Protein disulfide isomerase: the multifunctional redox chaperone of the endoplasmic reticulum

Identifying vaccine targets for anti-leishmanial vaccine development

Leishmaniasis is a neglected tropical disease spread by an arthropod vector. It remains a significant health problem with an incidence of 0.2–0.4 million visceral leishmaniasis and 0.7–1.2 million cutaneous leishmaniasis cases each year. There are limitations associated with the current therapeutic regimens for leishmaniasis and the fact that after recovery from infection the host becomes immune to subsequent infection therefore, these factors force the feasibility of a vaccine for leishmaniasis. Publication of the genome sequence of Leishmania has paved a new way to understand the pathogenesis and host immunological status therefore providing a deep insight in the field of vaccine research. This review is an effort to study the antigenic targets in Leishmania to develop an anti-leishmanial vaccine.

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.

Redox-sensitive materials for drug delivery: targeting the correct intracellular environment, tuning release rates, and appropriate predictive systems

SIGNIFICANCE

The development of responsive drug delivery systems (DDS) holds great promise as a tool for improving the pharmacokinetic properties of drug compounds. Redox-sensitive systems are particularly attractive given the rich variety of redox gradients present in vivo. These gradients, where the circulation is generally considered oxidizing and the cellular environment is substantially more reducing, provide attractive options for targeted, specific cargo delivery.

RECENT ADVANCES

Experimental evidence suggests that a "one size fits all" redox gradient does not exist. Rather, there are subtle differences in redox potential within a cell, while the chemical nature of reducing agents in these microenvironments varies. Recent works have demonstrated an ability to modulate the degradation rate of redox-susceptible groups and, hence, provide new tools to engineer precision-targeted DDS.

CRITICAL ISSUES

Modern synthetic and macromolecular chemistry provides access to a wide range of redox-susceptible architectures. However, in order to utilize these in real applications, the actual chemical nature of the redox-susceptible group, the sub-cellular location being targeted, and the redox microenvironment being encountered should be considered in detail. This is critical to avoid the over-simplification possible when using non-biological reducing agents, which may provide inaccurate kinetic information, and to ensure these materials can be advanced beyond simple "on/off" systems. Furthermore, a strong case can be made for the use of biorelevant reducing agents such as glutathione when demonstrating a materials redox response.

FUTURE DIRECTIONS

A further understanding of the complexities of the extra- and intracellular microenvironments would greatly assist with the design and application of DDS.

Bioreducible polycations as shuttles for therapeutic nucleic acid and protein transfection

SIGNIFICANCE

Nucleic acids such as gene-encoding DNAs, gene-silencing small interfering RNAs, or recombinant proteins addressing intracellular molecular targets present a major new therapeutic modality, provided efficient solutions for intracellular delivery can be found. The different physiological redox environments inside and outside the cell can be utilized for optimizing the involved transport processes.

RECENT ADVANCES

Intracellular delivery of nucleic acids or proteins requires dynamic carriers that discriminate between different cellular locations. Bioreducible cationic polymers can package their therapeutic cargo stably in the extracellular environment, but sense the reducing intracellular cytosolic environment. Based on disulfide cleavage, carriers are degraded into biocompatible fragments and release the cargo in functional form. Disulfide linkages between oligocations, between the carrier and the cargo, or spatial caging of complexed cargo by disulfides have been pursued, with polymers or precise sequence-defined peptides and oligomers.

CRITICAL ISSUES

A quantitative knowledge of the bioreductive capacities within different biological compartments and the involved cellular reduction processes would be greatly helpful for improved carriers with disulfides cleaved within the right compartment at the right time.

FUTURE DIRECTIONS

Novel designs of multifunctional nanocarriers will incorporate macromolecular disulfide entry mechanisms previously optimized by natural evolution of toxins and viruses. In addition to extracellular stabilization and intracellular disassembly, tuned disulfides will contribute to deshielding at the cell surface, or translocation from intracellular compartments to the cytosol.

S-Nitrosylating protein disulphide isomerase mediates α-synuclein aggregation caused by methamphetamine exposure in PC12 cells

Methamphetamine (METH) belongs to Amphetamine-type stimulants, METH abusers are at high risk of neurodegenerative disorders, including Parkinson's disease (PD). However, there are still no effective treatments to METH-induced neurodegeneration because its mechanism remains unknown. In order to investigate METH's neurotoxic mechanism, we established an in vitro PD pathology model by exposing PC12 cells to METH. We found the expression of nitric oxide synthase (NOS), nitric oxide (NO) and α-synuclein (α-syn) was significantly increased after METH treatment for 24h, in addition, the aggregattion of α-syn and the S-nitrosylation of protein disulphideisomerase(PDI) were also obviously enhanced. When we exposed PC12 cells to the NOS inhibitor N-nitro-L-arginine(L-NNA) with METH together, the L-NNA obviously inhibited these changes induced by METH. While when we exposed PC12 cells to the precursor of NO L-Arginine together with METH, the L-Arginine resulted in the opposite effect compared to L-NNA. And when we knocked down the PDI gene, the L-NNA did not have this effect. Therefore, PDI plays a significant role in neurological disorders related to α-syn aggregation, and it suggests that PDI could be as a potential target to prevent METH-induced neurodegeneration.

Deciphering a molecular mechanism of neonatal diabetes mellitus by the chemical synthesis of a protein diastereomer, [D-AlaB8]human proinsulin

Misfolding of proinsulin variants in the pancreatic β-cell, a monogenic cause of permanent neonatal-onset diabetes mellitus, provides a model for a disease of protein toxicity. A hot spot for such clinical mutations is found at position B8, conserved as glycine within the vertebrate insulin superfamily. We set out to investigate the molecular basis of the aberrant properties of a proinsulin clinical mutant in which residue Gly(B8) is replaced by Ser(B8). Modular total chemical synthesis was used to prepare the wild-type [Gly(B8)]proinsulin molecule and three analogs: [D-Ala(B8)]proinsulin, [L-Ala(B8)]proinsulin, and the clinical mutant [L-Ser(B8)]proinsulin. The protein diastereomer [D-Ala(B8)]proinsulin produced higher folding yields at all pH values compared with the wild-type proinsulin and the other two analogs, but showed only very weak binding to the insulin receptor. The clinical mutant [L-Ser(B8)]proinsulin impaired folding at pH 7.5 even in the presence of protein-disulfide isomerase. Surprisingly, although [L-Ser(B8)]proinsulin did not fold well under the physiological conditions investigated, once folded the [L-Ser(B8)]proinsulin protein molecule bound to the insulin receptor more effectively than wild-type proinsulin. Such paradoxical gain of function (not pertinent in vivo due to impaired secretion of the mutant insulin) presumably reflects induced fit in the native mechanism of hormone-receptor engagement. This work provides insight into the molecular mechanism of a clinical mutation in the insulin gene associated with diabetes mellitus. These results dramatically illustrate the power of total protein synthesis, as enabled by modern chemical ligation methods, for the investigation of protein folding and misfolding.

