MDG1/ERdj4, an ER-resident DnaJ family member, suppresses cell death induced by ER stress

Co-chaperones of the Human Endoplasmic Reticulum: An Update

In mammalian cells, the rough endoplasmic reticulum (ER) plays central roles in the biogenesis of extracellular plus organellar proteins and in various signal transduction pathways. For these reasons, the ER comprises molecular chaperones, which are involved in import, folding, assembly, export, plus degradation of polypeptides, and signal transduction components, such as calcium channels, calcium pumps, and UPR transducers plus adenine nucleotide carriers/exchangers in the ER membrane. The calcium- and ATP-dependent ER lumenal Hsp70, termed immunoglobulin heavy-chain-binding protein or BiP, is the central player in all these activities and involves up to nine different Hsp40-type co-chaperones, i.e., ER membrane integrated as well as ER lumenal J-domain proteins, termed ERj or ERdj proteins, two nucleotide exchange factors or NEFs (Grp170 and Sil1), and NEF-antagonists, such as MANF. Here we summarize the current knowledge on the ER-resident BiP/ERj chaperone network and focus on the interaction of BiP with the polypeptide-conducting and calcium-permeable Sec61 channel of the ER membrane as an example for BiP action and how its functional cycle is linked to ER protein import and various calcium-dependent signal transduction pathways.

Multi-Faceted Roles of DNAJB Protein in Cancer Metastasis and Clinical Implications

Heat shock proteins (HSPs) are highly conserved molecular chaperones with diverse cellular activities, including protein folding, assembly or disassembly of protein complexes, and maturation process under diverse stress conditions. HSPs also play essential roles in tumorigenesis, metastasis, and therapeutic resistance across cancers. Among them, HSP40s are widely accepted as regulators of HSP70/HSP90 chaperones and an accumulating number of biological functions as molecular chaperones dependent or independent of either of these chaperones. Despite large numbers of HSP40s, little is known about their physiologic roles, specifically in cancer progression. This article summarizes the multi-faceted role of DNAJB proteins as one subclass of the HSP40 family in cancer development and metastasis. Regulation and deregulation of DNAJB proteins at transcriptional, post-transcriptional, and post-translational levels contribute to tumor progression, particularly cancer metastasis. Furthermore, understanding differences in function and regulating mechanism between DNAJB proteins offers a new perspective on tumorigenesis and metastasis to improve therapeutic opportunities for malignant diseases.

The function of the co-chaperone ERdj4 in diverse (patho-)physiological conditions

Accumulation of misfolded proteins in the endoplasmic reticulum (ER) induces a well-orchestrated cellular response to reduce the protein burden within the ER. This unfolded protein response (UPR) is controlled primarily by three transmembrane proteins, IRE1α, ATF6, and PERK, the activity of which is controlled by BiP, the ER-resident Hsp70 protein. Binding of BiP to co-chaperones via their highly conserved J-domains stimulates the intrinsic ATPase activity of BiP, thereby providing the energy necessary for (re-)folding of proteins, or for targeting of misfolded proteins to the degradation pathway, processes specified and controlled by the respective co-chaperone. In this review, our aim is to elucidate the function of the co-chaperone ERDJ4, also known as MDG1, MDJ7, or DNAJB9. Knockout and knockin experiments clearly point to the central role of ERDJ4 in controlling lipogenesis and protein synthesis by promoting degradation of SREBP1c and the assembly of the protein complex mTORC2. Accumulating data reveal that ERDJ4 controls epithelial-to-mesenchymal transition, a central process during embryogenesis, in wound healing, and tumor development. Overexpression of ERdj4 has been shown to improve engraftment of transplanted human stem cells, possibly due to its ability to promote cellular survival in stressed cells. High ERDJ4-plasma levels are specific for fibrillary glomerulonephritis and serve as a diagnostic marker. As outlined in this review, the functions of ERDJ4 are manifold, depending on the cellular (patho-) physiological state, the cellular protein repertoire, and the subcellular localization of ERDJ4.

Regulation of p53 and Cancer Signaling by Heat Shock Protein 40/J-Domain Protein Family Members

Heat shock proteins (HSPs) are molecular chaperones that assist diverse cellular activities including protein folding, intracellular transportation, assembly or disassembly of protein complexes, and stabilization or degradation of misfolded or aggregated proteins. HSP40, also known as J-domain proteins (JDPs), is the largest family with over fifty members and contains highly conserved J domains responsible for binding to HSP70 and stimulation of the ATPase activity as a co-chaperone. Tumor suppressor p53 (p53), the most frequently mutated gene in human cancers, is one of the proteins that functionally interact with HSP40/JDPs. The majority of p53 mutations are missense mutations, resulting in acquirement of unexpected oncogenic activities, referred to as gain of function (GOF), in addition to loss of the tumor suppressive function. Moreover, stability and levels of wild-type p53 (wtp53) and mutant p53 (mutp53) are crucial for their tumor suppressive and oncogenic activities, respectively. However, the regulatory mechanisms of wtp53 and mutp53 are not fully understood. Accumulating reports demonstrate regulation of wtp53 and mutp53 levels and/or activities by HSP40/JDPs. Here, we summarize updated knowledge related to the link of HSP40/JDPs with p53 and cancer signaling to improve our understanding of the regulation of tumor suppressive wtp53 and oncogenic mutp53 GOF activities.

LncRNA-URHC Functions as ceRNA to Regulate DNAJB9 Expression by Competitively Binding to miR-5007-3p in Hepatocellular Carcinoma

BACKGROUND

Hepatocellular carcinoma (HCC) is often diagnosed at a late stage, when the prognosis is poor. The regulation of long noncoding RNAs (lncRNAs) plays a crucial role in HCC. However, the precise regulatory mechanisms of lncRNA signaling in HCC remain largely unknown. Our study aims to investigate the underlying mechanisms of lncRNA (upregulated in hepatocellular carcinoma) URHC in HCC.

OBJECTIVE

To study the in vivo and in vitro localization and biological effects of URHC on liver cancer cells. Through bioinformatics analysis, dual-luciferase reporter gene analysis and rescue experiments revealed the possible mechanism of URHC.

METHODS

RT-qPCR, fluorescence in situ hybridization (FISH) staining, EdU, colony formation, and tumor xenograft experiments were used to identify localized and biological effects of URHC on HCC cells in vitro and in vivo. The bioinformatics analysis, dual-luciferase reporter assay, and rescue experiments revealed the potential mechanism of URHC.

RESULTS

URHC silencing may inhibit the HCC cells' proliferation in vitro and in vivo. We found that URHC was mainly localized in the cytoplasm. The expression of miR-5007-3p was negatively regulated by URHC. And miR-5007-3p could reverse the effect of URHC in HCC cells. The expression of DNAJB9 was negatively regulated by miR-5007-3p but positively regulated by URHC. These suggestive of lncRNA-URHC positively regulated the level of DNAJB9 by sponging miR-5007-3p.

CONCLUSION

Together, our study elucidated the role of URHC as a miRNA sponge in HCC and shed new light on lncRNA-directed diagnostics and therapeutics in HCC.

Dual topology of co-chaperones at the membrane of the endoplasmic reticulum

Dual topologies of proteins at the ER membrane are known for a variety of proteins allowing the same protein to exert different functions according to the topology adopted. A dual topology of the co-chaperone ERdj4, which resides in the endoplasmic reticulum (ER), was proposed recently, a thesis that we found to align all published data and existing controversies into one whole picture. The aim of this review is to reassess all primary data available in the literature on ER-resident Hsp40 co-chaperones with respect to their topology. After careful and critical analyses of all experimental data published so far, we identified, next to ERdj4, two other co-chaperones, ERdj3 and ERdj6, that also display features of a dual topology at the ER membrane. We assume that during cellular stress subpools of some ER-resident J protein can alter their topology so that these proteins can exert different functions in order to adapt to cellular stress.

