CBP-140, a novel endoplasmic reticulum resident Ca(2+)-binding protein with a carboxy-terminal NDEL sequence showed partial homology with 70-kDa heat shock protein (hsp70)

Analysis of ER stress in developing rice endosperm accumulating beta-amyloid peptide

The common neurodegenerative disorder known as Alzheimer's disease is characterized by cerebral neuritic plaques of amyloid beta (Abeta) peptide. Plaque formation is related to the highly aggregative property of this peptide, because it polymerizes to form insoluble plaques or fibrils causing neurotoxicity. Here, we expressed Abeta peptide as a new causing agent to endoplasmic reticulum (ER) stress to study ER stress occurred in plant. When the dimer of Abeta(1-42) peptide was expressed in maturing seed under the control of the 2.3-kb glutelin GluB-1 promoter containing its signal peptide, a maximum of about 8 mug peptide per grain accumulated and was deposited at the periphery of distorted ER-derived PB-I protein bodies. Synthesis of Abeta peptide in the ER lumen severely inhibited the synthesis and deposition of seed storage proteins, resulting in the generation of many small and abnormally appearing PB bodies. This ultrastructural change was accounted for by ER stress leading to the accumulation of aggregated Abeta peptide in the ER lumen and a coordinated increase in ER-resident molecular chaperones such as BiPs and PDIs in Abeta-expressing plants. Microarray analysis also confirmed that expression of several BiPs, PDIs and OsbZIP60 containing putative transmembrane domains was affected by the ER stress response. Abeta-expressing transgenic rice kernels exhibited an opaque and shrunken phenotype. When grain phenotype and expression levels were compared among transgenic rice grains expressing several different recombinant peptides, such detrimental effects on grain phenotype were correlated with the expressed peptide causing ER stress rather than expression levels.

Vacuolar degeneration of skeletal muscle in transgenic mice overexpressing ORP150

ORP150 is a hypoxic stress-induced protein located in the endoplasmic reticulum. Transgenic mice overexpressing ORP150 (ORP-Tg) exhibit vacuolar degeneration in the heart. To determine whether vacuolization is present in skeletal muscle, we pathologically examined ORP-Tg mice. After 60 days of age, severe vacuolization was found in the soleus muscles of the hind legs of the ORP-Tg mice. Immunohistochemical staining of ORP150 revealed co-localization of ORP150 and vacuolization in the affected cells. Electron microscopy revealed a marked increase in the number of rough-surfaced endoplasmic reticula (rER) and distention of the cisterna. These findings suggest that overexpression of ORP150 causes accumulation of ORP150 in the rER, resulting in vacuolar degeneration in the skeletal muscle of ORP-Tg mice.

Glucose-depleted medium reduces the collagen content of human skin fibroblast cultures

Glucose deprivation appeared to be a factor which induces oxygen regulated protein (ORP) 150 expression in the human skin fibroblasts cultures. Whereas glucose deprivation resulted in a slight (statistically insignificant) decrease of protein content in these cultures, a marked decrease of collagen content was observed, resulting in a distinct reduction of hydroxyproline: protein ratio. Furthermore, the appearance of ORP150 in glucose-deprived cultures coexisted with an increase of gelatinolytic activity and slight reduction in the expression of insulin-like growth factor-I (IGF-I) receptor. Since IGF-I is a main stimulator of collagen synthesis, the reduction in the expression of IGF-I receptor may result in a decrease of collagen synthesis. It is suggested that ORP 150 is a chaperon, which protects intracellular proteins against proteolytic effects exerted by hypoxia or glucose shortage. Since the total amount of protein in fibroblast cultures did not change much, it appears that collagen (in contrast to other proteins) was not efficiently protected. The decrease in collagen synthesis and the enhancement of collagen degradation by gelatinases may result in distinct reduction of collagen content in glucose-deprived fibroblast cultures.

The effect of hypoxia on the expression of 150 kDa oxygen-regulated protein (ORP 150) in HeLa cells

Correct protein folding is an important factor, for the translocation of newly synthesised proteins to specific subcellular compartments, extracellular matrix or to biological fluids. This process is regulated by a group of specific proteins, referred to as chaperones. Many stress conditions, such as oxygen or glucose deprivation, slow down the folding process and cause accumulation of unfolded/misfolded proteins in the cell. Molecular chaperones are induced in these conditions; with some named as oxygen-regulated proteins (ORPs). These bind to unfolded / misfolded proteins to facilitate correct assembly. ORP 150 is the subject of this study. Hypoxia results in an enhancement of ORP 150 expression in several tumour cell lines cultured in vitro. HeLa cells grown in hypoxic conditions (despite an intensive expression of ORP 150) demonstrate higher rates of apoptosis in comparison to those cultured in normoxic conditions. Furthermore, the inhibition of ORP 150 synthesis by transfection of these cells with a specific siRNA resulted in an intensification of apoptosis, as indicated by specific markers of this process; the enhancement of poly ADP-ribose protein cleavage and the increase in Bim protein expression. We conclude from our study that the increase in ORP 150 synthesis protects the cells against the proapoptotic effect of hypoxia.

