Calnexin as a dual-role biomarker: antibody-based diagnosis and therapeutic targeting in lung cancer.

Lung cancer carries one of the highest mortality rates among all cancers. It is often diagnosed at more advanced stages with limited treatment options compared to other malignancies. This study focuses on calnexin as a potential biomarker for diagnosis and treatment of lung cancer. Calnexin, a molecular chaperone integral to N-linked glycoprotein synthesis, has shown some associations with cancer. However, targeted therapeutic or diagnostic methods using calnexin have been proposed. Through 1D-LCMSMS, we identified calnexin as a biomarker for lung cancer and substantiated its expression in human lung cancer cell membranes using Western blotting, flow cytometry, and immunocytochemistry. Anti-calnexin antibodies exhibited complement-dependent cytotoxicity to lung cancer cell lines, resulting in a notable reduction in tumor growth in a subcutaneous xenograft model. Additionally, we verified the feasibility of labeling tumors through in vivo imaging using antibodies against calnexin. Furthermore, exosomal detection of calnexin suggested the potential utility of liquid biopsy for diagnostic purposes. In conclusion, this study establishes calnexin as a promising target for antibody-based lung cancer diagnosis and therapy, unlocking novel avenues for early detection and treatment. [BMB Reports 2024; 57(3): 155-160].

The p24-family and COPII subunit SEC24C facilitate the clearance of alpha1-antitrypsin Z from the endoplasmic reticulum to lysosomes.

A subpopulation of the alpha-1-antitrypsin misfolding Z mutant (ATZ) is cleared from the endoplasmic reticulum (ER) via an ER-to-lysosome-associated degradation (ERLAD) pathway. Here, we report that the COPII subunit SEC24C and the p24-family of proteins facilitate the clearance of ATZ via ERLAD. In addition to the previously reported ERLAD components calnexin and FAM134B, we discovered that ATZ coimmunoprecipitates with the p24-family members TMP21 and TMED9. This contrasts with wild type alpha1-antitrypsin, which did not coimmunoprecipitate with FAM134B, calnexin or the p24-family members. Live-cell imaging revealed that ATZ and the p24-family members traffic together from the ER to lysosomes. Using chemical inhibitors to block ER exit or autophagy, we demonstrated that p24-family members and ATZ co-accumulate at SEC24C marked ER-exit sites or in ER-derived compartments, respectively. Furthermore, depletion of SEC24C, TMP21, or TMED9 inhibited lysosomal trafficking of ATZ and resulted in the increase of intracellular ATZ levels. Conversely, overexpression of these p24-family members resulted in the reduction of ATZ levels. Intriguingly, the p24-family members coimmunoprecipitate with ATZ, FAM134B, and SEC24C. Thus, we propose a model in which the p24-family functions in an adaptor complex linking SEC24C with the ERLAD machinery for the clearance of ATZ.

Involvement of endoplasmic reticulum and histone proteins in immunomodulation by TLR4-interacting SPA4 peptide against Escherichia coli.

