the parasites predicted secretome and membrane proteins, or only the secretome, depending on whether they are uni- or multi-cellular, respectively, to reduce the number of false predictions. Moreover, the host proteome is filtered for proteins expressed in selected cellular localizations and tissues supporting the parasite growth. We evaluated the inferred interactions by analyzing the enriched biological processes and pathways in the predicted networks and their association with known parasitic invasion and evasion mechanisms. The resulting PPI networks were compared across parasites to identify common mechanisms that may define a global pathogenic hallmark. We also provided a study case focusing on a closer examination of the human–S. mansoni predicted interactome, detecting central proteins that have relevant roles in the human–S. mansoni network, and identifying tissue-specific interactions with key roles in the life cycle of the parasite. The predicted PPI networks can be visualized and downloaded at http://orthohpi.jensenlab.org.

Arachidonic Acid and Nitroarachidonic: Effects on NADPH Oxidase Activity

Arachidonic acid (AA) is a polyunsaturated fatty acid that participates in the inflammatory response mainly through bioactive-lipids formation in macrophages and also in the phagocytic NADPH oxidase 2 (NOX2) activation. NOX2 is the enzyme responsible for a huge superoxide formation in macrophages, essential to eliminate pathogens inside the phagosome. The oxidase is an enzymatic complex comprised of a membrane-bound flavocytochrome b ₅₅₈ (gp91^phox/p22^phox), three cytosolic subunits (p47^phox, p40^phox and p67^phox) and a Rac-GTPase. The enzyme becomes active when macrophages are exposed to appropriate stimuli that trigger the phosphorylation of cytosolic subunits and its migration to plasmatic membrane to form the active complex. It is proposed that AA stimulates NOX2 activity through AA interaction with different components of the NADPH oxidase complex. In inflammatory conditions, there is an increase in reactive oxygen and nitrogen species that results in the production of nitrated derivatives of AA, such as nitroarachidonic acid (NO₂-AA). NO₂-AA is capable to inhibit NOX2 activity by interfering with p47^phox migration to the membrane without affecting phosphorylation of cytosolic proteins. Also, NO₂-AA is capable to interact with protein disulfide isomerase (PDI), which is involved on NOX2 active complex formation. It has been demonstrated that NO₂-AA forms a covalent adduct with PDI that could prevent the interaction with NOX2 and it would explain the inhibitory effects of the fatty acid upon NOX2. Together, current data indicate that AA is an important activator of NOX2 formed in the early events of the inflammatory response, leading to a massive production of oxidants that may, in turn, promote NO₂-AA formation and shutting down the oxidative burst. Hence, AA and its derivatives could have antagonistic roles on NOX2 activity regulation.

Regulation of NADPH Oxidases by G Protein-Coupled Receptors

SIGNIFICANCE

G protein-coupled receptors (GPCR) are the largest group of cell surface receptors, which link cells to their environment. Reactive oxygen species (ROS) can act as important cellular signaling molecules. The family of NADPH oxidases generates ROS in response to activated cell surface receptors. Recent Advances: Various signaling pathways linking GPCRs and activation of NADPH oxidases have been characterized.

CRITICAL ISSUES

Still, a more detailed analysis of G proteins involved in the GPCR-mediated activation of NADPH oxidases is needed. In addition, a more precise discrimination of NADPH oxidase activation due to either upregulation of subunit expression or post-translational subunit modifications is needed. Also, the role of noncanonical modulators of NADPH oxidase activation in the response to GPCRs awaits further analyses.

FUTURE DIRECTIONS

As GPCRs are one of the most popular classes of investigational drug targets, further detailing of G protein-coupled mechanisms in the activation mechanism of NADPH oxidases as well as better understanding of the link between newly identified NADPH oxidase interaction partners and GPCR signaling will provide new opportunities for improved efficiency and decreased off target effects of therapies targeting GPCRs.

The Endoplasmic Reticulum Stress Response in Neuroprogressive Diseases: Emerging Pathophysiological Role and Translational Implications

The endoplasmic reticulum (ER) is the main cellular organelle involved in protein synthesis, assembly and secretion. Accumulating evidence shows that across several neurodegenerative and neuroprogressive diseases, ER stress ensues, which is accompanied by over-activation of the unfolded protein response (UPR). Although the UPR could initially serve adaptive purposes in conditions associated with higher cellular demands and after exposure to a range of pathophysiological insults, over time the UPR may become detrimental, thus contributing to neuroprogression. Herein, we propose that immune-inflammatory, neuro-oxidative, neuro-nitrosative, as well as mitochondrial pathways may reciprocally interact with aberrations in UPR pathways. Furthermore, ER stress may contribute to a deregulation in calcium homoeostasis. The common denominator of these pathways is a decrease in neuronal resilience, synaptic dysfunction and even cell death. This review also discusses how mechanisms related to ER stress could be explored as a source for novel therapeutic targets for neurodegenerative and neuroprogressive diseases. The design of randomised controlled trials testing compounds that target aberrant UPR-related pathways within the emerging framework of precision psychiatry is warranted.

