Calreticulin signaling in health and disease

CSF3R and CALR mutations in paediatric myeloid disorders and the association of CSF3R mutations with translocations, including t(8; 21)

Mutations in the colony-stimulating factor 3 receptor (CSF3R) and calreticulin (CALR) genes have been reported in a proportion of adults with myeloproliferative disease. However, little is known about CSF3R or CALR mutations in paediatric myeloid disorders. We analysed CSF3R exons 14 and 17, and CALR exon 9, using direct sequencing in samples of paediatric acute myeloid leukaemia (AML; n = 521), juvenile myelomonocytic leukaemia (JMML; n = 40), myelodysplastic syndrome (MDS; n = 20) and essential thrombocythaemia (ET; n = 21). CSF3R mutations were found in 10 (1.2%) of 521 patients with AML; two in exon 14 (both missense mutations resulting in p.T618I) and eight in exon 17 (three frameshift mutations: p.S715X, p.Q774R, and p.S783Q; and five novel missense mutations: p.Q754K, p.R769H, p.L777F, p.T781I, and S795R). All of the patients with mutations in CSF3R exon 17 had chromosomal translocations, including four with t(8;21). At the time of reporting, seven of these ten patients are alive; three have died, due to side effects of chemotherapy. No CSF3R mutations were found in cases of MDS, JMML or ET. The only mutation found in the CALR gene was a frameshift (p.L367 fs) in one ET patient. We discuss the potential impact of these findings for the leukaemogenesis and clinical features of paediatric myeloid disorders.

Cytokine, antibody and proliferative cellular responses elicited by Taenia solium calreticulin upon experimental infection in hamsters

Taenia solium causes two diseases in humans, cysticercosis and taeniosis. Tapeworm carriers are the main risk factor for neurocysticercosis. Limited information is available about the immune response elicited by the adult parasite, particularly the induction of Th2 responses, frequently associated to helminth infections. Calreticulin is a ubiquitous, multifunctional protein involved in cellular calcium homeostasis, which has been suggested to play a role in the regulation of immune responses. In this work, we assessed the effect of recombinant T. solium calreticulin (rTsCRT) on the cytokine, humoral and cellular responses upon experimental infection in Syrian Golden hamsters (Mesocricetus auratus). Animals were infected with T. solium cysticerci and euthanized at different times after infection. Specific serum antibodies, proliferative responses in mesenteric lymph nodes and spleen cells, as well as cytokines messenger RNA (mRNA) were analyzed. The results showed that one third of the infected animals elicited anti-rTsCRT IgG antibodies. Interestingly, mesenteric lymph node (MLN) cells from either infected or non-infected animals did not proliferate upon in vitro stimulation with rTsCRT. Additionally, stimulation with a tapeworm crude extract resulted in increased expression of IL-4 and IL-5 mRNA. Upon stimulation, rTsCRT increased the expression levels of IL-10 in spleen and MLN cells from uninfected and infected hamsters. The results showed that rTsCRT favors a Th2-biased immune response characterized by the induction of IL-10 in mucosal and systemic lymphoid organs. Here we provide the first data on the cytokine, antibody and cellular responses to rTsCRT upon in vitro stimulation during taeniasis.

Endoplasmic reticulum stress signaling in mammalian oocytes and embryos: life in balance

Mammalian oocytes and embryos are exquisitely sensitive to a wide range of insults related to physical stress, chemical exposure, and exposures to adverse maternal nutrition or health status. Although cells manifest specific responses to various stressors, many of these stressors intersect at the endoplasmic reticulum (ER), where disruptions in protein folding and production of reactive oxygen species initiate downstream signaling events. These signals modulate mRNA translation and gene transcription, leading to recovery, activation of autophagy, or with severe and prolonged stress, apoptosis. ER stress signaling has recently come to the fore as a major contributor to embryo demise. Accordingly, agents that modulate or inhibit ER stress signaling have yielded beneficial effects on embryo survival and long-term developmental potential. We review here the mechanisms of ER stress signaling, their connections to mammalian oocytes and embryos, and the promising indications that interventions in this pathway may provide new opportunities for improving mammalian reproduction and health.

Expression and intracytoplasmic distribution of staufen and calreticulin in maturing human oocytes

PURPOSE

In this study we hypothesized that the mRNA vector Staufen mediates RNA relocalization during meiotic maturation, and by virtue of its interactions with endoplasmic reticulum, provides a possible mechanism by which protein synthesis is regulated.

METHODS

We assessed the expression of staufen (STAU) and calreticulin (CALR), the latter adopted as a marker of the endoplasmic reticulum, in human oocytes at different stages of maturation: GV, metaphase MI and MII. Oocytes were subjected to polymerase chain reaction in order to investigate the expression of STAU and CALR. The corresponding protein products were identified by immunofluorescence and confocal laser scanning microscopy.

RESULTS

STAU and CALR were constantly expressed and selectively localized during oocyte maturation. At the GV stage the both proteins displayed a dispersed distribution localization throughout the cytoplasm. Progressing to the MII stage, STAU tended to compartmentalize towards the cortical area of the oocyte clustering in granules of larger sizes. At the MII stage, CALR assumed a pattern reminiscent and possibly coincident with the position of the meiotic spindle.

CONCLUSIONS

The changing pattern of STAU distribution during meiotic maturation of human oocytes implicates a novel mechanism for the regulation of protein synthesis based on mRNA localization. Moreover, the unique disposition of CALR at the MII spindle uncovers a physical interaction with endoplasmic reticulum that may mediate cytoskeletal remodelling during oocyte maturation.