Pulmonary host defense is critical for the control of lung infection and inflammation. An increased expression and activity of Toll-like receptor 4 (TLR4) induce phagocytic uptake/clearance and inflammation against Gram-negative bacteria. In this study, we addressed the mechanistic aspect of the immunomodulatory activity of the TLR4-interacting SPA4 peptide (amino acid sequence GDFRYSDGTPVNYTNWYRGE) against Escherichia coli. Binding of the SPA4 peptide to bacteria and direct anti-bacterial effects were investigated using flow cytometric, microscopic, and bacteriological methods. The bacterial uptake and inflammatory cytokine response were studied in dendritic cells expressing endogenous basal level of TLR4 or overexpressing TLR4. The subcellular distribution and co-localization of TLR4 and bacteria were investigated by immunocytochemistry. Furthermore, we studied the cellular expression and co-localization of endoplasmic reticulum (ER) molecules (calnexin and ER membrane protein complex subunit 1; EMC1) with lysosomal-associated membrane protein 1 (LAMP1) in cells infected with E. coli and treated with the SPA4 peptide. Simultaneously, the expression of histone H2A protein was quantitated by immunoblotting. Our results demonstrate no binding or direct killing of the bacteria by SPA4 peptide. Instead, it induces the uptake and localization of E. coli in the phagolysosomes for lysis and simultaneously suppresses the secreted levels of TNF-α. Overexpression of TLR4 further augments the pro-phagocytic and anti-inflammatory activity of SPA4 peptide. A time-dependent change in subcellular distribution of TLR4 and an increased co-localization of TLR4 with E. coli in SPA4 peptide-treated cells suggest an enhanced recognition and internalization of bacteria in conjugation with TLR4. Furthermore, an increased co-localization of calnexin and EMC1 with LAMP1 indicates the involvement of ER in pro-phagocytic activity of SPA4 peptide. Simultaneous reduction in secreted amounts of TNF-α coincides with suppressed histone H2A protein expression in the SPA4 peptide-treated cells. These results provide initial insights into the plausible role of ER and histones in the TLR4-immunomodulatory activity of SPA4 peptide against Gram-negative bacteria.

Competition for calnexin binding regulates secretion and turnover of misfolded GPI-anchored proteins.

In mammalian cells, misfolded glycosylphosphatidylinositol (GPI)-anchored proteins (GPI-APs) are cleared out of the ER to the Golgi via a constitutive and a stress-inducible pathway called RESET. From the Golgi, misfolded GPI-APs transiently access the cell surface prior to rapid internalization for lysosomal degradation. What regulates the release of misfolded GPI-APs for RESET during steady-state conditions and how this release is accelerated during ER stress is unknown. Using mutants of prion protein or CD59 as model misfolded GPI-APs, we demonstrate that inducing calnexin degradation or upregulating calnexin-binding glycoprotein expression triggers the release of misfolded GPI-APs for RESET. Conversely, blocking protein synthesis dramatically inhibits the dissociation of misfolded GPI-APs from calnexin and subsequent turnover. We demonstrate an inverse correlation between newly synthesized calnexin substrates and RESET substrates that coimmunoprecipitate with calnexin. These findings implicate competition by newly synthesized substrates for association with calnexin as a key factor in regulating the release of misfolded GPI-APs from calnexin for turnover via the RESET pathway.

The structural principles underlying molybdenum insertase complex assembly.

Within the cell, the trace element molybdenum (Mo) is only biologically active when complexed either within the nitrogenase-specific FeMo cofactor or within the molybdenum cofactor (Moco). Moco consists of an organic part, called molybdopterin (MPT) and an inorganic part, that is, the Mo-center. The enzyme which catalyzes the Mo-center formation is the molybdenum insertase (Mo-insertase). Mo-insertases consist of two functional domains called G- and E-domain. The G-domain catalyzes the formation of adenylated MPT (MPT-AMP), which is the substrate for the E-domain, that catalyzes the actual molybdate insertion reaction. Though the functions of E- and G-domain have been elucidated to great structural and mechanistic detail, their combined function is poorly characterized. In this work, we describe a structural model of the eukaryotic Mo-insertase Cnx1 complex that was generated based on cross-linking mass spectrometry combined with computational modeling. We revealed Cnx1 to form an asymmetric hexameric complex which allows the E- and G-domain active sites to align in a catalytic productive orientation toward each other.

Mutant p53-ENTPD5 control of the calnexin/calreticulin cycle: a druggable target for inhibiting integrin-α5-driven metastasis.

