Discovery of 5-Hydroxy-1,4-naphthoquinone (Juglone) Derivatives as Dual Effective Agents Targeting Platelet-Cancer Interplay through Protein Disulfide Isomerase Inhibition

In this study, a series of 2- and/or 3-substituted juglone derivatives were designed and synthesized. Among them, 9, 18, 22, 30, and 31 showed stronger inhibition activity against cell surface PDI or recombinant PDI and higher inhibitory effects on U46619- and/or collagen-induced platelet aggregation than juglone. The glycosylated derivatives 18 and 22 showed improved selectivity for inhibiting the proliferation of multiple myeloma RPMI 8226 cells, and the IC50 values reached 61 and 48 nM, respectively, in a 72 h cell viability test. In addition, 18 and 22 were able to prevent tumor cell-induced platelet aggregation and platelet-enhanced tumor cell proliferation. The molecular docking showed the amino acid residues Gln243, Phe440, and Leu443 are important for the compound-protein interaction. Our results reveal the potential of juglone derivatives to serve as novel antiplatelet and anticancer dual agents, which are available to interrupt platelet-cancer interplay through covalent binding to PDI catalytic active site.

Activation of goblet-cell stress sensor IRE1β is controlled by the mucin chaperone AGR2

Intestinal goblet cells are secretory cells specialized in the production of mucins, and as such are challenged by the need for efficient protein folding. Goblet cells express Inositol-Requiring Enzyme-1β (IRE1β), a unique sensor in the unfolded protein response (UPR), which is part of an adaptive mechanism that regulates the demands of mucin production and secretion. However, how IRE1β activity is tuned to mucus folding load remains unknown. We identified the disulfide isomerase and mucin chaperone AGR2 as a goblet cell-specific protein that crucially regulates IRE1β-, but not IRE1α-mediated signaling. AGR2 binding to IRE1β disrupts IRE1β oligomerization, thereby blocking its downstream endonuclease activity. Depletion of endogenous AGR2 from goblet cells induces spontaneous IRE1β activation, suggesting that alterations in AGR2 availability in the endoplasmic reticulum set the threshold for IRE1β activation. We found that AGR2 mutants lacking their catalytic cysteine, or displaying the disease-associated mutation H117Y, were no longer able to dampen IRE1β activity. Collectively, these results demonstrate that AGR2 is a central chaperone regulating the goblet cell UPR by acting as a rheostat of IRE1β endonuclease activity.

ARID1A loss induces P4HB to activate fibroblasts to support lung cancer cell growth, invasion, and chemoresistance

Loss of AT-interacting domain-rich protein 1A (ARID1A) frequently occurs in human malignancies including lung cancer. The biological consequence of ARID1A mutation in lung cancer is not fully understood. This study was designed to determine the effect of ARID1A-depleted lung cancer cells on fibroblast activation. Conditioned media was collected from ARID1A-depleted lung cancer cells and employed to treat lung fibroblasts. The proliferation and migration of lung fibroblasts were investigated. The secretory genes were profiled in lung cancer cells upon ARID1A knockdown. Antibody-based neutralization was utilized to confirm their role in mediating the cross-talk between lung cancer cells and fibroblasts. NOD-SCID-IL2RgammaC-null (NSG) mice received tumor tissues from patients with ARID1A-mutated lung cancer to establish patient-derived xenograft (PDX) models. Notably, ARID1A-depleted lung cancer cells promoted the proliferation and migration of lung fibroblasts. Mechanistically, ARID1A depletion augmented the expression and secretion of prolyl 4-hydroxylase beta (P4HB) in lung cancer cells, which induced the activation of lung fibroblasts through the β-catenin signaling pathway. P4HB-activated lung fibroblasts promoted the proliferation, invasion, and chemoresistance in lung cancer cells. Neutralizing P4HB hampered the tumor growth and increased cisplatin cytotoxic efficacy in two PDX models. Serum P4HB levels were higher in ARID1A-mutated lung cancer patients than in healthy controls. Moreover, increased serum levels of P4HB were significantly associated with lung cancer metastasis. Together, our work indicates a pivotal role for P4HB in orchestrating the cross-talk between ARID1A-mutated cancer cells and cancer-associated fibroblasts during lung cancer progression. P4HB may represent a promising target for improving lung cancer treatment.

Biophysical and in-silico studies on the structure-function relationship of Brugia malayi protein disulfide isomerase

Human Lymphatic filariasis is caused by parasitic nematodes Wuchereria bancrofti, Brugia malayi, and Brugia timori. Protein disulfide isomerase (PDI), a redox-active enzyme, helps to form and isomerize the disulfide bonds, thereby acting as a chaperone. Such activity is essential for activating many essential enzymes and functional proteins. Brugia malayi protein disulfide isomerase (BmPDI) is crucial for parasite survival and an important drug target. Here, we used a combination of spectroscopic and computational analysis to study the structural and functional changes in the BmPDI during unfolding. Tryptophan fluorescence data revealed two well-separated transitions during the unfolding process, suggesting that the unfolding of the BmPDI is non-cooperative. The binding of the fluorescence probe 8-anilino-1-naphthalene sulfonic acid dye (ANS) validated the results obtained by the pH unfolding. The dynamics of molecular simulation performed at different pH conditions revealed the structural basis of BmPDI unfolding. Detailed analysis suggested that under different pH, both the global structure and the conformational dynamics of the active site residues were differentially altered. Our multiparametric study reveals the differential dynamics and collective motions of BmPDI unfolding, providing insights into its structure-function relationship.Communicated by Ramaswamy H. Sarma.

Secretome Analyses Identify FKBP4 as a GBA1-Associated Protein in CSF and iPS Cells from Parkinson's Disease Patients with GBA1 Mutations

Mutations in the GBA1 gene increase the risk of developing Parkinson's disease (PD). However, most carriers of GBA1 mutations do not develop PD throughout their lives. The mechanisms of how GBA1 mutations contribute to PD pathogenesis remain unclear. Cerebrospinal fluid (CSF) is used for detecting pathological conditions of diseases, providing insights into the molecular mechanisms underlying neurodegenerative disorders. In this study, we utilized the proximity extension assay to examine the levels of metabolism-linked protein in the CSF from 17 PD patients carrying GBA1 mutations (GBA1-PD) and 17 idiopathic PD (iPD). The analysis of CSF secretome in GBA1-PD identified 11 significantly altered proteins, namely FKBP4, THOP1, GLRX, TXNDC5, GAL, SEMA3F, CRKL, APLP1, LRP11, CD164, and NPTXR. To investigate GBA1-associated CSF changes attributed to specific neuronal subtypes responsible for PD, we analyzed the cell culture supernatant from GBA1-PD-induced pluripotent stem cell (iPSC)-derived midbrain dopaminergic (mDA) neurons. The secretome analysis of GBA1-PD iPSC-derived mDA neurons revealed that five differently regulated proteins overlapped with those identified in the CSF analysis: FKBP4, THOP1, GLRX, GAL, and CRKL. Reduced intracellular level of the top hit, FKPB4, was confirmed via Western Blot. In conclusion, our findings identify significantly altered CSF GBA1-PD-associated proteins with FKPB4 being firmly attributed to mDA neurons.

Integrated meta-analysis of colorectal cancer public proteomic datasets for biomarker discovery and validation

The cancer biomarker field has been an object of thorough investigation in the last decades. Despite this, colorectal cancer (CRC) heterogeneity makes it challenging to identify and validate effective prognostic biomarkers for patient classification according to outcome and treatment response. Although a massive amount of proteomics data has been deposited in public data repositories, this rich source of information is vastly underused. Here, we attempted to reuse public proteomics datasets with two main objectives: i) to generate hypotheses (detection of biomarkers) for their posterior/downstream validation, and (ii) to validate, using an orthogonal approach, a previously described biomarker panel. Twelve CRC public proteomics datasets (mostly from the PRIDE database) were re-analysed and integrated to create a landscape of protein expression. Samples from both solid and liquid biopsies were included in the reanalysis. Integrating this data with survival annotation data, we have validated in silico a six-gene signature for CRC classification at the protein level, and identified five new blood-detectable biomarkers (CD14, PPIA, MRC2, PRDX1, and TXNDC5) associated with CRC prognosis. The prognostic value of these blood-derived proteins was confirmed using additional public datasets, supporting their potential clinical value. As a conclusion, this proof-of-the-concept study demonstrates the value of re-using public proteomics datasets as the basis to create a useful resource for biomarker discovery and validation. The protein expression data has been made available in the public resource Expression Atlas.