Glucose effect on the expression of 150kDa oxygen-regulated protein in HeLa cells

Chaperones assist in the correct folding of newly synthesised proteins in the endoplasmic reticulum (ER) of cells, this being essential for the translocation of protein molecules to specific subcellular compartments, extracellular matrix or to biological fluids. The biosynthesis of some ER chaperones is regulated by glucose. They are named "glucose-regulated proteins" (GRPs). The function of some GRPs depends on oxygen, a subgroup named "oxygen-regulated proteins" (ORPs). The biosynthesis of ORPs is induced by deprivation of glucose or oxygen. Exposure of HeLa cells to glucose starvation induces the biosynthesis of various GRPs including ORP 150. The expression of ORP 150 is regulated by the concentration of glucose in the culture medium, being induced by a shortage and repressed by a presence of glucose. We have shown that both glucose starvation and transfection of cells with siRNA (specific to ORP 150 mRNA) evoke similar, but quantitatively different, effects. The cells grown for 72 h in a 4.5 mg/ml glucose-containing medium demonstrated low apoptosis (3.7%) whereas in a 0.5 mg/ml glucose-containing medium the apoptosis was increased to 10%. The effect of transfection on apoptosis was distinctly higher with almost 22% of apoptotic cells detected in 72 h cultures. One may conclude that ORP 150 reduces the pro-apoptotic effects of glucose starvation. Such a hypothesis is supported by the observation that the transfection procedure makes HeLa cells resistant to the regulatory effect of glucose on ORP 150 production. The transfected cells do not respond to glucose starvation with an overexpression of ORP 150. It is apparent from our experiments that ORP 150 plays an important role in adaptation of cells to the shortage of glucose and reduces the pro-apoptotic effect of glucose starvation.

150-kD oxygen-regulated protein is an essential factor for insulin release

OBJECTIVE

This study was designed to show the induction and function of 150-kD oxygen-regulated protein (ORP150) in insulin secretion in vitro.

METHODS

A mouse beta-cell line, MIN6 cells, was cultured in medium containing potassium channel openers or various concentrations of glucose (2-25 mmol/L). ORP150 expression was studied by reporter assay, Western blot, or Northern blot analysis, concomitantly with insulin secretion. In addition, MIN6 cells infected with ORP150 recombinant adenovirus were adopted to show the function of ORP150 in insulin release.

RESULTS

ORP150 expression in MIN6 cells was suppressed dose-dependently by the potassium channel opener diazoxide. Both low glucose (<2 mmol/L) and high glucose concentrations (25 mmol/L glucose) significantly induced more ORP150 expression compared with 10 mmol/L glucose. The treatment with diazoxide or infection of ORP150 antisense adenovirus suppressed ORP150 expression, and glucose-stimulated insulin secretion was effectively prevented.

CONCLUSION

These findings show the involvement of ORP150 in insulin secretion in MIN6 cells.

The 150-kilodalton oxygen-regulated protein ameliorates lipopolysaccharide-induced acute lung injury in mice

The 150-kd oxygen-regulated protein is a novel stress protein that is located in the endoplasmic reticulum and contributes to cell survival when this organelle is under stress. Expression of this protein was strongly increased in alveolar macrophages and alveolar epithelial cells from mice with acute lung injury induced by lipopolysaccharide. Transgenic mice overexpressing the 150-kd protein showed decreased histological severity of this lung injury, accompanied by lower total protein concentrations, and lactate dehydrogenase activity in bronchoalveolar lavage fluid. As indicated by nick end-labeling, lipopolysaccharide induced apoptosis in fewer alveolar wall cells in transgenic than in wild-type mice. Transgenic mice also showed increased survival after lipopolysaccharide injection (a log-rank test). Thus, the 150-kd protein, an endoplasmic reticulum-related molecular chaperone, is pivotal in resisting acute lung injury from lipopolysaccharide.

