Calreticulin and cancer

Endoplasmic reticulum stress as a driver and therapeutic target for kidney disease

The endoplasmic reticulum (ER) has crucial roles in metabolically active cells, including protein translation, protein folding and quality control, lipid biosynthesis, and calcium homeostasis. Adverse metabolic conditions or pathogenic genetic variants that cause misfolding and accumulation of proteins within the ER of kidney cells initiate an injurious process known as ER stress that contributes to kidney disease and its cardiovascular complications. Initiation of ER stress activates the unfolded protein response (UPR), a cellular defence mechanism that functions to restore ER homeostasis. However, severe or chronic ER stress rewires the UPR to activate deleterious pathways that exacerbate inflammation, apoptosis and fibrosis, resulting in kidney injury. This insidious crosstalk between ER stress, UPR activation, oxidative stress and inflammation forms a vicious cycle that drives kidney disease and vascular damage. Furthermore, genetic variants that disrupt protein-folding mechanisms trigger ER stress, as evidenced in autosomal-dominant tubulointerstitial kidney disease and Fabry disease. Emerging therapeutic strategies that enhance protein-folding capacity and reduce the burden of ER stress have shown promising results in kidney diseases. Thus, integrating knowledge of how genetic variants cause protein misfolding and ER stress into clinical practice will enhance treatment strategies and potentially improve outcomes for various kidney diseases and their vascular complications.

Calreticulin-driven autophagy enhances cell proliferation in laryngeal squamous cell carcinoma

BACKGROUND

Calreticulin (CALR) is a multifunctional calcium-binding protein. Recent studies have revealed that CALR contributes to tumor development and promotes cancer cell proliferation. However, how CALR affects the development of laryngeal squamous cell carcinoma (LSCC) remains mysterious. Thus, this study aimed to explore the effect of CALR on LSCC development and uncover its underlying mechanisms.

METHODS

CALR expression in LSCC cell lines and tissues was examined by qRT-PCR and western blot analysis and its functional role was detected via in vivo and in vitro assays. Cell proliferation was discriminated with CCK-8 and colony formation assays, while apoptosis was analyzed using flow cytometry. Autophagy levels were measured via LC3 immunofluorescence, and western blot assay was conducted to assess apoptosis- and autophagy-related proteins. Additionally, a mouse xenograft model was employed to determine the impact of CALR knockdown on tumor growth.

RESULTS

We found that CALR knockdown reduced LSCC cell viability and proliferation while enhancing apoptosis, whereas CALR overexpression showed opposite effects. In vivo experiments verified that CALR knockdown suppressed tumor growth. In addition, elevated CALR expression induced autophagy in LSCC cells, while autophagy inhibitor 3-MA (2.5 mM) reversed the anti-apoptosis effects of CALR overexpression.

CONCLUSION

Our study identifies CALR as an oncogene in LSCC, where it promotes tumor progression by inducing autophagy and inhibiting apoptosis. Targeting CALR or modulating autophagy may represent novel therapeutic strategies for LSCC.

Effects of artemisinin and cisplatin on the malignant progression of oral leukoplakia. In vitro and in vivo study

OBJECTIVES

Chemoprevention can be a treatment for potentially malignant lesions (PMLs). We aimed to evaluate whether artemisinin (ART) and cisplatin (CSP) are associated with apoptosis and immunogenic cell death (ICD) in vitro, using oral leukoplakia (OL) and oral squamous cell carcinoma (OSCC) cell lines, and whether these compounds prevent OL progression in vivo.

METHODS

Normal keratinocytes (HaCat), Dysplastic oral cells (DOK), and oral squamous cell carcinoma (SCC-180) cell lines were treated with ART, CSP, and ART + CSP to analyze cytotoxicity, genotoxicity, cell migration, and increased expression of proteins related to apoptosis and ICD. Additionally, 41 mice were induced with OL using 4NQO, treated with ART and CSP, and their tongues were histologically analyzed.

RESULTS

In vitro, CSP and CSP + ART showed dose-dependent cytotoxicity and reduced SCC-180 migration. No treatment was genotoxic, and none induced expression of proteins related to apoptosis and ICD; CSP considerably reduced High-mobility group box-1 (HMGB-1) protein expression in SCC-180. In vivo, there was a delay in OL progression with ART and CSP treatment; however, by the 16th week, only CSP prevented progression to OSCC.

CONCLUSION

Expression of proteins related to ICD and apoptosis did not increase with treatments, and CSP was shown to reduce immunogenic pathways in SCC-180, while reducing cell migration. ART did not prevent the malignant progression of OL in vivo; CSP did despite significant adverse effects.

Anticancer Effects of the Novel Pyrazolyl-Urea GeGe-3

In a screen of over 200 novel pyrazole compounds, ethyl 1-(2-hydroxypentyl)-5-(3-(3-(trifluoromethyl) phenyl)ureido)-1H-pyrazole-4-carboxylate (named GeGe-3) has emerged as a potential anticancer compound. GeGe-3 displays potent anti-angiogenic properties through the presumptive targeting of the protein kinase DMPK1 and the Ca2+-binding protein calreticulin. We further explored the anticancer potential of GeGe-3 on a range of established cancer cell lines, including PC3 (prostate adenocarcinoma), SKMEL-28 (cutaneous melanoma), SKOV-3 (ovarian adenocarcinoma), Hep-G2 (hepatocellular carcinoma), MDA-MB231, SKBR3, MCF7 (breast adenocarcinoma), A549 (lung carcinoma), and HeLa (cervix epithelioid carcinoma). At concentrations in the range of 10 μM, GeGe-3 significantly restricted cell proliferation and metabolism. GeGe-3 also reduced PC3 cell migration in a standard wound closure and trans-well assay. Together, these results confirm the anticancer potential of GeGe-3 and underline the need for more detailed pre-clinical investigations into its molecular targets and mechanisms of action.

DNA polymerase beta connects tumorigenicity with the circadian clock in liver cancer through the epigenetic demethylation of Per1

The circadian-controlled DNA repair exhibits a strong diurnal rhythm. Disruption in circadian clock and DNA repair is closely linked with hepatocellular carcinoma (HCC) progression, but the mechanism remains unknown. Here, we show that polymerase beta (POLB), a critical enzyme in the DNA base excision repair pathway, is rhythmically expressed at the translational level in mouse livers. Hepatic POLB dysfunction dampens clock homeostasis, whereas retards HCC progression, by mediating the methylation of the 4th CpG island on the 5'UTR of clock gene Per1. Clinically, POLB is overexpressed in human HCC samples and positively associated with poor prognosis. Furthermore, the hepatic rhythmicity of POLB protein expression is orchestrated by Calreticulin (CALR). Our findings provide important insights into the molecular mechanism underlying the synergy between clock and food signals on the POLB-driven BER system and reveal new clock-dependent carcinogenetic effects of POLB. Therefore, chronobiological modulation of POLB may help to promote precise interventions for HCC.

Identification and characterization of calreticulin as a novel plasminogen receptor

Calreticulin (CRT) was originally identified as a key calcium-binding protein of the endoplasmic reticulum. Subsequently, CRT was shown to possess multiple intracellular functions, including roles in calcium homeostasis and protein folding. Recently, several extracellular functions have been identified for CRT, including roles in cancer cell invasion and phagocytosis of apoptotic and cancer cells by macrophages. In the current report, we uncover a novel function for extracellular CRT and report that CRT functions as a plasminogen-binding receptor that regulates the conversion of plasminogen to plasmin. We show that human recombinant or bovine tissue-derived CRT dramatically stimulated the conversion of plasminogen to plasmin by tissue plasminogen activator or urokinase-type plasminogen activator. Surface plasmon resonance analysis revealed that CRT-bound plasminogen (KD = 1.8 μM) with moderate affinity. Plasminogen binding and activation by CRT were inhibited by ε-aminocaproic acid, suggesting that an internal lysine residue of CRT interacts with plasminogen. We subsequently show that clinically relevant CRT variants (lacking four or eight lysines in carboxyl-terminal region) exhibited decreased plasminogen activation. Furthermore, CRT-deficient fibroblasts generated 90% less plasmin and CRT-depleted MDA MB 231 cells also demonstrated a significant reduction in plasmin generation. Moreover, treatment of fibroblasts with mitoxantrone dramatically stimulated plasmin generation by WT but not CRT-deficient fibroblasts. Our results suggest that CRT is an important cellular plasminogen regulatory protein. Given that CRT can empower cells with plasmin proteolytic activity, this discovery may provide new mechanistic insight into the established role of CRT in cancer.