PDIA4 Is a Host Factor Important for Lymphocytic Choriomeningitis Virus Infection

Mammalian arenaviruses are rodent-borne zoonotic viruses, some of which can cause fatal hemorrhagic diseases in humans. The first discovered arenavirus, lymphocytic choriomeningitis virus (LCMV), has a worldwide distribution and can be fatal for transplant recipients. However, no FDA-approved drugs or vaccines are currently available. In this study, using a quantitative proteomic analysis, we identified a variety of host factors that could be needed for LCMV infection, among which we found that protein disulfide isomerase A4 (PDIA4), a downstream factor of endoplasmic reticulum stress (ERS), is important for LCMV infection. Biochemical analysis revealed that LCMV glycoprotein was the main viral component accounting for PDIA4 upregulation. The inhibition of ATF6-mediated ERS could prevent the upregulation of PDIA4 that was stimulated by LCMV infection. We further found that PDIA4 can affect the LCMV viral RNA synthesis processes and release. In summary, we conclude that PDIA4 could be a new target for antiviral drugs against LCMV.

Pan-Inhibition of Protein Disulfide Isomerase Caused Cell Death through Disrupting Cellular Proteostasis in Pancreatic Ductal Adenocarcinoma Cells

The protein disulfide isomerase (PDI) family is a group of thioredoxin endoplasmic reticulum (ER)-resident enzymes and molecular chaperones that play crucial roles in the correct folding of proteins. PDIs are upregulated in multiple cancer types and are considered a novel target for cancer therapy. In this study, we found that a potent pan-PDI inhibitor, E64FC26, significantly decreased the proliferation of pancreatic ductal adenocarcinoma (PDAC) cells. As expected, E64FC26 treatment increased ER stress and the unfolded protein response (UPR), as evidenced by upregulation of glucose-regulated protein, 78-kDa (GRP78), phosphorylated (p)-PKR-like ER kinase (PERK), and p-eukaryotic initiation factor 2α (eIF2α). Persistent ER stress was found to lead to apoptosis, ferroptosis, and autophagy, all of which are dependent on lysosomal functions. First, there was little cleaved caspase-3 in E64FC26-treated cells according to Western blotting, but a higher dose of E64FC26 was needed to induce caspase activity. Then, E64FC26-induced cell death could be reversed by adding the iron chelator, deferoxamine, and the reactive oxygen species scavengers, ferrostatin-1 and N-acetylcysteine. Furthermore, the autophagosome-specific marker, light chain 3B (LC3B)-II, increased, but the autolysosome marker, sequestosome 1 (SQSTM1)/p62, was not degraded in E64FC26-treated cells. Using the FUW mCherry-LC3 plasmid and acridine orange staining, we also discovered a lower number of acidic vesicles, such as autolysosomes and mature lysosomes, in E64FC26-treated cells. Finally, E64FC26 treatment increased the cathepsin L precursor (pre-CTSL) but decreased mature CTSL expression according to Western blotting, indicating a defective lysosome. These results suggested that the PDI inhibitor, E64FC26, might initially impede proper folding of proteins, and then induce ER stress and disrupt proteostasis, subsequently leading to lysosomal defects. Due to defective lysosomes, the extents of apoptosis and ferroptosis were limited, and fusion with autophagosomes was blocked in E64FC26-treated cells. Blockade of autolysosomal formation further led to the autophagic cell death of PDAC cells.

Establishment of prognostic model of bladder cancer based on apoptosis-related genes, in which P4HB promotes BLCA progression

BACKGROUND

A variety of apoptosis genes have been confirmed to be related to the occurrence and development of bladder cancer patients, but few studies have paid attention to their significance in the prognosis of bladder cancer. Therefore, this study explored the value of apoptosis-related genes in the prognosis of BLCA by using the data in TCGA database.

METHODS

We downloaded the mRNA expression profiles and corresponding clinical data of bladder cancer patients from TCGA database, and obtained 2411 apoptosis-related genes from Deathbase database. Screening out differentially expressed apoptosis-related genes. Cox regression was used to determine the prognostic value of apoptosis-related genes, and then a prognostic risk model was developed. A nomogram based on risk model was constructed to predict the prognosis of bladder cancer patients. At the same time, immune infiltration correlation analysis of genes in the prognosis model.

RESULTS

A prognostic model composed of 12 apoptosis-related genes was constructed. According to the risk score calculated by the model, patients were divided into high-risk group and low-risk group. There are significant differences in the expression of immune cells, immune function and immune checkpoint molecules between high-risk group and low-risk group. P4HB may promote bladder cancer progression.

CONCLUSION

Based on the differential expression of apoptosis-related genes, we established a risk model to predict the prognosis of bladder cancer patients, in which P4HB promotes BLCA progression.

Deciphering the immunological and prognostic features of bladder cancer through platinum-resistance-related genes analysis and identifying potential therapeutic target P4HB

Objectives

To identify the molecular subtypes and develop a scoring system for the tumor immune microenvironment (TIME) and prognostic features of bladder cancer (BLCA) based on the platinum-resistance-related (PRR) genes analysis while identifying P4HB as a potential therapeutic target.

Methods

In this study, we analyzed gene expression data and clinical information of 594 BLCA samples. We used unsupervised clustering to identify molecular subtypes based on the expression levels of PRR genes. Functional and pathway enrichment analyses were performed to understand the biological activities of these subtypes. We also assessed the TIME and developed a prognostic signature and scoring system. Moreover, we analyzed the efficacy of immune checkpoint inhibitors. Then we conducted real-time fluorescence quantitative polymerase chain reaction (RT-qPCR) experiments to detect the expression level of prolyl 4-hydroxylase subunit beta (P4HB) in BLCA cell lines. Transfection of small interference ribonucleic acid (siRNA) was performed in 5637 and EJ cells to knock down P4HB, and the impact of P4HB on cellular functions was evaluated through wound-healing and transwell assays. Finally, siRNA transfection of P4HB was performed in the cisplatin-resistant T24 cell to assess its impact on the sensitivity of BLCA to platinum-based chemotherapy drugs.

Results

In a cohort of 594 BLCA samples (TCGA-BLCA, n=406; GSE13507, n=188), 846 PRR-associated genes were identified by intersecting BLCA expression data from TCGA and GEO databases with the PRR genes from the HGSOC-Platinum database. Univariate Cox regression analysis revealed 264 PRR genes linked to BLCA prognosis. We identified three molecular subtypes (Cluster A-C) and the PRR scoring system based on PRR genes. Cluster C exhibited a better prognosis and lower immune cell infiltration compared to the other Clusters A and B. The high PRR score group was significantly associated with an immunosuppressive tumor microenvironment, poor clinical-pathological features, and a poor prognosis. Furthermore, the high PRR group showed higher expression of immune checkpoint molecules and a poorer response to immune checkpoint inhibitors than the low PRR group. The key PRR gene P4HB was highly expressed in BLCA cell lines, and cellular functional experiments in vitro indicate that P4HB may be an important factor influencing BLCA migration and invasion.

Conclusion

Our study demonstrates that the PRR signatures are significantly associated with clinical-pathological features, the TIME, and prognostic features. The key PRR gene, P4HB, s a biomarker for the individualized treatment of BLCA patients.

Naphthalimide-Based AIEgens for Sensing Protein Disulfide Isomerase through Thiol-Disulfide Redox Exchange

Aggregation-induced emission (AIE)-based fluorescent organic nanoparticles (FONPs) with distinctive characteristics are emerging as superior sensors due to their facile fabrication, high signal-to-noise ratio, and good biocompatibility. The present article delineates the detection and analysis of the redox behavior of the protein disulfide isomerase (PDI) enzyme by exploitation of the AIE of novel naphthalimide (NI) derivatives having thiol (-SH) and disulfide (-S-S-) moieties. Self-aggregated spherical-shaped organic nanoparticles were prepared by synthesized NI-based amphiphiles (NISH, NISS, NINSS, and TNINSH) through J-type aggregation in DMSO-water (fw = 99 vol %). Naphthyl residue containing NI-derived amphiphiles (NINSS and TNINSH) exhibited AIE (blue and yellow) at 470 and 550 nm, respectively, in DMSO-water (fw = 99 vol %). NINSS and TNINSH FONPs were suitably utilized in sensing PDI through their redox nature of thiol-disulfide exchange. Fluorescence quenching of NINSS FONPs was observed due to reduction of disulfide to thiol by PDI, whereas emission intensity was progressively red-shifted and enhanced ("Dual-AIE") for TNINSH (containing ER-targeting N-tosylethylenediamine), owing to oxidation of thiol to disulfide by PDI. NINSS and TNINSH FONPs were found to be highly efficient in sensing PDI through the AIE-based "fluorescence off/on" mechanism having limits of detection of ∼12.6-17.7 and ∼11.7-16.5 ng/mL, respectively. In vitro cell imaging for NIH3T3 (noncancer) and B16F10 (melanoma) cells with NINSS and TNINSH FONPs displayed excellent diagnosis of eukaryotic cells upon interaction with indigenous PDI. Notably, detection of cancer cells was more sensitive over the noncancerous cells by these FONPs due to overexpression of PDI within cancer cells.