17β-Estradiol alters oxidative stress response protein expression and oxidative damage in the uterus

The steroid hormone 17β-estradiol (E2) has profound effects on the uterus. However, with the E2-induced increase in uterine cell proliferation and metabolism comes increased production of reactive oxygen species (ROS). We examined the expression of an interactive network of oxidative stress response proteins including thioredoxin (Trx), Cu/Zn superoxide dismutase (SOD1), apurinic endonuclease (Ape1), and protein disulfide isomerase (PDI). We demonstrated that treatment of ovariectomized C57BL/6J female mice with E2 increased the mRNA and protein levels of Trx, but decreased SOD1 and Ape1 mRNA and protein expression. In contrast, E2 treatment increased PDI protein levels but had no effect on PDI transcript levels. Interestingly, E2 treatment also increased two markers of cellular damage, lipid peroxidation and protein carbonylation. Our studies suggest that the decreased expression of SOD1 and Ape1 caused by E2 treatment may in the long term result in disruption of ROS regulation and play a role in endometrial carcinogenesis.

Looking for protein expression signatures in European eel peripheral blood mononuclear cells after in vivo exposure to perfluorooctane sulfonate and a real world field study

The decline of European eel population can be attributed to many factors such as pollution by xenobiotics present in domestic and industrial effluents. Perfluorooctane sulfonate (PFOS) is a ubiquitous compound of a particular concern in Europe. PFOS can reach high concentrations in tissues of organisms and many toxic effects have been reported in fish. This study aimed at evaluating the toxicological effects of PFOS in European eel peripheral blood mononuclear cells (PBMCs) at the protein expression level. To identify proteins whose expression was modified by PFOS, we performed a proteomic analysis on the post-nuclear fraction of PBMCs after a chronic exposure (28 days) of yellow eels to zero, 1 or 10 μg/L PFOS. This in vivo study was completed by a proteomic field study on eels sampled in Belgian rivers presenting different PFOS pollution degrees. Proteins were separated by two-dimensional in-gel electrophoresis (2D-DIGE) to compare the post-nuclear fraction of PBMCs from the reference group with cells from fish exposed to the pollutant of interest. On the 28 spots that were significantly (p < 0.05; ANOVA followed by a Dunnett post-hoc test) affected by PFOS in the in vivo experiment, a total of 17 different proteins were identified using nano-LC ESI-MS/MS and the Peptide and Protein Prophet of Scaffold software. In the field experiment, 18 significantly (p < 0.05; ANOVA followed by Dunnett's test) affected spots conducted to the identification of 16 different proteins. Interestingly, only three proteins were found in common between in vivo and in situ experiments: plastin-2, alpha-enolase and glyceraldehyde 3-phosphate dehydrogenase. Comparing the results with a previous study, plastin-2 and alpha-enolase were also been found to be affected after in vitro exposure of PBMCs during 48 h to either 10 μg or 1 mg PFOS/L. Potential use of these proteins as biomarkers of PFOS exposure in European eel could indicate early warning signals.

Protein disulfide isomerase directly interacts with β-actin Cys374 and regulates cytoskeleton reorganization

Recent studies support the role of cysteine oxidation in actin cytoskeleton reorganization during cell adhesion. The aim of this study was to explain whether protein disulfide isomerase (PDI) is responsible for the thiol-disulfide rearrangement in the β-actin molecule of adhering cells. First, we showed that PDI forms a disulfide-bonded complex with β-actin with a molecular mass of 110 kDa. Specific interaction of both proteins was demonstrated by a solid phase binding assay, surface plasmon resonance analysis, and immunoprecipitation experiments. Second, using confocal microscopy, we found that both proteins colocalized when spreading MEG-01 cells on fibronectin. Colocalization of PDI and β-actin could be abolished by the membrane-permeable sulfhydryl blocker, N-ethylmaleimide, by the RGD peptide, and by anti-αIIbβ3 antibodies. Consequently, down-regulation of PDI expression by antisense oligonucleotides impaired the spreading of cells and initiated reorganization of the cytoskeleton. Third, because of transfection experiments followed by immunoprecipitation and confocal analysis, we provided evidence that PDI binds to the β-actin Cys(374) thiol. Formation of the β-actin-PDI complex was mediated by integrin-dependent signaling in response to the adhesion of cells to the extracellular matrix. Our data suggest that PDI is released from subcellular compartments to the cytosol and translocated toward the periphery of the cell, where it forms a disulfide bond with β-actin when MEG-01 cells adhere via the αIIbβ3 integrin to fibronectin. Thus, PDI appears to regulate cytoskeletal reorganization by the thiol-disulfide exchange in β-actin via a redox-dependent mechanism.

Endoplasmic reticulum stress and Nox-mediated reactive oxygen species signaling in the peripheral vasculature: potential role in hypertension

SIGNIFICANCE

Reactive oxygen species (ROS) are produced during normal endoplasmic reticulum (ER) metabolism. There is accumulating evidence showing that under stress conditions such as ER stress, ROS production is increased via enzymes of the NADPH oxidase (Nox) family, especially via the Nox2 and Nox4 isoforms, which are involved in the regulation of blood pressure. Hypertension is a major contributor to cardiovascular and renal disease, and it has a complex pathophysiology involving the heart, kidney, brain, vessels, and immune system. ER stress activates the unfolded protein response (UPR) signaling pathway that has prosurvival and proapoptotic components.

RECENT ADVANCES

Here, we summarize the evidence regarding the association of Nox enzymes and ER stress, and its potential contribution in the setting of hypertension, including the role of other conditions that can lead to hypertension (e.g., insulin resistance and diabetes).

CRITICAL ISSUES

A better understanding of this association is currently of great interest, as it will provide further insights into the cellular mechanisms that can drive the ER stress-induced adaptive versus maladaptive pathways linked to hypertension and other cardiovascular conditions. More needs to be learnt about the precise signaling regulation of Nox(es) and ER stress in the cardiovascular system.

FUTURE DIRECTIONS

The development of specific approaches that target individual Nox isoforms and the UPR signaling pathway may be important for the achievement of therapeutic efficacy in hypertension.

Lipid droplet binding thalidomide analogs activate endoplasmic reticulum stress and suppress hepatocellular carcinoma in a chemically induced transgenic mouse model

Background

Hepatocellular carcinoma (HCC) is the most frequent and aggressive primary tumor of the liver and it has limited treatment options.

Results

In this study, we report the in vitro and in vivo effects of two novel amino-trifluoro-phtalimide analogs, Ac-915 and Ac-2010. Both compounds bind lipid droplets and endoplasmic reticulum membrane, and interact with several proteins with chaperone functions (HSP60, HSP70, HSP90, and protein disulfide isomerase) as determined by affinity chromatography and resonant waveguide optical biosensor technology. Both compounds inhibited protein disulfide isomerase activity and induced cell death of different HCC cells at sub or low micromolar ranges detected by classical biochemical end-point assay as well as with real-time label-free measurements. Besides cell proliferation inhibiton, analogs also inhibited cell migration even at 250 nM. Relative biodistribution of the analogs was analysed in native tissue sections of different organs after administration of drugs, and by using fluorescent confocal microscopy based on the inherent blue fluorescence of the compounds. The analogs mainly accumulated in the liver. The effects of Ac-915 and Ac-2010 were also demonstrated on the advanced stages of hepatocarcinogenesis in a transgenic mouse model of N-nitrosodiethylamine (DEN)-induced HCC. Significantly less tumor development was found in the livers of the Ac-915- or Ac-2010-treated groups compared with control mice, characterized by less liver tumor incidence, fewer tumors and smaller tumor size.