Development and validation of a model based on immunogenic cell death related genes to predict the prognosis and immune response to bladder urothelial carcinoma

Background

Immunogenic cell death (ICD) has been categorized as a variant of regulated cell death that is capable of inducing an adaptive immune response. A growing body of evidence has indicated that ICD can modify the tumor immune microenvironment by releasing danger signals or damage-associated molecular patterns (DAMPs), potentially enhancing the efficacy of immunotherapy. Consequently, the identification of biomarkers associated with ICD that can classify patients based on their potential response to ICD immunotherapy would be highly advantageous. Therefore the goal of the study is to better understand and identify what patients with bladder urothelial carcinoma (BLCA) will respond to immunotherapy by analyzing ICD signatures and investigate ICD-related prognostic factors in the context of BLCA.

Methods

The data obtained from The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) databases regarding BLCA and normal samples was categorized based on ICD-related genes (IRGs). Specifically, we conducted an immunohistochemical (IHC) experiment to validate the expression levels of Calreticulin (CALR) in both tumor and adjacent tissues, and evaluated its prognostic significance using the Kaplan-Meier (KM) curve. Subsequently, the samples from TCGA were divided into two subtypes using consensus clustering. To obtain a more comprehensive comprehension of the biological functions, we utilized Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), and Gene Set Enrichment Analysis (GSEA). The calculation of immune landscape between two subtypes was performed through ESTIMATE and CIBERSORT. Risk models were constructed using Cox and Lasso regression and their prognosis predictive ability was evaluated using nomogram, receiver operating characteristic (ROC), and calibration curves. Finally, Tumor Immune Dysfunction and Exclusion (TIDE) algorithms was utilized to predict the response to immunotherapy.

Results

A total of 34 IRGs were identified, with most of them exhibiting upregulation in BLCA samples. The expression of CALR was notably higher in BLCA compared to the adjacent tissue, and this increase was associated with an unfavorable prognosis. The differentially expressed genes (DEGs) associated with ICD were linked to various immune-related pathways. The ICD-high subtypes exhibited an immune-activated tumor microenvironment (TME) compared to the ICD-low subtypes. Utilizing three IRGs including CALR, IFNB1, and IFNG, a risk model was developed to categorize BLCA patients into high- and low-risk groups. The overall survival (OS) was considerably greater in the low-risk group compared to the high-risk group, as evidenced by both the TCGA and GEO cohorts. The risk score was identified as an independent prognostic parameter (all p < 0.001). Our model demonstrated good predictive ability (The area under the ROC curve (AUC), AUC1-year= 0.632, AUC3-year= 0.637, and AUC5-year =0.653). Ultimately, the lower risk score was associated with a more responsive immunotherapy group.

Conclusion

The potential of the ICD-based risk signature to function as a marker for evaluating the prognosis and immune landscape in BLCA suggests its usefulness in identifying the suitable population for effective immunotherapy against BLCA.

3D culture boosting fullerenol nanoparticles to induce calreticulin exposure on MCF-7 cells for enhanced macrophage-mediated cell removal

Calreticulin (CRT) on the cell surface that acts as an "eat me" signal is vital for macrophage-mediated programmed cell removal. The polyhydroxylated fullerenol nanoparticle (FNP) has appeared as an effective inducer to cause CRT exposure on cancer cell surface, but it failed in treating some cancer cells such as MCF-7 cells based on previous findings. Here, we carried out the 3D culture of MCF-7 cells, and interestingly found that the FNP induced CRT exposure on cells in 3D spheres via re-distributing CRT from endoplasmic reticulum (ER) to cell surface. Phagocytosis experiments in vitro and in vivo illustrated the combination of FNP and anti-CD47 monoclonal antibody (mAb) further enhanced macrophage-mediated phagocytosis to cancer cells. The maximal phagocytic index in vivo was about three times higher than that of the control group. Moreover, in vivo tumorigenesis experiments in mice proved that FNP could regulate the progress of MCF-7 cancer stem-like cells (CSCs). These findings expand the application of FNP in tumor therapy of anti-CD47 mAb and 3D culture can be used as a screening tool for nanomedicine.

Immunogenic analysis of epitope-based vaccine candidate induced by photodynamic therapy in MDA-MB-231 triple-negative breast cancer cells

BACKGROUND

Photodynamic therapy (PDT) is used to treat tumors through selective cytotoxic effects. PDT induces damage-associated molecular patterns (DAMPs) expression, which can cause an immunogenic death cell (IDC). In this study we identified potential immunogenic epitopes generated by PDT on triple-negative breast cancer cell line (MDA-MB-231).

METHODS

MDA-MB-231 cells were exposed to PDT using ALA (160 µg/mL)/630 nm at 8 J/cm². Membrane proteins were extracted and separated by 2D PAGE. Proteins overexpressed were identified by LC-MS/MS and analyzed in silico through a peptide-HLA docking in order to identify the epitopes with more immunogenicity and antigenicity properties, as well as lower allergenicity and toxicity activity. The selected peptides were evaluated in response to macrophage activation and cytokine release by flow cytometry.

RESULTS

Differential proteins were overexpressed in the cells treated with PDT. A group of 16 peptides were identified from them, established in a rigorous selection by measuring antigenicity, immunogenicity, allergenicity, and toxicity in silico. The final selection was based on molecular dynamics, where 2 peptides showed the highest stability regarding to the RMSD value. These peptides were obtained from the proteins calreticulin and HSP90. The cytokine analysis evidenced macrophage activation by the releasing of TNF.

CONCLUSION

Two peptides were identified from calreticulin and HSP90; proteins induced by PDT in MDA-MB-231 cells. Both epitopes showed immunogenic potential as a peptide-based vaccine for triple-negative breast cancer.

Research progress in inducing immunogenic cell death of tumor cells

Immunogenic cell death (ICD) is a regulated cell death (RCD) pathway. In response to physical and chemical signals, tumor cells activate specific signaling pathways that stimulate stress responses in the endoplasmic reticulum (ER) and expose damage-associated molecular patterns (DAMPs), which promote antitumor immune responses. As a result, the tumor microenvironment is altered, and many tumor cells are killed. The ICD response in tumor cells requires inducers. These inducers can be from different sources and contribute to the development of the ICD either indirectly or directly. The combination of ICD inducers with other tumor treatments further enhances the immune response in tumor cells, and more tumor cells are killed; however, it also produces side effects of varying severity. New induction methods based on nanotechnology improve the antitumor ability and significantly reduces side effects because they can target tumor cells precisely. In this review, we introduce the characteristics and mechanisms of ICD responses in tumor cells and the DAMPs associated with ICD responses, summarize the current methods of inducing ICD response in tumor cells in five distinct categories: chemical sources, physical sources, pathogenic sources, combination therapies, and innovative therapies. At the same time, we introduce the limitations of current ICD inducers and make a summary of the use of ICD responses in clinical trials. Finally, we provide an outlook on the future of ICD inducer development and provide some constructive suggestions.

Ecto-calreticulin expression in multiple myeloma correlates with a failed anti-tumoral immune response and bad prognosis

Immunogenic cell death (ICD) has been proposed to be a crucial process for antitumor immunosurveillance. ICD is characterized by the exposure and emission of Damage Associated Molecular Patterns (DAMP), including calreticulin (CRT). A positive correlation between CRT exposure or total expression and improved anticancer immunosurveillance has been found in certain cancers, usually accompanied by favorable patient prognosis. In the present study, we sought to evaluate CRT levels in the plasma membrane of CD38⁺ bone marrow mononuclear cells (BMMCs) isolated from 71 patients with varying degrees of multiple myeloma (MM) disease and examine the possible relationship between basal CRT exposure and the bone marrow immune microenvironment, as well as its connection with different clinical markers. Data show that increased levels of cell surface-CRT were associated with more aggressive clinical features and with worse clinical prognosis in MM. High CRT expression in MM cells was associated with increased infiltration of NK cells, CD8⁺ T lymphocytes and dendritic cells (DC), indicative of an active anti-tumoral immune response, but also with a significantly higher presence of immunosuppressive Treg cells and increased expression of PD-L1 in myeloma cells.