LncRNA FAM225B Regulates PDIA4-Mediated Ovarian Cancer Cell Invasion and Migration via Modulating Transcription Factor DDX17

Objective

This study aimed to explore the roles and mechanisms of lncRNA FAM225B and PDIA4 in ovarian cancer.

Methods

RT-qPCR and Western blot assays were performed to detect the expression levels of the lncRNAs FAM225B, DDX17, and PDIA4 in the serum of patients with ovarian cancer and cell lines. Cells were transfected with lncRNA FAM225B- and PDIA4-related vectors to determine the malignant phenotypes using functional experiments. The mutual binding of lncRNA FAM225B and DDX17 was verified using RNA pull-down and RIP assays.

Results

The expression of lncRNAs FAM225B and PDIA4 was decreased in the serum of patients with ovarian cancer and cell lines. Restoration of lncRNA FAM225B or PDIA4 reduced cell proliferation, migration, and invasion abilities and elevated the apoptosis rate, whereas suppression of lncRNA FAM225B or PDIA4 exhibited an inverse trend. RNA pull-down and RIP assays revealed a direct interaction between lncRNA FAM225B and DDX17. ChIP assay revealed a relationship between DDX17 and the PDIA4 promoter. LncRNA FAM225B and DDX17 positively regulate PDIA4 expression. Downregulation of PDIA4 expression counteracts the suppressive effect of lncRNA FAM225B overexpression in ovarian cancer cells.

Conclusion

This research study supports the fact that lncRNA FAM225B in ovarian cancer can upregulate PDIA4 by directly binding to DDX17, inhibiting the activities of ovarian cancer cells.

Early plasma proteomic biomarkers and prediction model of acute respiratory distress syndrome after cardiopulmonary bypass: a prospective nested cohort study

BACKGROUND

Early recognition of the risk of acute respiratory distress syndrome (ARDS) after cardiopulmonary bypass (CPB) may improve clinical outcomes. The main objective of this study was to identify proteomic biomarkers and develop an early prediction model for CPB-ARDS.

METHODS

The authors conducted three prospective nested cohort studies of all consecutive patients undergoing cardiac surgery with CPB at Union Hospital of Tongji Medical College Hospital. Plasma proteomic profiling was performed in ARDS patients and matched controls (Cohort 1, April 2021-July 2021) at multiple timepoints: before CPB (T1), at the end of CPB (T2), and 24 h after CPB (T3). Then, for Cohort 2 (August 2021-July 2022), biomarker expression was measured and verified in the plasma. Furthermore, lung ischemia/reperfusion injury (LIRI) models and sham-operation were established in 50 rats to explore the tissue-level expression of biomarkers identified in the aforementioned clinical cohort. Subsequently, a machine learning-based prediction model incorporating protein and clinical predictors from Cohort 2 for CPB-ARDS was developed and internally validated. Model performance was externally validated on Cohort 3 (January 2023-March 2023).

RESULTS

A total of 709 proteins were identified, with 9, 29, and 35 altered proteins between ARDS cases and controls at T1, T2, and T3, respectively, in Cohort 1. Following quantitative verification of several predictive proteins in Cohort 2, higher levels of thioredoxin domain containing 5 (TXNDC5), cathepsin L (CTSL), and NPC intracellular cholesterol transporter 2 (NPC2) at T2 were observed in CPB-ARDS patients. A dynamic online predictive nomogram was developed based on three proteins (TXNDC5, CTSL, and NPC2) and two clinical risk factors (CPB time and massive blood transfusion), with excellent performance (precision: 83.33%, sensitivity: 93.33%, specificity: 61.16%, and F1 score: 85.05%). The mean area under the receiver operating characteristics curve (AUC) of the model after 10-fold cross-validation was 0.839 (95% CI: 0.824-0.855). Model discrimination and calibration were maintained during external validation dataset testing, with an AUC of 0.820 (95% CI: 0.685-0.955) and a Brier Score of 0.177 (95% CI: 0.147-0.206). Moreover, the considerably overexpressed TXNDC5 and CTSL proteins identified in the plasma of patients with CPB-ARDS, exhibited a significant upregulation in the lung tissue of LIRI rats.

CONCLUSIONS

This study identified several novel predictive biomarkers, developed and validated a practical prediction tool using biomarker and clinical factor combinations for individual prediction of CPB-ARDS risk. Assessing the plasma TXNDC5, CTSL, and NPC2 levels might identify patients who warrant closer follow-up and intensified therapy for ARDS prevention following major surgery.

PDI augments kainic acid-induced seizure activity and neuronal death by inhibiting PP2A-GluA2-PICK1-mediated AMPA receptor internalization in the mouse hippocampus

Protein disulfide isomerase (PDI) is a redox-active enzyme and also serves as a nitric oxide donor causing S-nitrosylation of cysteine residues in various proteins. Although PDI knockdown reduces α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor (AMPAR)-mediated neuronal activity, the underlying mechanisms are largely unknown. In the present study, we found that under physiological condition PDI knockdown increased CaMKII activity (phosphorylation) in the mouse hippocampus. However, PDI siRNA inhibited protein phosphatase (PP) 2A-mediated GluA2 S880 dephosphorylation by increasing PP2A oxidation, independent of S-nitrosylation. PDI siRNA also enhanced glutamate ionotropic receptor AMPA type subunit 1 (GluA1) S831 and GluA2 S880, but not GluA1 S845 and GluA2 Y869/Y873/Y876 phosphorylations, concomitant with the enhanced protein interacting with C kinase 1 (PICK1)-mediated AMPAR internalization. Furthermore, PDI knockdown attenuated seizure activity and neuronal damage in response to kainic acid (a non-desensitizing agonist of AMPAR). Therefore, these findings suggest that PDI may regulate surface AMPAR expression through PP2A-GluA2-PICK1 signaling pathway, and that PDI may be one of the therapeutic targets for epilepsy via AMPAR internalization without altering basal neurotransmission.

Protein disulfide isomerases as CSF biomarkers for the neuronal response to tau pathology

INTRODUCTION

Cerebrospinal fluid (CSF) biomarkers for specific cellular disease processes are lacking for tauopathies. In this translational study we aimed to identify CSF biomarkers reflecting early tau pathology-associated unfolded protein response (UPR) activation.

METHODS

We employed mass spectrometry proteomics and targeted immunoanalysis in a combination of biomarker discovery in primary mouse neurons in vitro and validation in patient CSF from two independent large multicentre cohorts (EMIF-AD MBD, n = 310; PRIDE, n = 771).

RESULTS

First, we identify members of the protein disulfide isomerase (PDI) family in the neuronal UPR-activated secretome and validate secretion upon tau aggregation in vitro. Next, we demonstrate that PDIA1 and PDIA3 levels correlate with total- and phosphorylated-tau levels in CSF. PDIA1 levels are increased in CSF from AD patients compared to controls and patients with tau-unrelated frontotemporal and Lewy body dementia (LBD).

HIGHLIGHTS

Neuronal unfolded protein response (UPR) activation induces the secretion of protein disulfide isomerases (PDIs) in vitro. PDIA1 is secreted upon tau aggregation in neurons in vitro. PDIA1 and PDIA3 levels correlate with total and phosphorylated tau levels in CSF. PDIA1 levels are increased in CSF from Alzheimer's disease (AD) patients compared to controls. PDIA1 levels are not increased in CSF from tau-unrelated frontotemporal dementia (FTD) and Lewy body dementia (LBD) patients.

Protein disulfide isomerase family mediated redox regulation in cancer

Protein disulfide isomerase (PDI) and its superfamilies are mainly endoplasmic reticulum (ER) resident proteins with essential roles in maintaining cellular homeostasis, via thiol oxidation/reduction cycles, chaperoning, and isomerization of client proteins. Since PDIs play an important role in ER homeostasis, their upregulation supports cell survival and they are found in a variety of cancer types. Despite the fact that the importance of PDI to tumorigenesis remains to be understood, it is emerging as a new therapeutic target in cancer. During the past decade, several PDI inhibitors has been developed and commercialized, but none has been approved for clinical use. In this review, we discuss the properties and redox regulation of PDIs within the ER and provide an overview of the last 5 years of advances regarding PDI inhibitors.