BACKGROUND: TP53, encoding the tumor suppressor p53, is frequently mutated in various cancers, producing mutant p53 proteins (mutp53) which can exhibit neomorphic, gain-of-function properties. The latter transform p53 into an oncoprotein that promotes metastatic tumor progression via downstream effectors such as ENTPD5, an endoplasmic reticulum UDPase involved in the calnexin/calreticulin cycle of N-glycoprotein biosynthesis. Elucidating the mechanisms underlying the pro-metastatic functions of the mutp53-ENTPD5 axis is crucial for developing targeted therapies for aggressive metastatic cancer. METHODS: We analyzed pancreatic, lung, and breast adenocarcinoma cells with p53 missense mutations to study the impact of mutp53 and ENTPD5 on the N-glycoproteins integrin-α5 (ITGA5) and integrin-ß1 (ITGB1), which heterodimerize to form the key fibronectin receptor. We assessed the role of the mutp53-ENTPD5 axis in integrin-dependent tumor-stroma interactions and tumor cell motility using adhesion, migration, and invasion assays, identifying and validating therapeutic intervention targets. We employed an orthotopic xenograft model of pancreatic ductal adenocarcinoma to examine in vivo targeting of mutp53-ENTPD5-mediated ITGA5 regulation for cancer therapy. RESULTS: Mutp53 depletion diminished ITGA5 and ITGB1 expression and impaired tumor cell adhesion, migration, and invasion, rescued by ENTPD5. The mutp53-ENTPD5 axis maintained ITGA5 expression and function via the calnexin/calreticulin cycle. Targeting this axis using ITGA5-blocking antibodies, α-glucosidase inhibitors, or pharmacological degradation of mutp53 by HSP90 inhibitors, such as Ganetespib, effectively inhibited ITGA5-mediated cancer cell motility in vitro. In the orthotopic xenograft model, Ganetespib reduced ITGA5 expression and metastasis in an ENTPD5-dependent manner. CONCLUSIONS: The mutp53-ENTPD5 axis fosters ITGA5 and ITGB1 expression and tumor cell motility through the calnexin/calreticulin cycle, contributing to cancer metastasis. ITGA5-blocking antibodies or α-glucosidase inhibitors target this axis and represent potential therapeutic options worth exploring in preclinical models. The pharmacologic degradation of mutp53 by HSP90 inhibitors effectively blocks ENTPD5-ITGA5-mediated cancer cell motility and metastasis in vivo, warranting further clinical evaluation in p53-mutant cancers. This research underscores the significance of understanding the complex interplay between mutp53, ENTPD5, and the calnexin/calreticulin cycle in integrin-mediated metastatic tumor progression, offering valuable insights for the development of potential therapeutic strategies.

Calnexin controls TrkB cell surface transport and ER-phagy in mouse cerebral cortex development.

Transactivation of Tropomyosin receptor kinase B (TrkB) by EGF leads to cell surface transport of TrkB, promoting its signaling responsiveness to brain-derived neurotrophic factor (BDNF), a critical process for proper cortical plate development. However, the mechanisms that regulate the transport of TrkB to the cell surface are not fully understood. Here, we identified Calnexin as a regulator for targeting TrkB either to the cell surface or toward autophagosomal processing. Calnexin-deficient mouse embryos show impaired cortical plate formation and elevated levels of transactivated TrkB. In Calnexin-depleted mouse neuronal precursor cells, we detected an impaired cell surface transport of TrkB in response to EGF and an impaired delivery to autophagosomes. Mechanistically, we show that Calnexin facilitates the interaction of TrkB with the ER-phagy receptor Fam134b, thereby targeting TrkB to ER-phagy. This mechanism appears as a critical process for fine-tuning the sensitivity of neurons to BDNF.

CD317 maintains proteostasis and cell survival in response to proteasome inhibitors by targeting calnexin for RACK1-mediated autophagic degradation.