Calreticulin nuclear translocalization alleviates CaM/CaMKII/CREB signaling pathway to enhance chemosensitivity in HDAC inhibitor-resistant hepatocellular carcinoma cells

Calreticulin (CRT) is located in the endoplasmic reticulum (ER), it helps proteins fold correctly inside the ER, and acts as a modulator of Ca²⁺ homeostasis. Aberrant expression of CRT is implicated in several cancer types, qualifying CRT as a potential therapeutic target. However, it remains unclear how CRT affects specific oncogenic pathways. In this study, we used histone deacetylase inhibitors (HDACis) to establish drug-resistant liver cancer cells and further analyzed the molecular mechanism of development of drug resistance in those cells. The 2D gel electrophoresis and RT-PCR data showed that CRT was downregulated in HDACis-resistant cells by comparing with HA22T parental cells. We previously elucidated the development of drug-resistance in HCC cells via activation of PP1-eIF2α pathway, but not via ER stress pathway. Here, we show that thapsigargin induced ER stress through mechanism other than ER stress downstream protein GRP78-PERK to regulate CRT expression in HDACis-R cells. Moreover, the expression level of CRT was not the main cause of apoptosis in HDACis-resistant cells. Mechanistic studies identified the apoptosis factors in the nucleus-the HDACis-mediated overexpression of CRT, CRT translocation to the cell nucleus, and reduced CaM/CaMKII/CREB pathway-that led to chemosensitivity in HDACis-R HCC cells.

Calreticulin enhances gastric cancer metastasis by dimethylating H3K9 in the E-cadherin promoter region mediating by G9a

The latest study shows that gastric cancer (GC) ranked the fifth most common cancer (5.6%) with over 1 million estimated new cases annually and the fourth most common cause of cancer death (7.7%) globally in 2020. Metastasis is the leading cause of GC treatment failure. Therefore, clarifying the regulatory mechanisms for GC metastatic process is necessary. In the current study, we discovered that calreticulin (CALR) was highly expressed in GC tissues and related to lymph node metastasis and patient’s terrible prognosis. The introduction of CALR dramatically promoted GC cell migration in vitro and in vivo, while the repression of CALR got the opposite effects. Cell migration is a functional consequence of the epithelial-mesenchymal transition (EMT) and is related to adhesion of cells. Additionally, we observed that CALR inhibition or overexpression regulated the expression of EMT markers (E-cadherin, ZO-1, Snail, N-cadherin, and ZEB1) and cellular adhesive moleculars (Fibronectin, integrin β1and MMP2). Mechanistically, our data indicated that CALR could mediate DNA methylation of E-cadherin promoter by interacting with G9a, a major euchromatin methyltransferase responsible for methylation of histone H3 on lysine 9(H3K9me2) and recruiting G9a to the E-cadherin promoter. Knockdown of G9a in CALR overexpressing models restored E-cadherin expression and blocked the stimulatory effects of CALR on GC cell migration. Taken together, these findings not only reveal critical roles of CALR medicated GC metastasis but also provide novel treatment strategies for GC.

Lactoferrin: A Nutraceutical with Activity against Colorectal Cancer

Homeostasis in the human body results from the tight regulation of several events, since too little inflammation disrupts the process of tissue repair and remodeling, whereas too much exerts a collateral effect by causing tissue damage with life-threatening consequences. In some clinical conditions, such as inflammatory bowel disease (IBD), inflammation functions as a double-edged sword by either enabling or inhibiting cancer development and progression. Generally, cancer develops through evasion mechanisms that regulate cell growth, causing a high rate of uncontrolled proliferation, and mechanisms for evading cell death, such as apoptosis. Moreover, chronic inflammation is a factor that contributes to colorectal cancer (CRC), as observed in individuals with IBD; all these conditions favor an increased rate of angiogenesis and eventual metastasis. Lactoferrin (Lf) is a mammalian iron-binding multifunctional glycoprotein regarded as a natural compound that up- and downregulates both humoral and cellular components of immunity involved in regulating the inflammatory response and maintaining gut homeostasis. Human and bovine Lf share high sequence homology and have very similar antimicrobial, anti-inflammatory, and immunomodulatory activities. Bovine Lf from milk is considered a safe molecule and is commercially available in large quantities. This review mainly focuses on the regulatory effects of orally administered bovine Lf on the inflammatory response associated with CRC; this approach indicates that CRC is one of the most frequently diagnosed cancers and affects the intestinal tract with high clinical and epidemiologic relevance. Thus, this review may provide foundations for the potential use of bovine Lf alone or as a natural adjunct agent to increase the effectiveness and reduce the side effects of anticancer chemotherapy.

Novel insights on the molecular mechanism of action of the anti-angiogenic pyrazolyl-urea GeGe-3 by functional proteomics

In recent years, 5-pyrazolyl-ureas have mostly been known for their attractive poly-pharmacological outline and, in particular, ethyl 1-(2-hydroxypentyl)-5-(3-(3-(trifluoromethyl) phenyl) ureido)-1H-pyrazole-4-carboxylate (named GeGe-3) has emerged as a capable anti-angiogenic compound. This paper examines its interactome by functional proteomics using a label-free mass spectrometry based platform, coupling Drug Affinity Responsive Target Stability and targeted Limited Proteolysis-Multiple Reaction Monitoring. Calreticulin has been recognized as the GeGe-3 principal target and this evidence has been supported by immunoblotting and in silico molecular docking. Furthermore, cell studies have shown that GeGe-3 lowers cell calcium mobilization, cytoskeleton organization and focal adhesion kinase expression, thus linking its biological potential to calreticulin binding and, ultimately, shedding light on the reasonable action mechanism of this molecule as an anti-angiogenic factor.

Feiyanning Formula Induces Apoptosis of Lung Adenocarcinoma Cells by Activating the Mitochondrial Pathway

Feiyanning formula (FYN) is a traditional Chinese medicine (TCM) prescription used for more than 20 years in the treatment of lung cancer. FYN is composed of Astragalus membranaceus, Polygonatum sibiricum, Atractylodes macrocephala, Cornus officinalis, Paris polyphylla, and Polistes olivaceous, etc. All of them have been proved to have anti-tumor effect. In this study, we used the TCM network pharmacological analysis to perform the collection of compound and disease target, the prediction of compound target and biological signal and the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis. It was found that the activation of mitochondrial pathway might be the molecular mechanism of the anti-lung cancer effect of FYN. The experimental results showed that FYN had an inhibitory effect on the growth of lung cancer cells in a dose-dependent and time-dependent manner. Moreover, FYN induced G₂/M cell cycle arrest and apoptotic cell death as early as 6 h after treatment. In addition, FYN significantly induced mitochondrial membrane depolarization and increased calreticulin expression. Metabolomics analysis showed the increase of ATP utilization (assessed by a significant increase of the AMP/ATP and ADP/ATP ratio, necessary for apoptosis induction) and decrease of polyamines (that reflects growth potential). Taken together, our study suggested that FYN induced apoptosis of lung adenocarcinoma cells by promoting metabolism and changing the mitochondrial membrane potential, further supporting the validity of network pharmacological prediction.

Calreticulin – a multifaced protein

Calreticulin (CALR) is a highly conserved multi-function protein that primarily localizes within the lumen of the endoplasmic reticulum (ER). It participates in various processes in the cells, including glycoprotein chaperoning, regulation of Ca2+ homeostasis, antigen processing and presentation for adaptive immune response, cell adhesion/migration, cell proliferation, immunogenic cell death, gene expression and RNA stability. The role of CALR in the assembly, retrieval and cell surface expression of MHC class I molecules is well known. A fraction of the total cellular CALR is localized in the cytosol, following its retro-translocation from the ER. In the cell stress conditions, CALR is also expressed on the cell surface via an interaction with phosphatidylserine localized on the inner leaflet of the plasma membrane. The abovementioned mechanism is relevant for the recognition of the cells, as well as immunogenicity and phagocytic uptake of proapoptotic and apoptotic cells. Lastly, the presence of CALR exon 9 gene mutations was confirmed in patients with myeloproliferative neoplasms. Their presence results in an abnormal CALR structure due to the loss of its ER-retention sequence, CALR extra-ER localisation, the formation of a complex with thrombopoietin receptor, and oncogenic transformation of hematopoietic stem cells. It is also known that CALR exon 9 mutants are highly immunogenic and induce T cell response. Despite this fact, CALR mutant positive hematopoietic cells emerge. The last phenomenon is probably the result of the inhibition of phagocytosis of the cancer cells exposing CALR mutant protein by dendritic cells.

Insights into the role of ERp57 in cancer

Endoplasmic reticulum resident protein 57 (ERp57) has a molecular weight of 57 kDa, belongs to the protein disulfide-isomerase (PDI) family, and is primarily located in the endoplasmic reticulum (ER). ERp57 functions in the quality control of nascent synthesized glycoproteins, participates in major histocompatibility complex (MHC) class I molecule assembly, regulates immune responses, maintains immunogenic cell death (ICD), regulates the unfolded protein response (UPR), functions as a 1,25-dihydroxy vitamin D3 (1,25(OH)2D3) receptor, regulates the NF-κB and STAT3 pathways, and participates in DNA repair processes and cytoskeletal remodeling. Recent studies have reported ERp57 overexpression in various human cancers, and altered expression and aberrant functionality of ERp57 are associated with cancer growth and progression and changes in the chemosensitivity of cancers. ERp57 may become a potential biomarker and therapeutic target to combat cancer development and chemoresistance. Here, we summarize the available knowledge of the role of ERp57 in cancer and the underlying mechanisms.