Protein Disulfide Isomerases Function as the Missing Link Between Diabetes and Cancer

Significance: Diabetes has long been recognized as an independent risk factor for cancer, but there is insufficient mechanistic understanding of biological mediators that bridge two disorders together. Understanding the pathogenic association between diabetes and cancer has become the focus of many studies, and findings are potentially valuable for the development of effective preventive or therapeutic strategies for both disorders. Recent Advances: A summary of literature reveals a possible connection between diabetes and cancer through the family of protein disulfide isomerase (PDI). Historical as well as the most recent findings on the structure, biochemistry, and biology of the PDI family were summarized in this review. Critical Issues: PDIs in general function as redox enzymes and protein chaperones to control the quality of proteins by correcting or otherwise eliminating misfolded proteins in conditions of oxidative stress and endoplasmic reticulum stress, respectively. However, individual members of the PDI family may contribute uniquely to the pathogenesis of diabetes and cancer. Studies of exemplary members such as protein disulfide isomerase-associated (PDIA) 1, PDIA6, and PDIA15 were reviewed to highlight their contributions in the pathogenesis of diabetes and cancer and how they can be potential links bridging the two disorders through the cross talk of signaling pathways. Future Directions: Apparently ubiquitous presence of the PDIs creates difficulties and challenges for scientific community to develop targeted therapeutics for the treatment of diabetes and cancer simultaneously. Understanding molecular contribution of individual PDI in the context of specific disease may provide some insights into the development of mechanism-based target-directed therapeutics. Antioxid. Redox Signal. 37, 1191-1205.

Association of Thrombin Generation With Leukocyte Inflammatory Profile in Patients With Acute Ischemic Stroke

BACKGROUND AND OBJECTIVES

Thrombosis is central to the pathogenesis of acute ischemic stroke, with higher thrombin generation being associated with increased stroke risk. The immune system may contribute to thrombin generation in stroke and thus may offer novel strategies for stroke prevention. This study addresses the research question regarding the relationship of thrombin generation to leukocyte gene expression in patients with acute ischemic stroke.

METHODS

We isolated RNA from whole blood and examined the relationship to thrombin generation capacity in patients with acute ischemic stroke. Due to its effects on thrombin generation, patients on anticoagulants were excluded from the study. The relationship of gene expression with peak thrombin was evaluated by analysis of covariance across peak thrombin quartiles adjusted for sex and age.

RESULTS

In 97 patients with acute ischemic stroke, peak thrombin was variable, ranging from 252.0 to 752.4 nM. Increased peak thrombin was associated with differences in thromboinflammatory leukocyte gene expression, including a decrease in ADAM metallopeptidase with thrombospondin type 1 motif 13 and an increase in nuclear factor κB (NF-κB)-activating protein, protein disulfide isomerase family A member 5, and tissue factor pathway inhibitor 2. Pathways associated with peak thrombin included interleukin 6 signaling, thrombin signaling, and NF-κB signaling. A linear discriminant analysis model summarizing the immune activation associated with peak thrombin in a first cohort of stroke could distinguish patients with low peak thrombin from high peak thrombin in a second cohort of 112 patients with acute ischemic stroke.

DISCUSSION

The identified genes and pathways support a role of the immune system contributing to thrombus formation in patients with stroke. These may have relevance to antithrombotic strategies for stroke prevention.

The Periplasmic Oxidoreductase DsbA Is Required for Virulence of the Phytopathogen Dickeya solani

In bacteria, the DsbA oxidoreductase is a crucial factor responsible for the introduction of disulfide bonds to extracytoplasmic proteins, which include important virulence factors. A lack of proper disulfide bonds frequently leads to instability and/or loss of protein function; therefore, improper disulfide bonding may lead to avirulent phenotypes. The importance of the DsbA function in phytopathogens has not been extensively studied yet. Dickeya solani is a bacterium from the Soft Rot Pectobacteriaceae family which is responsible for very high economic losses mainly in potato. In this work, we constructed a D. solani dsbA mutant and demonstrated that a lack of DsbA caused a loss of virulence. The mutant bacteria showed lower activities of secreted virulence determinants and were unable to develop disease symptoms in a potato plant. The SWATH-MS-based proteomic analysis revealed that the dsbA mutation led to multifaceted effects in the D. solani cells, including not only lower levels of secreted virulence factors, but also the induction of stress responses. Finally, the outer membrane barrier seemed to be disturbed by the mutation. Our results clearly demonstrate that the function played by the DsbA oxidoreductase is crucial for D. solani virulence, and a lack of DsbA significantly disturbs cellular physiology.

ER Stress in ERp57 Knockout Knee Joint Chondrocytes Induces Osteoarthritic Cartilage Degradation and Osteophyte Formation

Ageing or obesity are risk factors for protein aggregation in the endoplasmic reticulum (ER) of chondrocytes. This condition is called ER stress and leads to induction of the unfolded protein response (UPR), which, depending on the stress level, restores normal cell function or initiates apoptotic cell death. Here the role of ER stress in knee osteoarthritis (OA) was evaluated. It was first tested in vitro and in vivo whether a knockout (KO) of the protein disulfide isomerase ERp57 in chondrocytes induces sufficient ER stress for such analyses. ER stress in ERp57 KO chondrocytes was confirmed by immunofluorescence, immunohistochemistry, and transmission electron microscopy. Knee joints of wildtype (WT) and cartilage-specific ERp57 KO mice (ERp57 cKO) were analyzed by indentation-type atomic force microscopy (IT-AFM), toluidine blue, and immunofluorescence/-histochemical staining. Apoptotic cell death was investigated by a TUNEL assay. Additionally, OA was induced via forced exercise on a treadmill. ER stress in chondrocytes resulted in a reduced compressive stiffness of knee cartilage. With ER stress, 18-month-old mice developed osteoarthritic cartilage degeneration with osteophyte formation in knee joints. These degenerative changes were preceded by apoptotic death in articular chondrocytes. Young mice were not susceptible to OA, even when subjected to forced exercise. This study demonstrates that ER stress induces the development of age-related knee osteoarthritis owing to a decreased protective function of the UPR in chondrocytes with increasing age, while apoptosis increases. Therefore, inhibition of ER stress appears to be an attractive therapeutic target for OA.

Backbone resonance assignment of PDI b'xa' domain construct

Human protein disulfide isomerase (PDI), a protein containing 4 domains a, b, b', a', disordered x linker and C-terminus, plays critical roles in disulfide bond reactions and proper protein folding in the endoplasmic reticulum. The bb' domain contributes to client binding, the a, a' domain catalyse the rearrangement of the disulfide bonds. The x linker and a' domain were the main dynamics region for full-length PDI and the b'xa' construct has the minimum functional domain within full-length PDI. Herein, we report a new preparation strategy with 1, 6-hexandiol and backbone NMR chemical shift assignments for the monomer b'xa' domain.

Feasibility of Sijunzi Tang (Chinese medicine) to enhance protein disulfide isomerase activities for reactivating malate dehydrogenase deactivated by polycyclic aromatic hydrocarbons

The objective of this research is to investigate the enzymatic activities between protein disulfide isomerase (PDI) found in animals and plants and the properties found in a commonly used Chinese medicine called Sijunzi Tang. During the investigation, PDI, which is a monomer with a molecular mass of 57.0 kDa, was used to reactivate malate dehydrogenase (MDH). However, with the interference of polycyclic aromatic hydrocarbons (PAHs), evidence indicates that such chemicals are carcinogenic, mutagenic, and toxic to humans. The enzymatic activity of PDI found in animal's liver and plant was 1657 folds of purification; 0.284 unit/mg of enzyme activity, and 5694.4 folds of purification; 1.00 unit/mg of enzyme activity, respectively. PDI extracted in treated animal and plant tissue revealed 2.40% and 80.44% of regaining MDH enzymatic activity, respectively. Although in its initial phase of investigation, it is assumed that the properties found in Sijunzi Tang can help regain enzymatic activity in those affected by xenobiotic substances, thus, making it a potential ingredient in assisting with PDI functions.