Complexity and Specificity of Sec61-Channelopathies: Human Diseases Affecting Gating of the Sec61 Complex

The rough endoplasmic reticulum (ER) of nucleated human cells has crucial functions in protein biogenesis, calcium (Ca2+) homeostasis, and signal transduction. Among the roughly one hundred components, which are involved in protein import and protein folding or assembly, two components stand out: The Sec61 complex and BiP. The Sec61 complex in the ER membrane represents the major entry point for precursor polypeptides into the membrane or lumen of the ER and provides a conduit for Ca2+ ions from the ER lumen to the cytosol. The second component, the Hsp70-type molecular chaperone immunoglobulin heavy chain binding protein, short BiP, plays central roles in protein folding and assembly (hence its name), protein import, cellular Ca2+ homeostasis, and various intracellular signal transduction pathways. For the purpose of this review, we focus on these two components, their relevant allosteric effectors and on the question of how their respective functional cycles are linked in order to reconcile the apparently contradictory features of the ER membrane, selective permeability for precursor polypeptides, and impermeability for Ca2+. The key issues are that the Sec61 complex exists in two conformations: An open and a closed state that are in a dynamic equilibrium with each other, and that BiP contributes to its gating in both directions in cooperation with different co-chaperones. While the open Sec61 complex forms an aqueous polypeptide-conducting- and transiently Ca2+-permeable channel, the closed complex is impermeable even to Ca2+. Therefore, we discuss the human hereditary and tumor diseases that are linked to Sec61 channel gating, termed Sec61-channelopathies, as disturbances of selective polypeptide-impermeability and/or aberrant Ca2+-permeability.

Biomechanical Forces Regulate Gene Transcription During Stretch-Mediated Growth of Mammalian Neurons

At birth, there are 100 billion neurons in the human brain, with functional neural circuits extending through the spine to the epidermis of the feet and toes. Following birth, limbs and vertebrae continue to grow by several orders of magnitude, forcing established axons to grow by up to 200 cm in length without motile growth cones. The leading regulatory paradigm suggests that biomechanical expansion of mitotic tissue exerts tensile force on integrated nervous tissue, which synchronizes ongoing growth of spanning axons. Here, we identify unique transcriptional changes in embryonic rat DRG and cortical neurons while the corresponding axons undergo physiological levels of controlled mechanical stretch in vitro. Using bioreactors containing cultured neurons, we recapitulated the peak biomechanical increase in embryonic rat crown-rump-length. Biologically paired sham and “stretch-grown” DRG neurons spanned 4.6- and 17.2-mm in length following static or stretch-induced growth conditions, respectively, which was associated with 456 significant changes in gene transcription identified by genome-wide cDNA microarrays. Eight significant genes found in DRG were cross-validated in stretch-grown cortical neurons by qRT-PCR, which included upregulation of Gpat3, Crem, Hmox1, Hpse, Mt1a, Nefm, Sprr1b, and downregulation of Nrep. The results herein establish a link between biomechanics and gene transcription in mammalian neurons, which elucidates the mechanism underlying long-term growth of axons, and provides a basis for new research in therapeutic axon regeneration.

A Crucial Role for the Protein Quality Control System in Motor Neuron Diseases

Motor neuron diseases (MNDs) are fatal diseases characterized by loss of motor neurons in the brain cortex, in the bulbar region, and/or in the anterior horns of the spinal cord. While generally sporadic, inherited forms linked to mutant genes encoding altered RNA/protein products have also been described. Several different mechanisms have been found altered or dysfunctional in MNDs, like the protein quality control (PQC) system. In this review, we will discuss how the PQC system is affected in two MNDs—spinal and bulbar muscular atrophy (SBMA) and amyotrophic lateral sclerosis (ALS)—and how this affects the clearance of aberrantly folded proteins, which accumulate in motor neurons, inducing dysfunctions and their death. In addition, we will discuss how the PQC system can be targeted to restore proper cell function, enhancing the survival of affected cells in MNDs.

Fibrillary Glomerulonephritis and DnaJ Homolog Subfamily B Member 9 (DNAJB9)

Fibrillary GN (FGN) is a rare glomerular disease that is diagnosed based on the presence of fibrils in glomeruli. The fibrils are typically noncongophilic, randomly oriented, and measure 12–24 nm. Traditionally, electron microscopy (EM) has been an important tool to aid in the diagnosis of FGN by identifying the fibrils and to distinguish it from other entities that could mimic FGN. However, recently DnaJ homolog subfamily B member 9 (DNAJB9) has emerged as both a specific and sensitive biomarker in patients with FGN. It allows prompt diagnosis and alleviates reliance on EM. DNAJB9 is a cochaperone of heat shock protein 70 and is involved in endoplasmic reticulum protein-folding pathways. But its role in the pathogenesis of FGN remains elusive. DNAJB9 may act as a putative antigen or alternatively it may secondarily bind to misfolded IgG in the glomeruli. These hypotheses need future studies to elucidate the role of DNAJB9 in the pathogenesis of FGN. The treatment regimen for FGN has been limited due to paucity of studies. Most patients receive combination immunosuppressive regimens. Rituximab has been studied the most in FGN and it may delay disease progression. Prognosis of FGN remains poor and 50% require dialysis within 2 years of diagnosis. Despite its poor prognosis in native kidneys, the rate of recurrence post-transplantation is low (20%) and patient as well as allograft outcomes are similar to patients without FGN.

Protein expression pattern of the molecular chaperone Mdg1/ERdj4 during embryonic development

The vertebrate-specific co-chaperone Mdg1/ERdj4, which is localized in the endoplasmic reticulum, controls the folding and degradation of proteins. We characterized its protein pattern during chick embryonic development. During early development, Mdg1/ERdj4 protein is present in mesenchymal and epithelial cells. In mesenchymal cells, it has a salt and pepper pattern. In contrast, during epithelial tissue differentiation, Mdg1/ERdj4 marks the basal and/or apical compartment of epithelial linings. The distinct protein pattern in epithelial tissue might point to its role in organizing and maintaining the epithelial structure. This could be achieved, e.g. by controlling folding and secretion of membrane-bound receptors or by inhibiting the IRE1α-Xbp1s-SNAI1/2-induced mesenchymalization. High Mdg1/ERdj4 protein levels are maintained in tissue with sustained secretory activity as in ependymal cells or enterocytes, substantiating its important role for secretion. We conclude that the transient elevation of Mdg1/ERdj4 protein levels controls the differentiation of epithelial linings while constitutive high levels are closely linked to secretory activity.

DNAJB9 Inhibits p53-Dependent Oncogene-Induced Senescence and Induces Cell Transformation

DNAJB9 is known to be a member of the molecular chaperone gene family, whose cellular function has not yet been fully characterized. Here, we investigated the cellular function of DNAJB9 under strong mitogenic signals. We found that DNAJB9 inhibits p53-dependent oncogene-induced senescence (OIS) and induces neoplastic transformation under oncogenic RAS activation in mouse primary fibroblasts. In addition, we observed that DNAJB9 interacts physically with p53 under oncogenic RAS activation and that the p53-interacting region of DNAJB9 is critical for the inhibition of p53-dependent OIS and induction of neoplastic transformation by DNAJB9. These results suggest that DNAJB9 induces cell transformation under strong mitogenic signals, which is attributable to the inhibition of p53-dependent OIS by physical interactions with p53. This study might contribute to our understanding of the cellular function of DNAJB9 and the molecular basis of cell transformation.