Bone Marrow-Derived Mesenchymal Stem Cells Differentially Affect Glioblastoma Cell Proliferation, Migration, and Invasion: A 2D-DIGE Proteomic Analysis

Bone marrow-derived mesenchymal stem cells (BM-MSCs) display high tumor tropism and cause indirect effects through the cytokines they secrete. However, the effects of BM-MSCs on the biological behaviors of glioblastoma multiforme remain unclear. In this study, the conditioned medium from BM-MSCs significantly inhibited the proliferation of C6 cells (P < 0.05) but promoted their migration and invasion (P < 0.05). Two-dimensional fluorescence difference gel electrophoresis (2D-DIGE) proteomic analysis revealed 17 proteins differentially expressed in C6 cells exposed to the BM-MSC-conditioned medium including five upregulated proteins and 12 downregulated proteins. Among these, six differentially expressed proteins (Calr, Set, Oat, Npm1, Ddah1, and Tardbp) were closely related to cell proliferation and differentiation, and nine proteins (Pdia6, Sphk1, Anxa4, Vim, Tuba1c, Actr1b, Actn4, Rap2c, and Tpm2) were associated with motility and the cytoskeleton, which may modulate the invasion and migration of tumor cells. Above all, by identifying the differentially expressed proteins using proteomics and bioinformatics analysis, BM-MSCs could be genetically modified to specifically express tumor-suppressive factors when BM-MSCs are to be used as tumor-selective targeting carriers in the future.

Structural Analysis of Calreticulin, an Endoplasmic Reticulum-Resident Molecular Chaperone

Calreticulin (Calr) is an endoplasmic reticulum (ER) chaperone involved in protein quality control, Ca²⁺ regulation and other cellular processes. The structure of Calr is unusual, reflecting different functions of the protein: a proline-rich β-hairpin arm and an acidic C-terminal tail protrude from a globular core, composed of a β-sheet sandwich and an α-helix. The arm and tail interact in the presence of Ca²⁺ and cover the upper β-sheet, where a carbohydrate-binding site gives the chaperone glycoprotein affinity. At the edge of the carbohydrate-binding site is a conserved, strained disulphide bridge, formed between C¹⁰⁶ and C¹³⁷ of human Calr, which lies in a polypeptide-binding site. The lower β-sheet has several conserved residues, comprised of a characteristic triad, D¹⁶⁶-H¹⁷⁰-D¹⁸⁷, Tyr¹⁷² and the free C¹⁶³. In addition to its role in the ER, Calr translocates to the cell surface upon stress and functions as an immune surveillance marker. In some myeloproliferative neoplasms, the acidic Ca²⁺-binding C-terminal tail is transformed into a polybasic sequence.

A novel autoantibody targeting calreticulin is associated with cancer in patients with idiopathic inflammatory myopathies

Objectives

To investigate the prevalence and clinical significance of anti‐calreticulin autoantibodies (anti‐CRT Ab) in a large cohort of idiopathic inflammatory myopathy (IIM) patients.

Methods

Sera from 469 patients with IIM, 196 patients with other connective tissue diseases, 28 patients with solid tumors and 81 healthy controls were screened for anti‐CRT Ab by enzyme‐linked immunosorbent assay using human recombinant CRT protein. Sera from 35 IIM patients were tested using an immunoprecipitation assay to confirm the presence of anti‐CRT Ab. Subsequently, IIM–cancer patients were identified and divided into new‐onset, remission and recurrent groups based on their cancer status. The relationships between anti‐CRT Ab levels and IIM disease activity were also investigated.

Results

Serum anti‐CRT Ab was detected positive in 81 of the 469 (17.3%) IIM patients. Immunoprecipitated bands were observed at a molecular weight of 60 kDa corresponding to the CRT protein. The IIM patients with anti‐CRT Ab more frequently had cancers compared to the patients without anti‐CRT Ab. Moreover, the prevalence of anti‐CRT Ab differed according to the cancer status. The IIM patients with recurrent cancers had a much higher prevalence of anti‐CRT Ab than those with cancers in remission. Also, serum anti‐CRT Ab levels positively correlated with disease activity at baseline and at follow‐up visits.

Conclusion

We report the existence of serum anti‐CRT Ab in IIM patients and demonstrate the possible association of anti‐CRT Ab with malignancy in IIM patients. Serum anti‐CRT Ab could serve as a novel candidate marker of cancer in IIM patients.

Calreticulin promotes EMT in pancreatic cancer via mediating Ca2+ dependent acute and chronic endoplasmic reticulum stress

Background

Our previous study showed that calreticulin (CRT) promoted EGF-induced epithelial-mesenchymal transition (EMT) in pancreatic cancer (PC) via Integrin/EGFR-ERK/MAPK signaling. We next investigated the novel signal pathway and molecular mechanism involving the oncogenic role of CRT in PC.

Methods

We investigated the potential role and mechanism of CRT in regulating intracellular free Ca²⁺ dependent acute and chronic endoplasmic reticulum stress (ERS)-induced EMT in PC in vitro and vivo.

Results

Thapsigargin (TG) induced acute ERS via increasing intracellular free Ca²⁺ in PC cells, which was reversed by CRT silencing. Additionally, CRT silencing inhibited TG-induced EMT in vitro by reversing TG-induced changes of the key proteins in EMT signaling (ZO-1, E-cadherin and Slug) and ERK/MAPK signaling (pERK). TG-promoted cell invasion and migration was also rescued by CRT silencing but enhanced by IRE1α silencing (one of the key stressors in unfolded protein response). Meanwhile, CRT was co-immunoprecipitated and co-localized with IRE1α in vitro and its silencing led to the chronic ERS via upregulating IRE1α independent of IRE1-XBP1 axis. Moreover, CRT silencing inhibited IRE1α silencing-promoted EMT, including inhibiting the activation of EMT and ERK/MAPK signaling and the promotion of cell mobility. In vivo, CRT silencing decreased subcutaneous tumor size and distant liver metastasis following with the increase of IRE1α expression. A negative relationship between CRT and IRE1α was also observed in clinical PC samples, which coordinately promoted the advanced clinical stages and poor prognosis of PC patients.

Conclusions

CRT promotes EMT in PC via mediating intracellular free Ca²⁺ dependent TG-induced acute ERS and IRE1α-mediated chronic ERS via Slug and ERK/MAPK signaling.

Protein Oxidative Damage in UV-Related Skin Cancer and Dysplastic Lesions Contributes to Neoplastic Promotion and Progression

The ultraviolet (UV) component of solar radiation is the major driving force of skin carcinogenesis. Most of studies on UV carcinogenesis actually focus on DNA damage while their proteome-damaging ability and its contribution to skin carcinogenesis have remained largely underexplored. A redox proteomic analysis of oxidized proteins in solar-induced neoplastic skin lesion and perilesional areas has been conducted showing that the protein oxidative burden mostly concerns a selected number of proteins participating to a defined set of functions, namely: chaperoning and stress response; protein folding/refolding and protein quality control; proteasomal function; DNA damage repair; protein- and vesicle-trafficking; cell architecture, adhesion/extra-cellular matrix (ECM) interaction; proliferation/oncosuppression; apoptosis/survival, all of them ultimately concurring either to structural damage repair or to damage detoxication and stress response. In peri-neoplastic areas the oxidative alterations are conducive to the persistence of genetic alterations, dysfunctional apoptosis surveillance, and a disrupted extracellular environment, thus creating the condition for transformant clones to establish, expand and progress. A comparatively lower burden of oxidative damage is observed in neoplastic areas. Such a finding can reflect an adaptive selection of best fitting clones to the sharply pro-oxidant neoplastic environment. In this context the DNA damage response appears severely perturbed, thus sustaining an increased genomic instability and an accelerated rate of neoplastic evolution. In conclusion UV radiation, in addition to being a cancer-initiating agent, can act, through protein oxidation, as a cancer-promoting agent and as an inducer of genomic instability concurring with the neoplastic progression of established lesions.

