Identification of Ezrin-Radixin-Moesin proteins as novel regulators of pathogenic B-cell receptor signaling and tumor growth in diffuse large B-cell lymphoma

Pharmacological inhibition of ezrin reduces proliferative and invasive phenotype in acute lymphoblastic leukemia cells

Ezrin (EZR) is an actin-associated protein that is often upregulated in cancers. Here we investigate the role of EZR in acute lymphoblastic leukemia (ALL) and explore the therapeutic potential of a pharmacological EZR inhibitor, NSC305787. ALL patient cohorts exhibit significantly elevated EZR mRNA levels, indicating its association with the malignant phenotype. Notably, EZR expression does not impact survival outcomes or relevant clinical-laboratory characteristics, suggesting a role in disease initiation rather than therapy response. NSC305787 induces a dose-dependent reduction in ALL cell viability, and is more potent than a related EZR inhibitor, NSC668394. NSC305787 has multiple effects on ALL cells, including apoptosis induction, clonal growth reduction, and inhibition of cell cycle progression. Importantly, it diminishes adhesiveness and invasiveness in ALL cells. Proteomics analysis highlights changes in translation, RNA catabolism, and cell cycle regulation, emphasizing the broad impact of EZR inhibition on ALL cell biology. Ex vivo assays with primary cells from acute myeloid leukemia (AML) and ALL patients demonstrate NSC305787's efficacy across a molecularly heterogeneous group, independent of risk stratification or recurrent mutations. Notably, NSC305787 shows heightened potency in ALL cells, suggesting its potential as a targeted therapy. In conclusion, our results report high EZR expression in adult ALL patients and support NSC305787 as a promising targeted therapy for ALL that should be further explored.

Mechanical control of antigen detection and discrimination by T and B cell receptors

The adaptive immune response is orchestrated by just two cell types, T cells and B cells. Both cells possess the remarkable ability to recognize virtually any antigen through their respective antigen receptors-the T cell receptor (TCR) and B cell receptor (BCR). Despite extensive investigations into the biochemical signaling events triggered by antigen recognition in these cells, our ability to predict or control the outcome of T and B cell activation remains elusive. This challenge is compounded by the sensitivity of T and B cells to the biophysical properties of antigens and the cells presenting them-a phenomenon we are just beginning to understand. Recent insights underscore the central role of mechanical forces in this process, governing the conformation, signaling activity, and spatial organization of TCRs and BCRs within the cell membrane, ultimately eliciting distinct cellular responses. Traditionally, T cells and B cells have been studied independently, with researchers working in parallel to decipher the mechanisms of activation. While these investigations have unveiled many overlaps in how these cell types sense and respond to antigens, notable differences exist. To fully grasp their biology and harness it for therapeutic purposes, these distinctions must be considered. This review compares and contrasts the TCR and BCR, placing emphasis on the role of mechanical force in regulating the activity of both receptors to shape cellular and humoral adaptive immune responses.

Prediction significance of autophagy-related genes in survival probability and drug resistance in diffuse large B-cell lymphoma

BACKGROUND/AIMS

Diffuse large B-cell lymphoma (DLBCL), the most common subtype of non-Hodgkin lymphoma, has significant prognostic heterogeneity. This study aimed to generate a prognostic prediction model based on autophagy-related genes for DLBCL patients.

METHODS

Utilizing bioinformatics techniques, we analyzed the clinical information and transcriptome data of DLBCL patients from the Gene Expression Omnibus (GEO) database. Through unsupervised clustering, we identified new autophagy-related molecular subtypes and pinpointed differentially expressed genes (DEGs) between these subtypes. Based on these DEGs, a prognostic model was constructed using Cox and Lasso regression. The effectiveness, accuracy, and clinical utility of this prognostic model were assessed using numerous independent validation cohorts, survival analyses, receiver operating characteristic (ROC) curves, multivariate Cox regression analysis, nomograms, and calibration curves. Moreover, functional analysis, immune cell infiltration, and drug sensitivity analysis were performed.

RESULTS

DLBCL patients with different clinical characterizations (age, molecular subtypes, ECOG scores, and stages) showed different expression features of autophagy-related genes. The prediction model was constructed based on the eight autophagy-related genes (ADD3, IGFBP3, TPM1, LYZ, AFDN, DNAJC10, GLIS3, and CCDC102A). The prognostic nomogram for overall survival of DLBCL patients incorporated risk level, stage, ECOG scores, and molecular subtypes, showing excellent agreement between observed and predicted outcomes. Differences were noted in the proportions of immune cells (native B cells, Treg cells, CD8+ T cell, CD4+ memory activated T cells, gamma delta T cells, macrophages M1, and resting mast cells) between high-risk and low-risk groups. LYZ and ADD3 exhibited correlations with drug resistance to most chemotherapeutic drugs.