Honokiol confers immunogenicity by dictating calreticulin exposure, activating ER stress and inhibiting epithelial-to-mesenchymal transition

Peritoneal dissemination is a major clinical obstacle in gastrointestinal cancer therapy, and it accounts for the majority of cancer-related mortality. Calreticulin (CRT) is over-expressed in gastric tumors and has been linked to poor prognosis. In this study, immunohistochemistry studies revealed that the up-regulation of CRT was associated with lymph node and distant metastasis in patients with gastric cancer specimens. CRT was significantly down-regulated in highly metastatic gastric cancer cell lines and metastatic animal by Honokiol-treated. Small RNA interference blocking CRT by siRNA-CRT was translocated to the cells in the early immunogenic response to Honokiol. Honokiol activated endoplasmic reticulum (ER) stress and down-regulated peroxisome proliferator-activated receptor-γ (PPARγ) activity resulting in PPARγ and CRT degradation through calpain-II activity, which could be reversed by siRNA-calpain-II. The Calpain-II/PPARγ/CRT axis and interaction evoked by Honokiol could be blocked by gene silencing or pharmacological agents. Both transforming growth factor (TGF)-β1 and N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) induced cell migration, invasion and reciprocal down-regulation of epithelial marker E-cadherin, which could be abrogated by siRNA-CRT. Moreover, Honokiol significantly suppressed MNNG-induced gastrointestinal tumor growth and over-expression of CRT in mice. Knockdown CRT in gastric cancer cells was found to effectively reduce growth ability and metastasis in vivo. The present study provides insight into the specific biological behavior of CRT in epithelial-to-mesenchymal transition (EMT) and metastasis. Taken together, our results suggest that the therapeutic inhibition of CRT by Honokiol suppresses both gastric tumor growth and peritoneal dissemination by dictating early translocation of CRT in immunogenic cell death, activating ER stress, and blocking EMT.

CALR mutation screening in pediatric primary myelofibrosis

BACKGROUND

Primary myelofibrosis (PMF) is quite rare in children. Mutations of JAK2(V617F) or MPL(W515K/L) were absent in pediatric patients with PMF according to previous studies. Recently, mutations in calreticulin (CALR) were described in adult patients with JAK2/MPL-unmutated PMF. Our study aimed to analyze the clinical and genetic features of Chinese pediatric patients with PMF.

PROCEDURES

We retrospectively investigated 14 pediatric patients diagnosed as PMF according to WHO 2008 criteria. Direct sequencing was performed for the existence of genetic alterations in JAK2, MPL, TET2, CBL, ASXL1, IDH1, IDH2, SRSF2, EZH2, DNMT3A and CALR.

RESULTS

In our cohort, all patients had anemia, three patients (21%) had splenomegaly, six patients (43%) had micromegakaryocytes at time of diagnosis. No patient had spontaneous remission and six patients (43%) transformed to acute myelocytic leukemia. In nine patients with evaluable cytogenetic information, three subjects (33%) had abnormal karyotypes. The median survival from time of diagnosis was 28 months. Seven patients (50%) had type 2 mutations of CALR. No patient had mutations in the other candidate genes. There was no statistical differences in age, gender, hemoglobin, WBC, neutrophil and platelet counts, percentage of circulating blast, overall survival and leukemia transformation between patients with and without CALR mutation.

CONCLUSION

Our study documented that Chinese pediatric patients with PMF in our cohort had its own clinical characteristics and poor outcome. CALR mutations were detected in 50% of our pediatric patients with PMF. Based on our study, CALR mutations screening could be used as molecular marker for diagnosis of pediatric patients with PMF.

Calreticulin gene mutations in myeloproliferative neoplasms without Janus kinase 2 mutations

Calreticulin, an endoplasmic reticulum protein with multiple functions involving chaperone activity and calcium homeostasis, plays an important role in cellular proliferation and differentiation. Calreticulin dysfunction is known to be associated with different cancers. Very recently, calreticulin mutations have been identified in myeloproliferative neoplasms (MPNs), with a particularly high frequency in MPNs without Janus kinase 2 (JAK2) mutations, which exhibit clinical characteristics different from those with mutant JAK2. Here, we focus on the structure, function and carcinogenicity of calreticulin, as well as its relationship with MPNs not involving JAK2 mutations.

Calreticulin mutations in myeloproliferative neoplasms

With the discovery of the JAK2V617F mutation in patients with Philadelphia chromosome-negative (Ph(-)) myeloproliferative neoplasms (MPNs) in 2005, major advances have been made in the diagnosis of MPNs, in understanding of their pathogenesis involving the JAK/STAT pathway, and finally in the development of novel therapies targeting this pathway. Nevertheless, it remains unknown which mutations exist in approximately one-third of patients with non-mutated JAK2 or MPL essential thrombocythemia (ET) and primary myelofibrosis (PMF). At the end of 2013, two studies identified recurrent mutations in the gene encoding calreticulin (CALR) using whole-exome sequencing. These mutations were revealed in the majority of ET and PMF patients with non-mutated JAK2 or MPL but not in polycythemia vera patients. Somatic 52-bp deletions (type 1 mutations) and recurrent 5-bp insertions (type 2 mutations) in exon 9 of the CALR gene (the last exon encoding the C-terminal amino acids of the protein calreticulin) were detected and found always to generate frameshift mutations. All detected mutant calreticulin proteins shared a novel amino acid sequence at the C-terminal. Mutations in CALR are acquired early in the clonal history of the disease, and they cause activation of JAK/STAT signaling. The CALR mutations are the second most frequent mutations in Ph(-) MPN patients after the JAK2V617F mutation, and their detection has significantly improved the diagnostic approach for ET and PMF. The characteristics of the CALR mutations as well as their diagnostic, clinical, and pathogenesis implications are discussed in this review.

Calnexin functions in antibacterial immunity of Marsupenaeus japonicus

Calnexin (Cnx) is an endoplasmic reticulum membrane-bound lectin chaperone that comprises a dedicated maturation system with another lectin chaperone calreticulin (Crt). This maturation system is known as the Cnx/Crt cycle. The main functions of Cnx are Ca(2+) storage, glycoprotein folding, and quality control of synthesis. Recent studies have shown that Cnx is important in phagocytosis and in optimizing dendritic cell immunity. However, the functions of Cnx in invertebrate innate immunity remain unclear. In this research, we characterized Cnx in the kuruma shrimp Marsupenaeus japonicus (designated as MjCnx) and detected its function in shrimp immunity. The expression of MjCnx was upregulated in several tissues challenged with Vibrio anguillarum. Recombinant MjCnx could bind to bacteria by binding polysaccharides. MjCnx protein existed in the cytoplasm and on the membrane of hemocytes and was upregulated by bacterial challenge. The recombinant MjCnx enhanced the clearance of V. anguillarum in vivo, and the clearance effects were impaired after silencing MjCnx with RNA interference assay. Recombinant MjCnx promoted phagocytosis efficiency of hemocytes. These results suggest that MjCnx functions as one of the pattern recognition receptors and has crucial functions in shrimp antibacterial immunity.