Anticancer Properties of Curcumin and Interactions With the Circadian Timing System

The phytochemical curcumin is a major component of turmeric. It has recognized activity against cancer cells and affects several intracellular signaling pathways. Many molecules targeted by curcumin also regulate the circadian timing system that has effects on carcinogenesis, tumor growth, and metastasis. Although the circadian clock within cells may be suppressed in tumors, cancer cells are subjected to daily hormonal and neural activity that should be considered when timing optimal curcumin treatments. Rapid curcumin degradation in blood and tissues provides a challenge to maintaining sustained levels suitable for inducing cancer cell death, increasing the need to identify when during the circadian cycle rhythmically expressed molecular targets are present. Curcumin is well tolerated by individuals ingesting it for possible cancer prevention or in combination with conventional cancer therapies, and it shows low toxicity toward noncancerous cells at low dosages. In contrast, curcumin is particularly effective against cancer stem cells, which are treatment-resistant, aggressive, and tumor-initiating. Although curcumin has poor bioavailability, more stable curcumin analogs retain the anti-inflammatory, antioxidant, antimitotic, and pro-apoptotic benefits of curcumin. Anticancer properties are also present in congeners of curcumin in turmeric and after curcumin reduction by intestinal microbes. Various commercial curcuminoid products are highly popular dietary supplements, but caution is warranted. Although antioxidant properties of curcumin may prevent carcinogenesis, studies suggest curcumin interferes with certain chemotherapeutic agents. This review delves into the complex network of curcuminoid effects to identify potential anticancer strategies that may work in concert with daily physiological cycles controlled by the circadian timing system.

Calreticulin regulates vascular endothelial growth factor-A mRNA stability in gastric cancer cells

Calreticulin (CRT) and vascular endothelial growth factor-A (VEGF-A) are crucial for angiogenesis, and mediate multiple malignant behaviors in gastric cancer. In this study, we report that CRT is positively correlated with VEGF-A in gastric cancer patients. Moreover, high expressions of both CRT and VEGF-A are markedly associated with the pathological stage, progression, and poor prognosis in the patients. Therefore, we sought to elucidate the mechanism by which CRT affects VEGF-A in gastric cancer. Firstly, we demonstrate the novel finding that knockdown of CRT reduced VEGF-A mRNA stability in two gastric cancer cell lines, AGS and MKN45. The AU-Rich element (ARE) is believed to play a crucial role in the maintenance of VEGF-A mRNA stability. Luciferase reporter assay shows that knockdown of CRT significantly decreased the activity of renilla luciferase with VEGF-A ARE sequence. Additionally, competition results from RNA-binding/electrophoretic mobility shift assay indicate that CRT forms an RNA-protein complex with the VEGF-A mRNA by binding to the ARE. In addition, the proliferation rate of human umbilical vein endothelial cells (HUVEC) was significantly reduced when treated with conditioned medium from CRT knockdown cells; this was rescued by exogenous VEGF-A recombinant protein. Our results demonstrate that CRT is involved in VEGF-A ARE binding protein complexes to stabilize VEGF-A mRNA, thereby promoting the angiogenesis, and progression of gastric cancer.

An Update to Calcium Binding Proteins

Ca²⁺ binding proteins (CBP) are of key importance for calcium to play its role as a pivotal second messenger. CBP bind Ca²⁺ in specific domains, contributing to the regulation of its concentration at the cytosol and intracellular stores. They also participate in numerous cellular functions by acting as Ca²⁺ transporters across cell membranes or as Ca²⁺-modulated sensors, i.e. decoding Ca²⁺ signals. Since CBP are integral to normal physiological processes, possible roles for them in a variety of diseases has attracted growing interest in recent years. In addition, research on CBP has been reinforced with advances in the structural characterization of new CBP family members. In this chapter we have updated a previous review on CBP, covering in more depth potential participation in physiopathological processes and candidacy for pharmacological targets in many diseases. We review intracellular CBP that contain the structural EF-hand domain: parvalbumin, calmodulin, S100 proteins, calcineurin and neuronal Ca²⁺ sensor proteins (NCS). We also address intracellular CBP lacking the EF-hand domain: annexins, CBP within intracellular Ca²⁺ stores (paying special attention to calreticulin and calsequestrin), proteins that contain a C2 domain (such as protein kinase C (PKC) or synaptotagmin) and other proteins of interest, such as regucalcin or proprotein convertase subtisilin kexins (PCSK). Finally, we summarise the latest findings on extracellular CBP, classified according to their Ca²⁺ binding structures: (i) EF-hand domains; (ii) EGF-like domains; (iii) ɣ-carboxyl glutamic acid (GLA)-rich domains; (iv) cadherin domains; (v) Ca²⁺-dependent (C)-type lectin-like domains; (vi) Ca²⁺-binding pockets of family C G-protein-coupled receptors.

Calreticulin is a Critical Cell Survival Factor in Malignant Neoplasms

Calreticulin (CRT) is a high-capacity Ca²⁺ protein whose expression is up-regulated during cellular transformation and is associated with disease progression in multiple types of malignancies. At the same time, CRT has been characterized as an important stress-response protein capable of inducing immunogenic cell death (ICD) when translocated to the cell surface. It remains unclear why CRT expression is preserved by malignant cells during the course of transformation despite its immunogenic properties. In this study, we identify a novel, critical function of CRT as a cell survival factor in multiple types of human solid-tissue malignancies. CRT knockdown activates p53, which mediates cell-death response independent of executioner caspase activity and accompanied full-length poly ADP ribose polymerase (PARP) cleavage. Mechanistically, we show that down-regulation of CRT results in mitochondrial Ca²⁺ overload and induction of mitochondria permeability transition pore (mPTP)-dependent cell death, which can be significantly rescued by the mPTP inhibitor, Cyclosporin A (CsA). The clinical importance of CRT expression was revealed in the analysis of the large cohort of cancer patients (N = 2,058) to demonstrate that high levels of CRT inversely correlates with patient survival. Our study identifies intracellular CRT as an important therapeutic target for tumors whose survival relies on its expression.

This study reveals a novel role for the calcium-binding protein calreticulin in the survival of cancer cells; downregulation of calreticulin leads to mitochondrial calcium overload and an induction of non-apoptotic cell death. Calreticulin levels inversely correlate with the survival of patients diagnosed with various types of solid cancers.

High expression of calreticulin indicates poor prognosis and modulates cell migration and invasion via activating Stat3 in nasopharyngeal carcinoma

Objective: Emerging evidence suggests that calreticulin (CALR) has great impacts on the tumor formation and progression of various cancers, but the role of CALR remains controversial. We investigated the expression and clinical significance of CALR in nasopharyngeal carcinoma (NPC). Methods: Immunohistochemistry was used to detect the expression of CALR in NPC tissues, and the correlation of CALR with clinicopathological characteristics and prognosis were analyzed. The cell functions of CALR in NPC cells were also performed in vitro. Results: Compared with non-tumor nasopharyngeal epithelium (NPE) tissues, CALR expression was markedly up-regulated in NPC tissues (P < 0.001), and the high expression of CALR was positively associated with advanced clinical stage (P=0.003) and metastasis (P=0.023). Compared to the patients with low expression of CALR, patients who displayed high expression of CALR may achieve a poorer progression-free survival (PFS) and overall survival (OS) (P < 0.001). Furthermore, multivariate analysis showed that high expression of CALR was an independent predictor of poor prognosis. In addition, we found that knockdown of CALR significantly inhibited the proliferation, migration and invasion of CNE2 and HONE1 cells in vitro, and the mechanism might be associated with inactivation of Stat3 signaling pathway. Conclusion: CALR may promote NPC progression and metastasis via involving Stat3 signaling pathway, and can be regarded as an effective potential predictor for progression and prognosis of NPC.

Identification of Differentially Expressed Proteins from Smokeless Tobacco Addicted Patients Suffering from Oral Squamous Cell Carcinoma

Oral squamous cell carcinoma (OSCC) is the eight most common malignancy worldwide with an incidence rate of 40% in south-east Asia. Lack of effective diagnostic tools at early stage and disease recurrence despite extensive treatments are main reasons for high mortality and low survival rates. The aim of current study was to identify differentially expressed proteins to explore potential candidate biomarkers having diagnostic significance. We performed comparative proteomic analysis of paired protein samples (cancerous buccal mucosa and adjacent normal tissue) from OSCC patients using a combination of two dimensional gel electrophoresis and Mass spectrometric analysis. On the basis of spot intensity, seventeen proteins were found to be consistently differentially expressed among most of the samples which were identified through mass spectrometry. For validation of identified proteins, expression level of stratifin was determined using immuno-histochemistry and Western blot analysis. All identified proteins were analyzed by STRING to explore their interaction. Among uniquely identified proteins in this study, at least two candidate markers (Ig Kappa chain C region and Isoform 2 of fructose bisphosphate aldolase A) were found to be novel with respect to OSCC which can be explored further. Results presented in current study are likely to contribute in understanding the involvement of these molecules in carcinogenesis apart from their plausible role as diagnostic/prognostic markers.