Unbalanced protein homeostasis (proteostasis) networks are frequently linked to tumorigenesis, making cancer cells more susceptible to treatments that target proteostasis regulators. Proteasome inhibition is the first licensed proteostasis-targeting therapeutic strategy, and has been proven effective in hematological malignancy patients. However, drug resistance almost inevitably develops, pressing for a better understanding of the mechanisms that preserve proteostasis in tumor cells. Here we report that CD317, a tumor-targeting antigen with a unique topology, was upregulated in hematological malignancies and preserved proteostasis and cell viability in response to proteasome inhibitors (PIs). Knocking down CD317 lowered Ca2+ levels in the endoplasmic reticulum (ER), promoting PIs-induced proteostasis failure and cell death. Mechanistically, CD317 interacted with calnexin (CNX), an ER chaperone protein that limits calcium refilling via the Ca2+ pump SERCA, thereby subjecting CNX to RACK1-mediated autophagic degradation. As a result, CD317 decreased the level of CNX protein, coordinating Ca2+ uptake and thus favoring protein folding and quality control in the ER lumen. Our findings reveal a previously unrecognized role of CD317 in proteostasis control and imply that CD317 could be a promising target for resolving PIs resistance in the clinic.

Membrane Proteomics to Understand Enhancement Effects of Millimeter-Wave Irradiation on Wheat Root under Flooding Stress.

Millimeter-wave irradiation of wheat seeds enhances the growth of roots under flooding stress, but its mechanism is not clearly understood. To understand the role of millimeter-wave irradiation on root-growth enhancement, membrane proteomics was performed. Membrane fractions purified from wheat roots were evaluated for purity. H+-ATPase and calnexin, which are protein markers for membrane-purification efficiency, were enriched in a membrane fraction. A principal-component analysis of the proteomic results indicated that the millimeter-wave irradiation of seeds affects membrane proteins in grown roots. Proteins identified using proteomic analysis were confirmed using immunoblot or polymerase chain reaction analyses. The abundance of cellulose synthetase, which is a plasma-membrane protein, decreased under flooding stress; however, it increased with millimeter-wave irradiation. On the other hand, the abundance of calnexin and V-ATPase, which are proteins in the endoplasmic reticulum and vacuolar, increased under flooding stress; however, it decreased with millimeter-wave irradiation. Furthermore, NADH dehydrogenase, which is found in mitochondria membranes, was upregulated due to flooding stress but downregulated following millimeter-wave irradiation even under flooding stress. The ATP content showed a similar trend toward change in NADH dehydrogenase expression. These results suggest that millimeter-wave irradiation improves the root growth of wheat via the transitions of proteins in the plasma membrane, endoplasmic reticulum, vacuolar, and mitochondria.

N-glycosylation mediated folding and quality control in serine proteases of the hepsin family.

N-linked glycans are specifically attached to asparagine residues in a N-X-S/T motif of secretory pathway glycoproteins. N-glycosylation of newly synthesized glycoproteins directs their folding via the lectin chaperones calnexin and calreticulin that are associated with protein-folding enzymes and glycosidases of the endoplasmic reticulum (ER). Misfolded glycoproteins are retained in the ER by the same lectin chaperones. The work by Sun et al. (FEBS J 2023, 10.1111/febs.16757) in this issue focusses on hepsin, a serine protease on the surface of liver and other organs. The authors deduce that spatial positioning of N-glycans on one side of a conserved domain of hepsin, known as the scavenger receptor-rich cysteine domain, regulates calnexin selection for hepsin maturation and transport through the secretory pathway. If N-glycosylation is elsewhere on hepsin, then it is misfolded and has a prolonged accumulation with calnexin and BiP. This association coincides with the engagement of stress response pathways that sense glycoprotein misfolding. The topological considerations of N-glycosylation dissected by Sun et al. may help unravel how key sites of N-glycosylation sites required for protein folding and transport have evolved to select the lectin chaperone calnexin pathway for folding and quality control.

[miR-30e-3p in natural killer cell-derived exosomes inhibits the proliferation and invasion of human esophageal squamous carcinoma cells].