Identification of Differentially Expressed Proteins in Liver in Response to Subacute Ruminal Acidosis (SARA) Induced by High-concentrate Diet

The aim of this study was to evaluate protein expression patterns of liver in response to subacute ruminal acidosis (SARA) induced by high-concentrate diet. Sixteen healthy mid-lactating goats were randomly divided into 2 groups and fed either a high-forage (HF) diet or a high-concentrate (HC) diet. The HC diet was expected to induce SARA. After ensuring the occurrence of SARA, liver samples were collected. Proteome analysis with differential in gel electrophoresis technology revealed that, 15 proteins were significantly modulated in liver in a comparison between HF and HC-fed goats. These proteins were found mainly associated with metabolism and energy transfer after identified by matrix-assisted laser desorption ionization/time of flight. The results indicated that glucose, lipid and protein catabolism could be enhanced when SARA occurred. It prompted that glucose, lipid and amine acid in the liver mainly participated in oxidation and energy supply when SARA occurred, which possibly consumed more precursors involved in milk protein and milk fat synthesis. These results suggest new candidate proteins that may contribute to a better understanding of the mechanisms that mediate liver adaptation to SARA.

Iron, oxidative stress, and redox signaling in the cardiovascular system

The redox state of the cell is predominantly dependent on an iron redox couple and is maintained within strict physiological limits. Iron is an essential metal for hemoglobin synthesis in erythrocytes, for oxidation-reduction reactions, and for cellular proliferation. The maintenance of stable iron concentrations requires the coordinated regulation of iron transport into plasma from dietary sources in the duodenum, from recycled senescent red cells in macrophages, and from storage in hepatocytes. The absorption of dietary iron, which is present in heme or nonheme form, is carried out by mature villus enterocytes of the duodenum and proximal jejunum. Multiple physiological processes are involved in maintaining iron homeostasis. These include its storage at the intracellular and extracellular level. Control of iron balance in the whole organism requires communication between sites of uptake, utilization, and storage. Key protein transporters and the molecules that regulate their activities have been identified. In this field, ferritins and hepcidin are the major regulator proteins. A variety of transcription factors may be activated depending on the level of oxidative stress, leading to the expression of different genes. Major preclinical and clinical trials have shown advances in iron-chelation therapy for the treatment of iron-overload disease as well as cardiovascular and chronic inflammatory diseases.

The LIR motif - crucial for selective autophagy

(Macro)autophagy is a fundamental degradation process for macromolecules and organelles of vital importance for cell and tissue homeostasis. Autophagy research has gained a strong momentum in recent years because of its relevance to cancer, neurodegenerative diseases, muscular dystrophy, lipid storage disorders, development, ageing and innate immunity. Autophagy has traditionally been thought of as a bulk degradation process that is mobilized upon nutritional starvation to replenish the cell with building blocks and keep up with the energy demand. This view has recently changed dramatically following an array of papers describing various forms of selective autophagy. A main driving force has been the discovery of specific autophagy receptors that sequester cargo into forming autophagosomes (phagophores). At the heart of this selectivity lies the LC3-interacting region (LIR) motif, which ensures the targeting of autophagy receptors to LC3 (or other ATG8 family proteins) anchored in the phagophore membrane. LIR-containing proteins include cargo receptors, members of the basal autophagy apparatus, proteins associated with vesicles and of their transport, Rab GTPase-activating proteins (GAPs) and specific signaling proteins that are degraded by selective autophagy. Here, we comment on these new insights and focus on the interactions of LIR-containing proteins with members of the ATG8 protein family.

Endoplasmic Reticulum Stress-Associated Chaperones, Bip/GRP78 and Calnexin are Overexpressed in Keratocystic Odontogenic Tumours

Objectives

Odontogenic keratocysts (OKCs) are developmental cysts that have been reclassified according World Health Organization (WHO), to keratocystic odontogenic tumours (KCOTs), a term that better reflects their neoplastic nature. The aim of present study is to evaluate the induction of stress of the endoplasmic reticulum and execution of the resulting unfolded protein response in keratinocystic odontogenic tumours.

Material and Methods

We analyzed by immunohistochemistry the expression of the chaperones BiP/GRP78 and calnexin in 24 cases of KCOTs. As controls, we have used 9 cases of periapical or radicular cysts (PACs) and 5 cases of Fibromas (FBs). The PACs and the FBs were included in the analysis, as PACs are the most common type of inflammatory odontogenic cysts of and FBs, as lesions of the connective tissue with unaffected epithelium.

Results

Analysis revealed a strong association between both BiP/GRP78 and calnexin expression and KCOTs: 18 out of 24 (75%) KCOTs expressed BiP/GRP78 as opposed to 1 out of 9 (13%) PACs, and none of 5 FBs evaluated (P < 0.001, x²-test). Calnexin was expressed in 11 out of 24 KCOTs (46%) but only one out of 9 (13%) PACs, and none of the 5 FBs analyzed (P < 0.001, x²-test).

Conclusions

Study results imply that induction of endoplasmic reticulum stress maybe of diagnostic value in keratocystic odontogenic tumours characterization. In addition to recent findings suggesting that endoplasmic reticulum stress plays a causative role in keratinization of epithelia, pharmacological interference with the execution of the unfolded protein response should be considered for the management of keratocystic odontogenic tumours.