Meta-analysis uncovers genome-wide significant variants for rapid kidney function decline

Rapid decline of glomerular filtration rate estimated from creatinine (eGFRcrea) is associated with severe clinical endpoints. In contrast to cross-sectionally assessed eGFRcrea, the genetic basis for rapid eGFRcrea decline is largely unknown. To help define this, we meta-analyzed 42 genome-wide association studies from the Chronic Kidney Diseases Genetics Consortium and United Kingdom Biobank to identify genetic loci for rapid eGFRcrea decline. Two definitions of eGFRcrea decline were used: 3 mL/min/1.73m2/year or more ("Rapid3"; encompassing 34,874 cases, 107,090 controls) and eGFRcrea decline 25% or more and eGFRcrea under 60 mL/min/1.73m2 at follow-up among those with eGFRcrea 60 mL/min/1.73m2 or more at baseline ("CKDi25"; encompassing 19,901 cases, 175,244 controls). Seven independent variants were identified across six loci for Rapid3 and/or CKDi25: consisting of five variants at four loci with genome-wide significance (near UMOD-PDILT (2), PRKAG2, WDR72, OR2S2) and two variants among 265 known eGFRcrea variants (near GATM, LARP4B). All these loci were novel for Rapid3 and/or CKDi25 and our bioinformatic follow-up prioritized variants and genes underneath these loci. The OR2S2 locus is novel for any eGFRcrea trait including interesting candidates. For the five genome-wide significant lead variants, we found supporting effects for annual change in blood urea nitrogen or cystatin-based eGFR, but not for GATM or LARP4B. Individuals at high compared to those at low genetic risk (8-14 vs. 0-5 adverse alleles) had a 1.20-fold increased risk of acute kidney injury (95% confidence interval 1.08-1.33). Thus, our identified loci for rapid kidney function decline may help prioritize therapeutic targets and identify mechanisms and individuals at risk for sustained deterioration of kidney function.

Vascular thiol isomerases in thrombosis: The yin and yang

There has recently been considerable progress of the field of extracellular protein disulfide isomerases with vascular thiol isomerases in the forefront. Four members of protein disulfide isomerase (PDI) family of enzymes, PDI, ERp57, ERp72, and ERp5, have been shown to be secreted from activated platelets and endothelial cells at the site of vascular injury. Each isomerase individually supports platelet accumulation and coagulation, as indicated by multiple levels of evidence, including inhibitory antibodies, targeted knockout mice, and mutant isomerases. The transmembrane PDI family member TMX1 was recently shown to inhibit platelet function and thrombosis, demonstrating that the PDIs can have opposing functions in thrombosis. These observations provide a new concept that thiol isomerases can both positively and negatively regulate hemostasis, constituting off-on redox switches controlling activation of hemostatic factors. This redox network serves to maintain vascular homeostasis. Integrins such as the αIIbβ3 fibrinogen receptor on platelets appear to be major substrates, with the platelet receptor for von Willebrand factor, glycoprotein Ibα, as another substrate. S-nitrosylation of the prothrombotic PDIs may additionally negatively regulate platelets and thrombosis. Thiol isomerases also regulate coagulation in mouse models, and a clinical trial with the oral PDI inhibitor isoquercetin substantially decreased markers of coagulation in patients at risk for thrombosis. This review updates recent findings in the field and addresses emerging evidence that thiol/disulfide-based reactions mediated by the prothrombotic secreted PDIs are balanced by the transmembrane member of this family, TMX1.

Thiol/disulfide exchange occurs in rotavirus structural proteins during contact with intestinal villus cell surface

Protein disulfide isomerase (PDI) is an enzyme that catalyzes disulfide bond reduction or formation and rearrangements of disulfide bridges, and also functions as a chaperone. During entry of some of the viruses PDI participates in thiol-disulfide exchange. Previous reports show that rotavirus entry is interfered by impermeant thiol/disulfide exchange inhibitors and antibodies against PDI. Our objective was to assess the interaction between PDI and triple-layered particles (TLPs) from rotavirus strains ECwt and RRV and from a human rotavirus isolate (HI) during the early steps of virus entry in a system of isolated small intestinal villi. Purified soluble PDI was incubated with either isolated intestinal villi or cell membrane-enriched fractions in the presence or absence of thiol/disulfide inhibitors such as bacitracin, DTNB or N- ethylmaleimide followed by the assessment of the PDI interactions with TLPs and rotavirus structural proteins in terms of their redox state changes. Soluble and membrane-bound PDI was found to interact with TLPs from all the rotaviruses assayed and also with the isolated structural proteins represented by the recombinant rVP5* (a tryptic cleavage product of VP4), rVP6 and the native VP7. PDI interaction with TLPs and rotavirus structural proteins was decreased by the presence of thiol/disulfide exchange inhibitors. Interactions of cell membrane-enriched fractions with TLPs produced rearrangements in the disulfide bridges of rotavirus structural proteins. We conclude that PDI interacts with rotavirus virions through redox reactions that could facilitate the rotavirus entry into the host cell. Keywords: cell surface PDI; thiol-disulfide exchange; rotavirus TLPs; virus entry; bacitracin; DTNB.

NOVEL MUTATIONS IN THE WNT1, TMEM38B, P4HB, AND PLS3 GENES IN FOUR UNRELATED CHINESE FAMILIES WITH OSTEOGENESIS IMPERFECTA

OBJECTIVE

Osteogenesis imperfecta (OI) is a group of heritable fragile bone diseases, and the majority are caused by pathogenic variants in the COL1A1 and COL1A2 genes. We sought to identify the genetic causes and phenotypes of OI in Chinese patients without COL1A1 or COL1A2 mutations.

METHODS

Twenty-three patients who were diagnosed with sporadic OI but did not carry COL1A1/2 mutations were recruited, and their genomic DNA was analyzed using targeted next-generation sequencing of rare OI-related genes. The resulting damaging mutations in the probands and their parents were verified using Sanger sequencing. Moreover, the efficacy of long-term bisphosphonate treatment was evaluated in proband 1.

RESULTS

Compound heterozygous variants in the WNT1 and TMEM38B genes were identified in proband 1 and proband 2, respectively. A heterozygous mutation in the P4HB gene was identified in proband 3, and a hemizygous mutation in PLS3 was identified in proband 4. The unaffected parents of the probands (except the father of proband 4) with mutations in the WNT1, TMEM38B, and PLS3 genes were heterozygous carriers of each of the variants, respectively. Notably, proband 3 had the characteristic exophthalmos, flat nasal bridge and flat, wide forehead. None of the patients presented with dentinogenesis imperfecta or hearing loss. Furthermore, bisphosphonates exerted beneficial effects on proband 1, who carried the WNT1 mutations, by increasing bone mineral density Z-score, reshaping the compressed vertebrae and decreasing the fracture risk.

CONCLUSION

We identified novel mutations and expanded the spectrum of phenotypes and genotypes of the extremely rare disorder OI.

ABBREVIATIONS

BMD = bone mineral density; MIM = Mendelian Inheritance in Man; OI = osteogenesis imperfecta; PDI = protein disulfide isomerase.

Expression and characterization of protein disulfide isomerase family proteins in bread wheat

BACKGROUND

The major wheat seed proteins are storage proteins that are synthesized in the rough endoplasmic reticulum (ER) of starchy endosperm cells. Many of these proteins have intra- and intermolecular disulfide bonds. In eukaryotes, the formation of most intramolecular disulfide bonds in the ER is thought to be catalyzed by protein disulfide isomerase (PDI) family proteins. The cDNAs that encode eight groups of bread wheat (Triticum aestivum L.) PDI family proteins have been cloned, and their expression levels in developing wheat grains have been determined. The purpose of the present study was to characterize the enzymatic properties of the wheat PDI family proteins and clarify their expression patterns in wheat caryopses.

RESULTS

PDI family cDNAs, which are categorized into group I (TaPDIL1Aα, TaPDIL1Aβ, TaPDIL1Aγ, TaPDIL1Aδ, and TaPDIL1B), group II (TaPDIL2), group III (TaPDIL3A), group IV (TaPDIL4D), and group V (TaPDIL5A), were cloned. The expression levels of recombinant TaPDIL1Aα, TaPDIL1B, TaPDIL2, TaPDIL3A, TaPDIL4D, and TaPDIL5A in Escherichia coli were established from the cloned cDNAs. All recombinant proteins were expressed in soluble forms and purified. Aside from TaPDIL3A, the recombinant proteins exhibited oxidative refolding activity on reduced and denatured ribonuclease A. Five groups of PDI family proteins were distributed throughout wheat caryopses, and expression levels of these proteins were higher during grain filling than in the late stage of maturing. Localization of these proteins in the ER was confirmed by fluorescent immunostaining of the immature caryopses. In mature grains, the five groups of PDI family proteins remained in the aleurone cells and the protein matrix of the starchy endosperm.