Objective To investigate the effects of natural killer (NK)-cell-derived miR-30e-3p-containing exosomes (Exo) on esophageal squamous cell carcinoma (ESCC) cell proliferation, apoptosis and invasion. Methods NK cells were isolated and amplified from the peripheral blood of healthy donors, and NK cell-derived Exo was isolated and identified, which were further co-cultured with NEC cells and were randomly grouped into Exo1 and Exo2 groups. Transmission electron microscopy (TEM) was used to observe the morphology and size of exosomes. Western blot analysis was used to detect the expression levels of exosome markers apoptosis related gene 2- interacting protein X(ALIX), tumor susceptibility gene 101(TSG101), CD81 and calnexin. The NC plasmids, mimics and inhibitors of miR030e-3p were respectively delivered into the NK cells, and the corresponding NK cells-derived Exo were co-cultured with NEC cells, which were divided into NC, Exo, mimic and inhibitor groups. CCK-8 assay was used to evaluate cell proliferation, flow cytometry was conducted to determine cell cycle, annexin V-FITC/PI double staining was employed to detect cell apoptosis, and TranswellTM assay was performed to detect cell invasion abilities. Real-time quantitative PCR was used to detect the expression of miR-23b, miR-422a, miR-133b, miR-124, miR-30e-3p and miR-99a in NCE cells and exosomes. Results The percentages of CD56+CD3+ cells and CD56+CD16+ cells in NK cells were (0.071±0.008)% and (90.6±10.6)%, respectively. Exosome isolated from NK cells ranged from 30 nm to 150 nm, and was positive for ALIX, TSG101 and CD81, while negative for calnexin. NK cell-derived Exos inhibited the proliferation, reduced the proportion of S-phase cells and the number of invaded cells of NEC cells, and promoted the apoptosis and the proportion of G1 phase cells. Overexpression of miR-30E-3p in NK cell-derived exosome inhibited the proliferation and invasion of NEC cells, and blocked cell cycle and promoted apoptosis, while knockdown miR-30e-3p in NK cell-derived exosomes did the opposite. Conclusion miR-30e-3p in NK cell-derived exosomes can inhibit the proliferation and invasion of ESCC cells, block their cell cycle and induce their apoptosis.

Sodium arsenite-induced cytotoxicity is regulated by BNIP3L/Nix-mediated endoplasmic reticulum stress responses and CCPG1-mediated endoplasmic reticulum-phagy.

We elucidated the BNIP3L/Nix and SQSTM1/p62 molecular mechanisms in sodium arsenite (NaAR)-induced cytotoxicity. Considerable changes in the morphology and adhesion of H460 cells were observed in response to varying NaAR concentrations. NaAR exposure induced DNA damage-mediated apoptosis and Nix accumulation via proteasome inhibition. Nix targets the endoplasmic reticulum (ER), inducing ER stress responses. p62 and Nix were colocalized and their expressions were inversely correlated. Autophagy inhibition upregulated Nix, p62, cell cycle progression gene 1 (CCPG1), heme oxygenase (HO)- 1, and calnexin expression. Nix knockdown decreased the NaAR-induced ER stress and microtubule-associated protein 1 A/1B light-chain 3 (LC3) B-II levels and increased the CCPG1 and calnexin levels. p62 knockdown upregulated Nix, LC3-II, and CCPG1 expressions and the ER stress responses, indicating that p62 regulates Nix levels. Nix downstream pathways were mitigated by Ca2+ chelators. We demonstrate the critical roles of Nix and p62 in ER stress and ER-phagy in response to NaAR.