Tax posttranslational modifications and interaction with calreticulin in MT-2 cells and human peripheral blood mononuclear cells of human T cell lymphotropic virus type-I-associated myelopathy/tropical spastic paraparesis patients

The human retrovirus human T cell lymphotropic virus type-I (HTLV-1) is the etiologic agent of HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Axonal degeneration in HAM/TSP patients occurs without neuron infection, with the secreted viral Tax protein proposed to be involved. We previously found that Tax secreted into the culture medium of MT-2 cells (HTLV-1-infected cell line) produced neurite retraction in neuroblastoma cells differentiated to neuronal type. To assess the relevance of Tax posttranslational modifications on this effect, we addressed the question of whether Tax secreted by MT-2 cells and peripheral blood mononuclear cells (PBMCs) of HTLV-1-infected subjects is modified. The interaction of Tax with calreticulin (CRT) that modulates intracellular Tax localization and secretion has been described. We studied Tax localization and modifications in MT-2 cells and its interaction with CRT. Intracellular Tax in MT-2 cells was assessed by flow cytometry, corresponding mainly to a 71-kDa protein followed by western blot. This protein reported as a chimera with gp21 viral protein-confirmed by mass spectrometry-showed no ubiquitination or SUMOylation. The Tax-CRT interaction was determined by confocal microscopy and coimmunoprecipitation. Extracellular Tax from HAM/TSP PBMCs is ubiquitinated according to western blot, and its interaction with CRT was shown by coimmunoprecipitation. A positive correlation between Tax and CRT secretion was observed in HAM/TSP PBMCs and asymptomatic carriers. For both proteins inhibitors and activators of secretion showed secretion through the endoplasmic reticulum-Golgi complex. Tax, present in PBMC culture medium, produced neurite retraction in differentiated neuroblastoma cells. These results suggest that Tax, whether ubiquitinated or not, is active for neurite retraction.

Cyclin-dependent kinase inhibitor 2B regulates efferocytosis and atherosclerosis

Genetic variation at the chromosome 9p21 risk locus promotes cardiovascular disease; however, it is unclear how or which proteins encoded at this locus contribute to disease. We have previously demonstrated that loss of one candidate gene at this locus, cyclin-dependent kinase inhibitor 2B (Cdkn2b), in mice promotes vascular SMC apoptosis and aneurysm progression. Here, we investigated the role of Cdnk2b in atherogenesis and found that in a mouse model of atherosclerosis, deletion of Cdnk2b promoted advanced development of atherosclerotic plaques composed of large necrotic cores. Furthermore, human carriers of the 9p21 risk allele had reduced expression of CDKN2B in atherosclerotic plaques, which was associated with impaired expression of calreticulin, a ligand required for activation of engulfment receptors on phagocytic cells. As a result of decreased calreticulin, CDKN2B-deficient apoptotic bodies were resistant to efferocytosis and not efficiently cleared by neighboring macrophages. These uncleared SMCs elicited a series of proatherogenic juxtacrine responses associated with increased foam cell formation and inflammatory cytokine elaboration. The addition of exogenous calreticulin reversed defects associated with loss of Cdkn2b and normalized engulfment of Cdkn2b-deficient cells. Together, these data suggest that loss of CDKN2B promotes atherosclerosis by increasing the size and complexity of the lipid-laden necrotic core through impaired efferocytosis.

Glycoprotein folding and quality-control mechanisms in protein-folding diseases

Biosynthesis of proteins--from translation to folding to export--encompasses a complex set of events that are exquisitely regulated and scrutinized to ensure the functional quality of the end products. Cells have evolved to capitalize on multiple post-translational modifications in addition to primary structure to indicate the folding status of nascent polypeptides to the chaperones and other proteins that assist in their folding and export. These modifications can also, in the case of irreversibly misfolded candidates, signal the need for dislocation and degradation. The current Review focuses on the glycoprotein quality-control (GQC) system that utilizes protein N-glycosylation and N-glycan trimming to direct nascent glycopolypeptides through the folding, export and dislocation pathways in the endoplasmic reticulum (ER). A diverse set of pathological conditions rooted in defective as well as over-vigilant ER quality-control systems have been identified, underlining its importance in human health and disease. We describe the GQC pathways and highlight disease and animal models that have been instrumental in clarifying our current understanding of these processes.

Cyclin-dependent kinase inhibitor 2B regulates efferocytosis and atherosclerosis

Genetic variation at the chromosome 9p21 risk locus promotes cardiovascular disease; however, it is unclear how or which proteins encoded at this locus contribute to disease. We have previously demonstrated that loss of one candidate gene at this locus, cyclin-dependent kinase inhibitor 2B (Cdkn2b), in mice promotes vascular SMC apoptosis and aneurysm progression. Here, we investigated the role of Cdnk2b in atherogenesis and found that in a mouse model of atherosclerosis, deletion of Cdnk2b promoted advanced development of atherosclerotic plaques composed of large necrotic cores. Furthermore, human carriers of the 9p21 risk allele had reduced expression of CDKN2B in atherosclerotic plaques, which was associated with impaired expression of calreticulin, a ligand required for activation of engulfment receptors on phagocytic cells. As a result of decreased calreticulin, CDKN2B-deficient apoptotic bodies were resistant to efferocytosis and not efficiently cleared by neighboring macrophages. These uncleared SMCs elicited a series of proatherogenic juxtacrine responses associated with increased foam cell formation and inflammatory cytokine elaboration. The addition of exogenous calreticulin reversed defects associated with loss of Cdkn2b and normalized engulfment of Cdkn2b-deficient cells. Together, these data suggest that loss of CDKN2B promotes atherosclerosis by increasing the size and complexity of the lipid-laden necrotic core through impaired efferocytosis.