Conclusion

These results imply that these amino-trifluoro-phthalimide analogs could serve potent clinical candidates against HCC alone or in combination with dietary polyunsaturated fatty acids.

The effects of high concentrations of vitamin C on cancer cells

The effect of high doses of vitamin C for the treatment of cancer has been controversial. Our previous studies, and studies by others, have reported that vitamin C at concentrations of 0.25–1.0 mM induced a dose- and time-dependent inhibition of proliferation in acute myeloid leukemia (AML) cell lines and in leukemic cells from peripheral blood specimens obtained from patients with AML. Treatment of cells with high doses of vitamin C resulted in an immediate increase in intracellular total glutathione content and glutathione-S transferase activity that was accompanied by the uptake of cysteine. These results suggest a new role for high concentrations of vitamin C in modulation of intracellular sulfur containing compounds, such as glutathione and cysteine. This review, discussing biochemical pharmacologic studies, including pharmacogenomic and pharmacoproteomic studies, presents the different pharmacological effects of vitamin C currently under investigation.

Molecular modeling indicates distinct classes of missense variants with mild and severe XLRS phenotypes

X-linked retinoschisis (XLRS) is a vitreo-retinal degeneration caused by mutations in the RS1 gene which encodes the protein retinoschisin (RS1), required for the structural and functional integrity of the retina. Data are presented from a group of 38 XLRS patients from Moorfields Eye Hospital (London, UK) who had one of 18 missense mutations in RS1. Patients were grouped based on mutation severity predicted by molecular modeling: mild (class I), moderate (intermediate) and severe (class II). Most patients had an electronegative scotopic bright flash electroretinogram (ERG) (reduced b/a-wave ratio) in keeping with predominant inner retinal dysfunction. An association between the type of structural RS1 alterations and the severity of b/a-wave reduction was found in all but the oldest group of patients, significant in patients aged 15-30 years. Severe RS1 missense changes were associated with a lower ERG b/a ratio than were mild changes, suggesting that the extent of inner retinal dysfunction is influenced by the effect of the mutations on protein structure. The majority of class I mutations showed no changes involving cysteine residues. Class II mutations caused severe perturbations due to the removal or insertion of cysteine residues or due to changes in the hydrophobic core. The ERG b/a ratio in intermediate cases was abnormal but showed significant variability, possibly related to the role of proline or arginine residues. We also conducted a second study, using a completely independent cohort, to indicate a genotype-ERG phenotype correlation.

Diabetes mellitus due to the toxic misfolding of proinsulin variants

Dominant mutations in the human insulin gene can lead to pancreatic β-cell dysfunction and diabetes mellitus due to toxic folding of a mutant proinsulin. Analogous to a classical mouse model (the Akita mouse), this monogenic syndrome highlights the susceptibility of human β-cells to endoreticular stress due to protein misfolding and aberrant aggregation. The clinical mutations directly or indirectly perturb native disulfide pairing. Whereas the majority of mutations introduce or remove a cysteine (leading in either case to an unpaired residue), non-cysteine-related mutations identify key determinants of folding efficiency. Studies of such mutations suggest that the evolution of insulin has been constrained not only by its structure and function, but also by the susceptibility of its single-chain precursor to impaired foldability.

Proteomic responses of peripheral blood mononuclear cells in the European eel (Anguilla anguilla) after perfluorooctane sulfonate exposure

Since the 1980s, the stocks of European eel have been declining in most of their geographical distribution area. Many factors can be attributed to this decline such as pollution by xenobiotics like perfluorooctane sulfonate (PFOS). This study aimed at evaluating the in vitro toxicity of eel peripheral blood mononuclear cells (PBMC) exposed to PFOS. Exposure time and two concentrations were chosen to avoid cell mortality (48 h exposure at 10 μg PFOS/L and 1mg PFOS/L). After in vitro contaminations, the post-nuclear fraction was isolated and a proteomic analysis using 2D-DIGE was performed to compare PBMC from the control group with cells exposed to the pollutant. On the 158 spots that were significantly affected by PFOS exposure, a total of 48 different proteins were identified using nano-LCESI-MS/MS and the Peptide and Protein Prophet of Scaffold software. These proteins can be categorized into diverse functional classes, related to cytoskeleton, protein folding, cell signaling, proteolytic pathway and carbohydrate and energy metabolism, which provide clues on the cellular pathways mainly affected by PFOS. Some of the identified proteins are rarely found in other ecotoxicological proteomic studies and could constitute potential biomarkers of exposure to PFOS in fish.

Inhibition of prolyl 4-hydroxylase, beta polypeptide (P4HB) attenuates temozolomide resistance in malignant glioma via the endoplasmic reticulum stress response (ERSR) pathways

BACKGROUND

Glioblastoma multiforme (GBM), the most aggressive malignant primary brain tumor of the central nervous system, is characterized by a relentless disease recurrence despite continued advancement in surgery, radiotherapy, and chemotherapy. Resistance to temozolomide (TMZ), a standard chemotherapeutic agent for GBM, remains a major challenge. Understanding the mechanisms behind TMZ resistance can direct the development of novel strategies for the prevention, monitoring, and treatment of tumor relapse.

METHODS AND RESULTS

Our research platform, based on the establishment of 2 pairs of TMZ-sensitive/resistant GBM cells (D54-S and D54-R; U87-S and U87-R), has successfully identified prolyl 4-hydroxylase, beta polypeptide (P4HB) over-expression to be associated with an increased IC50 of TMZ. Elevated P4HB expression was verified using in vivo xenografts developed from U87-R cells. Clinically, we found that P4HB was relatively up-regulated in the recurrent GBM specimens that were initially responsive to TMZ but later developed acquired resistance, when compared with treatment-naive tumors. Functionally, P4HB inhibition by RNAi knockdown and bacitracin inhibition could sensitize D54-R and U87-R cells to TMZ in vitro and in vivo, whereas over-expression of P4HB in vitro conferred resistance to TMZ in both D54-S and U87-S cells. Moreover, targeting P4HB blocked its protective function and sensitized glioma cells to TMZ through the PERK arm of the endoplasmic reticulum stress response.

CONCLUSIONS

Our study identified a novel target together with its functional pathway in the development of TMZ resistance. P4HB inhibition may be used alone or in combination with TMZ for the treatment of TMZ-resistant GBM.