Conserved Gene Microsynteny Unveils Functional Interaction Between Protein Disulfide Isomerase and Rho Guanine-Dissociation Inhibitor Families

Protein disulfide isomerases (PDIs) support endoplasmic reticulum redox protein folding and cell-surface thiol-redox control of thrombosis and vascular remodeling. The family prototype PDIA1 regulates NADPH oxidase signaling and cytoskeleton organization, however the related underlying mechanisms are unclear. Here we show that genes encoding human PDIA1 and its two paralogs PDIA8 and PDIA2 are each flanked by genes encoding Rho guanine-dissociation inhibitors (GDI), known regulators of RhoGTPases/cytoskeleton. Evolutionary histories of these three microsyntenic regions reveal their emergence by two successive duplication events of a primordial gene pair in the last common vertebrate ancestor. The arrangement, however, is substantially older, detectable in echinoderms, nematodes, and cnidarians. Thus, PDI/RhoGDI pairing in the same transcription orientation emerged early in animal evolution and has been largely maintained. PDI/RhoGDI pairs are embedded into conserved genomic regions displaying common cis-regulatory elements. Analysis of gene expression datasets supports evidence for PDI/RhoGDI coexpression in developmental/inflammatory contexts. PDIA1/RhoGDIα were co-induced in endothelial cells upon CRISP-R-promoted transcription activation of each pair component, and also in mouse arterial intima during flow-induced remodeling. We provide evidence for physical interaction between both proteins. These data support strong functional links between PDI and RhoGDI families, which likely maintained PDI/RhoGDI microsynteny along > 800-million years of evolution.

Molecular cloning and characterization of protein disulfide isomerase of Brugia malayi, a human lymphatic filarial parasite

Lymphatic filariasis results in an altered lymphatic system and the abnormal enlargement of body parts, causing pain, serious disability and social stigma. Effective vaccines are still not available nowadays, drugs against the disease is required. Protein disulfide isomerase (PDI) is an essential catalyst of the endoplasmic reticulum which is involved in folding and chaperone activities in different biological systems. Here, we report the enzymatic characterization of a Brugia malayi Protein disulfide isomerase (BmPDI), which was expressed and purified from Escherichia coli BL21 (DE3). Western blotting analysis showed the recombinant BmPDI could be recognized by anti-BmPDI Rabbit serum. The rBmPDI exhibited an optimum activity at pH 8 and 40 °C. The enzyme was inhibited by aurin and PDI inhibitor. Recombinant BmPDI showed interaction with recombinant Brugia malayi calreticulin (rBmCRT). The three-dimensional model for BmPDI and BmCRT was generated by homology modelling. A total of 25 hydrogen bonds were found to be formed between two interfaces. There are 259 non-bonded contacts present in the BmPDI-BmCRT complex and 12 salt bridges were formed in the interaction.

Vascular remodeling: A redox-modulated mechanism of vessel caliber regulation

Vascular remodeling, i.e. whole-vessel structural reshaping, determines lumen caliber in (patho)physiology. Here we review mechanisms underlying vessel remodeling, with emphasis in redox regulation. First, we discuss confusing terminology and focus on strictu sensu remodeling. Second, we propose a mechanobiological remodeling paradigm based on the concept of tensional homeostasis as a setpoint regulator. We first focus on shear-mediated models as prototypes of remodeling closely dominated by highly redox-sensitive endothelial function. More detailed discussions focus on mechanosensors, integrins, extracellular matrix, cytoskeleton and inflammatory pathways as potential of mechanisms potentially coupling tensional homeostasis to redox regulation. Further discussion of remodeling associated with atherosclerosis and injury repair highlights important aspects of redox vascular responses. While neointima formation has not shown consistent responsiveness to antioxidants, vessel remodeling has been more clearly responsive, indicating that despite the multilevel redox signaling pathways, there is a coordinated response of the whole vessel. Among mechanisms that may orchestrate redox pathways, we discuss roles of superoxide dismutase activity and extracellular protein disulfide isomerase. We then discuss redox modulation of aneurysms, a special case of expansive remodeling. We propose that the redox modulation of vascular remodeling may reflect (1) remodeling pathophysiology is dominated by a particularly redox-sensitive cell type, e.g., endothelial cells (2) redox pathways are temporospatially coordinated at an organ level across distinct cellular and acellular structures or (3) the tensional homeostasis setpoint is closely connected to redox signaling. The mechanobiological/redox model discussed here can be a basis for improved understanding of remodeling and helps clarifying mechanisms underlying prevalent hard-to-treat diseases.