CONCLUSIONS

This study established a novel prognostic assessment model based on the expression profile of autophagy-related genes and clinical characteristics of DLBCL patients, explored immune infiltration and predicted drug resistance, which may guide precise and individualized immunochemotherapy regimens.

Identification of high-performing antibodies for Moesin for use in Western Blot, immunoprecipitation, and immunofluorescence

Moesin is a cytoskeletal adaptor protein, involved in the modification of the actin cytoskeleton, with relevance to Alzheimer's Disease. Well characterized anti-Moesin antibodies would benefit the scientific community. In this study, we have characterized ten Moesin commercial antibodies in Western Blot, immunoprecipitation, and immunofluorescence using a standardized experimental protocol based on comparing read-outs in knockout cell lines and isogenic parental controls. These studies are part of a larger, collaborative initiative seeking to address antibody reproducibility by characterizing commercially available antibodies for human proteins and publishing the results openly as a resource for the scientific community. While use of antibodies and protocols vary between laboratories, we encourage readers to use this report as a guide to select the most appropriate antibodies for their specific needs.

Hypoxia enhances interactions between Na+/H+ exchanger isoform 1 and actin filaments via ezrin in pulmonary vascular smooth muscle

Exposure to hypoxia, due to high altitude or chronic lung disease, leads to structural changes in the pulmonary vascular wall, including hyperplasia and migration of pulmonary arterial smooth muscle cells (PASMCs). Previous studies showed that hypoxia upregulates the expression of Na⁺/H⁺ exchanger isoform 1 (NHE1) and that inhibition or loss of NHE1 prevents hypoxia-induced PASMC migration and proliferation. The exact mechanism by which NHE1 controls PASMC function has not been fully delineated. In fibroblasts, NHE1 has been shown to act as a membrane anchor for actin filaments, via binding of the adaptor protein, ezrin. Thus, in this study, we tested the role of ezrin and NHE1/actin interactions in controlling PASMC function. Using rat PASMCs exposed to in vitro hypoxia (4% O₂, 24 h) we found that hypoxic exposure increased phosphorylation (activation) of ezrin, and promoted interactions between NHE1, phosphorylated ezrin and smooth muscle specific α-actin (SMA) as measured via immunoprecipitation and co-localization. Overexpression of wild-type human NHE1 in the absence of hypoxia was sufficient to induce PASMC migration and proliferation, whereas inhibiting ezrin phosphorylation with NSC668394 suppressed NHE1/SMA co-localization and migration in hypoxic PASMCs. Finally, overexpressing a version of human NHE1 in which amino acids were mutated to prevent NHE1/ezrin/SMA interactions was unable to increase PASMC migration and proliferation despite exhibiting normal Na⁺/H⁺ exchange activity. From these results, we conclude that hypoxic exposure increases ezrin phosphorylation in PASMCs, leading to enhanced ezrin/NHE1/SMA interaction. We further speculate that these interactions promote anchoring of the actin cytoskeleton to the membrane to facilitate the changes in cell movement and shape required for migration and proliferation.

NSC305787, a pharmacological ezrin inhibitor, exhibits antineoplastic activity in pancreatic cancer cells

Pancreatic cancer is one of the most lethal human neoplasms, and despite advances in the understanding of the molecular complexity involved in the development and progression of this disease, little of this new information has been translated into improvements in therapy and prognosis. Ezrin (EZR) is a protein that regulates multiple cellular functions, including cell proliferation, survival, morphogenesis, adhesion, and motility. In pancreatic cancer, EZR is highly expressed and reflects an unfavorable prognosis, whereas EZR silencing ameliorates the malignant phenotype of pancreatic cancer cells. NSC305787 was identified as a pharmacological EZR inhibitor with favorable pharmacokinetics and antineoplastic activity. Here, we endeavored to investigate the impact of EZR expression on survival outcomes and its associations with molecular and biological characteristics in The Cancer Genome Atlas pancreatic adenocarcinoma cohort. We also assessed the potential antineoplastic effects of NSC305787 in pancreatic cancer cell lines. High EZR expression was an independent predictor of worse survival outcomes. Functional genomics analysis indicated that EZR contributes to multiple cancer-related pathways, including PI3K/AKT/mTOR signaling, NOTCH signaling, estrogen-mediated signaling, and apoptosis. In pancreatic cells, NSC305787 reduced cell viability, clonal growth, and migration. Our exploratory molecular studies identified that NSC305787 modulates the expression and activation of key regulators of the cell cycle, proliferation, DNA damage, and apoptosis, favoring a tumor-suppressive molecular network. In conclusion, EZR expression is an independent prognosis marker in pancreatic cancer. Our study identifies a novel molecular axis underlying the antineoplastic activity of NSC305787 and provides insights into the development of therapeutic strategies for pancreatic cancer.