Enforced expression of oxygen-regulated protein, ORP150, induces vacuolar degeneration in mouse myocardium

Although the 150 kDa oxygen-regulated protein (ORP150) is known as a protein induced by low oxygen tension or ischemical insult, its possible role has not been fully investigated in vivo. To investigate the intracellular function of this protein, we generated the ORP150 over-expressing transgenic mice (ORP-Tg mice) under beta-actin promoter, and established three independent lines of the transgene expressed mice. All lines invariably showed growth retardation. Over-expression of ORP150 was confirmed by western blotting in heart, brain, spleen, skeletal muscle, pancreas, lung, thymus, and kidney. To ascertain the relationship between the over-expression of the ORP150 and the growth retardation in the transgenic mice, we examined pathological changes in the transgenics. In the ORP-Tg mice, vacuolar degeneration appeared in the heart. The degeneration in the myocytes became conspicuous with advancing age. Immunostaining demonstrated ORP150 in the vacuoles of degenerating myocytes. Electron microscopical findings revealed striking development of intracellular membrane system, for example, rough endoplasmic reticula (rER), vacuoles and Golgi bodies, swelling of sarcoplasmic reticulum, and lysis of myofibrils and mitochondria. These findings indicate that ORP150 may locate in the rER and other outer compartment of ER, and that constitutive over-expression of ORP150 in the heart induces vacuolar degeneration in myocytes, resulting in growth retardation of the transgenics.

Expression of 150-kd oxygen-regulated protein in the hippocampus suppresses delayed neuronal cell death

ORP150-150-kd oxygen-regulated protein-is a novel stress protein localized in the endoplasmic reticulum (ER). To investigate the role of ORP150 in delayed neuronal cell death, the authors examined its expression in the gerbil brain after an ischemic insult. The expression of ORP150 antigen, as well as its transcripts, was observed in the CA1 region after the occlusion of the common carotid artery, and the preconditioning enhanced this expression. In cultured neurons, exposure either to hypoxia or to glutamate induced the expression of ORP150, and this effect was also observed by treating the culture with breferdin A or thapsigargin, indicating that both glutamate and hypoxia can cause stress in the ER (ER stress). Neurons became more vulnerable to these stresses following treatment with cycloheximide or after infection with an adenovirus carrying the ORP150-antisense structure. In contrast, the overexpression of ORP150 by an adenovirus suppressed neuronal cell death, and this was accompanied by the suppression of Ca2+ elevation and proteolytic activity induced by glutamate. Further, overexpression of ORP150 in CA1 neurons by an adenovirus carrying the ORP150-sense structure suppressed delayed neuronal cell death after ischemia. These data suggest a possible function of ORP150 as an intracellular apparatus that participates in a protective response in ischemic tolerance.

Expression of the endoplasmic reticulum molecular chaperone (ORP150) rescues hippocampal neurons from glutamate toxicity

A series of events initiated by glutamate-receptor interaction perturbs cellular homeostasis resulting in elevation of intracellular free calcium and cell death. Cells subject to such environmental change express stress proteins, which contribute importantly to maintenance of metabolic homeostasis and viability. We show that an inducible chaperone present in endoplasmic reticulum (ER), the 150-kDa oxygen-regulated protein (ORP150), is expressed both in the human brain after seizure attack and in mouse hippocampus after kainate administration. Using mice heterozygous for ORP150 deficiency, exposure to excitatory stimuli caused hippocampal neurons to display exaggerated elevation of cytosolic calcium accompanied by activation of mu-calpain and cathepsin B, as well as increased vulnerability to glutamate-induced cell death in vitro and decreased survival to kainate in vivo. In contrast, targeted neuronal overexpression of ORP150 suppressed each of these events and enhanced neuronal and animal survival in parallel with diminished seizure intensity. Studies using cultured hippocampal neurons showed that ORP150 regulates cytosolic free calcium and activation of proteolytic pathways causing cell death in neurons subject to excitatory stress. Our data underscore a possible role for ER stress in glutamate toxicity and pinpoint a key ER chaperone, ORP150, which contributes to the stress response critical for neuronal survival.