Nitroxide 4-hydroxy-2,2',6,6'-tetramethylpiperidine 1-oxyl (Tempol) inhibits the reductase activity of protein disulfide isomerase via covalent binding to the Cys400 residue on CXXC redox motif at the a'active site

BACKGROUND AND AIM

Oxidative stress arising from inflammatory processes is a serious cause of cell and tissue damage. Tempol is an efficient antioxidant with superoxide dismutase-like activity. The purpose of this paper is to address the inhibition of protein disulfide isomerase (PDI), an essential redox chaperone whose active sites contain the Cys-Gly-His-Cys (CXXC) motif, by the nitroxide Tempol.

RESULTS

In the presence of Tempol (5-120 μM), the reductase activity of PDI was reversibly affected both in vitro and in activated mice neutrophils, with an IC₅₀ of 22.9 ± 10.8 μM. Inhibitory activity was confirmed by using both the insulin method and fluorescent formation of eosin-glutathione (E-GSH). The capacity of Tempol to bind the enzyme was determined by EPR and mass spectrometry. EPR Tempol signal decreased in the presence of PDI while remained unaffected when PDI thiols were previously blocked with NEM. When total protein was analyzed, 1 and 4 molecules of Tempol were bound to the protein. However, only one was found to be covalently bound to PDI at the a'active site. More specifically, Cys₄₀₀ was modified by Tempol.

CONCLUSION

We have shown that the nitroxide Tempol acts as an inhibitor of PDI through covalent binding to the Cys400 of the protein structure. Since PDI is coupled with the assembly of the NADPH oxidase complex of phagocytes, these findings reveal a novel action of Tempol that presents potential clinical applications for therapeutic intervention to target PDI knockdown in pathological processes in which this protein is engaged.

Nitroarachidonic acid (NO2AA) inhibits protein disulfide isomerase (PDI) through reversible covalent adduct formation with critical cysteines

BACKGROUND

Nitroarachidonic acid (NO₂AA) exhibits pleiotropic anti-inflammatory actions in a variety of cell types. We have recently shown that NO₂AA inhibits phagocytic NADPH oxidase 2 (NOX2) by preventing the formation of the active complex. Recent work indicates the participation of protein disulfide isomerase (PDI) activity in NOX2 activation. Cysteine (Cys) residues at PDI active sites could be targets for NO₂AA- nitroalkylation regulating PDI activity which could explain our previous observation.

METHODS

PDI reductase and chaperone activities were assessed using the insulin and GFP renaturation methods in the presence or absence of NO₂AA. To determine the covalent reaction with PDI as well as the site of reaction, the PEG-switch assay and LC-MS/MS studies were performed.

RESULTS AND CONCLUSIONS

We determined that both activities of PDI were inhibited by NO₂AA in a dose- and time- dependent manner and independent from release of nitric oxide. Since nitroalkenes are potent electrophiles and PDI has critical Cys residues for its activity, then formation of a covalent adduct between NO₂AA and PDI is feasible. To this end we demonstrated the reversible covalent modification of PDI by NO₂AA. Trypsinization of modified PDI confirmed that the Cys residues present in the active site a' of PDI were key targets accounting for nitroalkene modification.

GENERAL SIGNIFICANCE

PDI may contribute to NOX2 activation. As such, inhibition of PDI by NO₂AA might be involved in preventing NOX2 activation. Future work will be directed to determine if the covalent modifications observed play a role in the reported NO₂AA inhibition of NOX2 activity.