Comprehensive analysis of cytoskeleton regulatory genes identifies ezrin as a prognostic marker and molecular target in acute myeloid leukemia

PURPOSE

Despite great advances that have been made in the understanding of the molecular complexity of acute myeloid leukemia (AML), very little has been translated into new therapies. Here, we set out to investigate the impact of cytoskeleton regulatory genes on clinical outcomes and their potential as therapeutic targets in AML.

METHODS

Gene expression and clinical data were retrieved from The Cancer Genome Atlas (TCGA) AML study and used for survival and functional genomics analyses. For pharmacological tests, AML cells were exposed to ezrin (EZR) inhibitors and submitted to several cellular and molecular assays.

RESULTS

High EZR expression was identified as an independent marker of worse outcomes in AML patients from the TCGA cohort (p < 0.05). Functional genomics analyses suggested that EZR contributes to responses to stimuli and signal transduction pathways in leukemia cells. EZR pharmacological inhibition with NSC305787 and NSC668394 reduced viability, proliferation, autonomous clonal growth, and cell cycle progression in AML cells (p < 0.05). NSC305787 had a greater potency and efficiency than NSC668394 in leukemia models. At the molecular level, EZR inhibitors reduced EZR, S6 ribosomal protein and 4EBP1 phosphorylation, and induced PARP1 cleavage in AML cells. NSC305787, but not NSC668394, favored a gene network involving cell cycle arrest and apoptosis in Kasumi 1 AML cells.

CONCLUSIONS

From our data we conclude that EZR expression may serve as a prognostic factor in AML. Our preclinical findings indicate that ezrin inhibitors may be employed as a putative novel class of AML targeting drugs.

Moesin as a prognostic indicator of lung adenocarcinoma improves prognosis by enhancing immune lymphocyte infiltration

BACKGROUND

Ezrin-radixin-moesin (ERM) have been explored in many cancer processes. Moesin, as its component, has also been found to play an important role in the prognosis of cancer patients, tumor metastasis, drug resistance, and others. Especially in regulating the immunity, but most results came from direct studies on immune cells, there is no clear conclusion on whether moesin has similar effects in tumor cells. And moesin has certain research results in many cancers in other aspects, but there are few about moesin in lung adenocarcinoma (LUAD).

METHODS

We detect the expression of moesin in 82 LUAD and matched normal tissue samples by immunohistochemistry. Besides, for the pathological feature, we did a detailed statistical analysis. And with the help of various databases, we have done in-depth exploration of moesin's ability to enhance the extent of immune lymphocyte infiltration.

RESULTS

Moesin is a poor expression in lung cancer tissues than the corresponding normal samples. And this phenomenon had a strongly associated with the prognosis and TNM stage of these LUAD patients. Moesin can enhance the infiltration of multiple immune lymphocytes in lung cancer. And this may be related to the interaction between moesin and various inflammatory molecules.

CONCLUSIONS

Moesin is a newly index for the prognosis of LUAD and improves the prognosis of LUAD patients by regulating a variety of inflammation-related molecules to enhance immune lymphocytes infiltration.

Lipid Rafts Interaction of the ARID3A Transcription Factor with EZRIN and G-Actin Regulates B-Cell Receptor Signaling

Several diseases originate via dysregulation of the actin cytoskeleton. The ARID3A/Bright transcription factor has also been implicated in malignancies, primarily those derived from hematopoietic lineages. Previously, we demonstrated that ARID3A shuttles between the nucleus and the plasma membrane, where it localizes within lipid rafts. There it interacts with components of the B-cell receptor (BCR) to reduce its ability to transmit downstream signaling. We demonstrate here that a direct component of ARID3A-regulated BCR signal strength is cortical actin. ARID3A interacts with actin exclusively within lipid rafts via the actin-binding protein EZRIN, which confines unstimulated BCRs within lipid rafts. BCR ligation discharges the ARID3A-EZRIN complex from lipid rafts, allowing the BCR to initiate downstream signaling events. The ARID3A-EZRIN interaction occurs almost exclusively within unpolymerized G-actin, where EZRIN interacts with the multifunctional ARID3A REKLES domain. These observations provide a mechanism by which a transcription factor directly regulates BCR signaling via linkage to the actin cytoskeleton with consequences for B-cell-related neoplasia.