Fibrillary Glomerulonephritis: Clinicopathologic Features and Atypical Cases from a Multi-Institutional Cohort

BACKGROUND AND OBJECTIVES

Fibrillary GN has been defined as an immune complex-mediated GN with amyloid-like fibrils larger than amyloid which are IgG positive and Congo red negative. With discovery of DNAJB9 as a highly sensitive and specific marker for fibrillary GN, the specificity of the morphologic criteria for establishing the diagnosis of fibrillary GN has come into question.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We sought to (1) determine anatomic characteristics that best define fibrillary GN and (2) identify clinical and pathologic features that predict outcomes.

RESULTS

We retrospectively reviewed kidney biopsies from patients diagnosed with fibrillary GN or suspected fibrillary GN between 1997 and 2017 (n=266, 65% female, median age 61). Approximately 11% of kidney biopsies had one or more unusual feature including monotypic deposits, Congo red positivity, or unusual fibril diameter. Fibrillary GN as a possible monoclonal gammopathy of renal significance represented <1% of cases. Immunostaining for DNAJB9 confirmed fibrillary GN in 100% of cases diagnosed as fibrillary GN and 79% of atypical cases diagnosed as possible fibrillary GN. At a median time of 24 months (interquartile range, 8-46 months) after biopsy (n=100), 53% of patients reached the combined primary outcome of ESKD or death, 18% had CKD, and 18% had partial remission. On multivariable analysis, male sex (adjusted hazard ratio [aHR], 3.82; 95% confidence interval [95% CI], 1.97 to 7.37) and eGFR were the most significant predictors of primary outcome (aHR of 8.02 if eGFR <30 ml/min per 1.73 m2 [95% CI, 1.85 to 34.75]; aHR of 6.44 if eGFR 30 to <45 ml/min per 1.73 m2 [95% CI, 1.38 to 29.99]). Immunosuppressive therapy with rituximab was significantly associated with stabilization of disease progression.

CONCLUSIONS

Detection of DNAJB9 is a useful diagnostic tool for diagnosing atypical forms of fibrillary GN. The outcomes for fibrillary GN are poor and progression to ESKD is influenced predominantly by the degree of kidney insufficiency at the time of diagnosis and male sex. Rituximab may help preserve kidney function for select patients with fibrillary GN.

PODCAST

This article contains a podcast at https://www.asn-online.org/media/podcast/CJASN/2019_11_04_CJN03870319.mp3.

Targeting DNAJB9, a novel ER luminal co-chaperone, to rescue ΔF508-CFTR

The molecular mechanism of Endoplasmic Reticulum-associated degradation (ERAD) of Cystic fibrosis transmembrane-conductance regulator (CFTR) is largely unknown. Particularly, it is unknown what ER luminal factor(s) are involved in ERAD. Herein, we used ProtoArray to identify an ER luminal co-chaperone, DNAJB9, which can directly interact with CFTR. For both WT- and ΔF508 (deletion of phenylalanine at position 508, the most common CF-causing mutant)-CFTR, knockdown of DNAJB9 by siRNA increased their expression levels on the cell surface and, consequently, upregulated their function. Furthermore, genetic ablation of DNAJB9 in WT mice increased CFTR expression and enhanced CFTR-dependent fluid secretion in enteroids. Importantly, DNAJB9 deficiency upregulated enteroids' fluid secretion in CF mice (homozygous for ΔF508), and silencing one allele of DNAJB9 is sufficient to rescue ΔF508-CFTR in vitro and in vivo, suggesting that DNAJB9 may be a rate-limiting factor in CFTR ERAD pathway. Our studies identified the first ER luminal co-chaperone involved in CFTR ERAD, and DNAJB9 could be a novel therapeutic target for CF.

The Best for the Most Important: Maintaining a Pristine Proteome in Stem and Progenitor Cells

Pluripotent stem cells give rise to reproductively enabled offsprings by generating progressively lineage-restricted multipotent stem cells that would differentiate into lineage-committed stem and progenitor cells. These lineage-committed stem and progenitor cells give rise to all adult tissues and organs. Adult stem and progenitor cells are generated as part of the developmental program and play critical roles in tissue and organ maintenance and/or regeneration. The ability of pluripotent stem cells to self-renew, maintain pluripotency, and differentiate into a multicellular organism is highly dependent on sensing and integrating extracellular and extraorganismal cues. Proteins perform and integrate almost all cellular functions including signal transduction, regulation of gene expression, metabolism, and cell division and death. Therefore, maintenance of an appropriate mix of correctly folded proteins, a pristine proteome, is essential for proper stem cell function. The stem cells' proteome must be pristine because unfolded, misfolded, or otherwise damaged proteins would interfere with unlimited self-renewal, maintenance of pluripotency, differentiation into downstream lineages, and consequently with the development of properly functioning tissue and organs. Understanding how various stem cells generate and maintain a pristine proteome is therefore essential for exploiting their potential in regenerative medicine and possibly for the discovery of novel approaches for maintaining, propagating, and differentiating pluripotent, multipotent, and adult stem cells as well as induced pluripotent stem cells. In this review, we will summarize cellular networks used by various stem cells for generation and maintenance of a pristine proteome. We will also explore the coordination of these networks with one another and their integration with the gene regulatory and signaling networks.

New developments in the diagnosis of fibrillary glomerulonephritis

Fibrillary glomerulonephritis is a glomerular disease historically defined by glomerular deposition of Congo red-negative, randomly oriented straight fibrils that lack a hollow center and stain with antisera to immunoglobulins. It was initially considered to be an idiopathic disease, but recent studies highlighted association in some cases with autoimmune disease, malignant neoplasm, or hepatitis C viral infection. Prognosis is poor with nearly half of patients progressing to end-stage renal disease within 4 years. There is currently no effective therapy, aside from kidney transplantation, which is associated with disease recurrence in a third of cases. The diagnosis has been hampered by the lack of biomarkers for the disease and the necessity of electron microscopy for diagnosis, which is not widely available. Recently, through the use of laser microdissection-assisted liquid chromatography-tandem mass spectrometry, a novel biomarker of fibrillary glomerulonephritis, DnaJ homolog subfamily B member 9, has been identified. Immunohistochemical studies confirmed the high sensitivity and specificity of DnaJ homolog subfamily B member 9 for this disease; dual immunofluorescence showed its colocalization with IgG in glomeruli; and immunoelectron microscopy revealed its localization to individual fibrils of fibrillary glomerulonephritis. The identification of this tissue biomarker has already entered clinical practice and undoubtingly will improve the diagnosis of this rare disease, particularly in developing countries where electron microscopy is less available. Future research is needed to determine whether DnaJ homolog subfamily B member 9 is an autoantigen or just an associated protein in fibrillary glomerulonephritis, whether it can serve as a noninvasive biomarker, and whether therapies that target this protein are effective in improving prognosis.