Calreticulin as A Novel Potential Metastasis-Associated Protein in Myxoid Liposarcoma, as Revealed by Two-Dimensional Difference Gel Electrophoresis

Myxoid liposarcoma (MLS) is a mesenchymal malignancy. To identify innovate seeds for clinical applications, we examined the proteomes of primary tumor tissues from 10 patients with MLS with different statuses of postoperative metastasis. The protein expression profiles of tumor tissues were created, and proteins with differential expression associated with postoperative metastasis were identified by two-dimensional difference gel electrophoresis (2D-DIGE) and mass spectrometry. The validation was performed using specific antibodies and in vitro analyses. Using 2D-DIGE, we observed 1726 protein species and identified proteins with unique expression levels in metastatic MLS. We focused on the overexpression of calreticulin in metastatic MLS. The higher expression of calreticulin was confirmed by Western blotting, and gene silencing assays demonstrated that reduced expression of calreticulin inhibited cell growth and invasion. Our findings suggested the important roles of calreticulin in MLS metastasis and supported its potential utility as a prognostic biomarker in MLS. Further investigations of the functional properties of calreticulin and other proteins identified in this study will improve our understanding of the biology of MLS and facilitate novel clinical applications.

EVI‑1 acts as an oncogene and positively regulates calreticulin in breast cancer

Ecotropic viral integration site‑1 (EVI‑1) is an important transcription factor involved in oncogenesis. Aberrant EVI‑1 expression has been reported to be a characteristic of multiple types of malignancies; however, very little is known about how EVI‑1 regulates breast cancer. Current knowledge of how target genes mediate the biological function of EVI‑1 remains limited. In the present study, overexpression of EVI‑1 promoted cell proliferation, migration, and invasion, and inhibited apoptosis in breast cancer. By contrast, silencing of EVI‑1 inhibited cell proliferation, migration and invasion, and enhanced apoptosis in breast cancer. In addition, the results also revealed that the aberrant expression of EVI‑1 regulates genes associated with the apoptotic pathway in breast cancer. Furthermore, EVI‑1 was also likely to target the promoter region of calreticulin (CRT) in vitro. It was concluded that EVI‑1 can affect epithelial mesenchymal transition‑associated genes by regulating the expression of CRT in breast cancer. The results revealed that EVI‑1 may be a potential effective therapeutic target in breast cancer.

Laminar shear stress alters endothelial KCa2.3 expression in H9c2 cells partially via regulating the PI3K/Akt/p300 axis

In cardiac tissues, myoblast atrial myocytes continue to be exposed to mechanical forces including shear stress. However, little is known about the effects of shear stress on atrial myocytes, particularly on ion channel function, in association with disease. The present study demonstrated that the Ca²⁺-activated K⁺ channel (KCa)2.3 serves a vital role in regulating arterial tone. As increased intracellular Ca²⁺ levels and activation of histone acetyltransferase p300 (p300) are early responses to laminar shear stress (LSS) that result in the transcriptional activation of genes, the role of p300 and the phosphoinositide3-kinase (PI3K)/protein kinase B (Akt) pathway, an intracellular pathway that promotes the growth and proliferation rather than the differentiation of adult cells, in the LSS-dependent regulation of KCa2.3 in cardiac myoblasts was examined. In cultured H9c2 cells, exposure to LSS (15 dyn/cm²) for 12 h markedly increased KCa2.3 mRNA expression. Inhibiting PI3K attenuated the LSS-induced increases in the expression and channel activity of KCa2.3, and decreased the phosphorylation levels of p300. The upregulation of these channels was abolished by the inhibition of Akt through decreasing p300 phosphorylation. ChIP assays indicated that p300 was recruited to the promoter region of the KCa2.3 gene. Therefore, the PI3K/Akt/p300 axis serves a crucial role in the LSS-dependent induction of KCa2.3 expression, by regulating cardiac myoblast function and adaptation to hemodynamic changes. The key novel insights gained from the present study are: i) KCa2.3 was upregulated in patients with atrial fibrillation (AF) and in patients with AF combined with mitral value disease; ii) LSS induced a profound upregulation of KCa2.3 mRNA and protein expression in H9c2 cells; iii) PI3K activation was associated with LSS-induced upregulation of the KCa2.3 channel; iv) PI3K activation was mediated by PI3K/Akt-dependent Akt activation; and v) LSS induction of KCa2.3 involved the binding of p300 to transcription factors in the promoter region of the KCa2.3 gene.

Differential expression and molecular interactions of chromosome region maintenance 1 and calreticulin exportins in breast cancer cells

Chromosome region maintenance 1 (CRM-1) and calreticulin (CALR) are two proteins that act as exportins for some nuclear receptors, in addition to other critical functions for cellular homeostasis. In several cancer types, CRM-1 and CALR are upregulated suggesting an imbalance in their functions. However, the regulation of CRM-1 and CALR, and their biological implications, are not completely known. Here, we evaluated the interplay between the levels of CRM-1 and CALR, and estrogen receptor alpha (ERα) status, in breast cancer cells. CRM-1 and CALR were upregulated in mammary tumors relative to normal mammary tissue. Furthermore, the mRNA and protein levels of CRM-1 and CALR were higher in breast cancer cells lacking ERα, in comparison with those that express ERα. Additionally, both proteins were distributed in the nucleus and cytoplasm in the two cell types. Importantly, we identified novel interactions for these exportins. First, we showed an interaction between CRM-1 and CALR, and then we identified that SUN1 and SUN2, two proteins localized in the nuclear envelop, were able to interact specifically with CRM-1, but not CALR. Interestingly, SUN1 and SUN2 expression seemed to be decreased in breast cancer, thereby affecting the interactions of these proteins with CRM-1, and possibly its actions as an exportin. Thus, our data suggest that expression levels for CRM-1 and CALR, the interaction between these exportins, and specific interactions of SUN1 and SUN2 with CRM-1 but not CALR, may be central elements in nucleo-cytoplasmic transport. Furthermore, deregulation of these elements may have serious implications in the progression of breast and other types of cancer.

Calnexin Impairs the Antitumor Immunity of CD4+ and CD8+ T Cells

Elucidation of the mechanisms of T-cell-mediated antitumor responses will provide information for the rational design and development of cancer immunotherapies. Here, we found that calnexin, an endoplasmic reticulum (ER) chaperone protein, is significantly upregulated in oral squamous cell carcinoma (OSCC). Upregulation of its membranous expression on OSCC cells is associated with inhibited T-cell infiltration in tumor tissues and correlates with poor survival of patients with OSCC. We found that calnexin inhibits the proliferation of CD4⁺ and CD8⁺ T cells isolated from the whole blood of healthy donors and patients with OSCC and inhibits the secretion of IFNγ, TNFα, and IL2 from these cells. Furthermore, in a melanoma model, knockdown of calnexin enhanced the infiltration and effector functions of T cells in the tumor microenvironment and conferred better control of tumor growth, whereas treatment with a recombinant calnexin protein impaired the infiltration and effector functions of T cells and promoted tumor growth. We also found that calnexin enhanced the expression of PD-1 on CD4⁺ and CD8⁺ T cells by restraining the DNA methylation status of a CpG island in the PD-1 promoter. Thus, this work uncovers a mechanism by which T-cell antitumor responses are regulated by calnexin in tumor cells and suggests that calnexin might serve as a potential target for the improvement of antitumor immunotherapy.