SARS-CoV-2 ORF8 Protein Induces Endoplasmic Reticulum Stress-like Responses and Facilitates Virus Replication by Triggering Calnexin: an Unbiased Study.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the viral pathogen responsible for the worldwide coronavirus disease 2019 (COVID-19) pandemic. The novel SARS-CoV-2 ORF8 protein is not highly homologous with known proteins, including accessory proteins of other coronaviruses. ORF8 contains a 15-amino-acid signal peptide in the N terminus that localizes the mature protein to the endoplasmic reticulum. Oligomannose-type glycosylation has been identified at the N78 site. Here, the unbiased molecular functions of ORF8 are also demonstrated. Via an immunoglobulin-like fold in a glycan-independent manner, both exogenous and endogenous ORF8 interacts with human calnexin and HSPA5. The key ORF8-binding sites of Calnexin and HSPA5 are indicated on the globular domain and the core substrate-binding domain, respectively. ORF8 induces species-dependent endoplasmic reticulum stress-like responses in human cells exclusively via the IRE1 branch, including intensive HSPA5 and PDIA4 upregulation, with increases in other stress-responding effectors, including CHOP, EDEM and DERL3. ORF8 overexpression facilitates SARS-CoV-2 replication. Both stress-like responses and viral replication induced by ORF8 have been shown to result from triggering the Calnexin switch. Thus, ORF8 serves as a key unique virulence gene of SARS-CoV-2, potentially contributing to COVID-19-specific and/or human-specific pathogenesis. IMPORTANCE Although SARS-CoV-2 is basically regarded as a homolog of SARS-CoV, with their genomic structure and the majority of their genes being highly homologous, the ORF8 genes of SARS-CoV and SARS-CoV-2 are distinct. The SARS-CoV-2 ORF8 protein also shows little homology with other viral or host proteins and is thus regarded as a novel special virulence gene of SARS-CoV-2. The molecular function of ORF8 has not been clearly known until now. Our results reveal the unbiased molecular characteristics of the SARS-CoV-2 ORF8 protein and demonstrate that it induces rapidly generated but highly controllable endoplasmic reticulum stress-like responses and facilitates virus replication by triggering Calnexin in human but not mouse cells, providing an explanation for the superficially known in vivo virulence discrepancy of ORF8 between SARS-CoV-2-infected patients and mouse.

Antibodies to calnexin and mutated calreticulin are common in human sera.

PURPOSE OF THE STUDY: Calreticulin is an endoplasmic reticulum chaperone protein, which is involved in protein folding and in peptide loading of major histocompatibility complex class I molecules together with its homolog calnexin. Mutated calreticulin is associated with a group of hemopoietic disorders, especially myeloproliferative neoplasms. Currently only the cellular immune response to mutated calreticulin has been described, although preliminary findings have indicated that antibodies to mutated calreticulin are not specific for myeloproliferative disorders. These findings have prompted us to characterize the humoral immune response to mutated calreticulin and its chaperone homologue calnexin. PATIENTS AND METHODS: We analyzed sera from myeloproliferative neoplasm patients, healthy donors and relapsing-remitting multiple sclerosis patients for the occurrence of autoantibodies to wild type and mutated calreticulin forms and to calnexin by enzyme-linked immunosorbent assay. RESULTS: Antibodies to mutated calreticulin and calnexin were present at similar levels in serum samples of myeloproliferative neoplasm and multiple sclerosis patients as well as healthy donors. Moreover, a high correlation between antibodies to mutated calreticulin and calnexin was seen for all patient and control groups. Epitope binding studies indicated that cross-reactive antibodies bound to a three-dimensional epitope encompassing a short linear sequence in the C-terminal of mutated calreticulin and calnexin. CONCLUSION: Collectively, these findings indicate that calreticulin mutations may be common and not necessarily lead to onset of myeloproliferative neoplasm, possibly due to elimination of cells with mutations. This, in turn, may suggest that additional molecular changes may be required for development of myeloproliferative neoplasm.

Spatial position is a key determinant of N-glycan functionality of the scavenger receptor cysteine-rich domain of human hepsin.