Treatment with the proteasome inhibitor MG132 during the end of oocyte maturation improves oocyte competence for development after fertilization in cattle

Maturation of the oocyte involves nuclear and cytoplasmic changes that include post-translational processing of proteins. The objective was to investigate whether inhibition of proteasomes during maturation would alter competence of the bovine oocyte for fertilization and subsequent development. Cumulus-oocyte complexes were cultured in the presence or absence of the proteasomal inhibitor MG132 from either 0-6 h or 16-22 h after initiation of maturation. Treatment with MG132 early in maturation prevented progression to meiosis II and reduced fertilization rate and the proportion of oocytes and cleaved embryos that became blastocysts. Conversely, treatment with MG132 late in maturation improved the percentage of oocytes and cleaved embryos that became blastocysts without affecting nuclear maturation or fertilization rate. Optimal results with MG132 were achieved at a concentration of 10 µM - effects were generally not observed at lower or higher concentrations. Using proteomic analysis, it was found that MG132 at the end of maturation increased relative expression of 6 proteins and decreased relative expression of 23. Among those increased by MG132 that are potentially important for oocyte competence are GAPDH, involved in glycolysis, TUBA1C, needed for organellar movement, and two proteins involved in protein folding (P4HB and HYOU1). MG132 decreased amounts of several proteins that exert anti-apoptotic actions including ASNS, HSP90B1, PDIA3 and VCP. Another protein decreased by MG132, CDK5, can lead to apoptosis if aberrantly activated and one protein increased by MG132, P4HB, is anti-apoptotic. Finally, the pregnancy rate of cows receiving embryos produced from oocytes treated with MG132 from 16-22 h of maturation was similar to that for control embryos, suggesting that use of MG132 for production of embryos in vitro does not cause a substantial decrease in embryo quality.

S-nitrosylated protein disulfide isomerase contributes to mutant SOD1 aggregates in amyotrophic lateral sclerosis

A major hallmark of mutant superoxide dismutase (SOD1)-linked familial amyotrophic lateral sclerosis is SOD1-immunopositive inclusions found within motor neurons. The mechanism by which SOD1 becomes aggregated, however, remains unclear. In this study, we aimed to investigate the role of nitrosative stress and S-nitrosylation of protein disulfide isomerase (PDI) in the formation of SOD1 aggregates. Our data show that with disease progression inducible nitric oxide synthase (iNOS) was up-regulated, which generated high levels of nitric oxide (NO) and subsequently induced S-nitrosylation of PDI in the spinal cord of mutant SOD1 transgenic mice. This was further confirmed by in vitro observation that treating SH-SY5Y cells with NO donor S-nitrosocysteine triggered a dose-dependent formation of S-nitrosylated PDI. When mutant SOD1 was over-expressed in SH-SY5Y cells, the iNOS expression was up-regulated, and NO generation was consequently increased. Furthermore, both S-nitrosylation of PDI and the formation of mutant SOD1 aggregates were detected in the cells expressing mutant SOD1(G93A). Blocking NO generation with the NOS inhibitor N-nitro-L-arginine attenuated the S-nitrosylation of PDI and inhibited the formation of mutant SOD1 aggregates. We conclude that NO-mediated S-nitrosylation of PDI is a contributing factor to the accumulation of mutant SOD1 aggregates in amyotrophic lateral sclerosis.

SOD1 aggregation in astrocytes following ischemia/reperfusion injury: a role of NO-mediated S-nitrosylation of protein disulfide isomerase (PDI)

Background

Ubiquitinated-protein aggregates are implicated in cerebral ischemia/reperfusion injury. The very presence of these ubiquitinated-protein aggregates is abnormal and seems to be disease-related. However, it is not clear what leads to aggregate formation and whether the aggregations represent a reaction to aggregate-mediated neurodegeneration.

Methods

To study the nitrosative stress-induced protein aggregation in cerebral ischemia/reperfusion injury, we used primary astrocyte cultures as a cell model, and systematically examined their iNOS expression and consequent NO generation following oxygen glucose deprivation and reperfusion. The expression of protein disulfide isomerase (PDI) and copper-zinc superoxide dismutase (SOD1) were also examined, and the biochemical interaction between PDI and SOD1 was determined by immunoprecipitation. In addition, the levels of S-nitrosylated PDI in cultured astrocytes after oxygen glucose deprivation and reperfusion treatment were measured using the biotin-switch assay. The formation of ubiquitinated-protein aggregates was detected by immunoblot and immunofluorescence staining.

Results

Our data showed that the up-regulation of iNOS expression after oxygen glucose deprivation and reperfusion treatment led to excessive NO generation. Up-regulation of PDI and SOD1 was also identified in cultured astrocytes following oxygen glucose deprivation and reperfusion, and these two proteins were found to bind to each other. Furthermore, the increased nitrosative stress due to ischemia/reperfusion injury was highly associated with NO-induced S-nitrosylation of PDI, and this S-nitrosylation of PDI was correlated with the formation of ubiquitinated-protein aggregates; the levels of S-nitrosylated PDI increased in parallel with the formation of aggregates. When NO generation was pharmacologically inhibited by iNOS specific inhibitor 1400W, S-nitrosylation of PDI was significantly blocked. In addition, the formation of ubiquitinated-protein aggregates in cultured astrocytes following oxygen glucose deprivation and reperfusion was also suppressed by 1400W. Interestingly, these aggregates were colocalized with SOD1, which was found to co-immunoprecipitate with PDI.

Conclusions

NO-mediated S-nitrosylation of PDI may be involved in the formation of the SOD1-linked ubiquitinated-protein aggregates in cerebral ischemia/reperfusion injury.

Discovery of an orally active small-molecule irreversible inhibitor of protein disulfide isomerase for ovarian cancer treatment

Protein disulfide isomerase (PDI), an endoplasmic reticulum chaperone protein, catalyzes disulfide bond breakage, formation, and rearrangement. The effect of PDI inhibition on ovarian cancer progression is not yet clear, and there is a need for potent, selective, and safe small-molecule inhibitors of PDI. Here, we report a class of propynoic acid carbamoyl methyl amides (PACMAs) that are active against a panel of human ovarian cancer cell lines. Using fluorescent derivatives, 2D gel electrophoresis, and MS, we established that PACMA 31, one of the most active analogs, acts as an irreversible small-molecule inhibitor of PDI, forming a covalent bond with the active site cysteines of PDI. We also showed that PDI activity is essential for the survival and proliferation of human ovarian cancer cells. In vivo, PACMA 31 showed tumor targeting ability and significantly suppressed ovarian tumor growth without causing toxicity to normal tissues. These irreversible small-molecule PDI inhibitors represent an important approach for the development of targeted anticancer agents for ovarian cancer therapy, and they can also serve as useful probes for investigating the biology of PDI-implicated pathways.