CONCLUSIONS

High expression of PDI family proteins during grain filling in the starchy endosperm suggest that these proteins play an important role in forming intramolecular disulfide bonds in seed storage proteins. In addition, these PDI family proteins that remain in the aleurone layers of mature grains likely assist in folding newly synthesized hydrolytic enzymes during germination.

Protein disulfide bond generation in Escherichia coli DsbB-DsbA

Protein disulfide bond formation is catalyzed by a series of Dsb enzymes present in the periplasm of Escherichia coli. The crystal structure of the DsbB-DsbA-ubiquinone ternary complex provided important insights into mechanisms of the de novo disulfide bond generation cooperated by DsbB and ubiquinone and of the disulfide bond shuttle from DsbB to DsbA. The structural basis for prevention of the crosstalk between the DsbA-DsbB oxidative and the DsbC-DsbD reductive pathways has also been proposed.

Activation of the Heterodimeric Central Complex SoxYZ of Chemotrophic Sulfur Oxidation Is Linked to a Conformational Change and SoxY-Y Interprotein Disulfide Formation,

The central protein of the four component sulfur oxidizing (Sox) enzyme system of Paracoccus pantotrophus, SoxYZ, carries at the SoxY subunit the covalently bound sulfur substrate which the other three proteins bind, oxidize, and release as sulfate. SoxYZ of different preparations resulted in different specific thiosulfate-oxidizing activities of the reconstituted Sox enzyme system. From these preparations SoxYZ was activated up to 24-fold by different reductants with disodium sulfide being the most effective and yielded a uniform specific activity of the Sox system. The activation comprised the activities with hydrogen sulfide, thiosulfate, and sulfite. Sulfide-activation decreased the predominant beta-sheet character of SoxYZ by 4%, which caused a change in its conformation as determined by infrared spectroscopy. Activation of SoxYZ by sulfide exposed the thiol of the C-terminal Cys-138 of SoxY as evident from alkylation by 4-acetamido-4'-maleimidylstilbene-2,2'-disulfonic acid. Also, SoxYZ activation enhanced the formation of the Sox(YZ)2 heterotetramer as evident from density gradient gel electrophoresis. The tetramer was formed due to an interprotein disulfide between SoxY to yield a SoxY-Y dimer as determined by combined high pressure liquid chromatography and mass spectrometry. The significance of the conformational change of SoxYZ and the interprotein disulfide between SoxY-Y is discussed.

Intracellular catalysis of disulfide bond formation by the human sulfhydryl oxidase, QSOX1

The discovery that the flavoprotein oxidase, Erv2p, provides oxidizing potential for disulfide bond formation in yeast, has led to investigations into the roles of the mammalian homologues of this protein. Mammalian homologues of Erv2p include QSOX (sulfhydryl oxidases) from human lung fibroblasts, guinea-pig endometrial cells and rat seminal vesicles. In the present study we show that, when expressed in mammalian cells, the longer version of human QSOX1 protein (hQSOX1a) is a transmembrane protein localized primarily to the Golgi apparatus. We also present the first evidence showing that hQSOX1a can act in vivo as an oxidase. Overexpression of hQSOX1a suppresses the lethality of a complete deletion of ERO1 (endoplasmic reticulum oxidase 1) in yeast and restores disulfide bond formation, as assayed by the folding of the secretory protein carboxypeptidase Y.

The optimization of peptide cargo bound to MHC class I molecules by the peptide-loading complex

Major histocompatibility complex (MHC) class I complexes present peptides from both self and foreign intracellular proteins on the surface of most nucleated cells. The assembled heterotrimeric complexes consist of a polymorphic glycosylated heavy chain, non-polymorphic beta(2) microglobulin, and a peptide of typically nine amino acids in length. Assembly of the class I complexes occurs in the endoplasmic reticulum and is assisted by a number of chaperone molecules. A multimolecular unit termed the peptide-loading complex (PLC) is integral to this process. The PLC contains a peptide transporter (transporter associated with antigen processing), a thiooxido-reductase (ERp57), a glycoprotein chaperone (calreticulin), and tapasin, a class I-specific chaperone. We suggest that class I assembly involves a process of optimization where the peptide cargo of the complex is edited by the PLC. Furthermore, this selective peptide loading is biased toward peptides that have a longer off-rate from the assembled complex. We suggest that tapasin is the key chaperone that directs this action of the PLC with secondary contributions from calreticulin and possibly ERp57. We provide a framework model for how this may operate at the molecular level and draw parallels with the proposed mechanism of action of human leukocyte antigen-DM for MHC class II complex optimization.

Calnexin and ERp57 facilitate the assembly of the neonatal Fc receptor for IgG with beta 2-microglobulin in the endoplasmic reticulum

The neonatal FcR (FcRn) consists of an MHC class I-like H chain in noncovalent association with beta(2)-microglobulin (beta(2)m). The proper folding of FcRn in the endoplasmic reticulum is essential for FcRn function. Using a low stringency immunoprecipitation of human FcRn, we observed the coprecipitation of an 88-kDa band. Mass spectrometry analysis revealed that this band was identical with calnexin (CNX). This association was verified by Western blotting the CNX or FcRn immunoprecipitates with either an anti-FcRn or anti-CNX Ab. In the beta(2)m-null FO-1 cell transfected with FcRn H chain alone or both FcRn H chain and beta(2)m, CNX bound to the FcRn H chain before the FcRn H chain association with beta(2)m. However, calreticulin only bound to the FcRn H chain-beta(2)m complex. Furthermore, the thiol oxidoreductase ERp57 was detected in FcRn-CNX complexes, suggesting its role in disulfide bond formation of the FcRn H chain. Removal of the N-linked glycosylation site from the FcRn H chain resulted in a decreased association of the FcRn H chain for beta(2)m. However, the absence of CNX did not significantly affect FcRn assembly as defined by the ability of FcRn to bind IgG and exit to the cell surface. This suggests that other chaperones compensate for the function of CNX in FcRn assembly. In addition, we found that tapasin and TAP were not involved in FcRn assembly, as shown by coimmunoprecipitation in THP-1 cells and IgG-binding assays in 721.220 (tapasin-deficient) and 721.174 (TAP-deficient) cells transfected with FcRn. These findings show the importance of chaperones in FcRn assembly.

AGR2, an androgen-inducible secretory protein overexpressed in prostate cancer

AGR2, the human homologue of Xenopus anterior gradient 2 (XAG2), was identified by a suppression subtractive hybridization-based technique as an androgen-inducible gene. There are two AGR2 transcripts, which encode the same secretory protein of 175 amino acids. The androgen induction was time- and dose-dependent, with more than a 10-fold increase in the level of AGR2 mRNA after 48 hr of treatment with 10(-9) M R1881. Expression of AGR2 mRNA was specifically detected in limited human tissue rich in epithelial cells, including the prostate gland. Analysis of 46 microdissected primary prostate adenocarcinoma samples showed that AGR2 mRNA expression was markedly elevated in the majority of tumors as compared to matched adjacent benign tissues. Androgen-induced AGR2 protein expression was demonstrated in LNCaP cells by Western blot analysis with an anti-AGR2 antibody. Immunohistochemistry analysis indicated that AGR2 protein expression was highly restricted to the secretory epithelial cells in the prostate gland. In tissue sections from radical prostatectomy specimens, immunohistochemical staining of AGR2 showed markedly increased expression in high-grade prostatic intraepithelial neoplasia and Gleason pattern 3-4 prostatic adenocarcinoma. Therefore, the androgen-induced secretory protein AGR2 may serve as a potential therapeutic target and/or molecular marker for prostate cancer.

Prelamin A endoproteolytic processing in vitro by recombinant Zmpste24

The nuclear lamins form a karyoskeleton providing structural rigidity to the nucleus. One member of the lamin family, lamin A, is first synthesized as a 74 kDa precursor, prelamin A. After the endopeptidase and methylation reactions which occur after farnesylation of the CAAX-box cysteine, there is a second endoproteolysis that occurs 15 amino acids upstream from the C-terminal farnesylated cysteine residue. Studies with knockout mice have implicated the enzyme Zmpste24 (Face-1) as a suitable candidate to perform one or both of these proteolytic reactions. Evidence has been presented elsewhere establishing that Zmpste24 possesses a zinc-dependent CAAX endopeptidase activity. In the present study, we confirm this CAAX endopeptidase activity with recombinant, membrane-reconstituted Zmpste24 and show that it can accept a prelamin A farnesylated tetrapeptide as substrate. To monitor the second upstream endoproteolytic cleavage of prelamin A, we expressed a 33 kDa prelamin A C-terminal tail in insect cells. We demonstrate that this purified substrate possesses a C-terminal farnesylated and carboxyl-methylated cysteine and, therefore, constitutes a valid substrate for assaying the second endoproteolytic step in lamin A maturation. With this substrate, we demonstrate that insect cell membranes bearing recombinant Zmpste24 can also catalyse the second upstream endoproteolytic cleavage.