Potential Role of Protein Disulfide Isomerase in Metabolic Syndrome-Derived Platelet Hyperactivity

Metabolic Syndrome (MetS) has become a worldwide epidemic, alongside with a high socioeconomic cost, and its diagnostic criteria must include at least three out of the five features: visceral obesity, hypertension, dyslipidemia, insulin resistance, and high fasting glucose levels. MetS shows an increased oxidative stress associated with platelet hyperactivation, an essential component for thrombus formation and ischemic events in MetS patients. Platelet aggregation is governed by the peroxide tone and the activity of Protein Disulfide Isomerase (PDI) at the cell membrane. PDI redox active sites present active cysteine residues that can be susceptible to changes in plasma oxidative state, as observed in MetS. However, there is a lack of knowledge about the relationship between PDI and platelet hyperactivation under MetS and its metabolic features, in spite of PDI being a mediator of important pathways implicated in MetS-induced platelet hyperactivation, such as insulin resistance and nitric oxide dysfunction. Thus, the aim of this review is to analyze data available in the literature as an attempt to support a possible role for PDI in MetS-induced platelet hyperactivation.

Protein disulfide isomerases: Redox connections in and out of the endoplasmic reticulum

Protein disulfide isomerases are thiol oxidoreductase chaperones from thioredoxin superfamily. As redox folding catalysts from the endoplasmic reticulum (ER), their roles in ER-related redox homeostasis and signaling are well-studied. PDIA1 exerts thiol oxidation/reduction and isomerization, plus chaperone effects. Also, substantial evidence indicates that PDIs regulate thiol-disulfide switches in other cell locations such as cell surface and possibly cytosol. Subcellular PDI translocation routes remain unclear and seem Golgi-independent. The list of signaling and structural proteins reportedly regulated by PDIs keeps growing, via thiol switches involving oxidation, reduction and isomerization, S-(de)nytrosylation, (de)glutathyonylation and protein oligomerization. PDIA1 is required for agonist-triggered Nox NADPH oxidase activation and cell migration in vascular cells and macrophages, while PDIA1-dependent cytoskeletal regulation appears a converging pathway. Extracellularly, PDIs crucially regulate thiol redox signaling of thrombosis/platelet activation, e.g., integrins, and PDIA1 supports expansive caliber remodeling during injury repair via matrix/cytoskeletal organization. Some proteins display regulatory PDI-like motifs. PDI effects are orchestrated by expression levels or post-translational modifications. PDI is redox-sensitive, although probably not a mass-effect redox sensor due to kinetic constraints. Rather, the "all-in-one" organization of its peculiar redox/chaperone properties likely provide PDIs with precision and versatility in redox signaling, making them promising therapeutic targets.

Inflammatory and oxidative stress in rotavirus infection

Rotaviruses are the single leading cause of life-threatening diarrhea affecting children under 5 years of age. Rotavirus entry into the host cell seems to occur by sequential interactions between virion proteins and various cell surface molecules. The entry mechanisms seem to involve the contribution of cellular molecules having binding, chaperoning and oxido-reducing activities. It appears to be that the receptor usage and tropism of rotaviruses is determined by the species, cell line and rotavirus strain. Rotaviruses have evolved functions which can antagonize the host innate immune response, whereas are able to induce endoplasmic reticulum (ER) stress, oxidative stress and inflammatory signaling. A networking between ER stress, inflammation and oxidative stress is suggested, in which release of calcium from the ER increases the generation of mitochondrial reactive oxygen species (ROS) leading to toxic accumulation of ROS within ER and mitochondria. Sustained ER stress potentially stimulates inflammatory response through unfolded protein response pathways. However, the detailed characterization of the molecular mechanisms underpinning these rotavirus-induced stressful conditions is still lacking. The signaling events triggered by host recognition of virus-associated molecular patterns offers an opportunity for the development of novel therapeutic strategies aimed at interfering with rotavirus infection. The use of N-acetylcysteine, non-steroidal anti-inflammatory drugs and PPARγ agonists to inhibit rotavirus infection opens a new way for treating the rotavirus-induced diarrhea and complementing vaccines.

Reactive oxygen species in development and infection processes

Reactive oxygen species (ROS) are important signaling molecules that affect vegetative and pathogenic processes in pathogenic fungi. There is growing evidence that ROS are not only secreted during the interaction of host and pathogen but also involved in tightly controlled intracellular processes. The major ROS producing enzymes are NADPH oxidases (Nox). Recent investigations in fungi revealed that Nox-activity is responsible for the formation of infection structures, cytoskeleton architecture as well as interhyphal communication. However, information about the localization and site of action of the Nox complexes in fungi is limited and signaling pathways and intracellular processes affected by ROS have not been fully elucidated. This review focuses on the role of ROS as signaling molecules in fungal "model" organisms: it examines the role of ROS in vegetative and pathogenic processes and gives special attention to Nox complexes and their function as important signaling hubs.