Channel catfish (Ictalurus punctatus) protein disulphide isomerase, PDIA6: molecular characterization and expression regulated by bacteria and virus inoculation

Protein disulfide isomerases (PDIs) are thought to aid protein folding and assembly by catalyzing formation and shuffling of cysteine disulfide bonds in the endoplasmic reticulum (ER). Currently, increasing evidence suggests PDIs play an important role in host cell invasion and they are relevant targets for the host immune response. However the roles of specific PDIs in teleosts are little known. Here, we characterized the Protein disulfide isomerase family A, member 6 (PDIA6) from channel catfish, Ictalurus punctatus (named as ccPDIA6). The catfish ccPDIA6 gene was homologous to those of other vertebrate species with 13 exons and 12 introns. The consensus full-length ccPDIA6 cDNA contained an ORF of 1320 bp encoding a putative protein of 439 amino acids. It had a 19 amino acid signal peptide and two active thioredoxin-like domains. Sequence of phylogenic analysis and multiple alignments showed that ccPDIA6 was conserved throughout vertebrate evolution. Southern blot analysis suggested the presence of one copy of the ccPDIA6 gene in the catfish genome. Tissue distribution shows that ccPDIA6 was expressed in all examined tissues at the mRNA level. When using the aquatic zoonotic pathogens such as Edwardsiella tara, Streptococcus iniae, and channel catfish reovirus （CCRV） to challenge channel catfish, ccPDIA6 expression was significant changed in immune-related tissues such as head kidney, intestine, liver and spleen. The results suggested that ccPDIA6 might play an important role in the immunity of channel catfish. This is the first report that the PDI gene may be involved in fish host defense against pathogen infection.

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

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

Exploring the limit of metazoan thermal tolerance via comparative proteomics: thermally induced changes in protein abundance by two hydrothermal vent polychaetes

Temperatures around hydrothermal vents are highly variable, ranging from near freezing up to 300°C. Nevertheless, animals thrive around vents, some of which live near the known limits of animal thermotolerance. Paralvinella sulfincola, an extremely thermotolerant vent polychaete, and Paralvinella palmiformis, a cooler-adapted congener, are found along the Juan de Fuca Ridge in the northwestern Pacific. We conducted shipboard high-pressure thermotolerance experiments on both species to characterize the physiological adaptations underlying P. sulfincola's pronounced thermotolerance. Quantitative proteomics, expressed sequence tag (EST) libraries and glutathione assays revealed that P. sulfincola (i) exhibited an upregulation in the synthesis and recycling of glutathione with increasing temperature, (ii) downregulated nicotinamide adenine dinucleotide (NADH) and succinate dehydrogenases (key enzymes in oxidative phosphorylation) with increasing temperature, and (iii) maintained elevated levels of heat shock proteins (HSPs) across all treatments. In contrast, P. palmiformis exhibited more typical responses to increasing temperatures (e.g. increasing HSPs at higher temperatures). These data reveal differences in how a mesotolerant and extremely thermotolerant eukaryote respond to thermal stress, and suggest that P. sulfincola's capacity to mitigate oxidative stress via increased synthesis of antioxidants and decreased flux through the mitochondrial electron transport chain enable pronounced thermotolerance. Ultimately, oxidative stress may be the key factor in limiting all metazoan thermotolerance.

Protein disulfide isomerase in redox cell signaling and homeostasis

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

The critical roles of endoplasmic reticulum chaperones and unfolded protein response in tumorigenesis and anticancer therapies

Cancer progression is characterized by rapidly proliferating cancer cells that are in need of increased protein synthesis. Therefore, enhanced endoplasmic reticulum (ER) activity is required to facilitate the folding, assembly and transportation of membrane and secretory proteins. These functions are carried out by ER chaperones. It is now becoming clear that the ER chaperones have critical functions outside of simply facilitating protein folding. For example, cancer progression requires glucose regulated protein (GRP) 78 for cancer cell survival and proliferation, as well as angiogenesis in the microenvironment. GRP78 can translocate to the cell surface acting as a receptor regulating oncogenic signaling and cell viability. Calreticulin, another ER chaperone, can translocate to the cell surface of apoptotic cancer cells and induce immunogenic cancer cell death and antitumor responses in vivo. Tumor-secreted GRP94 has been shown to elicit antitumor immune responses when used as antitumor vaccines. Protein disulfide isomerase is another ER chaperone that demonstrates pro-oncogenic and pro-survival functions. Because of intrinsic alterations of cellular metabolism and extrinsic factors in the tumor microenvironment, cancer cells are under ER stress, and they respond to this stress by activating the unfolded protein response (UPR). Depending on the severity and duration of ER stress, the signaling branches of the UPR can activate adaptive and pro-survival signals, or induce apoptotic cell death. The protein kinase RNA-like ER kinase signaling branch of the UPR has a dual role in cancer proliferation and survival, and is also required for ER stress-induced autophagy. The activation of the inositol-requiring kinase 1α branch promotes tumorigenesis, cancer cell survival and regulates tumor invasion. In summary, perturbance of ER homeostasis has critical roles in tumorigenesis, and therapeutic modulation of ER chaperones and/or UPR components presents potential antitumor treatments.

Serendipitous discovery of a novel protein signaling mechanism in heart failure

A number of protein signaling mechanisms are known to be involved in the progression of heart failure, yet the mechanism(s) by which the heart fails remains poorly understood. Therefore, we undertook a global approach to this question and used an antibody microarray to identify proteins differentially expressed in dysfunctional right ventricles in a bovine model of heart failure and the results were validated using cardiac tissue from both bovine and human heart failure. We found that protein disulfide isomerase 3, PDIA3, a protein that resides in the lumen of the endoplasmic reticulum, is significantly upregulated in both animal and human models of right and left heart failure. Altered expression of this protein has not previously been described in models of heart failure. In our initial microarray analysis, we found that CSK (c-Src kinase) was among the proteins upregulated in failing bovine ventricle. To further elucidate the role of CSK in heart failure, we studied the expression of its downstream target, Src, and found that Src expression and phosphorylation were markedly upregulated in failing ventricles. However, we also noted a smaller immunologically reactive protein that was only seen in experimental animals. In order to positively identify the smaller, Src-reactive protein, we used 2-dimensional gel electrophoresis and mass spectrophotometry. Surprisingly, we identified this protein as PDIA3, a protein that did not belong to the Src family of proteins. Upon sequence examination we found that PDIA3 contains a short C-terminal sequence with strong homology to Src and that it was this short sequence to which the antibody was generated. PDIA3 participates in MHC class I presentation and is implicated in the progression of valvular dysfunction in rheumatic heart disease, as well as calcium modulation in the sarcoplasmic reticulum. The molecule resides in the lumen of the endoplasmic reticulum and participates in disulfide bond formation during protein folding by interacting with calnexin and calreticulin. This interaction may indirectly effect SERCA (sarco/endoplasmic reticulum Ca(2+)-transport ATPase) activity and by extension contribute to the calcium dysregulation that characterizes progressive heart failure. Further studies are needed to elucidate the role that PDIA3 may play in the progression of heart failure.

Proteome profile changes in SH-SY5y neuronal cells after treatment with neurotrophic factors

Artemin, one of glial cell line-derived neurotrophic factors (GDNFs) supports sensory neuron. Although a role of artemin and GDNF as neurite outgrowth regulators in early neuron development has been suggested, the immediate effects of artemin and GDNF on neuronal cells have not been elucidated. Here, we investigated artemin and GDNF actions on the neuronal cell proteome. To identify immediate-early protein changes by artemin and GDNF in neuronal cells, we used a differential proteomics approach in SH-SY5y human neuronal cells treated with artemin or GDNF for 1 h. Eleven proteins that changed after both artemin and GDNF treatment were identified using two-dimensional gel electrophoresis and matrix-assisted laser desorption ionization time-of-flight tandem mass spectroscopy. The calcium ion-binding chaperone calreticulin and calcium/calmodulin-binding nuclear matrix protein matrin 3 showed common quantitative differences after both artemin and GDNF treatment. Cytoskeletal proteins also showed quantitative profile differences, which are functionally relevant to cytoskeletal rearrangement leading to the neurite elongation in neurons. These protein changes were detected in neuronal cells without accompanying changes in mRNA levels. These results suggest that immediate changes induced by artemin and GDNF are related to cytoskeletal protein level changes without transcriptional regulation.