The hsp110 and Grp1 70 stress proteins: newly recognized relatives of the Hsp70s

Both the Grp170 and Hsp110 families represent relatively conserved and distinct sets of stress proteins, within a more diverse category that also includes the Hsp70s. All of these families are found in a wide variety of organisms from yeasts to humans. Although Hsp110s or Grp170s are not Hsp70s any more than Hsp70s are Hsp110s or Grp170s, it is still reasonable to refer to this combination of related families as the Hsp70 superfamily based on arguments discussed above and since no obvious prokaryotic Hsp110 or Grp170 has yet been identified. These proteins are related to their counterparts in the Hsp70/Grp78 family of eukaryotic stress proteins but are characterized by significantly larger molecular weights. The members of the Grp170 family are characterized by C-terminal ER retention sequences and are ER localized in yeasts and mammals. As a Grp, Grp170 is recognized to be coregulated with other major Grps by a well-known set of stress conditions, sometimes referred to as the unfolded protein response (Kozutsumi et al 1988; Nakaki et al 1989). The Hsp110 family members are localized in the nucleus and cytoplasm and, with other major Hsps, are also coregulated by a specific set of stress conditions, most notably including hyperthermic exposures. Hsp110 is sometimes called Hsp105, although it would be preferable to have a uniform term. The large Hsp70-like proteins are structurally similar to the Hsp70s but differ from them in important ways. In both the Grp170 and Hspl10 families, there is a long loop structure that is interposed between the peptide-binding ,-domain and the alpha-helical lid. In the Hsp110 family and Grp170, there are differing degrees of expansion in the alpha-helical domain and the addition of a C-terminal loop. This gives the appearance of much larger lid domains for Hsp110 and Grp170 compared with Hsp70. Both Hsp110 and Grp170 families have relatively conserved short sequences in the alpha-helical domain in the lid, which are conserved motifs in numerous proteins (we termed these motifs Magic and TedWylee as discussed earlier). The structural differences detailed in this review result in functional differences between the large (Grp170 and Hspl10) members of the Hsp70 superfamily, the most distinctive being an increased ability of these proteins to bind (hold) denatured polypeptides compared with Hsc70, perhaps related to the enlarged C-terminal helical domain. However, there is also a major difference between these large stress proteins; Hsp110 does not bind ATP in vitro, whereas Grp170 binds ATP avidly. The role of the Grp170 and Hsp110 stress proteins in cellular physiology is not well understood. Overexpression of Hsp110 in cultured mammalian cells increases thermal tolerance. Grp170 binds to secreted proteins in the ER and may be cooperatively involved in folding these proteins appropriately. These roles are similar to those of the Hsp70 family members, and, therefore, the question arises as to the differential roles played by the larger members of the superfamily. We have discussed evidence that the large members of the superfamily cooperate with members of the Hsp70 family, and these chaperones probably interact with a large number of chaperones and cochaperones in their functional activities. The fundamental point is that Hsp110 is found in conjunction with Hsp70 in the cytoplasm (and nucleus) and Grp170 is found in conjunction with78 in tha ER in every eucaryotic cell examined from yeast to humans. This would strongly argue that Hsp110 Grp170 exhibit functions in eucaryotes not effectively performed by Hsp70s or Grp78, respectively. Of interest in this respect is the observation that all Hsp110s loss of function or deletion mutants listed in the Drosophila deletion project database are lethal. The important task for the future is to determine the roles these conserved molecular chaperones play in normal and physiologically stressed cells.

Abundant expression of 150-kDa oxygen-regulated protein in mouse pancreatic beta cells is correlated with insulin secretion

The 150-kDa oxygen-regulated protein (ORP150) is a member of glucose-regulated proteins (GRPs), which are induced by stressful conditions such as oxygen or glucose deprivation. Here we investigated the highly abundant expression of ORP150 in mouse pancreas and its relationship with insulin secretion. Immunohistochemical analysis revealed that ORP150 expression was restricted to islets, especially to beta cells. The beta cell-specific expression was also observed in a mouse insulinoma cell line, MIN6, which secretes insulin in response to increased glucose concentration. Furthermore, ORP150 in islets dramatically diminished by fasting, concomitant with reduction of the serum insulin level. These results strongly suggest the role for ORP150 in insulin secretion.

Cloning and expression of cDNA encoding the human 150 kDa oxygen-regulated protein, ORP150

We have cloned a cDNA encoding the human 150 kDa oxygen-regulated protein (ORP150) from hypoxia-treated astrocytoma U373 cDNA library. The deduced amino acid sequence of 999 residues contains a signal peptide and an ER retention-like signal at the N- and C-termini, respectively. It has a striking sequence similarity (91% identity) with Chinese hamster 170 kDa glucose-regulated protein (GRP170). The N-terminal half of ORP150 exhibits significant similarity to the ATPase domain of HSP70 family proteins with well-conserved ATP binding motifs. Northern blot analysis revealed that induction of ORP150 in U373 cells was not limited to hypoxia but also observed by 2-deoxyglucose or tunicamycin treatment. Furthermore, tissue specificity of expression of ORP150 was quite similar to that of GRP78. These findings suggest that ORP150 participates in quality control of proteins in the ER in response to diverse environmental stresses.