LPA1/3 signaling mediates tumor lymphangiogenesis through promoting CRT expression in prostate cancer

Lysophosphatidic acid (LPA) is a bioactive lipid growth factor which is present in high levels in serum and platelets. LPA binds to its specific G-protein-coupled receptors, including LPA₁ to LPA₆, thereby regulating various physiological functions, including cancer growth, angiogenesis, and lymphangiogenesis. Our previous study showed that LPA promotes the expression of the lymphangiogenic factor vascular endothelial growth factor (VEGF)-C in prostate cancer (PCa) cells. Interestingly, LPA has been shown to regulate the expression of calreticulin (CRT), a multifunctional chaperone protein, but the roles of CRT in PCa progression remain unclear. Here we investigated the involvement of CRT in LPA-mediated VEGF-C expression and lymphangiogenesis in PCa. Knockdown of CRT significantly reduced LPA-induced VEGF-C expression in PC-3 cells. Moreover, LPA promoted CRT expression through LPA receptors LPA₁ and LPA₃, reactive oxygen species (ROS) production, and phosphorylation of eukaryotic translation initiation factor 2α (eIF2α). Tumor-xenografted mouse experiments further showed that CRT knockdown suppressed tumor growth and lymphangiogenesis. Notably, clinical evidence indicated that the LPA-producing enzyme autotaxin (ATX) is related to CRT and that CRT level is highly associated with lymphatic vessel density and VEGF-C expression. Interestingly, the pharmacological antagonist of LPA receptors significantly reduced the lymphatic vessel density in tumor and lymph node metastasis in tumor-bearing nude mice. Together, our results demonstrated that CRT is critical in PCa progression through the mediation of LPA-induced VEGF-C expression, implying that targeting the LPA signaling axis is a potential therapeutic strategy for PCa.

Homomultimerization of mutant calreticulin is a prerequisite for MPL binding and activation

Studies have previously shown that mutant calreticulin (CALR), found in a subset of patients with myeloproliferative neoplasms (MPNs), interacts with and subsequently promotes the activation of the thrombopoietin receptor (MPL). However, the molecular mechanism behind the activity of mutant CALR remains unknown. Here we show that mutant, but not wild-type, CALR interacts to form a homomultimeric complex. This intermolecular interaction among mutant CALR proteins depends on their carboxyl-terminal domain, which is generated by a unique frameshift mutation found in patients with MPN. With a competition assay, we demonstrated that the formation of mutant CALR homomultimers is required for the binding and activation of MPL. Since association with MPL is required for the oncogenicity of mutant CALR, we propose a model in which the constitutive activation of the MPL downstream pathway by mutant CALR multimers induces the development of MPN. This study provides a potential novel therapeutic strategy against mutant CALR-dependent tumorigenesis via targeting the intermolecular interaction among mutant CALR proteins.

Aberrant Glycosylation Augments the Immuno-Stimulatory Activities of Soluble Calreticulin

Calreticulin (CRT), a luminal resident calcium-binding glycoprotein of the cell, is a tumor-associated antigen involved in tumorigenesis and also an autoantigen targeted by autoantibodies found in patients with various autoimmune diseases. We have previously shown that prokaryotically expressed recombinant murine CRT (rCRT) exhibits strong stimulatory activities against monocytes/macrophages in vitro and potent immunogenicity in vivo, which is partially attributable to self-oligomerization of soluble rCRT. However, even in oligomerized form native CRT (nCRT) isolated from mouse liver is much less active than rCRT, arguing against the possibility that self-oligomerization alone would license potent pro-inflammatory properties to nCRT. Since rCRT differs from nCRT in its lack of glycosylation, we wondered if aberrant glycosylation of eukaryotically expressed CRT (eCRT) would significantly enhance its immunological activity. In the present study, tunicamycin, an N-glycosyltransferase inhibitor, was employed to treat CHO cells (CHO-CRT) stably expressing full-length recombinant mouse CRT in secreted form for preparation of aberrantly glycosylated eCRT (tun-eCRT). Our biochemical and immunological analysis results indicate that eCRT produced by CHO-CRT cells is similar to nCRT in terms of glycosylation level, lack of self-oligomerization, relatively poor immunogenicity and weak macrophage-stimulatory activity, while tun-eCRT shows reduced glycosylation yet much enhanced ability to elicit specific humoral responses in mice and TNF-α and nitric oxide production by macrophages in vitro. Given that abberant glycosylation of proteins is a hallmark of cancer cells and also related to the development of autoimmune disorders in humans, our data may provide useful clues for better understanding of potentiating roles of dysregulated glycosylation of molecules such as CRT in tumorigenesis and autoimmunity.

Calreticulin inhibits inflammation-induced osteoclastogenesis and bone resorption

Osteoclasts play key roles in bone remodeling and pathologic osteolytic disorders such as inflammation, infection, bone implant loosening, rheumatoid arthritis, metastatic bone cancers, and pathological fractures. Osteoclasts are formed by the fusion of monocytes in response to receptor activators of NF-κB-ligand (RANKL) and macrophage colony stimulating factor 1 (M-CSF). Calreticulin (CRT), a commonly known intracellular protein as a calcium-binding chaperone, has an unexpectedly robust anti-osteoclastogenic effect when its recombinant form is applied to osteoclast precursors in vitro or at the site of bone inflammation externally in vivo. Externally applied Calreticulin was internalized inside the cells. It inhibited key pro-osteoclastogenic transcription factors such as c-Fos and nuclear factor of activated T cells, cytoplasmic 1 (NFATc1)-in osteoclast precursor cells that were treated with RANKL in vitro. Recombinant human Calreticulin (rhCRT) inhibited lipopolysaccharide (LPS)-induced inflammatory osteoclastogenesis in the mouse calvarial bone in vivo. Cathepsin K molecular imaging verified decreased Cathepsin K activity when rhCalreticulin was applied at the site of LPS application in vivo. Recombinant forms of intracellular proteins or their derivatives may act as novel extracellular therapeutic agents. We anticipate our findings to be a starting point in unraveling hidden extracellular functions of other intracellular proteins in different cell types of many organs for new therapeutic opportunities. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2658-2666, 2017.

Calreticulin: Challenges Posed by the Intrinsically Disordered Nature of Calreticulin to the Study of Its Function

Calreticulin is a Ca²⁺-binding chaperone protein, which resides mainly in the endoplasmic reticulum but also found in other cellular compartments including the plasma membrane. In addition to Ca²⁺, calreticulin binds and regulates almost all proteins and most of the mRNAs deciding their intracellular fate. The potential functions of calreticulin are so numerous that identification of all of them is becoming a nightmare. Still the recent discovery that patients affected by the Philadelphia-negative myeloproliferative disorders essential thrombocytemia or primary myelofibrosis not harboring JAK2 mutations carry instead calreticulin mutations disrupting its C-terminal domain has highlighted the clinical need to gain a deeper understanding of the biological activity of this protein. However, by contrast with other proteins, such as enzymes or transcription factors, the biological functions of which are strictly defined by a stable spatial structure imprinted by their amino acid sequence, calreticulin contains intrinsically disordered regions, the structure of which represents a highly dynamic conformational ensemble characterized by constant changes between several metastable conformations in response to a variety of environmental cues. This article will illustrate the Theory of calreticulin as an intrinsically disordered protein and discuss the Hypothesis that the dynamic conformational changes to which calreticulin may be subjected by environmental cues, by promoting or restricting the exposure of its active sites, may affect its function under normal and pathological conditions.

Relevance of the chaperone-like protein calreticulin for the biological behavior and clinical outcome of cancer

The death of cancer cells can be categorized as either immunogenic (ICD) or nonimmunogenic, depending on the initiating stimulus. The immunogenic processes of immunogenic cell death are mainly mediated by damage-associated molecular patterns (DAMPs), which include surface exposure of calreticulin (CRT), secretion of adenosine triphosphate (ATP), release of non-histone chromatin protein high-mobility group box 1 (HMGB1) and the production of type I interferons (IFNs). DAMPs are recognized by various receptors that are expressed by antigen-presenting cells (APCs) and potentiate the presentation of tumor antigens to T lymphocytes. Accumulating evidence indicates that CRT exposure constitutes one of the major checkpoints, that determines the immunogenicity of cell death both in vitro and in vivo in mouse models. Moreover, recent studies have identified CRT expression on tumor cells not only as a marker of ICD and active anti-tumor immune reactions but also as a major predictor of a better prognosis in various cancers. Here, we discuss the recent information on the CRT capacity to activate anticancer immune response as well as its prognostic and predictive role for the clinical outcome in cancer patients.

Calreticulin Is Involved in Invasion of Human Extravillous Trophoblasts Through Functional Regulation of Integrin β1

Calreticulin (CRT), a molecular chaperone in the endoplasmic reticulum (ER), plays a variety of roles in cell growth, differentiation, apoptosis, immunity, and cancer biology. It has been reported that CRT is expressed in the human placenta, although its function in placental development is poorly understood. Appropriate invasion of extravillous trophoblasts (EVTs) into the maternal decidua is necessary for successful pregnancy. The objective of the present study was to investigate the expression and functional role of CRT in EVTs using the human EVT cell line HTR8/SVneo, in which CRT gene expression was knocked down. We found that CRT was highly expressed in the human placenta in the early stage of pregnancy and localized to the EVTs. CRT knockdown markedly suppressed the invasion ability of HTR8/SVneo cells. Furthermore, the adhesion to fibronectin was suppressed in the CRT-knockdown cells via the dysfunction of integrin α5β1. In the CRT-knockdown cells, terminal sialylation and fucosylation were decreased, and the core galactose-containing structure was increased in the N-glycans of integrin β1. In addition, the expression levels of several critical glycosyltransferases were changed in the CRT-knockdown cells, consistent with the changes in the N-glycans. These results showed that CRT regulates the function of integrin β1 by affecting the synthesis of N-glycans in HTR8/SVneo cells. Collectively, the results of the present study demonstrate that the ER chaperone CRT plays a regulatory role in the invasion of EVTs, suggesting the importance of CRT expression in placental development during early pregnancy.