The scavenger receptor cysteine-rich (SRCR) domain is a key constituent in diverse proteins. N-glycosylation is important in protein expression and function. In the SRCR domain of different proteins, N-glycosylation sites and functionality vary substantially. In this study, we examined the importance of N-glycosylation site positions in the SRCR domain of hepsin, a type II transmembrane serine protease involved in many pathophysiological processes. We analysed hepsin mutants with alternative N-glycosylation sites in the SRCR and protease domains using three-dimensional modelling, site-directed mutagenesis, HepG2 cell expression, immunostaining, and western blotting. We found that the N-glycan function in the SRCR domain in promoting hepsin expression and activation on the cell surface cannot be replaced by alternatively created N-glycans in the protease domain. Within the SRCR domain, the presence of an N-glycan in a confined surface area was essential for calnexin-assisted protein folding, endoplasmic reticulum (ER) exiting, and zymogen activation of hepsin on the cell surface. Hepsin mutants with alternative N-glycosylation sites on the opposite side of the SRCR domain were trapped by ER chaperones, resulting in the activation of the unfolded protein response in HepG2 cells. These results indicate that the spatial N-glycan positioning in the SRCR domain is a key determinant in the interaction with calnexin and subsequent cell surface expression of hepsin. These findings may help to understand the conservation and functionality of N-glycosylation sites in the SRCR domains of different proteins.

PON2 ameliorates Ang II-induced cardiomyocyte injury by targeting the CANX/NOX4 signaling pathway.

BACKGROUND: The incidence of heart failure (HF) presents an escalating trend annually, second only to cancer. Few literatures are available regarding on the role of paraoxonase 2 (PON2) in HF so far despite the protective role of PON2 in cardiovascular diseases. METHODS: PON2 expression in AC16 cells was examined with reverse transcriptase-quantitative polymerase chain reaction and western blot following angiotensin II (Ang II) challenging. After PON2 elevation, 2, 7-dichlorofluorescein diacetate assay estimated reactive oxygen species content, related kits appraised oxidative stress, enzyme-linked immunosorbent assay evaluated inflammatory levels, and Western blot was applied to the analysis of apoptosis levels. Research on cytoskeleton was conducted by immunofluorescence (IF), and Western blot analysis of the expressions of hypertrophy-related proteins was performed. BioGRID and GeneMania databases were used to analyze the relationship between PON2 and Calnexin (CANX), which was corroborated by co-immunoprecipitation experiment. Subsequently, PON2 and CANX were simultaneously overexpressed in AC16 cells induced by Ang II to further figure out the mechanism. RESULTS: PON2 expression was depleted in Ang II-induced AC16 cells. PON2 might mediate CANX/NOX4 signaling to inhibit oxidation, inflammatory, hypertrophy, and damage in Ang II-induced AC16 cells. CONCLUSION: PON2 can ease Ang II-induced cardiomyocyte injury via targeting CANX/NOX4 signaling.

Calnexin, More Than Just a Molecular Chaperone.

Calnexin is a type I integral endoplasmic reticulum (ER) membrane protein with an N-terminal domain that resides in the lumen of the ER and a C-terminal domain that extends into the cytosol. Calnexin is commonly referred to as a molecular chaperone involved in the folding and quality control of membrane-associated and secreted proteins, a function that is attributed to its ER- localized domain with a structure that bears a strong resemblance to another luminal ER chaperone and Ca2+-binding protein known as calreticulin. Studies have discovered that the cytosolic C-terminal domain of calnexin undergoes distinct post-translational modifications and interacts with a variety of proteins. Here, we discuss recent findings and hypothesize that the post-translational modifications of the calnexin C-terminal domain and its interaction with specific cytosolic proteins play a role in coordinating ER functions with events taking place in the cytosol and other cellular compartments.

Endoplasmic reticulum calnexins participate in the primary root growth response to phosphate deficiency.