Molecular cloning and transcriptional activity of a new Petunia calreticulin gene involved in pistil transmitting tract maturation, progamic phase, and double fertilization

Calreticulin (CRT) is a highly conserved and ubiquitously expressed Ca²⁺-binding protein in multicellular eukaryotes. As an endoplasmic reticulum-resident protein, CRT plays a key role in many cellular processes including Ca²⁺ storage and release, protein synthesis, and molecular chaperoning in both animals and plants. CRT has long been suggested to play a role in plant sexual reproduction. To begin to address this possibility, we cloned and characterized the full-length cDNA of a new CRT gene (PhCRT) from Petunia. The deduced amino acid sequence of PhCRT shares homology with other known plant CRTs, and phylogenetic analysis indicates that the PhCRT cDNA clone belongs to the CRT1/CRT2 subclass. Northern blot analysis and fluorescent in situ hybridization were used to assess PhCRT gene expression in different parts of the pistil before pollination, during subsequent stages of the progamic phase, and at fertilization. The highest level of PhCRT mRNA was detected in the stigma-style part of the unpollinated pistil 1 day before anthesis and during the early stage of the progamic phase, when pollen is germinated and tubes outgrow on the stigma. In the ovary, PhCRT mRNA was most abundant after pollination and reached maximum at the late stage of the progamic phase, when pollen tubes grow into the ovules and fertilization occurs. PhCRT mRNA transcripts were seen to accumulate predominantly in transmitting tract cells of maturing and receptive stigma, in germinated pollen/growing tubes, and at the micropylar region of the ovule, where the female gametophyte is located. From these results, we suggest that PhCRT gene expression is up-regulated during secretory activity of the pistil transmitting tract cells, pollen germination and outgrowth of the tubes, and then during gamete fusion and early embryogenesis.

CALR vs JAK2 vs MPL-mutated or triple-negative myelofibrosis: clinical, cytogenetic and molecular comparisons

Calreticulin (CALR) mutations were recently described in JAK2 and MPL unmutated primary myelofibrosis (PMF) and essential thrombocythemia. In the current study, we compared the clinical, cytogenetic and molecular features of patients with PMF with or without CALR, JAK2 or MPL mutations. Among 254 study patients, 147 (58%) harbored JAK2, 63 (25%) CALR and 21 (8.3%) MPL mutations; 22 (8.7%) patients were negative for all three mutations, whereas one patient expressed both JAK2 and CALR mutations. Study patients were also screened for ASXL1 (31%), EZH2 (6%), IDH (4%), SRSF2 (12%), SF3B1 (7%) and U2AF1 (16%) mutations. In univariate analysis, CALR mutations were associated with younger age (P<0.0001), higher platelet count (P<0.0001) and lower DIPSS-plus score (P=0.02). CALR-mutated patients were also less likely to be anemic, require transfusions or display leukocytosis. Spliceosome mutations were infrequent (P=0.0001) in CALR-mutated patients, but no other molecular or cytogenetic associations were evident. In multivariable analysis, CALR mutations had a favorable impact on survival that was independent of both DIPSS-plus risk and ASXL1 mutation status (P=0.001; HR 3.4 for triple-negative and 2.2 for JAK2-mutated). Triple-negative patients also displayed inferior LFS (P=0.003). The current study identifies 'CALR(-)ASXL1(+)' and 'triple-negative' as high-risk molecular signatures in PMF.

Endoplasmic reticulum stress in drug- and environmental toxicant-induced liver toxicity

Liver injury resulting from exposure to drugs and environmental chemicals is a major health problem. Endoplasmic reticulum stress (ER stress) is considered to be an important factor in a wide range of diseases, such as cancer, neurological and cardiovascular disease, diabetes, and inflammatory diseases. The role of ER stress in drug-induced and environmental toxicant-induced liver toxicity has been underestimated in the past; emerging evidence indicates that ER stress makes a substantial contribution to the pathogenesis of drug-induced liver toxicity. In this review, we summarize current knowledge on drugs and environmental toxicants that trigger ER stress in liver and on the underlying molecular mechanisms. We also discuss experimental approaches for ER stress studies.

JAK2 or CALR mutation status defines subtypes of essential thrombocythemia with substantially different clinical course and outcomes

Patients with essential thrombocythemia may carry JAK2 (V617F), an MPL substitution, or a calreticulin gene (CALR) mutation. We studied biologic and clinical features of essential thrombocythemia according to JAK2 or CALR mutation status and in relation to those of polycythemia vera. The mutant allele burden was lower in JAK2-mutated than in CALR-mutated essential thrombocythemia. Patients with JAK2 (V617F) were older, had a higher hemoglobin level and white blood cell count, and lower platelet count and serum erythropoietin than those with CALR mutation. Hematologic parameters of patients with JAK2-mutated essential thrombocythemia or polycythemia vera were related to the mutant allele burden. While no polycythemic transformation was observed in CALR-mutated patients, the cumulative risk was 29% at 15 years in those with JAK2-mutated essential thrombocythemia. There was no significant difference in myelofibrotic transformation between the 2 subtypes of essential thrombocythemia. Patients with JAK2-mutated essential thrombocythemia and those with polycythemia vera had a similar risk of thrombosis, which was twice that of patients with the CALR mutation. These observations are consistent with the notion that JAK2-mutated essential thrombocythemia and polycythemia vera represent different phenotypes of a single myeloproliferative neoplasm, whereas CALR-mutated essential thrombocythemia is a distinct disease entity.

Somatic CALR mutations in myeloproliferative neoplasms with nonmutated JAK2

BACKGROUND

Somatic mutations in the Janus kinase 2 gene (JAK2) occur in many myeloproliferative neoplasms, but the molecular pathogenesis of myeloproliferative neoplasms with nonmutated JAK2 is obscure, and the diagnosis of these neoplasms remains a challenge.

METHODS

We performed exome sequencing of samples obtained from 151 patients with myeloproliferative neoplasms. The mutation status of the gene encoding calreticulin (CALR) was assessed in an additional 1345 hematologic cancers, 1517 other cancers, and 550 controls. We established phylogenetic trees using hematopoietic colonies. We assessed calreticulin subcellular localization using immunofluorescence and flow cytometry.