Up-regulation of calreticulin in mouse liver tissues after long-term irradiation with low-dose-rate gamma rays

The biological effects of low-dose or low-dose-rate ionizing radiation on normal tissues has attracted attention. Based on previous research, we observed the morphology of liver tissues of C57BL/6J mice that received <50, 50–500, and 500–1000 μGy/h of ¹³⁷Cs radiation for 180 d. We found that the pathological changes in liver tissues were more obvious as the irradiation dose rates increased. Additionally, differential protein expression in liver tissues was analyzed using a proteomics approach. Compared with the matched group in the 2D gel analysis of the irradiated groups, 69 proteins had ≥ 1.5-fold changes in expression. Twenty-three proteins were selected based on ≥2.5-fold change in expression, and 22 of them were meaningful for bioinformatics and protein fingerprinting analysis. These molecules were relevant to cytoskeleton processes, cell metabolism, biological defense, mitochondrial damage, detoxification and tumorigenesis. The results from real-time PCR and western blot (WB) analyses showed that calreticulin (CRT) was up-regulated in the irradiated groups, which indicates that CRT may be relevant to stress reactions when mouse livers are exposed to low-dose irradiation and that low-dose-rate ionizing radiation may pose a cancer risk. The CRT protein can be a potential candidate for low-dose or low-dose-rate ionizing radiation early-warning biomarkers. However, the underlying mechanism requires further investigation.

Dissecting physical structure of calreticulin, an intrinsically disordered Ca2+-buffering chaperone from endoplasmic reticulum

Calreticulin (CALR) is a Ca²⁺ binding multifunctional protein that mostly resides in the endoplasmic reticulum (ER) and plays a number of important roles in various physiological and pathological processes. Although the major functions ascribed to CALR are controlling the Ca²⁺ homeostasis in ER and acting as a lectin-like ER chaperon for many glycoproteins, this moonlighting protein can be found in various cellular compartments where it has many non-ER functions. To shed more light on the mechanisms underlying polyfunctionality of this moonlighting protein that can be found in different cellular compartments and that possesses a wide spectrum of unrelated biological activities, being able to interact with Ca²⁺ (and potentially other metal ions), RNA, oligosaccharides, and numerous proteins, we used a set of experimental and computational tools to evaluate the intrinsic disorder status of CALR and the role of calcium binding on structural properties and conformational stability of the full-length CALR and its isolated P- and C-domains.

Comparative proteomics-network analysis of proteins responsible for ursolic acid-induced cytotoxicity in colorectal cancer cells

Ursolic acid is a key active compound present in many medicinal herbs that have been widely used in traditional Chinese medicine for the clinical treatment of various cancers. However, the precise mechanisms of its antitumor activity have been poorly understood. To identify the cellular targets of ursolic acid, two-dimensional gel electrophoresis combined with mass spectrometry was performed in this study, which identified 15 proteins with significantly altered levels in protein expression. This demonstrated that ursolic acid-induced cytotoxicity in colorectal cancer cells involves dysregulation in protein folding, signal transduction, cell proliferation, cell cycle, and apoptosis. Corresponding protein regulation was also confirmed by Western blotting. Furthermore, the study of functional association between these 15 proteins revealed that 10 were closely related in a protein-protein interaction network, whereby the proteins either had a direct interaction with each other or were associated via only one intermediary protein. In this instance, the ATP5B/CALR/HSP90B1/HSPB1/HSPD1-signaling network was revealed as the predominant target which was associated with the majority of the observed protein-protein interactions. As a result, the identified targets may be useful in explaining the anticancer mechanisms of ursolic acid and as potential targets for colorectal cancer therapy.

The nerve growth factor alters calreticulin translocation from the endoplasmic reticulum to the cell surface and its signaling pathway in epithelial ovarian cancer cells

Ovarian cancer is the seventh most common cancer among women worldwide, causing approximately 120,000 deaths every year. Immunotherapy, designed to boost the body's natural defenses against cancer, appears to be a promising option against ovarian cancer. Calreticulin (CRT) is an endoplasmic reticulum (ER) resident chaperone that, translocated to the cell membrane after ER stress, allows cancer cells to be recognized by the immune system. The nerve growth factor (NGF) is a pro-angiogenic molecule overexpressed in this cancer. In the present study, we aimed to determine weather NGF has an effect in CRT translocation induced by cytotoxic and ER stress. We treated A2780 ovarian cancer cells with NGF, thapsigargin (Tg), an ER stress inducer and mitoxantrone (Mtx), a chemotherapeutic drug; CRT subcellular localization was analyzed by immunofluorescence followed by confocal microscopy. In order to determine NGF effect on Mtx and Tg-induced CRT translocation from the ER to the cell membrane, cells were preincubated with NGF prior to Mtx or Tg treatment and CRT translocation to the cell surface was determined by flow cytometry. In addition, by western blot analyses, we evaluated proteins associated with the CRT translocation pathway, both in A2780 cells and human ovarian samples. We also measured NGF effect on cell apoptosis induced by Mtx. Our results indicate that Mtx and Tg, but not NGF, induce CRT translocation to the cell membrane. NGF, however, inhibited CRT translocation induced by Mtx, while it had no effect on Tg-induced CRT exposure. NGF also diminished cell death induced by Mtx. NGF effect on CRT translocation could have consequences in immunotherapy, potentially lessening the effectiveness of this type of treatment.

DNA vaccine encoding human papillomavirus antigens flanked by a signal peptide and a KDEL sequence induces a potent therapeutic antitumor effect

Cellular immune responses play a critical role in the eradication of intracellular infections and malignant cells through the recognition and subsequent removal of the infection or malignant cells. Effective antigen presentation is crucial for stimulating the immune system against malignant cells. Calreticulin (CRT) has been used to improve antigen presentation. However, CRT overexpression has been previously associated with the development of pancreatic and breast cancer. The import and retention signals of CRT in the endoplasmic reticulum (ER) can be used to overcome CRT overexpression. The present study describes the potent antitumor effect of a DNA vaccine encoding human papillomavirus type 16 E6 and E7 antigens flanked by ER import and retention signals (SP-E6E7m-KDEL). The effect of this vaccine was compared with that of E6 and E7 antigens fused to human full-length CRT (hCRT-E6E7m). In the present study, the effectiveness of SP-E6E7m-KDEL for inducing an interferon-γ antigen-specific, response and its therapeutic effect against tumors was demonstrated, which was as effective as immunization against those antigens fused to CRT. This simplified strategy, using ER import and retention signal peptides to direct antigens to this organelle, provides an efficient alternative to traditional vaccines and, more importantly, a safe and potent system to induce a therapeutic antitumor response.

Identification of potential targets for differentiation in human leukemia cells induced by diallyl disulfide

Diallyl disulfide (DADS) is a primary component of garlic, which has chemopreventive potential. We previously found that moderate doses (15-120 µM) of DADS induced apoptosis and G2/M phase cell cycle arrest. In this study, we observed the effect of low doses (8 µM) of DADS on human leukemia HL-60 cells. We found that DADS could inhibit proliferation, migration and invasion in HL-60 cells, and arrested cells at G0/G1 stage. Then, cell differentiation was displayed by morphologic observation, NBT reduction activity and CD11b evaluation of cytometric flow. It showed that DADS induced differentiation, reduced the ability of NBT and increased CD11b expression. Likewise, DADS inhibited xenograft tumor growth and induced differentiation in vivo. In order to make sure how DADS induced differentiation, we compared the protein expression profile of DADS-treated cells with that of untreated control. Using high resolution mass spectrometry, we identified 18 differentially expressed proteins after treatment with DADS, including four upregulated and 14 downregulated proteins. RT-PCR and western blot assay showed that DJ-1, cofilin 1, RhoGDP dissociation inhibitor 2 (RhoGDI2), Calreticulin (CTR) and PCNA were decreased by DADS. These data suggest that the effects of DADS on leukemia may be due to multiple targets for intervention.