Thioredoxin-1 and protein disulfide isomerase catalyze the reduction of similar disulfides in HIV gp120

HIV-1 enters cells via interaction of the viral glycoprotein gp120, the host cell surface receptor CD4 and the co-receptors CCR5 or CXCR4. For entry, gp120 undergoes conformational changes that depend on the reduction of one or more disulfides. Previous studies indicate that protein disulfide isomerase (PDI), thioredoxin-1 (Trx1), and glutaredoxin-1 (Grx1) catalyze gp120 reduction, but their specific disulfide targets are not known. Here, it was demonstrated that PDI and Trx1 have similar gp120 disulfide targets as determined by labeling after reduction, but with some pattern differences, including overall stronger labeling with Trx1 than with PDI. Furthermore, uneven labeling of the residues of a disulfide may reflect altered accessibility by conformational changes upon the reduction process. Since both PDI and Trx1 may be involved in viral entry, compounds that target the host redox system or the viral gp120 were tested in vitro to investigate whether redox regulation is a target for anti-HIV therapy. Carbohydrate binding agents (CBAs), previously shown to bind gp120 and inhibit HIV entry, were now demonstrated to inhibit gp120 disulfide reduction. Auranofin, an inhibitor of thioredoxin reductase 1 (TrxR1), also showed inhibitory activity towards HIV infection, although close to its cytotoxic concentration. Our results demonstrate that both the host redox system and the viral surface glycoproteins are of interest for the development of new generations of anti-HIV therapeutics.

PDIA3 mRNA expression and IL-2, IL-4, IL-6, and CRP levels of acute kidney allograft rejection in rat

Kidney transplantation to treat end-stage renal disease has evolved rapidly from the first successful transplantations to the current widespread use of grafts from both cadaveric and living donors. But acute rejection is still a strong risk factor for chronic rejection in recipients of renal grafts. To investigate possible mechanisms, we describe a comparison between differentially proteins expression and immune markers profile (IL-2, IL-4, IL-6, and CRP) of acute rejection and the controls. Through quantitative real-time RT-PCR confirmation, PDIA3 mRNA and protein expression levels in serum and transplanted kidney in experiment group was significantly (P < 0.05) higher than that in control group. Immunity analysis showed that plasma IL-2, IL-4, IL-6, and CRP levels were higher in experimental rats than those in control rats. Our data thus indicate that PDIA3 might be potentially involve into the occurence and development of acute rejection response in renal transplantation and increased plasma IL-2, IL-4, IL-6, and CRP levels play an important role to prevent acute kidney allograft rejection in rats.

Protein disulfide isomerase and host-pathogen interaction

Reactive oxygen species (ROS) production by immunological cells is known to cause damage to pathogens. Increasing evidence accumulated in the last decade has shown, however, that ROS (and redox signals) functionally regulate different cellular pathways in the host-pathogen interaction. These especially affect (i) pathogen entry through protein redox switches and redox modification (i.e., intra- and interdisulfide and cysteine oxidation) and (ii) phagocytic ROS production via Nox family NADPH oxidase enzyme and the control of phagolysosome function with key implications for antigen processing. The protein disulfide isomerase (PDI) family of redox chaperones is closely involved in both processes and is also implicated in protein unfolding and trafficking across the endoplasmic reticulum (ER) and towards the cytosol, a thiol-based redox locus for antigen processing. Here, we summarise examples of the cellular association of host PDI with different pathogens and explore the possible roles of pathogen PDIs in infection. A better understanding of these complex regulatory steps will provide insightful information on the redox role and coevolutional biological process, and assist the development of more specific therapeutic strategies in pathogen-mediated infections.

The interrelating dynamics of hypoxic tumor microenvironments and cancer cell phenotypes in cancer metastasis

The interrelating dynamics of the primary tumor cells and their surrounding microenvironment might determine phenotypic characteristics of disseminated tumor cells and contribute to cancer metastasis. Cytoprotective mechanisms (e.g., energy metabolism control, DNA damage response, global translation control and unfolded protein response) exert selective pressure in the tumor microenvironment. In particular, adaptation to hypoxia is vital for survival of malignant cells in the tumor and at distant sites such as the bone marrow. In addition to the stress response, the ability of tumor cells to undergo certain cellular re-differentiation programmes like the epithelial-mesenchymal transition (EMT), which is linked to cancer stemness, appears to be important for successful cancer cell spread. Here we will discuss the selection pressures that eventually lead to the formation of overt metastases. We will focus the properties of the microenvironment including (i) metabolic and cytoprotective programs that ensure survival of disseminated tumor cells, (ii) blood vessel structure, and (iii) the hypoxia-normoxia switch as well as intrinsic factors affecting the evolvement of novel tumor cell populations.

Arbuscular mycorrhizal symbiosis elicits shoot proteome changes that are modified during cadmium stress alleviation in Medicago truncatula

BACKGROUND

Arbuscular mycorrhizal (AM) fungi, which engage a mutualistic symbiosis with the roots of most plant species, have received much attention for their ability to alleviate heavy metal stress in plants, including cadmium (Cd). While the molecular bases of Cd tolerance displayed by mycorrhizal plants have been extensively analysed in roots, very little is known regarding the mechanisms by which legume aboveground organs can escape metal toxicity upon AM symbiosis. As a model system to address this question, we used Glomus irregulare-colonised Medicago truncatula plants, which were previously shown to accumulate and tolerate heavy metal in their shoots when grown in a substrate spiked with 2 mg Cd kg(-1).

RESULTS

The measurement of three indicators for metal phytoextraction showed that shoots of mycorrhizal M. truncatula plants have a capacity for extracting Cd that is not related to an increase in root-to-shoot translocation rate, but to a high level of allocation plasticity. When analysing the photosynthetic performance in metal-treated mycorrhizal plants relative to those only Cd-supplied, it turned out that the presence of G. irregulare partially alleviated the negative effects of Cd on photosynthesis. To test the mechanisms by which shoots of Cd-treated mycorrhizal plants avoid metal toxicity, we performed a 2-DE/MALDI/TOF-based comparative proteomic analysis of the M. truncatula shoot responses upon mycorrhization and Cd exposure. Whereas the metal-responsive shoot proteins currently identified in non-mycorrhizal M. truncatula indicated that Cd impaired CO2 assimilation, the mycorrhiza-responsive shoot proteome was characterised by an increase in photosynthesis-related proteins coupled to a reduction in glugoneogenesis/glycolysis and antioxidant processes. By contrast, Cd was found to trigger the opposite response coupled the up-accumulation of molecular chaperones in shoot of mycorrhizal plants relative to those metal-free.