Chasing stress signals - Exposure to extracellular stimuli differentially affects the redox state of cell compartments in the wild type and signaling mutants of Botrytis cinerea

Reactive oxygen species (ROS) are important molecules influencing intracellular developmental processes as well as plant pathogen interactions. They are produced at the infection site and affect the intracellular redox homeostasis. However, knowledge of ROS signaling pathways, their connection to other signaling cascades, and tools for the visualization of intra- and extracellular ROS levels and their impact on the redox state are scarce. By using the genetically encoded biosensor roGFP2 we studied for the first time the differences between the redox states of the cytosol, the intermembrane space of mitochondria and the ER in the filamentous fungus Botrytis cinerea. We showed that the ratio of oxidized to reduced glutathione inside of the cellular compartments differ and that the addition of hydrogen peroxide (H2O2), calcium chloride (CaCl2) and the fluorescent dye calcofluor white (CFW) have a direct impact on the cellular redox states. Dependent on the type of stress agents applied, the redox states were affected in the different cellular compartments in a temporally shifted manner. By integrating the biosensor in deletion mutants of bcnoxA, bcnoxB, bctrx1 and bcltf1 we further elucidated the putative roles of the different proteins in distinct stress-response pathways. We showed that the redox states of ΔbcnoxA and ΔbcnoxB display a wild-type pattern upon exposure to H2O2, but appear to be strongly affected by CaCl2 and CFW. Moreover, we demonstrated the involvement of the light-responsive transcription factor BcLtf1 in the maintenance of the redox state in the intermembrane space of the mitochondria. Finally, we report that CaCl2 as well as cell wall stress-inducing agents stimulate ROS production and that ΔbcnoxB produces significantly less ROS than the wild type and ΔbcnoxA.

von Willebrand factor is dimerized by protein disulfide isomerase

The protein disulfide isomerase is involved in VWF dimerization by initiating disulfide bond formation at cysteines 2771 and 2773. von Willebrand disease-associated mutations in the dimerization domain of von Willebrand factor disturb processing by the protein disulfide isomerase.

Endoplasmic Reticulum Stress and Associated ROS

The endoplasmic reticulum (ER) is a fascinating network of tubules through which secretory and transmembrane proteins enter unfolded and exit as either folded or misfolded proteins, after which they are directed either toward other organelles or to degradation, respectively. The ER redox environment dictates the fate of entering proteins, and the level of redox signaling mediators modulates the level of reactive oxygen species (ROS). Accumulating evidence suggests the interrelation of ER stress and ROS with redox signaling mediators such as protein disulfide isomerase (PDI)-endoplasmic reticulum oxidoreductin (ERO)-1, glutathione (GSH)/glutathione disuphide (GSSG), NADPH oxidase 4 (Nox4), NADPH-P450 reductase (NPR), and calcium. Here, we reviewed persistent ER stress and protein misfolding-initiated ROS cascades and their significant roles in the pathogenesis of multiple human disorders, including neurodegenerative diseases, diabetes mellitus, atherosclerosis, inflammation, ischemia, and kidney and liver diseases.

An ERp57-mediated disulphide exchange promotes the interaction between Burkholderia cenocepacia and epithelial respiratory cells

Previous studies have demonstrated that extracellular glutathione reduces the ability of the Cystic Fibrosis pathogen Burkholderia cenocepacia to infect primary or immortalized epithelial respiratory cells. We report here that the adhesion and invasion ability of B. cenocepacia is limited also by thiol-oxidizing and disulphide-reducing agents and by protein disulfide isomerase (PDI) inhibitors. PDI inhibitors also reduce the proinflammatory response elicited by cells in response to Burkholderia. These findings indicate that a membrane-associated PDI catalyzes thiol/disulphide exchange reactions which favor bacterial infection. The combined use of selective PDI inhibitors, RNA silencing and specific antibodies identified ERp57 as a major PDI involved in the interaction between B. cenocepacia and epithelial cells. This study contributes to the elucidation of the Burkholderia pathogenic mechanisms by showing that this microorganism exploits a membrane-associated host protein to infect epithelial cells and identifies ERp57 as a putative pharmacological target for the treatment of Burkholderia lung infections.