Amyotrophic lateral sclerosis (ALS) and Alzheimer's disease (AD) are characterised by differential activation of ER stress pathways: focus on UPR target genes

The endoplasmic reticulum (ER) plays an important role in maintenance of proteostasis through the unfolded protein response (UPR), which is strongly activated in most neurodegenerative disorders. UPR signalling pathways mediated by IRE1α and ATF6 play a crucial role in the maintenance of ER homeostasis through the transactivation of an array of transcription factors. When activated, these transcription factors induce the expression of genes involved in protein folding and degradation with pro-survival effects. However, the specific contribution of these transcription factors to different neurodegenerative diseases remains poorly defined. Here, we characterised 44 target genes strongly influenced by XBP1 and ATF6 and quantified the expression of a subset of genes in the human post-mortem spinal cord from amyotrophic lateral sclerosis (ALS) cases and in the frontal and temporal cortex from frontotemporal lobar degeneration (FTLD) and Alzheimer's disease (AD) cases and controls. We found that IRE1α-XBP1 and ATF6 pathways were strongly activated both in ALS and AD. In ALS, XBP1 and ATF6 activation was confirmed by a substantial increase in the expression of both known and novel target genes involved particularly in co-chaperone activity and ER-associated degradation (ERAD) such as DNAJB9, SEL1L and OS9. In AD cases, a distinct pattern emerged, where targets involved in protein folding were more prominent, such as CANX, PDIA3 and PDIA6. These results reveal that both overlapping and disease-specific patterns of IRE1α-XBP1 and ATF6 target genes are activated in AD and ALS, which may be relevant to the development of new therapeutic strategies. Graphical abstract The endoplasmic reticulum (ER) plays an important role in maintenance of proteostasis through the unfolded protein response (UPR). Two major UPR signalling pathways are mediated by IRE1α and ATF6. Here, we demonstrate that these pathways activate differential gene sets in human post-mortem tissues derived from amyotrophic lateral sclerosis (ALS) compared to Alzheimer's disease (AD) cases. Our results identify IRE1α and ATF6 specific targets that can have major implications in the development of new therapeutic strategies and potential biomarkers.

Tauroursodeoxycholic acid alleviates secondary injury in the spinal cord via up-regulation of CIBZ gene

Spinal cord injury (SCI) is generally divided into primary and secondary injuries, and apoptosis is an important event of the secondary injury. As an endogenous bile acid and recognized endoplasmic reticulum (ER) stress inhibitor, tauroursodeoxycholic acid (TUDCA) administration has been reported to have a potentially therapeutic effect on neurodegenerative diseases, but its real mechanism is still unclear. In this study, we evaluated whether TUDCA could alleviate traumatic damage of the spinal cord and improve locomotion function in a mouse model of SCI. Traumatic SCI mice were intraperitoneally injected with TUDCA, and the effects were evaluated based on motor function assessment, histopathology, apoptosis detection, qRT-PCR, and western blot at different time periods. TUDCA administration can improve motor function and reduce secondary injury and lesion area after SCI. Furthermore, the apoptotic ratios were significantly reduced; Grp78, Erdj4, and CHOP were attenuated by the treatment. Unexpectedly, the levels of CIBZ, a novel therapeutic target for SCI, were specifically up-regulated. Taken together, it is suggested that TUDCA effectively suppressed ER stress through targeted up-regulation of CIBZ. This study also provides a new strategy for relieving secondary damage by inhibiting apoptosis in the early treatment of spinal cord injury.

DnaJ Homolog Subfamily B Member 9 Is a Putative Autoantigen in Fibrillary GN

Fibrillary GN is a rare form of GN of uncertain pathogenesis that is characterized by the glomerular accumulation of randomly arranged, nonbranching fibrils (12-24 nm) composed of Ig and complement proteins. In this study, we used mass spectrometry to comprehensively define the glomerular proteome in fibrillary GN compared with that in controls and nonfibrillary GN renal diseases. We isolated glomeruli from formalin-fixed and paraffin-embedded biopsy specimens using laser capture microdissection and analyzed them with liquid chromatography and data-dependent tandem mass spectrometry. These studies identified DnaJ homolog subfamily B member 9 (DNAJB9) as a highly sampled protein detected only in fibrillary GN cases. The glomerular proteome of fibrillary GN cases also contained IgG1 as the dominant Ig and proteins of the classic complement pathway. In fibrillary GN specimens only, immunofluorescence and immunohistochemistry with an anti-DNAJB9 antibody showed strong and specific staining of the glomerular tufts in a distribution that mimicked that of the immune deposits. Our results identify DNAJB9 as a putative autoantigen in fibrillary GN and suggest IgG1 and classic complement effector pathways as likely mediators of the destructive glomerular injury in this disease.

High concentration calcitriol induces endoplasmic reticulum stress related gene profile in breast cancer cells

Calcitriol, the active form of vitamin D, is known for its anticancer properties including induction of apoptosis as well as the inhibition of angiogenesis and metastasis. Understanding the mechanisms of action for calcitriol will help with the development of novel treatment strategies. Since vitamin D exerts its cellular actions via binding to its receptor and by altering expressions of a set of genes, we aimed to evaluate the effect of calcitriol on transcriptomic profile of breast cancer cells. We previously demonstrated that calcitriol alters endoplasmic reticulum (ER) stress markers, therefore in this study we have focused on ER-stress-related genes to reveal calcitriols action on these genes in particular. We have treated breast cancer cell lines MCF-7 and MDA-MB-231 with previously determined IC50 concentrations of calcitriol and evaluated the transcriptomic alterations via microarray. During analysis, only genes altered by at least 2-fold with a P value < 0.05 were taken into consideration. Our findings revealed an ER-stress-associated transcriptomic profile induced by calcitriol. Induced genes include genes with a pro-survival function (NUPR1, DNAJB9, HMOX1, LCN2, and LAMP3) and with a pro-death function (CHOP (DDIT3), DDIT4, NDGR1, NOXA, and CLGN). These results suggest that calcitriol induces an ER-stress-like response inducing both pro-survival and pro-death transcripts in the process.

Patatin-like phospholipase domain-containing protein 3 is involved in hepatic fatty acid and triglyceride metabolism through X-box binding protein 1 and modulation of endoplasmic reticulum stress in mice

AIM

Non-alcoholic steatohepatitis (NASH) is the major cause of chronic liver disease worldwide. Endoplasmic reticulum (ER) stress is considered to be an important pathological characteristic in NASH. A sequence variation (I148M) in the patatin-like phospholipase domain-containing protein 3/adiponutrin (PNPLA3) gene is known to be associated with the development of NASH. However, PNPLA3 deficiency has been considered to not be associated with fatty liver disease. To clarify, therefore, the role of PNPLA3 in liver, we established PNPLA3 knockout (KO) mice and investigated the phenotypes and involved factors under ER stress.

METHODS

ER stress was induced by i.p. injection with tunicamycin or with saline at 0 and 24 h in KO and C57BL/6 (wild-type [WT]) mice. At 48 h after the starting of treatment, blood and liver samples were studied.

RESULTS

Hepatic steatosis and triglyceride content were remarkably increased in WT mice than in KO mice under ER stress. The hepatic palmitate/oleate ratio was significantly higher originally in KO mice than in WT mice. Moreover, the expression of stearoyl-coenzyme A desaturase-1 (SCD1) in KO mice under ER stress was decreased further than that in WT mice. Expression of ER stress markers X-box binding protein 1 (XBP1) and ERdj4 was increased in WT mice but not in KO mice under ER stress.

CONCLUSION

We first demonstrated the hepatic phenotype of PNPLA3 deficiency under ER stress. Our observations would indicate that PNPLA3 has an important role in hepatic fatty acid metabolism and triglyceride accumulation through XBP1 under ER stress.