CONCLUSION

Besides drawing a first picture of shoot proteome modifications upon AM symbiosis and/or heavy metal stress in legume plants, the current work argues for allocation plasticity as the main driving force for Cd extraction in aboveground tissues of M. truncatula upon mycorrhization. Additionally, according to the retrieved proteomic data, we propose that shoots of mycorrhizal legume plants escape Cd toxicity through a metabolic shift implying the glycolysis-mediated mobilization of defence mechanisms at the expense of the photosynthesis-dependent symbiotic sucrose sink.

Molecular cloning and expression pattern analysis of two novel disulfide isomerases in shrimp

Protein disulfide isomerase (PDI) catalyzes formation and isomerization of disulfide bridges and has chaperone activity. Currently, increasing evidence suggests the significance of PDI in immune and stress responses. To clarify the role of PDIs in the innate immunity of shrimp, two PDI genes were isolated and identified from Fenneropenaeus chinensis (fleshy prawn). FcPDI1 is 1878bp in length and encodes a protein of 383 amino acids. It has 18-amino acid signal peptide, 3 thioredoxin domains with 3 active sites of CGHC, and KEDL retention signal at its C-end. FcPDI1 is an atypical PDI. The open reading frame of FcPDI2 encodes a 497-amino acid protein and shows the classical domain organization a-b-b'-a'. Phylogenic analysis and multiple alignments show that FcPDI1 is similar to PDI that contains 3 thioredoxin domains from other species including invertebrates and vertebrates. FcPDI2, LvPDI, and insect PDIs are grouped into one cluster and are similar to PDIs having a-b-b'-a' domain organization. Tissue distribution shows that FcPDI1 and FcPDI2 were expressed in all detected tissues at the mRNA level. Changes in FcPDI1 and FcPDI2 expression at the mRNA level in hemocytes, hepatopancreas, gills, and ovaries upon Vibrio or white spot syndrome virus challenge were also analyzed. The results suggest that FcPDI1 and FcPDI2 might have roles in the innate immunity of shrimp. FcPDI1 was also successfully expressed in Escherichia coli and the recombinant FcPDI1 showed insulin reductase activity. Results show that FcPDI might play an important role in the innate immunity of shrimp.

Ca2+-signaling, alternative splicing and endoplasmic reticulum stress responses

Ca(2+)-signaling, alternative splicing, and stress responses by the endoplasmic reticulum are three important cellular activities which can be strongly interconnected to alter the expression of protein isoforms in a tissue dependent manner or during development depending on the environmental conditions. This integrated network of signaling pathways permits a high degree of versatility and adaptation to metabolic, developmental and stress processes. Defects in its regulation may lead to cellular malfunction.

Exosome-driven antigen transfer for MHC class II presentation facilitated by the receptor binding activity of influenza hemagglutinin

The mechanisms underlying MHC class I-restricted cross-presentation, the transfer of Ag from an infected cell to a professional APC, have been studied in great detail. Much less is known about the equivalent process for MHC class II-restricted presentation. After infection or transfection of class II-negative donor cells, we observed minimal transfer of a proteasome-dependent "class I-like" epitope within the influenza neuraminidase glycoprotein but potent transfer of a classical, H-2M-dependent epitope within the hemagglutinin (HA) glycoprotein. Additional experiments determined transfer to be exosome-mediated and substantially enhanced by the receptor binding activity of incorporated HA. Furthermore, a carrier effect was observed in that incorporated HA improved exosome-mediated transfer of a second membrane protein. This route of Ag presentation should be relevant to other enveloped viruses, may skew CD4(+) responses toward exosome-incorporated glycoproteins, and points toward novel vaccine strategies.

Design of an in vivo cleavable disulfide linker in recombinant fusion proteins

In order to achieve optimal biological activity and desired pharmacokinetic profiles, a dithiocyclopeptide linker was designed for in vivo release of protein domains from a recombinant fusion protein. This novel in vivo cleavable disulfide linker, based on a dithiocyclopeptide containing a thrombin-sensitive sequence and an intramolecular disulfide bond, was inserted between transferrin and granulocyte colony-stimulating factor (G-CSF) recombinant fusion protein domains. After expression of the fusion protein, G-C-T, from HEK293 cells, thrombin treatment in vitro generated a fusion protein linked via a reversible disulfide bond that was quickly cleaved in vivo, separating the protein domains. After release from the fusion protein, free G-CSF exhibited an improved biological activity in a cell proliferation assay. Although reversible disulfide bonds are commonly used in protein chemical conjugation methods, to our knowledge this report is the first example of the construction of a recombinant fusion protein with a disulfide linkage for the release of the functional domain. This linker design can be adapted to diverse recombinant fusion proteins in which in vivo separation of protein domains is required to achieve an improved therapeutic effect and a desirable pharmacokinetic profile and biodistribution of the functional domain.

Induction of liver steatosis and lipid droplet formation in ATF6alpha-knockout mice burdened with pharmacological endoplasmic reticulum stress

We burdened mice with intraperitoneal injection of the endoplasmic reticulum stress-inducing reagent tunicamycin, and found that wild-type mice were able to recover from the insult, whereas ATF6α-knockout mice exhibited liver dysfunction and steatosis. Our results establish links between endoplasmic reticulum stress, lipid metabolism and steatosis

Accumulation of unfolded proteins in the endoplasmic reticulum (ER) activates homeostatic responses collectively termed the unfolded protein response. Among the three principal signaling pathways operating in mammals, activating transcription factor (ATF)6α plays a pivotal role in transcriptional induction of ER-localized molecular chaperones and folding enzymes as well as components of ER-associated degradation, and thereby mouse embryonic fibroblasts deficient in ATF6α are sensitive to ER stress. However, ATF6α-knockout mice show no apparent phenotype under normal growing conditions. In this report, we burdened mice with intraperitoneal injection of the ER stress-inducing reagent tunicamycin and found that wild-type mice were able to recover from the insult, whereas ATF6α-knockout mice exhibited liver dysfunction and steatosis. Thus, ATF6α-knockout mice accumulated neutral lipids in the liver such as triacylglycerol and cholesterol, which was ascribable to blockage of β-oxidation of fatty acids caused by decreased mRNA levels of the enzymes involved in the process, suppression of very-low-density lipoprotein formation due to destabilized apolipoprotein B-100, and stimulation of lipid droplet formation resulting from transcriptional induction of adipose differentiation-related protein. Accordingly, the hepatocytes of tunicamycin-injected knockout mice were filled with many lipid droplets. These results establish links among ER stress, lipid metabolism, and steatosis.

Quantitative proteome profiling of respiratory virus-infected lung epithelial cells

Respiratory virus infections are among the primary causes of morbidity and mortality in humans. Influenza virus, respiratory syncytial virus (RSV), parainfluenza (PIV) and human metapneumovirus (hMPV) are major causes of respiratory illness in humans. Especially young children and the elderly are susceptible to infections with these viruses. In this study we aim to gain detailed insight into the molecular pathogenesis of respiratory virus infections by studying the protein expression profiles of infected lung epithelial cells. A549 cells were exposed to a set of respiratory viruses [RSV, hMPV, PIV and Measles virus (MV)] using both live and UV-inactivated virus preparations. Cells were harvested at different time points after infection and processed for proteomics analysis by 2-dimensional difference gel electrophoresis. Samples derived from infected cells were compared to mock-infected cells to identify proteins that are differentially expressed due to infection. We show that RSV, hMPV, PIV3, and MV induced similar core host responses and that mainly proteins involved in defense against ER stress and apoptosis were affected which points towards an induction of apoptosis upon infection. By 2-D DIGE analyses we have gathered information on the induction of apoptosis by respiratory viruses in A549 cells.