RESULTS

Exome sequencing identified 1498 mutations in 151 patients, with medians of 6.5, 6.5, and 13.0 mutations per patient in samples of polycythemia vera, essential thrombocythemia, and myelofibrosis, respectively. Somatic CALR mutations were found in 70 to 84% of samples of myeloproliferative neoplasms with nonmutated JAK2, in 8% of myelodysplasia samples, in occasional samples of other myeloid cancers, and in none of the other cancers. A total of 148 CALR mutations were identified with 19 distinct variants. Mutations were located in exon 9 and generated a +1 base-pair frameshift, which would result in a mutant protein with a novel C-terminal. Mutant calreticulin was observed in the endoplasmic reticulum without increased cell-surface or Golgi accumulation. Patients with myeloproliferative neoplasms carrying CALR mutations presented with higher platelet counts and lower hemoglobin levels than patients with mutated JAK2. Mutation of CALR was detected in hematopoietic stem and progenitor cells. Clonal analyses showed CALR mutations in the earliest phylogenetic node, a finding consistent with its role as an initiating mutation in some patients.

CONCLUSIONS

Somatic mutations in the endoplasmic reticulum chaperone CALR were found in a majority of patients with myeloproliferative neoplasms with nonmutated JAK2. (Funded by the Kay Kendall Leukaemia Fund and others.).

Comparative proteomic and bioinformatic analysis of the effects of a high-grain diet on the hepatic metabolism in lactating dairy goats

To gain insight on the impart of high-grain diets on liver metabolism in ruminants, we employed a comparative proteomic approach to investigate the proteome-wide effects of diet in lactating dairy goats by conducting a proteomic analysis of the liver extracts of 10 lactating goats fed either a control diet or a high-grain diet. More than 500 protein spots were detected per condition by two-dimensional electrophoresis (2-DE). In total, 52 differentially expressed spots (≥2.0-fold changed) were excised and analyzed using MALDI TOF/TOF. Fifty-one protein spots were successfully identified. Of these, 29 proteins were upregulated, while 22 were downregulated in the high-grain fed vs. control animals. Differential expressions of proteins including alpha enolase, elongation factor 2, calreticulin, cytochrome b5, apolipoprotein A-I, catalase, was verified by mRNA analysis and/or Western blotting. Database searches combined with Gene Ontology (GO) analysis and KEGG pathway analysis revealed that the high-grain diet resulted in altered expression of proteins related to amino acids metabolism. These results suggest new candidate proteins that may contribute to a better understanding of the signaling pathways and mechanisms that mediate liver adaptation to high-grain diet.

Comparative proteomic analysis of the hepatic response to heat stress in Muscovy and Pekin ducks: insight into thermal tolerance related to energy metabolism

The Pekin duck, bred from the mallard (Anas platyrhynchos) in china, is one of the most famous meat duck species in the world. However, it is more sensitive to heat stress than Muscovy duck, which is believed to have originated in South America. With temperature raising, mortality, laying performance, and meat quality of the Pekin duck are severely affected. This study aims to uncover the temperature-dependent proteins of two duck species using comparative proteomic approach. Duck was cultured under 39°C ± 0.5°C for 1 h, and then immediately returned to 20°C for a 3 h recovery period, the liver proteins were extracted and electrophoresed in two-dimensional mode. After analysis of gel images, 61 differentially expressed proteins were detected, 54 were clearly identified by MALDI TOF/TOF MS. Of the 54 differentially expressed protein spots identified, 7 were found in both species, whereas 47 were species specific (25 in Muscovy duck and 22 in Pekin duck). As is well known, chaperone proteins, such as heat shock protein (HSP) 70 and HSP10, were abundantly up-regulated in both species in response to heat stress. However, we also found that several proteins, such as α-enolase, and S-adenosylmethionine synthetase, showed different expression patterns in the 2 duck species. The enriched biological processes were grouped into 3 main categories according to gene ontology analysis: cell death and apoptosis (20.93%), amino acid metabolism (13.95%) and oxidation reduction (20.93%). The mRNA levels of several differentially expressed protein were investigated by real-time RT-PCR. To our knowledge, this study is the first to provide insights into the differential expression of proteins following heat stress in ducks and enables better understanding of possible heat stress response mechanisms in animals.

Interaction of the tick immune system with transmitted pathogens

Ticks are hematophagous arachnids transmitting a wide variety of pathogens including viruses, bacteria, and protozoans to their vertebrate hosts. The tick vector competence has to be intimately linked to the ability of transmitted pathogens to evade tick defense mechanisms encountered on their route through the tick body comprising midgut, hemolymph, salivary glands or ovaries. Tick innate immunity is, like in other invertebrates, based on an orchestrated action of humoral and cellular immune responses. The direct antimicrobial defense in ticks is accomplished by a variety of small molecules such as defensins, lysozymes or by tick-specific antimicrobial compounds such as microplusin/hebraein or 5.3-kDa family proteins. Phagocytosis of the invading microbes by tick hemocytes is likely mediated by the primordial complement-like system composed of thioester-containing proteins, fibrinogen-related lectins and convertase-like factors. Moreover, an important role in survival of the ingested microbes seems to be played by host proteins and redox balance maintenance in the tick midgut. Here, we summarize recent knowledge about the major components of tick immune system and focus on their interaction with the relevant tick-transmitted pathogens, represented by spirochetes (Borrelia), rickettsiae (Anaplasma), and protozoans (Babesia). Availability of the tick genomic database and feasibility of functional genomics based on RNA interference greatly contribute to the understanding of molecular and cellular interplay at the tick-pathogen interface and may provide new targets for blocking the transmission of tick pathogens.