Limited Unfolded Protein Response and Inflammation in Neuroserpinopathy

Familial encephalopathy with neuroserpin inclusion bodies (FENIB) is a rare disease characterized by the deposition of multiple intracytoplasmic neuronal inclusions that contain mutated neuroserpin. Tg-Syracuse (Tg-Syr) mice express Ser49Pro mutated neuroserpin and develop clinical and neuropathological features of human FENIB. We used 8-, 34-, 45- and 80-week-old Tg-Syr mice to characterize neuroinflammation and the unfolded protein response (UPR) in a neurodegenerative disease in which abnormal protein aggregates accumulate within the endoplasmic reticulum (ER). There were scattered neuroserpin inclusions in Tg-Syr mice at 8 weeks of age; the numbers of neurons involved and the amount of neuroserpin per neuron increased with age throughout the CNS to 80 weeks of age; no similar inclusions were found in wild type (Tg-WT) mice at any age. Increases in numbers of astrocytes and microglia occurred at advanced disease stages. Among 22 markers in 80-week-old Tg-Syr mice, only II1b and II10rb mRNAs in the somatosensory cortex and CxCl10 and Il10rb mRNAs in the olfactory bulb were upregulated when compared with Tg-WT mice indicating a limited relationship between neuroserpin inclusions and inflammatory responses. The changes were accompanied by a transient increase in expression of Xbp1 spliced at 45 weeks and increased ERdJ4 mRNAs at 80 weeks. The sequestration of UPR activators GRP78 and GRP94 in neuroserpin inclusions might explain the limited UPR responses despite the accumulation of neuroserpin in the ER in this FENIB mouse model.

Cloning and analysis of DnaJ family members in the silkworm, Bombyx mori

Heat shock proteins (Hsps) are involved in a variety of critical biological functions, including protein folding, degradation, and translocation and macromolecule assembly, act as molecular chaperones during periods of stress by binding to other proteins. Using expressed sequence tag (EST) and silkworm (Bombyx mori) transcriptome databases, we identified 27 cDNA sequences encoding the conserved J domain, which is found in DnaJ-type Hsps. Of the 27 J domain-containing sequences, 25 were complete cDNA sequences. We divided them into three types according to the number and presence of conserved domains. By analyzing the gene structures, intron numbers, and conserved domains and constructing a phylogenetic tree, we found that the DnaJ family had undergone convergent evolution, obtaining new domains to expand the diversity of its family members. The acquisition of the new DnaJ domains most likely occurred prior to the evolutionary divergence of prokaryotes and eukaryotes. The expression of DnaJ genes in the silkworm was generally higher in the fat body. The tissue distribution of DnaJ1 proteins was detected by western blotting, demonstrating that in the fifth-instar larvae, the DnaJ1 proteins were expressed at their highest levels in hemocytes, followed by the fat body and head. We also found that the DnaJ1 transcripts were likely differentially translated in different tissues. Using immunofluorescence cytochemistry, we revealed that in the blood cells, DnaJ1 was mainly localized in the cytoplasm.

Co-chaperones of the mammalian endoplasmic reticulum

In mammalian cells, the rough endoplasmic reticulum or ER plays a central role in the biogenesis of most extracellular plus many organellar proteins and in cellular calcium homeostasis. Therefore, this organelle comprises molecular chaperones that are involved in import, folding/assembly, export, and degradation of polypeptides in millimolar concentrations. In addition, there are calcium channels/pumps and signal transduction components present in the ER membrane that affect and are affected by these processes. The ER lumenal Hsp70, termed immunoglobulin-heavy chain binding protein or BiP, is the central player in all these activities and involves up to seven different co-chaperones, i.e. ER-membrane integrated as well as ER-lumenal Hsp40s, which are termed ERj or ERdj, and two nucleotide exchange factors.

Transcriptional network analysis reveals that AT1 and AT2 angiotensin II receptors are both involved in the regulation of genes essential for glioma progression

Gliomas are aggressive primary brain tumors with high infiltrative potential. The expression of Angiotensin II (Ang II) receptors has been associated with poor prognosis in human astrocytomas, the most common type of glioma. In this study, we investigated the role of Angiotensin II in glioma malignancy through transcriptional profiling and network analysis of cultured C6 rat glioma cells exposed to Ang II and to inhibitors of its membrane receptor subtypes. C6 cells were treated with Ang II and specific antagonists of AT1 and AT2 receptors. Total RNA was isolated after three and six hours of Ang II treatment and analyzed by oligonucleotide microarray technology. Gene expression data was evaluated through transcriptional network modeling to identify how differentially expressed (DE) genes are connected to each other. Moreover, other genes co-expressing with the DE genes were considered in these analyses in order to support the identification of enriched functions and pathways. A hub-based network analysis showed that the most connected nodes in Ang II-related networks exert functions associated with cell proliferation, migration and invasion, key aspects for glioma progression. The subsequent functional enrichment analysis of these central genes highlighted their participation in signaling pathways that are frequently deregulated in gliomas such as ErbB, MAPK and p53. Noteworthy, either AT1 or AT2 inhibitions were able to down-regulate different sets of hub genes involved in protumoral functions, suggesting that both Ang II receptors could be therapeutic targets for intervention in glioma. Taken together, our results point out multiple actions of Ang II in glioma pathogenesis and reveal the participation of both Ang II receptors in the regulation of genes relevant for glioma progression. This study is the first one to provide systems-level molecular data for better understanding the protumoral effects of Ang II in the proliferative and infiltrative behavior of gliomas.

The BiP cochaperone ERdj4 is required for B cell development and function

ERdj4 is a BiP cochaperone regulated by the unfolded protein response to facilitate degradation of unfolded and/or misfolded proteins in the endoplasmic reticulum. As the unfolded protein response plays a critical role in B cell maturation and antibody production, ERdj4 gene trap mice were generated to determine if this chaperone was required for B cell homeostasis. Homozygosity for the trapped allele resulted in hypomorphic expression of ERdj4 in bone marrow cells and abnormal development of hematopoietic lineages in the bone marrow. The number of myeloid cells was increased, while the number of erythroid and B lymphoid cells was reduced in ERdj4 gene trap mice compared to controls. An intrinsic B cell defect was identified that decreased survival of B cell precursors including large and small pre-B, and immature B cells. Consistent with impaired B lymphopoiesis, the number of mature follicular B cells was reduced in both the bone marrow and spleen of ERdj4 gene trap mice. Paradoxically, unchallenged ERdj4 gene trap mice showed non-specific hypergammaglobulinemia and gene trap B cells exhibited increased proliferation, survival and isotype switching in response to LPS stimulation. Although ERdj4 gene trap mice responded normally to T cell-independent antigen, they failed to mount a specific antibody response to T cell-dependent antigen in vivo. Collectively, these findings demonstrate that the chaperone activity of ERdj4 is required for survival of B cell progenitors and normal antibody production.

Genotoxic stress/p53-induced DNAJB9 inhibits the pro-apoptotic function of p53

DNAJB9 is a recently isolated member of the molecular chaperone gene family, whose precise function is largely unknown. In the present study, we have identified DNAJB9 as an inducible gene of the tumor suppressor p53. DNAJB9 expression was induced by p53 or genotoxic stress in a p53-dependent manner, which was mediated by the Ras/Raf/ERK pathway. In addition, depletion of DNAJB9 by using siRNAs greatly increased genotoxic stress/p53-induced apoptosis, suggesting that DNAJB9 inhibits the pro-apoptotic function of p53. We also found that DNAJB9 physically interacts with p53 through its J domain, through which it inhibits the pro-apoptotic function of p53. Moreover, DNAJB9 colocalized with p53 in both cytoplasm and nucleus under genotoxic conditions. Together, these results demonstrate that DNAJB9 is a downstream target of p53 that belongs to the group of negative feedback regulators of p53.