The Endoplasmic Reticulum Chaperone Calnexin Is a NADPH Oxidase NOX4 Interacting Protein

Within the family of NADPH oxidases, NOX4 is unique as it is predominantly localized in the endoplasmic reticulum, has constitutive activity, and generates hydrogen peroxide (H₂O₂). We hypothesize that these features are consequences of a so far unidentified NOX4-interacting protein. Two-dimensional blue native (BN) electrophorese combined with SDS-PAGE yielded NOX4 to reside in macromolecular complexes. Interacting proteins were screened by quantitative SILAC (stable isotope labeling of amino acids in cell culture) co-immunoprecipitation (Co-IP) in HEK293 cells stably overexpressing NOX4. By this technique, several interacting proteins were identified with calnexin showing the most robust interaction. Calnexin also resided in NOX4-containing complexes as demonstrated by complexome profiling from BN-PAGE. The calnexin NOX4 interaction could be confirmed by reverse Co-IP and proximity ligation assay, whereas NOX1, NOX2, or NOX5 did not interact with calnexin. Calnexin deficiency as studied in mouse embryonic fibroblasts from calnexin^−/− mice or in response to calnexin shRNA reduced cellular NOX4 protein expression and reactive oxygen species formation. Our results suggest that endogenous NOX4 forms macromolecular complexes with calnexin, which are needed for the proper maturation, processing, and function of NOX4 in the endoplasmic reticulum.

Disulfide Bonds as Regulators of Integrin Function in Thrombosis and Hemostasis

SIGNIFICANCE

Disulfide bonds are generally viewed as structure-stabilizing elements in proteins, but some display an alternative functional role as redox switches. Functional disulfide bonds have recently emerged as important regulators of integrin function in thrombosis and hemostasis.

RECENT ADVANCES

Functional disulfide bonds were identified in the β subunit of the major platelet integrin αIIbβ3 and in other integrins involved in thrombus formation that is, αvβ3 and α2β1. Most of these functional bonds are located in the four epidermal growth factor-like domains of the integrins. Redox agents such as glutathione and nitric oxide and enzymatic thiol isomerase activity were shown to regulate the function of these integrins by disulfide bond reduction and thiol/disulfide exchange.

CRITICAL ISSUES

Increasing evidence suggests that thiol isomerases such as protein disulfide isomerase (PDI) and Erp57 directly bind to the β3 subunit of αIIbβ3 and αvβ3 and regulate their function during thrombus formation. αIIbβ3 also exhibits an endogenous thiol isomerase activity. The specific functional disulfide bonds identified in the β3 subunit might be the targets for both exogenous and endogenous thiol isomerase activity.

FUTURE DIRECTIONS

Targeting redox sites of integrins or redox agents and enzymes that regulate their function can provide a useful tool for development of anti-thrombotic therapy. Hence, inhibitors of PDI are currently studied for this purpose.

Blastomyces Virulence Adhesin-1 Protein Binding to Glycosaminoglycans Is Enhanced by Protein Disulfide Isomerase

Blastomyces adhesin-1 (BAD-1) protein mediates the virulence of the yeast Blastomyces dermatitidis, in part by binding host lung tissue, the extracellular matrix, and cellular receptors via glycosaminoglycans (GAGs), such as heparan sulfate. The tandem repeats that make up over 90% of BAD-1 appear in their native state to be tightly folded into an inactive conformation, but recent work has shown that they become activated and adhesive upon reduction of a disulfide linkage. Here, atomic force microscopy (AFM) of a single BAD-1 molecule interacting with immobilized heparin revealed that binding is enhanced upon treatment with protein disulfide isomerase and dithiothreitol (PDI/DTT). PDI/DTT treatment of BAD-1 induced a plateau effect in atomic force signatures that was consistent with sequential rupture of tandem binding domains. Inhibition of PDI in murine macrophages blunted BAD-1 binding to heparin in vitro. Based on AFM, we found that a short Cardin-Weintraub sequence paired with a WxxWxxW sequence in the first, degenerate repeat at the N terminus of BAD-1 was sufficient to initiate heparin binding. Removal of half of the 41 BAD-1 tandem repeats led to weaker adhesion, illustrating their role in enhanced binding. Mass spectroscopy of the tandem repeat revealed that the PDI-induced interaction with heparin is characterized by ruptured disulfide bonds and that cysteine thiols remain reduced. Further binding studies showed direct involvement of thiols in heparin ligation. Thus, we propose that the N-terminal domain of BAD-1 governs the initial association with host GAGs and that proximity to GAG-associated host PDI catalyzes activation of additional binding motifs conserved within the tandem repeats, leading to enhanced avidity and availability of reduced thiols.

Pathogenic fungi and other microbes must adhere to host tissue to initiate infection. Surface adhesins promote this event and may be required for disease pathogenesis. We studied a fungal adhesin essential for virulence (BAD-1; Blastomyces adhesin-1) and found that host products induce its structural reconfiguration and foster its optimal binding to tissue structures.