Calreticulin and other components of endoplasmic reticulum stress in rat and human inflammatory demyelination

BACKGROUND

Calreticulin (CRT) is a chaperone protein, which aids correct folding of glycosylated proteins in the endoplasmic reticulum (ER). Under conditions of ER stress, CRT is upregulated and may be displayed on the surface of cells or be secreted. This 'ecto-CRT' may activate the innate immune response or it may aid clearance of apoptotic cells. Our and other studies have demonstrated upregulation of ER stress markers CHOP, BiP, ATF4, XBP1 and phosphorylated e-IF2 alpha (p-eIF2 alpha) in biopsy and post-mortem human multiple sclerosis (MS) samples. We extend this work by analysing changes in expression of CRT, BiP, CHOP, XBP1 and p-eIF2 alpha in a rat model of inflammatory demyelination. Demyelination was induced in the spinal cord by intradermal injection of recombinant mouse MOG mixed with incomplete Freund's adjuvant (IFA) at the base of the tail. Tissue samples were analysed by semi-quantitative scoring of immunohistochemically stained frozen tissue sections. Data generated following sampling of tissue from animals with spinal cord lesions, was compared to that obtained using tissue derived from IFA- or saline-injected controls. CRT present in rat serum and in a cohort of human serum derived from 14 multiple sclerosis patients and 11 healthy controls was measured by ELISA.

RESULTS

Stained tissue scores revealed significantly (p<0.05) increased amounts of CRT, CHOP and p-eIF2 alpha in the lesion, lesion edge and normal-appearing white matter when compared to controls. CHOP and p-eIF2 alpha were also significantly raised in regions of grey matter and the central canal (p<0.05). Immunofluorescent dual-label staining confirmed expression of these markers in astrocytes, microglia or neurons. Dual staining of rat and human spinal cord lesions with Oil Red O and CRT antibody showed co-localisation of CRT with the rim of myelin fragments. ELISA testing of sera from control and EAE rats demonstrated significant down-regulation (p<0.05) of CRT in the serum of EAE animals, compared to saline and IFA controls. This contrasted with significantly increased amounts of CRT detected in the sera of MS patients (p<0.05), compared to controls.

CONCLUSION

This data highlights the potential importance of CRT and other ER stress proteins in inflammatory demyelination.

Calreticulin negatively regulates the surface expression of Cav1.3 L-type calcium channel

BACKGROUND

The neuroendocrine Cav1.3 L-type Ca channels have been recently found in the Human fetal heart and shown to play a vital role in Ca entry from the sarcolemma into the cell and in Ca homeostasis. Calreticulin, a Ca binding endoplasmic reticulum (ER) resident protein, has been recently shown to translocate to the cell surface where its role and function are just emerging. Here, we demonstrated a novel mechanism of Cav1.3 and calreticulin interaction resulting in downregulation of Cav1.3 channel densities in native Human fetal cardiac cells and Human Embryonic Kidney cell lines (tsA201).

METHODS AND RESULTS

Cell surface and cytoplasmic staining of calreticulin was demonstrated first in cultured human fetal cardiomyocytes (HFC), gestational age 18-24 weeks, using confocal microscopy thereby establishing that calreticulin is present at the cell surface in HFC. Co-immunoprecipitation from HFC using anti-Cav1.3 Ca channel antibody, and probing with anti-calreticulin antibody revealed a 46 kDa band corresponding to calreticulin suggesting that Cav1.3 Ca channel and calreticulin co-assemble in a macromolecular complex. Co-expression of Cav1.3 and calreticulin in tsA201 cells resulted in a decrease in surface expression of Cav1.3 Ca channels. These findings were consistent with the electrophysiological studies showing that co-transfection of Cav1.3 Ca channel and calreticulin resulted in 55% reduction of Cav1.3 Ca current densities recorded from tsA201 cells.

CONCLUSIONS

The results show the first evidence that calreticulin: (1) is localized outside the ER on the cell surface of HFC; (2) coimmunoprecipitates with Cav1.3 L-type Ca channel; (3) negatively regulates Cav1.3 surface expression thus resulting in decreased Cav1.3 Ca current densities. The data demonstrate a novel mechanism of modulation of Cav1.3 Ca channel by calreticulin, which may be involved in pathological settings such as autoimmune associated congenital heart block where Cav1.3 Ca channels are downregulated.

Molecular cloning and characterization of sea bass (Dicentrarchus labrax, L.) calreticulin

Mammalian calreticulin (CRT) is a key molecular chaperone and regulator of Ca(2+) homeostasis in endoplasmic reticulum (ER), also being implicated in a variety of physiological/pathological processes outside the ER. Importantly, it is involved in assembly of MHC class I molecules. In this work, sea bass (Dicentrarchus labrax) CRT (Dila-CRT) gene and cDNA have been isolated and characterized. The mature protein retains two conserved motifs, three structural/functional domains (N, P and C), three type 1 and 2 motifs repeated in tandem, a conserved pair of cysteines and ER-retention motif. It is a single-copy gene composed of 9 exons. Dila-CRT three-dimensional homology models are consistent with the structural features described for mammalian molecules. Together, these results are supportive of a highly conserved structure of CRT through evolution. Moreover, the present data provides information that will allow further studies on sea bass CRT involvement in immunity and in particular class I antigen presentation.

Changes in the proteomic profiles of mouse brain after infection with cyst-forming Toxoplasma gondii

Background

Toxoplasma gondii is an opportunistic pathogenic protozoan parasite, which infects approximately one third of the human population worldwide, causing opportunistic zoonotic toxoplasmosis. The predilection of T. gondii for the central nervous system (CNS) causes behavioral disorders and fatal necrotizing encephalitis and thus constitutes a major threat especially to AIDS patients.

Methods

In the present study, we explored the proteomic profiles of brain tissues of the specific pathogen-free (SPF) Kunming mice at 7 d, 14 d and 21 d after infection with cysts of the Toxoplasma gondii Prugniaud (PRU) strain (Genotype II), by two-dimensional gel electrophoresis (2-DE) combined with MALDI-TOF/TOF tandem mass spectrometry (MS/MS).

Results

A total of 60 differentially expressed protein spots were selected. Fifty-six spots were successfully identified, which corresponded to 45 proteins of the mouse. Functional analysis using a Gene Ontology database showed that these proteins were mainly involved in metabolism, cell structure, signal transduction and immune responses, and will be beneficial for the understanding of molecular mechanisms of T. gondii pathogenesis.