Endoplasmic reticulum stress is involved in the neuroprotective effect of propofol

Propofol is a common clinically used intravenous anaesthetic agent with antioxidative property. It has been thought to have neuroprotection in vitro and in vivo. However, the underlying mechanisms remain unclear. Endoplasmic reticulum (ER) stress plays an important role in regulating the signaling pathways concerning cell death and survival. Therefore, we wondered whether the neuroprotective effects of propofol are associated with its regulation on ER stress. In this study, we found that propofol up-regulated BiP and attenuated tunicamycin-induced neural cell death. Propofol pretreatment also inhibited tunicamycin-induced up-regulation of C/EBP homologous protein (CHOP). We also found that propofol or tunicamycin alone increased the levels of spliced XBP1 (XBP1s) and cleaved activating transcription factor 6 (ATF6), an active form of ATF6. However, pretreatment with propofol attenuated the levels of phosphorylated protein kinase receptor-like ER kinase, phosphorylated elF2α, ATF4, and caspase-3, but failed to affect the increase of cleaved ATF6 and XBP1s, induced by tunicamycin. Knockdown endogenous BiP with siRNA abolished the suppression of propofol on tunicamycin-mediated activation of CHOP and caspase-3. Meanwhile, knockdown BiP attenuated the protective effects of propofol on the neural cells exposed to tunicamycin. These data suggest that ER stress is involved in the neuroprotection of propofol via differentially regulating the unfolded protein response pathway, in which BiP plays an important role in initiating the adaptive ER stress and inhibiting the apoptotic ER stress.

Mechanistic rationale for targeting the unfolded protein response in pre-B acute lymphoblastic leukemia

The unfolded protein response (UPR) pathway, a stress-induced signaling cascade emanating from the endoplasmic reticulum (ER), regulates the expression and activity of molecules including BiP (HSPA5), IRE1 (ERN1), Blimp-1 (PRDM1), and X-box binding protein 1 (XBP1). These molecules are required for terminal differentiation of B cells into plasma cells and expressed at high levels in plasma cell-derived multiple myeloma. Although these molecules have no known role at early stages of B-cell development, here we show that their expression transiently peaks at the pre-B-cell receptor checkpoint. Inducible, Cre-mediated deletion of Hspa5, Prdm1, and Xbp1 consistently induces cellular stress and cell death in normal pre-B cells and in pre-B-cell acute lymphoblastic leukemia (ALL) driven by BCR-ABL1- and NRAS(G12D) oncogenes. Mechanistically, expression and activity of the UPR downstream effector XBP1 is regulated positively by STAT5 and negatively by the B-cell-specific transcriptional repressors BACH2 and BCL6. In two clinical trials for children and adults with ALL, high XBP1 mRNA levels at the time of diagnosis predicted poor outcome. A small molecule inhibitor of ERN1-mediated XBP1 activation induced selective cell death of patient-derived pre-B ALL cells in vitro and significantly prolonged survival of transplant recipient mice in vivo. Collectively, these studies reveal that pre-B ALL cells are uniquely vulnerable to ER stress and identify the UPR pathway and its downstream effector XBP1 as novel therapeutic targets to overcome drug resistance in pre-B ALL.

Predicting the types of J-proteins using clustered amino acids

J-proteins are molecular chaperones and present in a wide variety of organisms from prokaryote to eukaryote. Based on their domain organizations, J-proteins can be classified into 4 types, that is, Type I, Type II, Type III, and Type IV. Different types of J-proteins play distinct roles in influencing cancer properties and cell death. Thus, reliably annotating the types of J-proteins is essential to better understand their molecular functions. In the present work, a support vector machine based method was developed to identify the types of J-proteins using the tripeptide composition of reduced amino acid alphabet. In the jackknife cross-validation, the maximum overall accuracy of 94% was achieved on a stringent benchmark dataset. We also analyzed the amino acid compositions by using analysis of variance and found the distinct distributions of amino acids in each family of the J-proteins. To enhance the value of the practical applications of the proposed model, an online web server was developed and can be freely accessed.

Emerging features of ER resident J-proteins in plants

J-proteins are co-chaperone components of the HSP70 system. J-proteins stimulate Hsp70ATPase activity, which is responsible for stabilizing the interaction of Hsp70 with client proteins. J-proteins are localized in various intracellular compartments including the cytoplasm, mitochondria and endoplasmic reticulum (ER). Five types of ER resident J-proteins (ERdjs) have been found in plants (P58, ERdj2, ERdj2A, ERdj3B and ERdj7). Rice OsERdj3A is located in the vacuoleand protein storage vacuoles (PSV, PB-II) under conditions of ER stress. J-proteins that are localized to the vacuole or lysosome are not found in mammals and yeast, suggesting that the presence of OsERdj3A in the vacuole is plant-specific and one of the features unique to plant ERdjs. In this review, we summarize the current state of knowledge andrecent research advancements regarding plant ERdjs, and compare mammalian and yeast ERdjs with plant ERdjs.

Deficiency of the BiP cochaperone ERdj4 causes constitutive endoplasmic reticulum stress and metabolic defects

The BiP cochaperone ERdj4 removes misfolded proteins from the ER lumen by associating with ERAD machinery. Global deficiency of ERdj4 results in widespread constitutive ER stress, decreased survival, and metabolic derangements in mice. These findings indicate that the chaperone activity of ERdj4 is important for ER homeostasis in vivo.

Endoplasmic reticulum–localized DnaJ 4 (ERdj4) is an immunoglobulin-binding protein (BiP) cochaperone and component of the endoplasmic reticulum–associated degradation (ERAD) pathway that functions to remove unfolded/misfolded substrates from the ER lumen under conditions of ER stress. To elucidate the function of ERdj4 in vivo, we disrupted the ERdj4 locus using gene trap (GT) mutagenesis, leading to hypomorphic expression of ERdj4 in mice homozygous for the trapped allele (ERdj4^GT/GT). Approximately half of ERdj4^GT/GT mice died perinatally associated with fetal growth restriction, reduced hepatic glycogen stores, and hypoglycemia. Surviving adult mice exhibited evidence of constitutive ER stress in multiple cells/tissues, including fibroblasts, lung, kidney, salivary gland, and pancreas. Elevated ER stress in pancreatic β cells of ERdj4^GT/GT mice was associated with β cell loss, hypoinsulinemia, and glucose intolerance. Collectively these results suggest an important role for ERdj4 in maintaining ER homeostasis during normal fetal growth and postnatal adaptation to metabolic stress.

Spatial patterning of endothelium modulates cell morphology, adhesiveness and transcriptional signature

Microscale and nanoscale structures can spatially pattern endothelial cells (ECs) into parallel-aligned organization, mimicking their cellular alignment in blood vessels exposed to laminar shear stress. However, the effects of spatial patterning on the function and global transcriptome of ECs are incompletely characterized. We used both parallel-aligned micropatterned and nanopatterned biomaterials to evaluate the effects of spatial patterning on the phenotype of ECs, based on gene expression profiling, functional characterization of monocyte adhesion, and quantification of cellular morphology. We demonstrate that both micropatterned and aligned nanofibrillar biomaterials could effectively guide EC organization along the direction of the micropatterned channels or nanofibrils, respectively. The ability of ECs to sense spatial patterning cues were abrogated in the presence of cytoskeletal disruption agents. Moreover, both micropatterned and aligned nanofibrillar substrates promoted an athero-resistant EC phenotype by reducing endothelial adhesiveness for monocytes and platelets, as well as by downregulating the expression of adhesion proteins and chemokines. We further found that micropatterned ECs have a transcriptional signature that is unique from non-patterned ECs, as well as from ECs aligned by shear stress. These findings highlight the importance of spatial patterning cues in guiding EC organization and function, which may have clinical relevance in the development of vascular grafts that promote patency.