Molecular modeling of retinoschisin with functional analysis of pathogenic mutations from human X-linked retinoschisis

Gene mutations that encode retinoschisin (RS1) cause X-linked retinoschisis (XLRS), a form of juvenile macular and retinal degeneration that affects males. RS1 is an adhesive protein which is proposed to preserve the structural and functional integrity of the retina, but there is very little evidence of the mechanism by which protein changes are related to XLRS disease. Here, we report molecular modeling of the RS1 protein and consider perturbations caused by mutations found in human XLRS subjects. In 60 XLRS patients who share 27 missense mutations, we then evaluated possible correlations of the molecular modeling with retinal function as determined by the electroretinogram (ERG) a- and b-waves. The b/a-wave ratio reflects visual-signal transfer in retina. We sorted the ERG b/a-ratios by patient age and by the mutation impact on protein structure. The majority of RS1 mutations caused minimal structure perturbation and targeted the protein surface. These patients' b/a-ratios were similar across younger and older subjects. Maximum structural perturbations from either the removal or insertion of cysteine residues or changes in the hydrophobic core were associated with greater difference in the b/a-ratio with age, with a significantly smaller ratio at younger ages, analogous to the ERG changes with age observed in mice with no RS1-protein expression due to a recombinant RS1-knockout gene. The molecular modeling suggests an association between the predicted structural alteration and/or damage to retinoschisin and the severity of XLRS as measured by the ERG analogous to the RS1-knockout mouse.

Oxidative stress induces a reversible flux of cysteine from tissues to blood in vivo in the rat

Glutathione (GSH) plays a key role in defense against oxidative stress. The availability of GSH is ensured in tissues by systems devoted to its maintenance in the reduced state and by the flux of GSH and cysteine between sites of biosynthesis and sites of utilization. Little is known about the effect of oxidative stress on the distribution of low-molecular-mass thiols and their exchange rate between tissues. In this study, we found that a slow infusion of diamide (a specific thiol-oxidizing compound) evoked a dramatic increase in blood cysteine in rats. Our data suggest that inter-organ exchange of cysteine occurs, that cysteine derives from both glutathione via gamma-glutamyl transpeptidase and methionine via homocysteine and the trans-sulfuration pathway, and that these pathways are considerably influenced by oxidative stress.

Proinsulin and the genetics of diabetes mellitus

Insulin plays a central role in the regulation of vertebrate metabolism. The hormone, the post-translational product of a single-chain precursor, is a globular protein containing two chains, A (21 residues) and B (30 residues). Recent advances in human genetics have identified dominant mutations in the insulin gene causing permanent neonatal-onset DM(2) (1-4). The mutations are predicted to block folding of the precursor in the ER of pancreatic beta-cells. Although expression of the wild-type allele would in other circumstances be sufficient to maintain homeostasis, studies of a corresponding mouse model (5-7) suggest that the misfolded variant perturbs wild-type biosynthesis (8, 9). Impaired beta-cell secretion is associated with ER stress, distorted organelle architecture, and cell death (10). These findings have renewed interest in insulin biosynthesis (11-13) and the structural basis of disulfide pairing (14-19). Protein evolution is constrained not only by structure and function but also by susceptibility to toxic misfolding.

Protein disulfide isomerase increases in myocardial endothelial cells in mice exposed to chronic hypoxia: a stimulatory role in angiogenesis

Previous studies have shown that exposure to chronic hypoxia protects against myocardial infarction, but little is known about the cellular and molecular mechanisms involved. Here we observed that chronic hypoxia for 3 wk resulted in improved survival of mice (from 64% to 83%), reduced infarction size (from 45 +/- 4% to 32 +/- 4%, P < 0.05), increased cardiac ejection fraction (from 19 +/- 4% to 35 +/- 5%, P < 0.05), coronary flow velocity under adenosine-induced hyperemia (from 58 +/- 2 to 75 +/- 5 cm/s, P < 0.05), myocardial capillary density (from 3,772 +/- 162 to 4,760 +/- 197 capillaries/mm(2), P < 0.01), and arteriolar density (from 8.04 +/- 0.76 to 10.34 +/- 0.69 arterioles/mm(2), P < 0.05) 3 wk after myocardial infarction. With two-dimensional gel electrophoresis, we identified that protein disulfide isomerase (PDI) was highly upregulated in hypoxic myocardial capillary endothelial cells. The loss of PDI function in endothelial cells by small interfering RNA significantly increased the number of apoptotic cells (by 3.4-fold at hypoxia, P < 0.01) and reduced migration (by 52% at hypoxia, P < 0.001) and adhesion to collagen I (by 42% at hypoxia, P < 0.01). In addition, the specific inhibition of PDI by PDI small interfering RNA (by 46%, P < 0.01) and bacitracin (by 72%, P < 0.001) reduced the formation of tubular structures by endothelial cells. Our data indicate that chronic hypoxic exposure improves coronary blood flow and protects the myocardium against infarction. These beneficial effects may be partly explained by the increased endothelial expression of PDI, which protects cells against apoptosis and increases cellular migration, adhesion, and tubular formation. The increased PDI expression in endothelial cells may be a novel mechanism to protect the myocardium against myocardial ischemic diseases.

Heat induced ‘masking’ of redox sensitive component(s) of the DNA-nuclear matrix anchoring complex

The 'masking effect' is the observation that heat shock reduces or masks the apparent expression of ionizing radiation (IR) damage to DNA. The mechanism of this effect is thought to involve the aggregation of proteins to the nuclear matrix or chromatin, thereby stabilizing these structures and masking actual DNA damage from assays and presumably from DNA repair complexes. Previously, using the 'halo assay', it has been shown that nucleoids treated with 1 mM dithiothreitol (DTT) and/or inhibited the rewinding of DNA supercoils and that this effect was masked in nucloids isolated from heated cells. Here it is reported that treatment of living cells with reducing agents diminishes the interaction between DNA and Protein Disulphide Isomerase (PDI) and that hyperthermia restored the PDI-DNA interaction, indicating that the masking effect occurred in vivo. PDI is a nuclear matrix protein which binds MAR DNA sequences and may be involved in regulating the degree of DNA supercoiling. It is hypothesized that heat-induced stabilization of PDI-DNA interaction will mask changes in supercoiling observed with reducing reagents and also IR. This stabilization may be affected through either the heat-induced association or enhancement of the binding of proteins to MAR DNA at the NM. Several proteins, including B23 and Hsp60, have been identified whose interaction with DNA increased following heat shock. Further work will be needed to determine if these proteins do, in fact, play a role in the masking effect.