Conclusions

This study identified some mouse brain proteins involved in the response with cyst-forming T. gondii PRU strain. These results provided an insight into the responsive relationship between T. gondii and the host brain tissues, which will shed light on our understanding of the mechanisms of pathogenesis in toxoplasmic encephalitis, and facilitate the discovery of new methods of diagnosis, prevention, control and treatment of toxoplasmic encephalopathy.

Calreticulin-dimerization induced by post-translational arginylation is critical for stress granules scaffolding

Protein arginylation mediated by arginyl-tRNA protein transferase is a post-translational modification that occurs widely in biology, it has been shown to regulate protein and properties and functions. Post-translational arginylation is critical for embryogenesis, cardiovascular development and angiogenesis but the molecular effects of proteins arginylated in vivo are largely unknown. In the present study, we demonstrate that arginylation reduces CRT (calreticulin) thermostability and induces a greater degree of dimerization and oligomerization. R-CRT (arginylated calreticulin) forms disulfide-bridged dimers that are increased in low Ca(2+) conditions at physiological temperatures, a similar condition to the cellular environment that it required for arginylation of CRT. Moreover, R-CRT self-oligomerizes through non-covalent interactions that are enhanced at temperatures above 40 °C, condition that mimics the heat shock treatment where R-CRT is the only isoespecies of CRT that associates in cells to SGs (stress granules). We show that in cells lacking CRT the scaffolding of larger SGs is impaired; the transfection with CRT (hence R-CRT expression) restores SGs assembly whereas the transfection with CRT mutated in Cys146 does not. Thus, R-CRT disulfide-bridged dimers (through Cys146) are essential for the scaffolding of larger SGs under heat shock, although these dimers are not required for R-CRT association to SGs. The alteration in SGs assembly is critical for the normal cellular recover of cells after heat induced stress. We conclude that R-CRT is emerging as a novel protein that has an impact on the regulation of SGs scaffolding and cell survival.

Immunogenic cell death: can it be exploited in PhotoDynamic Therapy for cancer?

Immunogenic Cell Death (ICD) could represent the keystone in cancer management since tumor cell death induction is crucial as well as the control of cancer cells revival after neoplastic treatment. In this context, the immune system plays a fundamental role. The concept of Damage-Associated Molecular Patterns (DAMPs) has been proposed to explain the immunogenic potential of stressed or dying/dead cells. ICD relies on DAMPs released by or exposed on dying cells. Once released, DAMPs are sensed by immune cells, in particular Dendritic Cells (DCs), acting as activators of Antigen-Presenting Cells (APCs), that in turn stimulate both innate and adaptive immunity. On the other hand, by exposing DAMPs, dying cancer cells change their surface composition, recently indicated as vital for the stimulation of the host immune system and the control of residual ill cells. It is well established that PhotoDynamic Therapy (PDT) for cancer treatment ignites the immune system to elicit a specific antitumor immunity, probably linked to its ability in inducing exposure/release of certain DAMPs, as recently suggested. In the present paper, we discuss the DAMPs associated with PDT and their role in the crossroad between cancer cell death and immunogenicity in PDT.

Analysis of the endoplasmic reticulum subproteome in the livers of type 2 diabetic mice

Type 2 diabetes is a chronic metabolic disease that results from insulin resistance in the liver, muscle, and adipose tissue and relative insulin deficiency. The endoplasmic reticulum (ER) plays a crucial role in the regulation of the cellular response to insulin. Recently, ER stress has been known to reduce the insulin sensitivity of the liver and lead to type 2 diabetes. However, detailed mechanisms of ER stress response that leads to type 2 diabetes remains unknown. To obtain a global view of ER function in type 2 diabetic liver and identify proteins that may be responsible for hepatic ER stress and insulin resistance, we performed proteomics analysis of mouse liver ER using nano UPLC-MS^E. A total of 1584 proteins were identified in control C57 and type 2 diabetic db/db mice livers. Comparison of the rER and sER proteomes from normal mice showed that proteins involved in protein synthesis and metabolic process were enriched in the rER, while those associated with transport and cellular homeostasis were localized to the sER. In addition, proteins involved in protein folding and ER stress were found only in the rER. In the livers of db/db mice, however, the functions of the rER and sER were severely disrupted, including the capacity to resolve ER stress. These results provide new insight into the research on hepatic insulin resistance and type 2 diabetes and are suggestive of the potential use of the differentially expressed hepatic ER proteins as biomarkers for hepatic insulin resistance and type 2 diabetes.

Molecular cloning and functional study of calreticulin from a lepidopteran pest, Pieris rapae

Insects have an effective innate immune system to protect themselves from exogenous invaders. Calreticulin is a multifunctional protein mainly involved in directing proper conformation of proteins, controlling calcium level, and participating in immune responses. Previous suppression subtractive hybridization assay showed that the expression of Pieris rapae calreticulin (PrCRT) was suppressed after injection of Pteromalus puparum venom. In this study, we obtained a full length cDNA of PrCRT and expressed recombinant wild type and the N-domain deleted mutant PrCRT in bacteria. Real time quantitative PCR and western blot analyses showed that PrCRT mRNA and protein were expressed in hemocytes, Malpighian tubule, midgut, epidermis and fat body, with a higher level in hemocytes. PrCRT was probably located in endoplasmic reticulum distributing in the cytoplasm of hemocytes. Recombinant PrCRT was first able to attach and then enter the hemocytes by endocytosis. PrCRT mRNA in hemocytes was significantly induced after injection of yeast or beads, but did not change noticeably after injection of Escherichia coli or Micrococcus lysodeikticus. Recombinant PrCRT enhanced cellular encapsulation by P. rapae hemocytes in vitro, and the N-domain of PrCRT was required for encapsulation. RNAi of PrCRT by dsRNA injection impaired the ability of hemocytes to encapsulate beads. After parasitization by P. puparum, PrCRT mRNA and protein levels in P. rapae pupal hemocytes were significantly suppressed compared to non-parasitized control. Our results suggest that PrCRT is involved in cellular encapsulation and the pupal parasitoid P. puparum can decrease PrCRT expression to impair host cellular immune response.