ERdj3 regulates BiP occupancy in living cells

Co-chaperones regulate chaperone activities and are likely to impact a protein-folding environment as much as the chaperone itself. As co-chaperones are expressed substoichiometrically, the ability of co-chaperones to encounter a chaperone is crucial for chaperone activity. ERdj3, an abundant soluble endoplasmic reticulum (ER) co-chaperone of the Hsp70 BiP, stimulates the ATPase activity of BiP to increase BiP's affinity for client (or substrate) proteins. We investigated ERdj3 availability, how ERdj3 levels impact BiP availability, and the significance of J proteins for regulating BiP binding of clients in living cells. FRAP analysis revealed that overexpressed ERdj3-sfGFP dramatically decreases BiP-GFP mobility in a client-dependent manner. By contrast, ERdj3-GFP mobility remains low regardless of client protein levels. Native gels and co-immunoprecipitations established that ERdj3 associates with a large complex including Sec61α. Translocon binding probably ensures rapid encounters between emerging nascent peptides and stimulates BiP activity in the crucial early stages of secretory protein folding. Importantly, mutant BiP exhibited significantly increased mobility when it could not interact with any ERdjs. Thus, ERdjs appear to play the dual roles of increasing BiP affinity for clients and regulating delivery of clients to BiP. Our data suggest that BiP engagement of clients is enhanced in ER subdomains enriched in ERdj proteins.

A novel ER J-protein DNAJB12 accelerates ER-associated degradation of membrane proteins including CFTR

Cytosolic Hsc70/Hsp70 are known to contribute to the endoplasmic reticulum (ER)-associated degradation of membrane proteins. However, at least in mammalian cells, its partner ER-localized J-protein for this cellular event has not been identified. Here we propose that this missing protein is DNAJB12. Protease protection assay and immunofluorescence study revealed that DNAJB12 is an ER-localized single membrane-spanning protein carrying a J-domain facing the cytosol. Using co-immunoprecipitation assay, we found that DNAJB12 is able to bind Hsc70 and thus can recruit Hsc70 to the ER membrane. Remarkably, cellular overexpression of DNAJB12 accelerated the degradation of misfolded membrane proteins including cystic fibrosis transmembrane conductance regulator (CFTR), but not a misfolded luminal protein. The DNAJB12-dependent degradation of CFTR was compromised by a proteasome inhibitor, lactacystin, suggesting that this process requires the ubiquitin-proteasome system. Conversely, knockdown of DNAJB12 expression attenuated the degradation of CFTR. Thus, DNAJB12 is a novel mammalian ER-localized J-protein that plays a vital role in the quality control of membrane proteins.

Endoplasmic reticulum stress response in an INS-1 pancreatic beta-cell line with inducible expression of a folding-deficient proinsulin

Background

Cells respond to endoplasmic reticulum stress (ER) stress by activating the unfolded protein response. To study the ER stress response in pancreatic β-cells we developed a model system that allows for pathophysiological ER stress based on the Akita mouse. This mouse strain expresses a mutant insulin 2 gene (C96Y), which prevents normal proinsulin folding causing ER stress and eventual β-cell apoptosis. A double-stable pancreatic β-cell line (pTet-ON INS-1) with inducible expression of insulin 2 (C96Y) fused to EGFP was generated to study the ER stress response.

Results

Expression of Ins 2 (C96Y)-EGFP resulted in activation of the ER stress pathways (PERK, IRE1 and ATF6) and caused dilation of the ER. To identify gene expression changes resulting from mutant insulin expression we performed microarray expression profiling and real time PCR experiments. We observed an induction of various ER chaperone, co-chaperone and ER-associated degradation genes after 24 h and an increase in pro-apoptotic genes (Chop and Trib3) following 48 h of mutant insulin expression. The latter changes occurred at a time when general apoptosis was detected in the cell population, although the relative amount of cell death was low. Inhibiting the proteasome or depleting Herp protein expression increased mutant insulin levels and enhanced cell apoptosis, indicating that ER-associated degradation is maintaining cell survival.

Conclusions

The inducible mutant insulin expressing cell model has allowed for the identification of the ER stress response in β-cells and the repertoire of genes/proteins induced is unique to this cell type. ER-associated degradation is essential in maintaining cell survival in cells expressing mutant insulin. This cell model will be useful for the molecular characterization of ER stress-induced genes.

Effect of methylene blue on the genomic response to reperfusion injury induced by cardiac arrest and cardiopulmonary resuscitation in porcine brain

BACKGROUND

Cerebral ischemia/reperfusion injury is a common secondary effect of cardiac arrest which is largely responsible for postresuscitative mortality. Therefore development of therapies which restore and protect the brain function after cardiac arrest is essential. Methylene blue (MB) has been experimentally proven neuroprotective in a porcine model of global ischemia-reperfusion in experimental cardiac arrest. However, no comprehensive analyses have been conducted at gene expression level.

METHODS

Pigs underwent either untreated cardiac arrest (CA) or CA with subsequent cardiopulmonary resuscitation (CPR) accompanied with an infusion of saline or an infusion of saline with MB. Genome-wide transcriptional profiling using the Affymetrix porcine microarray was performed to 1) gain understanding of delayed neuronal death initiation in porcine brain during ischemia and after 30, 60 and 180 min following reperfusion, and 2) identify the mechanisms behind the neuroprotective effect of MB after ischemic injury (at 30, 60 and 180 min).

RESULTS

Our results show that restoration of spontaneous circulation (ROSC) induces major transcriptional changes related to stress response, inflammation, apoptosis and even cytoprotection. In contrast, the untreated ischemic and anoxic insult affected only few genes mainly involved in intra-/extracellular ionic balance. Furthermore, our data show that the neuroprotective role of MB is diverse and fulfilled by regulation of the expression of soluble guanylate cyclase and biological processes accountable for inhibition of apoptosis, modulation of stress response, neurogenesis and neuroprotection.

CONCLUSIONS

Our results support that MB could be a valuable intervention and should be investigated as a therapeutic agent against neural damage associated with I/R injury induced by cardiac arrest.

Protective unfolded protein response in human pancreatic beta cells transplanted into mice

BACKGROUND

There is great interest about the possible contribution of ER stress to the apoptosis of pancreatic beta cells in the diabetic state and with islet transplantation.

METHODS AND FINDINGS

Expression of genes involved in ER stress were examined in beta cell enriched tissue obtained with laser capture microdissection (LCM) from frozen sections of pancreases obtained from non-diabetic subjects at surgery and from human islets transplanted into ICR-SCID mice for 4 wk. Because mice have higher glucose levels than humans, the transplanted beta cells were exposed to mild hyperglycemia and the abnormal environment of the transplant site. RNA was extracted from the LCM specimens, amplified and then subjected to microarray analysis. The transplanted beta cells showed an unfolded protein response (UPR). There was activation of many genes of the IRE-1 pathway that provide protection against the deleterious effects of ER stress, increased expression of ER chaperones and ERAD (ER-associated protein degradation) proteins. The other two arms of ER stress, PERK and ATF-6, had many down regulated genes. Downregulation of EIF2A could protect by inhibiting protein synthesis. Two genes known to contribute to apoptosis, CHOP and JNK, were downregulated.

CONCLUSIONS

Human beta cells in a transplant site had UPR changes in gene expression that protect against the proapoptotic effects of unfolded proteins.