In cerebrospinal fluid ER chaperones ERp57 and calreticulin bind beta-amyloid

The beta-amyloids (abetas) are the major components of the plaque observed in the brains of patients with Alzheimer's disease. The conundrum is that although they are produced in everyone during the posttranslational processing in the endoplasmic reticulum (ER) of the amyloid precursor protein (APP), deposits are only observed in the elderly. Our work suggests that normals have a carrier protein(s) keeping them in solution. Based on immunoblotting studies of cerebrospinal fluid (CSF) from normals, we find that the bulk of the abetas are bound to the ER chaperones, ERp57 and calreticulin, suggesting that these may be carrier proteins which prevent aggregation of the abetas and that the deposits are due to faulty ER posttranslational processing of APP with the failure to form this complex. If membrane protein synthesis is similarly affected, it could explain the neuronal dysfunction characteristic of Alzheimer's disease.

The cotranslational maturation of the type I membrane glycoprotein tyrosinase: the heat shock protein 70 system hands off to the lectin-based chaperone system

The maturation of eukaryotic secretory cargo initiates cotranslationally and cotranslocationally as the polypeptide chain emerges into the endoplasmic reticulum lumen. Here, we characterized the cotranslational maturation pathway for the human type I membrane glycoprotein tyrosinase. To recapitulate the cotranslational events, including glycosylation, signal sequence cleavage, chaperone binding, and oxidation, abbreviated transcripts lacking a stop codon were in vitro translated in the presence of semipermeabilized melanocyte membranes. This created a series of ribosome/translocon-arrested chains of increasing lengths, simulating intermediates in the cotranslational folding process. Initially, nascent chains were found to associate with the heat shock protein (Hsp) 70 family member BiP. As the nascent chains elongated and additional glycans were transferred, BiP binding rapidly decreased and the lectin-based chaperone system was recruited in its place. The lectin chaperone calnexin bound to the nascent chain after the addition of two glycans, and calreticulin association followed upon the addition of a third. The glycan-specific oxidoreductase ERp57 was cross-linked to tyrosinase when calnexin and calreticulin were associated. This timing coincided with the formation of disulfide bonds within tyrosinase and the cleavage of its signal sequence. Therefore, tyrosinase maturation initiates cotranslationally with the Hsp70 system and is handed off to the lectin chaperone system that first uses calnexin before calreticulin. Interestingly, divergence in the maturation pathways of wild-type and mutant albino tyrosinase can already be observed for translocon-arrested nascent chains.

The 1,25D3-MARRS protein: contribution to steroid stimulated calcium uptake in chicks and rats

There are currently two main candidates for the membrane receptor for 1,25(OH)2D3: the 1,25D3-MARRS protein/ERp57; and the classical VDR. The 1,25D3-MARRS protein is essential for hormone-stimulated phosphate and calcium uptake in chick intestinal cells, whereas the VDR is not. The 1,25D3-MARRS protein also shows a high degree of correlation with growth periods in which bone is rapidly formed, whereas the VDR does not. However, in rat enterocytes, both the 1,25D3-MARRS protein and the VDR play a role in the rapid, steroid-mediated uptake of phosphate or calcium. Therefore, the theory that alternate binding sites on the VDR for various analogs account for all membrane-initiated phenomena, is incorrect.

Identification and characterization of 1,25D3-membrane-associated rapid response, steroid (1,25D3-MARRS)-binding protein in rat IEC-6 cells

We report the presence of a mammalian equivalent of the avian Membrane-Associated Rapid Response, Steroid (1,25D3-MARRS)-binding protein specific for 1,25(OH)2D3 in a rat small intestinal cell line, IEC-6, that demonstrates rapid responses to the steroid hormone. Identification of transcript and protein was achieved using RT-PCR with several specific primer sets, Western blot analysis with two separate antibodies recognizing distinct regions of the protein, ribozyme knockdown and immunohistochemistry. Promoter analysis of the 1000-bp upstream region of the 1,25D3-MARRS gene in several species revealed the presence of a conserved smad-3 element in the 5' proximal promoter region, but no classical vitamin D response element (VDRE). Treatment of IEC-6 cells with transforming growth factor beta1 (TGFbeta1) increased steady-state levels of 1,25D3-MARRS (mRNA and protein) approximately two-fold over a 24-h period. In contrast, treatment with 1,25(OH)2D3 failed to significantly change 1,25D3-MARRS protein or mRNA levels. Localization studies showed rapid nuclear translocation of a pool of 1,25D3-MARRS protein after 1,25(OH)2D3 treatment, suggesting that the protein is subject to membrane-initiated signal pathway activation. Together these data point to complex interactions between the two important 1,25(OH)2D3 sensitive response systems in intestinal cells, 1,25D3-MARRS protein and the well-studied nVDR, that together work to fine tune intestinal Ca2+ absorption in a variety of avian and mammalian species.

A Charged Amino Acid Residue in the Transmembrane/Cytoplasmic Region of Tapasin Influences MHC Class I Assembly and Maturation

Tapasin influences the quantity and quality of MHC/peptide complexes at the cell surface; however, little is understood about the structural features that underlie its effects. Because tapasin, MHC class I, and TAP are transmembrane proteins, the tapasin transmembrane/cytoplasmic region has the potential to affect interactions at the endoplasmic reticulum membrane. In this study, we have assessed the influence of a conserved lysine at position 408, which lies in the tapasin transmembrane/cytoplasmic domain. We found that substitutions at position K408 in tapasin affected the expression of MHC class I molecules at the cell surface, and down-regulated tapasin stabilization of TAP. In addition to affecting TAP interaction with tapasin, the substitution of alanine, but not tryptophan, for the lysine at tapasin position 408 increased the amount of tapasin found in association with the open, peptide-free form of the HLA-B8 H chain. Tapasin K408A was also associated with more folded, beta(2)-microglobulin-assembled HLA-B8 molecules than wild-type tapasin. Consistent with our observation of a large pool of tapasin K408A-associated HLA-B8 molecules, the rate at which HLA-B8 migrated from the endoplasmic reticulum was slower in tapasin K408A-expressing cells than in wild-type tapasin-expressing cells. Thus, the alanine substitution at position 408 in tapasin may interfere with the stable acquisition by MHC class I molecules of peptides that are sufficiently optimal to allow MHC class I release from tapasin.

Evolutionary and functional perspectives of the major histocompatibility complex class I antigen-processing machinery

Major histocompatibility complex (MHC) class I molecules present antigenic peptides to CD8+ T cells, providing the basis for immune recognition of pathogen-infected cells. Peptides generated mainly by proteasomes in the cytosol are transported into the lumen of the endoplasmic reticulum by transporters associated with antigen processing (TAP). The maturation of MHC class I molecules is controlled by a number of accessory proteins and chaperones that are to a varying degree dedicated to the assembly of MHC class I. Several newly characterised proteins have been demonstrated to play important roles in this process. This review focuses on the functional relationship and evolutionary history of the antigen-processing machinery (APM) components and MHC class I itself. These are of great interest for further elucidating the origin of the immune system and understanding the mechanisms of antigen presentation and immunology in general.

Chaperone proteins involved in troglitazone-induced toxicity in human hepatoma cell lines

Troglitazone (TRO), an effective thiazolidinedione antidiabetic agent, was reported to produce idiosyncratic hepatotoxic effects in some individuals. In contrast, rosiglitazone (RSG), in the same group of agents, has no significant toxic effects and now is widely used. In this study, human hepatoma (HepG2) cell lines were exposed to various doses of TRO as well as RSG (0, 25, 50, and 75 microM) for 48 h. Cell lysates were separated by two-dimensional electrophoresis, and the gels were stained with coomassie brilliant blue to compare the spot profiles. The greatest protein expression at a MW of 75 kDa and isoelectric point of 5 was specifically increased with TRO treatments of 50 and 75 microM. The spot was identified as a mixture of immunoglobulin heavy chain binding protein (BiP) and, to a lesser extent, protein disulfide isomerase-related protein (PDIrp). Immunoblot analyses showed that the BiP protein was dose-dependently increased by TRO treatment and, to a lower degree, by RSG. These effects were also correlated with the high induction of BiP mRNA by TRO (50 and 75 microM) and the lower induction by RSG. However, both treatments showed no significant effects on PDIrp expression. The toxic effects of TRO in relation to the overexpression of BiP were also demonstrated in HLE cells, another human hepatoma cell line. In HLE cells, the inhibition of BiP expression by small interference RNA rendered cells more susceptible to the toxic effects of TRO. These results suggest that the overexpression of BiP is a defense mechanism of the endoplasmic reticulum in response to TRO-induced toxicity.