Mitochondria and endoplasmic reticulum crosstalk in amyotrophic lateral sclerosis

Physical and functional interactions between mitochondria and the endoplasmic reticulum (ER) are crucial for cell life. These two organelles are intimately connected and collaborate to essential processes, such as calcium homeostasis and phospholipid biosynthesis. The connections between mitochondria and endoplasmic reticulum occur through structures named mitochondria associated membranes (MAMs), which contain lipid rafts and a large number of proteins, many of which serve multiple functions at different cellular sites. Growing evidence strongly suggests that alterations of ER-mitochondria interactions are involved in neurodegenerative disorders, including amyotrophic lateral sclerosis (ALS), a devastating and rapidly fatal motor neuron disease. Mutations in proteins that participate in ER-mitochondria interactions and MAM functions are increasingly being associated with genetic forms of ALS and other neurodegenerative diseases. This evidence strongly suggests that, rather than considering the two organelles separately, a better understanding of the disease process can derive from studying the alterations in their crosstalk. In this review we discuss normal and pathological ER-mitochondria interactions and the evidence that link them to ALS.

Protein disulfide isomerase expression increases in resistance arteries during hypertension development. Effects on Nox1 NADPH oxidase signaling

NADPH oxidases derived reactive oxygen species (ROS) play an important role in vascular function and remodeling in hypertension through redox signaling processes. Previous studies demonstrated that protein disulfide isomerase (PDI) regulates Nox1 expression and ROS generation in cultured vascular smooth muscle cells. However, the role of PDI in conductance and resistance arteries during hypertension development remains unknown. The aim of the present study was to investigate PDI expression and NADPH oxidase dependent ROS generation during hypertension development. Mesenteric resistance arteries (MRA) and thoracic aorta were isolated from 6, 8, and 12 week-old spontaneously hypertensive (SHR) and Wistar rats. ROS production (dihydroethidium fluorescence), PDI (WB, imunofluorescence), Nox1 and NOX4 (RT-PCR) expression were evaluated. Results show a progressive increase in ROS generation in MRA and aorta from 8 to 12 week-old SHR. This effect was associated with a concomitant increase in PDI and Nox1 expression only in MRA. Therefore, suggesting a positive correlation between PDI and Nox1 expression during the development of hypertension in MRA. In order to investigate if this effect was due to an increase in arterial blood pressure, pre hypertensive SHR were treated with losartan (20 mg/kg/day for 30 days), an AT1 receptor antagonist. Losartan decreased blood pressure and ROS generation in both vascular beds. However, only in SHR MRA losartan treatment lowered PDI and Nox1 expression to control levels. In MRA PDI inhibition (bacitracin, 0.5 mM) decreased Ang II redox signaling (p-ERK 1/2). Altogether, our results suggest that PDI plays a role in triggering oxidative stress and vascular dysfunction in resistance but not in conductance arteries, increasing Nox1 expression and activity. Therefore, PDI could be a new player in oxidative stress and functional alterations in resistance arteries during the establishment of hypertension.

Heterogeneous nuclear ribonucleoprotein E1 regulates protein disulphide isomerase translation in oxidized low-density lipoprotein-activated endothelial cells

AIMS

Endothelium-derived protein disulphide isomerase (PDI) is required for thrombus formation in vivo. But, how to control PDI overproduction in oxidized low-density lipoprotein (oxLDL)-activated vascular endothelial cells (VECs) is not well understood. In this study, we try to answer this question using our newly identified activator of mTOC1 3-benzyl-5-((2-nitrophenoxy) methyl)-dihydrofuran-2 (3H)-one (3BDO) that has been shown to protect VECs.

METHODS

First, we performed a proteomics analysis on the oxLDL-activated vascular VECs in the presence or absence of 3BDO. Next, we constructed the heterogeneous nuclear ribonucleoprotein E1 (hnRNP E1) mutants at Ser43 and used the RNA-ChIP technique to investigate the relationship between hnRNP E1 and PDI production. Furthermore, we examined the effect of 3BDO on oxLDL-altered phosphorylation of Akt1 and Akt2. Finally, we studied the effect of 3BDO on oxLDL-altered PDI protein level in apolipoprotein E(-/-) mice with advanced atherosclerosis.