Coxsackievirus B3 infection activates the unfolded protein response and induces apoptosis through downregulation of p58IPK and activation of CHOP and SREBP1

Cardiomyocyte apoptosis is a hallmark of coxsackievirus B3 (CVB3)-induced myocarditis. We used cardiomyocytes and HeLa cells to explore the cellular response to CVB3 infection, with a focus on pathways leading to apoptosis. CVB3 infection triggered endoplasmic reticulum (ER) stress and differentially regulated the three arms of the unfolded protein response (UPR) initiated by the proximal ER stress sensors ATF6a (activating transcription factor 6a), IRE1-XBP1 (X box binding protein 1), and PERK (PKR-like ER protein kinase). Upon CVB3 infection, glucose-regulated protein 78 expression was upregulated, and in turn ATF6a and XBP1 were activated via protein cleavage and mRNA splicing, respectively. UPR activity was further confirmed by the enhanced expression of UPR target genes ERdj4 and EDEM1. Surprisingly, another UPR-associated gene, p58(IPK), which often is upregulated during infections with other types of viruses, was downregulated at both mRNA and protein levels after CVB3 infection. These findings were observed similarly for uninfected Tet-On HeLa cells induced to overexpress ATF6a or XBP1. In exploring potential connections between the three UPR pathways, we found that the ATF6a-induced downregulation of p58(IPK) was associated with the activation of PKR (PERK) and the phosphorylation of eIF2alpha, suggesting that p58(IPK), a negative regulator of PERK and PKR, mediates cross-talk between the ATF6a/IRE1-XBP1 and PERK arms. Finally, we found that CVB3 infection eventually produced the induction of the proapoptoic transcription factor CHOP and the activation of SREBP1 and caspase-12. Taken together, these data suggest that CVB3 infection activates UPR pathways and induces ER stress-mediated apoptosis through the suppression of P58(IPK) and induction/activation of CHOP, SREBP1, and caspase-12.

Alteration of the unfolded protein response modifies neurodegeneration in a mouse model of Marinesco-Sjögren syndrome

Endoplasmic reticulum (ER) stress has been linked to the onset and progression of many diseases. SIL1 is an adenine nucleotide exchange factor of the essential ER lumen chaperone HSPA5/BiP that senses ER stress and is involved in protein folding. Mutations in the Sil1 gene have been associated with Marinesco-Sjögren syndrome, hallmarks of which include ataxia and cerebellar atrophy. We have previously shown that loss of SIL1 function in mouse results in ER stress, ubiquitylated protein inclusions, and degeneration of specific Purkinje cells in the cerebellum. Here, we report that overexpression of HYOU1/ORP150, an exchange factor that works in parallel to SIL1, prevents ER stress and rescues neurodegeneration in Sil1(-/-) mice, whereas decreasing expression of HYOU1 exacerbates these phenotypes. In addition, loss of DNAJC3/p58(IPK), a co-chaperone that promotes ATP hydrolysis by BiP, ameliorates ER stress and neurodegeneration in Sil1(-/-) mice. These findings suggest that alterations in the nucleotide exchange cycle of BiP cause ER stress and neurodegeneration in Sil1-deficient mice. Our results present the first evidence of important genetic modifiers of Marinesco-Sjögren syndrome, and provide additional pathways for therapeutic intervention for this, and other ER stress-induced, diseases.

Life and death of a BiP substrate

BiP is the mammalian endoplasmic reticulum (ER) Hsp70 orthologue that plays a major role in all functions of this organelle including the seemingly opposing functions of aiding the maturation of unfolded nascent proteins and identifying and targeting chronically unfolded proteins for degradation. The recent identification of mammalian BiP co-factors combined with delineation of the ER degradation machinery and data suggesting that the ER is subdivided into unique regions helps explain how these different functions can occur in the same organelle and raises some unresolved issues.

Regulation of PERK signaling and leukemic cell survival by a novel cytosolic isoform of the UPR regulator GRP78/BiP

The unfolded protein response (UPR) is an evolutionarily conserved mechanism to allow cells to adapt to stress targeting the endoplasmic reticulum (ER). Induction of ER chaperone GRP78/BiP increases protein folding capacity; as such it represents a major survival arm of UPR. Considering the central importance of the UPR in regulating cell survival and death, evidence is emerging that cells evolve feedback regulatory pathways to modulate the key UPR executors, however, the precise mechanisms remain to be elucidated. Here, we report the fortuitous discovery of GRP78va, a novel isoform of GRP78 generated by alternative splicing (retention of intron 1) and alternative translation initiation. Bioinformatic and biochemical analyses revealed that expression of GRP78va is enhanced by ER stress and is notably elevated in human leukemic cells and leukemia patients. In contrast to the canonical GRP78 which is primarily an ER lumenal protein, GRP78va is devoid of the ER signaling peptide and is cytosolic. Through specific knockdown of endogenous GRP78va by siRNA without affecting canonical GRP78, we showed that GRP78va promotes cell survival under ER stress. We further demonstrated that GRP78va has the ability to regulate PERK signaling and that GRP78va is able to interact with and antagonize PERK inhibitor P58(IPK). Our study describes the discovery of GRP78va, a novel cytosolic isoform of GRP78/BiP, and the first characterization of the modulation of UPR signaling via alternative splicing of nuclear pre-mRNA. Our study further reveals a novel survival mechanism in leukemic cells and other cell types where GRP78va is expressed.

Proautophagic drugs: a novel means to combat apoptosis-resistant cancers, with a special emphasis on glioblastomas

The therapeutic goal of cancer treatment has been to trigger tumor-selective cell death. Although cell death can be achieved not only by apoptosis (type I programmed cell death) but also by necrosis, mitotic catastrophe, and autophagy, drugs inducing apoptosis remain the main chemotherapeutic agents in medical oncology. However, cancer cells in their relentless drive to survive, hijack cell processes, resulting in apoptosis resistance, which underlies not only tumorigenesis but also the inherent resistance of certain cancers to radiotherapy and chemotherapy. Unlike apoptosis, which is a caspase-dependent process characterized by nuclear condensation and fragmentation, autophagic cell death is a caspase-independent process characterized by the accumulation of autophagic vacuoles in the cytoplasm accompanied by extensive degradation of the Golgi apparatus, the polyribosomes, and the endoplasmic reticulum, which precedes the destruction of the nucleus. The most striking evidence for proautophagic chemotherapy to overcome apoptosis resistance in cancer cells comes from the use of temozolomide, a proautophagic cytotoxic drug, which has demonstrated real therapeutic benefits in glioblastoma patients and is in clinical trials for several types of apoptosis-resistant cancers. A number of potential common targets in autophagy and apoptosis resistance pathways, that is, mammalian target of rapamycin (mTOR), phosphatidylinositol 3' kinase (PI3K), and Akt have been identified. Thus, further success in certain devastating cancers might be achieved by the combination of proautophagic drugs such as temozolomide with mTOR, PI3K, or Akt inhibitors, or with endoplasmic reticulum stress inhibitors as adjuvant chemotherapies.

Comparison of Intra-organellar Chaperone Capacity for Dealing with Stress-induced Protein Unfolding

Molecular chaperones are essential for cells to prevent that partially unfolded proteins form non-functional, toxic aggregates. This requirement is increased when cells experience protein unfolding stresses and such could affect all compartments in the eukaryotic cell. Whether all organelles are equipped with comparable chaperone capacities is largely unknown, mainly due to the lack of suitable reporters that allow such a comparison. Here we describe the development of fluorescent luciferase reporters that are sorted to various cellular locations (nucleus, cytoplasm, endoplasmic reticulum, and peroxisomes) and that differ minimally in their intrinsic thermal stability properties. When heating living cells, the rate of inactivation was most rapid for the nuclear-targeted luciferase, indicating that the nucleus is the most sensitive organelle toward heat-induced denaturing stress. Post-heat re-activation, however, occurred at equal kinetics irrespective of luciferase localization. Also, induction of thermotolerance by a priming heat treatment, that coordinately up-regulates all heat-inducible chaperones, resulted in a transient heat resistance of the luciferase in all organelles in a comparable manner. Overexpression of the main heat-inducible Hsp70 family member, HspA1A, protected only the cytosolic and nuclear, but not the other luciferases. Together, our data suggest that in each compartment investigated, including the peroxisome in which so far no chaperones could be detected, chaperone machines are present and can be induced with activities similar to those present in the cytosolic/nuclear compartment.