Glutathione directly reduces an oxidoreductase in the endoplasmic reticulum of mammalian cells

The formation of disulfide bonds is an essential step in the folding of many glycoproteins and secretory proteins. Non-native disulfide bonds are often formed between incorrect cysteine residues, and thus the cell has dedicated a family of oxidoreductases that are thought to isomerize non-native bonds. For an oxidoreductase to be capable of performing isomerization or reduction reactions, it must be maintained in a reduced state. Here we show that most of the oxidoreductases are predominantly reduced in vivo. Following oxidative stress the oxidoreductases are quickly reduced, demonstrating that a robust reductive pathway is in place in mammalian cells. Using ERp57 as a model we show that the reductive pathway is cytosol-dependent and that the component responsible for the reduction of the oxidoreductases is the low molecular mass thiol glutathione. In addition, ERp57 is not reduced following oxidative stress when inhibitors of glutathione synthesis or glutathione reduction are added to cells. Glutathione directly reduces ERp57 at physiological concentrations in vitro, and biotinylated glutathione forms a mixed disulfide with ERp57 in microsomes. Our results demonstrate that glutathione plays a direct role in the isomerization of disulfide bonds by maintaining the mammalian oxidoreductases in a reduced state.

A novel 110 kDa form of myosin XVIIIA (MysPDZ) is tyrosine-phosphorylated after colony-stimulating factor-1 receptor signalling

Macrophage colony-stimulating factor (M-CSF or CSF-1) controls the development of macrophage lineage cells via activation of its tyrosine kinase receptor, c-Fms. After adding CSF-1 to M1 myeloid cells expressing CSF-1R (CSF-1 receptor), tyrosine phosphorylation of many cellular proteins occurs, which might be linked to subsequent macrophage differentiation. The biological significance and characterization of such proteins were explored by a dual strategy comprising two-dimensional SDS/PAGE analysis of cell lysates of CSF-1-treated M1 cells expressing the wild-type or a mutated receptor, together with an enrichment strategy involving a tyrosine-phosphorylated receptor construct. In the present study, we report the identification by MS of a novel, low-abundance, 110 kDa form of myosin XVIIIA (MysPDZ, myosin containing PDZ domain), which appears to be preferentially tyrosine-phosphorylated after CSF-1R activation when compared with other known isoforms. Receptor mutation studies indicate that CSF-1R-dependent tyrosine phosphorylation of p110myosin XVIIIA requires Tyr-559 in the cytoplasmic domain of the receptor and is therefore Src-family kinase-dependent. Gelsolin, Erp61 protein disulphide-isomerase and possibly non-muscle myosin IIA were also tyrosine-phosphorylated under similar conditions. Similar to the more abundant p190 isoform, p110 myosin XVIIIA lacks a PDZ domain and, in addition, it may lack motor activity. The phosphorylation of p110 myosin XVIIIA by CSF-1 may alter its cellular localization or target its association with other proteins.

Synthesis of peptide nucleic acid-peptide conjugates

Synthetic oligonucleotides are versatile tools for recognizing ribonucleic acid and deoxyribonucleic acid. This chapter describes methods for enhancing recognition by derivatizing oligonucleotides with either proteins or peptides.

ERp57 is present in STAT3–DNA complexes

STAT3 has been found constitutively activated in M14 melanoma cell line, as previously found in other melanoma cells. Using EMSA, DNA affinity experiments, and chromatin immunoprecipitation, STAT3 was found in M14 to bind the alpha2-macroglobulin gene enhancer in association with the protein disulfide isomerase isoform ERp57. The two proteins have also been found to be associated when bound to the SIE sequence in HepG2 cells stimulated by IL-6. In both cases an anti-ERp57 antibody hinders the binding of STAT3 to its consensus sequence on DNA, indicating that ERp57 is a necessary component of the DNA-bound STAT3 complex. Considering the functional association of the two proteins, the overexpression of ERp57 observed in a variety of transformed cells might be relevant to the oncogenic properties of STAT3.

Disruption of endothelial-cell caveolin-1alpha/raft scaffolding during development of monocrotaline-induced pulmonary hypertension

BACKGROUND

In the monocrotaline (MCT)-treated rat, there is marked stimulation of DNA synthesis and megalocytosis of pulmonary arterial endothelial cells (PAECs) within 3 to 4 days, followed by pulmonary hypertension (PH) 10 to 14 days later. Growing evidence implicates caveolin-1 (cav-1) in plasma membrane rafts as a negative regulator of promitogenic signaling. We have investigated the integrity and function of endothelial cell-selective cav-1alpha/raft signaling in MCT-induced PH.

METHODS AND RESULTS

Although PH and right ventricular hypertrophy developed by 2 weeks after MCT, a reduction in cav-1alpha levels in the lung was apparent within 48 hours, declining to approximately 30% by 2 weeks, accompanied by an increase in activation of the promitogenic transcription factor STAT3 (PY-STAT3). Immunofluorescence studies showed a selective loss of cav-1alpha and platelet endothelial cell adhesion molecule-1 in the PAEC layer within 48 hours after MCT but an increase in PY-STAT3. PAECs with cav-1alpha loss displayed high PY-STAT3 and nuclear immunostaining for proliferating cell nuclear antigen (PCNA). Biochemical studies showed a loss of cav-1alpha from the detergent-resistant lipid raft fraction concomitant with hyperactivation of STAT3. Moreover, cultured PAECs treated with MCT-pyrrole for 48 hours developed megalocytosis associated with hypo-oligomerization and reduction of cav-1alpha, hyperactivation of STAT3 and ERK1/2 signaling, and stimulation of DNA synthesis.

CONCLUSIONS

MCT-induced disruption of cav-1alpha chaperone and scaffolding function in PAECs likely accounts for diverse alterations in endothelial cell signaling in this model of PH.

Tapasin enhances MHC class I peptide presentation according to peptide half-life

Understanding how peptides are selected for presentation by MHC class I is crucial to vaccination strategies based on cytotoxic T lymphocyte priming. We have studied this selection of the MHC class I peptide repertoire in terms of the presentation of a series of individual peptides with a wide range of binding to MHC class I. This series was expressed as minigenes, and the presentation of each peptide variant was determined with the same MHC class I peptide-specific antibody. In wild-type cells, the hierarchy of presentation followed peptide half-life. This hierarchy broke down in cells lacking tapasin but not in cells lacking calreticulin or in cells lacking transporter associated with antigen processing-associated ERp57. We demonstrate a key role for tapasin in shaping the MHC class I peptide repertoire, as enhancement of presentation in the presence of tapasin correlated with peptide half-life.

Antigen-Processing Machinery in Human Dendritic Cells: Up-Regulation by Maturation and Down-Regulation by Tumor Cells

It has been known for some time that functional properties of dendritic cells (DC), and in particular their ability to process and present Ags to T cells, can be modulated by cytokine-induced maturation and by interactions with tumor cells. However, the molecular basis for these functional changes is unknown. We have investigated whether changes in expression of Ag-processing machinery (APM) components in DC are associated with alterations in their ability to present tumor-derived Ags to T cells. Using a panel of mAbs specific for individual APM components and a quantitative flow cytometry-based method, the level of APM components was measured in DC generated from peripheral blood monocytes of 12 normal donors and of 8 patients with cancer. Immature DC had significantly lower (p < 0.01) expression of MB1, LMP-7, LMP-10, TAP-1, and tapasin than mature DC. However, maturation in the presence of a cytokine mixture up-regulated expression of these components in DC obtained from normal donors and patients with cancer. Immature DC incubated with tumor cells had significantly lower (p < 0.001) expression of MB1, LMP-2, LMP-7, LMP-10, and endoplasmic reticulum p75 than controls. These changes were associated with a decreased ability of DC to present tumor-derived Ags to T cells, as measured in ELISPOT assays and with apoptosis of T cells in DC-T cell cultures. Thus, tumor cells have a significant suppressive effect on DC; however, ex vivo maturation of DC derived from patients with cancer in a polarizing cytokine mix restores normal expression of APM components and Ag-processing capabilities.