Accumulation of incompletely folded proteins in the endoplasmic reticulum (ER) leads to ER stress, activates ER protein degradation pathways, and upregulates genes involved in protein folding. This process is known as the unfolded protein response (UPR). The role of ER protein folding in plant responses to nutrient deficiencies is unclear. We analyzed Arabidopsis (Arabidopsis thaliana) mutants affected in ER protein quality control and established that both CALNEXIN (CNX) genes function in the primary root response to phosphate (Pi) deficiency. CNX1 and CNX2 are homologous ER lectins promoting protein folding of N-glycosylated proteins via the recognition of the GlcMan9GlcNAc2 glycan. Growth of cnx1-1 and cnx2-2 single mutants was similar to that of the wild type under high and low Pi conditions, but the cnx1-1 cnx2-2 double mutant showed decreased primary root growth under low Pi conditions due to reduced meristematic cell division. This phenotype was specific to Pi deficiency; the double mutant responded normally to osmotic and salt stress. Expression of CNX2 mutated in amino acids involved in binding the GlcMan9GlcNAc2 glycan failed to complement the cnx1-1 cnx2-2 mutant. The root growth phenotype was Fe-dependent and was associated with root apoplastic Fe accumulation. Two genes involved in Fe-dependent inhibition of primary root growth under Pi deficiency, the ferroxidase LOW PHOSPHATE 1 (LPR1) and P5-type ATPase PLEIOTROPIC DRUG RESISTANCE 2 (PDR2) were epistatic to CNX1/CNX2. Overexpressing PDR2 failed to complement the cnx1-1 cnx2-2 root phenotype. The cnx1-1 cnx2-2 mutant showed no evidence of UPR activation, indicating a limited effect on ER protein folding. CNX might process a set of N-glycosylated proteins specifically involved in the response to Pi deficiency.

miR-30e-3p in natural killer cell-derived exosomes inhibits the proliferation and invasion of human esophageal squamous carcinoma cells / 细胞与分子免疫学杂志

Objective To investigate the effects of natural killer (NK)-cell-derived miR-30e-3p-containing exosomes (Exo) on esophageal squamous cell carcinoma (ESCC) cell proliferation, apoptosis and invasion. Methods NK cells were isolated and amplified from the peripheral blood of healthy donors, and NK cell-derived Exo was isolated and identified, which were further co-cultured with NEC cells and were randomly grouped into Exo1 and Exo2 groups. Transmission electron microscopy (TEM) was used to observe the morphology and size of exosomes. Western blot analysis was used to detect the expression levels of exosome markers apoptosis related gene 2- interacting protein X(ALIX), tumor susceptibility gene 101(TSG101), CD81 and calnexin. The NC plasmids, mimics and inhibitors of miR030e-3p were respectively delivered into the NK cells, and the corresponding NK cells-derived Exo were co-cultured with NEC cells, which were divided into NC, Exo, mimic and inhibitor groups. CCK-8 assay was used to evaluate cell proliferation, flow cytometry was conducted to determine cell cycle, annexin V-FITC/PI double staining was employed to detect cell apoptosis, and TranswellTM assay was performed to detect cell invasion abilities. Real-time quantitative PCR was used to detect the expression of miR-23b, miR-422a, miR-133b, miR-124, miR-30e-3p and miR-99a in NCE cells and exosomes. Results The percentages of CD56+CD3+ cells and CD56+CD16+ cells in NK cells were (0.071±0.008)% and (90.6±10.6)%, respectively. Exosome isolated from NK cells ranged from 30 nm to 150 nm, and was positive for ALIX, TSG101 and CD81, while negative for calnexin. NK cell-derived Exos inhibited the proliferation, reduced the proportion of S-phase cells and the number of invaded cells of NEC cells, and promoted the apoptosis and the proportion of G1 phase cells. Overexpression of miR-30E-3p in NK cell-derived exosome inhibited the proliferation and invasion of NEC cells, and blocked cell cycle and promoted apoptosis, while knockdown miR-30e-3p in NK cell-derived exosomes did the opposite. Conclusion miR-30e-3p in NK cell-derived exosomes can inhibit the proliferation and invasion of ESCC cells, block their cell cycle and induce their apoptosis.