RESULTS

In VECs, oxLDL-increased PDI protein level, induced hnRNP E1 phosphorylation at Ser43, suppressed the binding of hnRNP E1 to PDI 5'UTR and induced the phosphorylation of Akt2 but not Akt1. All of these processes were blocked by 3BDO. Importantly, Ser43 mutant of hnRNP E1 inhibited the increase of PDI protein level and the decrease of the binding of hnRNP E1 and PDI 5'UTR induced by oxLDL. Furthermore, 3BDO suppressed oxLDL-induced PDI protein increase in the serum and plaque endothelium of apolipoprotein E(-/-) mice.

CONCLUSION

hnRNP E1 is a new regulator of PDI translation in oxLDL-activated VECs, and 3BDO is a powerful agent for controlling PDI overproduction.

The dehydrogenase region of the NADPH oxidase component Nox2 acts as a protein disulfide isomerase (PDI) resembling PDIA3 with a role in the binding of the activator protein p67 (phox.)

The superoxide (O(·-) 2)-generating NADPH oxidase of phagocytes consists of a membrane component, cytochrome b 558 (a heterodimer of Nox2 and p22 (phox) ), and four cytosolic components, p47 (phox) , p67 (phox) , p40 (phox) , and Rac. The catalytic component, responsible for O(·-) 2 generation, is Nox2. It is activated by the interaction of the dehydrogenase region (DHR) of Nox2 with the cytosolic components, principally with p67 (phox) . Using a peptide-protein binding assay, we found that Nox2 peptides containing a (369)CysGlyCys(371) triad (CGC) bound p67 (phox) with high affinity, dependent upon the establishment of a disulfide bond between the two cysteines. Serially truncated recombinant Nox2 DHR proteins bound p67 (phox) only when they comprised the CGC triad. CGC resembles the catalytic motif (CGHC) of protein disulfide isomerases (PDIs). This led to the hypothesis that Nox2 establishes disulfide bonds with p67 (phox) via a thiol-dilsulfide exchange reaction and, thus, functions as a PDI. Evidence for this was provided by the following: (1) Recombinant Nox2 protein, which contained the CGC triad, exhibited PDI-like disulfide reductase activity; (2) Truncation of Nox2 C-terminal to the CGC triad or mutating C369 and C371 to R, resulted in loss of PDI activity; (3) Comparison of the sequence of the DHR of Nox2 with PDI family members revealed three small regions of homology with PDIA3; (4) Two monoclonal anti-Nox2 antibodies, with epitopes corresponding to regions of Nox2/PDIA3 homology, reacted with PDIA3 but not with PDIA1; (5) A polyclonal anti-PDIA3 (but not an anti-PDIA1) antibody reacted with Nox2; (6) p67 (phox) , in which all cysteines were mutated to serines, lost its ability to bind to a Nox2 peptide containing the CGC triad and had an impaired capacity to support oxidase activity in vitro. We propose a model of oxidase assembly in which binding of p67 (phox) to Nox2 via disulfide bonds, by virtue of the intrinsic PDI activity of Nox2, stabilizes the primary interaction between the two components.

ER stress and unfolded protein response in amyotrophic lateral sclerosis-a controversial role of protein disulphide isomerase

Accumulation of proteins in aberrant conformation occurs in many neurodegenerative diseases. Furthermore, dysfunctions in protein handling in endoplasmic reticulum (ER) and the following ER stress have been implicated in a vast number of diseases, such as amyotrophic lateral sclerosis (ALS). During excessive ER stress unfolded protein response (UPR) is activated to return ER to its normal physiological balance. The exact mechanisms of protein misfolding, accumulation and the following ER stress, which could lead to neurodegeneration, and the question whether UPR is a beneficial compensatory mechanism slowing down the neurodegenerative processes, are of interest. Protein disulphide isomerase (PDI) is a disulphide bond-modulating ER chaperone, which can also facilitate the ER-associated degradation (ERAD) of misfolded proteins. In this review we discuss the recent findings of ER stress, UPR and especially the role of PDI in ALS.

Protein disulfide isomerase a multifunctional protein with multiple physiological roles

Protein disulfide isomerase (PDI), is a member of the thioredoxin superfamily of redox proteins. PDI has three catalytic activities including, thiol-disulfide oxireductase, disulfide isomerase and redox-dependent chaperone. Originally, PDI was identified in the lumen of the endoplasmic reticulum and subsequently detected at additional locations, such as cell surfaces and the cytosol. This review will provide an overview of the recent advances in relating the structural features of PDI to its multiple catalytic roles as well as its physiological and pathophysiological functions related to redox regulation and protein folding.