Ezrin Mediates Invasion and Metastasis in Tumorigenesis: A Review

Ezrin, as encoded by the EZR gene, is a member of the Ezrin/Radixin/Moesin (ERM) family. The ERM family includes three highly related actin filament binding proteins, Ezrin, Radixin, and Moesin. These three members share similar structural properties containing an N-terminal domain named FERM, a central helical linker region, and a C-terminal domain that mediates the interaction with F-actin. Ezrin protein is highly regulated through the conformational change between a closed, inactivate form and an open, active form. As a membrane-cytoskeleton linker protein, Ezrin facilitates numerous signal transductions in tumorigenesis and mediates diverse essential functions through interactions with a variety of growth factor receptors and adhesion molecules. Emerging evidence has demonstrated that Ezrin is an oncogene protein, as high levels of Ezrin are associated with metastatic behavior in various types of cancer. The diverse functions attributed to Ezrin and the understanding of how Ezrin drives the deadly process of metastasis are complex and often controversial. Here by reviewing recent findings across a wide spectrum of cancer types we will highlight the structures, protein interactions and oncogenic roles of Ezrin as well as the emerging therapeutic agents targeting Ezrin. This review provides a comprehensive framework to guide future studies of Ezrin and other ERM proteins in basic and clinical studies.

Pharmacologic Inhibition of Ezrin-Radixin-Moesin Phosphorylation is a Novel Therapeutic Strategy in Rhabdomyosarcoma

Intermediate and high-risk rhabdomyosarcoma (RMS) patients have poor prognosis with available treatment options, highlighting a clear unmet need for identification of novel therapeutic strategies. Ezrin-radixin-moesin (ERM) family members are membrane-cytoskeleton linker proteins with well-defined roles in tumor metastasis, growth, and survival. ERM protein activity is regulated by dynamic changes in the phosphorylation at a conserved threonine residue in their C-terminal actin-binding domain. Interestingly, ERM family member, ezrin, has elevated expression in the RMS tissue. Despite this, the translational scope of targeting ERM family proteins in these tumors through pharmacological inhibition has never been considered. This study investigates the inhibition of ERM phosphorylation using a small molecule pharmacophore NSC668394 as a potential strategy against RMS. Upon in vitro treatment with NSC668394, RMS cells exhibit a dose-dependent decrease in cell viability and proliferation, with induction of caspase-3 cleavage and apoptosis. siRNA-mediated knockdown of individual ERM protein expression revealed that each regulates RMS survival to a different degree. In vivo administration of NSC668394 in RMS xenografts causes significant decrease in tumor growth, with no adverse effect on body weight. Collectively, this study highlights the importance of the active conformation of ERM proteins in RMS progression and survival and supports pharmacologic inhibition of these proteins as a novel therapeutic approach.

Neratinib degrades MST4 via autophagy that reduces membrane stiffness and is essential for the inactivation of PI3K, ERK1/2, and YAP/TAZ signaling

The irreversible ERBB1/2/4 inhibitor neratinib causes plasma membrane-associated K-RAS to mislocalize into intracellular vesicles liminal to the plasma membrane; this effect is enhanced by HDAC inhibitors and is now a Phase I trial (NCT03919292). The combination of neratinib and HDAC inhibitors killed pancreatic cancer and lymphoma T cells. Neratinib plus HDAC inhibitor exposure was as efficacious as (paclitaxel+gemcitabine) at killing pancreatic cancer cells. Neratinib reduced the phosphorylation of PAK1, Merlin, LATS1/2, AKT, mTOR, p70 S6K, and ERK1/2 which required expression of Rubicon, Beclin1, and Merlin. Neratinib altered pancreatic tumor cell morphology which was associated with MST4 degradation reduced Ezrin phosphorylation and enhanced phosphorylation of MAP4K4 and LATS1/2. Knockdown of the MAP4K4 activator and sensor of membrane rigidity RAP2A reduced basal LATS1/2 and YAP phosphorylation but did not prevent neratinib from stimulating LATS1/2 or YAP phosphorylation. Beclin1 knockdown prevented MST4 degradation, Ezrin dephosphorylation and neratinib-induced alterations in tumor cell morphology. Our findings demonstrate that neratinib enhances LATS1/2 phosphorylation independently of RAP2A/MAP4K4 and that MST4 degradation and Ezrin dephosphorylation may represent a universal trigger for the biological actions of neratinib.

Ezrin Orchestrates Signal Transduction in Airway Cells

Ezrin is a critical structural protein that organizes receptor complexes and orchestrates their signal transduction. In this study, we review the ezrin-meditated regulation of critical receptor complexes, including the epidermal growth factor receptor (EGFR), CD44, vascular cell adhesion molecule (VCAM), and the deleted in colorectal cancer (DCC) receptor. We also analyze the ezrin-meditated regulation of critical pathways associated with asthma, such as the RhoA, Rho-associated protein kinase (ROCK), and protein kinase A (cAMP/PKA) pathways. Mounting evidence suggests that ezrin plays a role in controlling airway cell function and potentially contributes to respiratory diseases. Ezrin can participate in asthma pathogenesis by affecting bronchial epithelium repair, T lymphocyte regulation, and the contraction of the airway smooth muscle cells. These studies provide new insights for the design of novel therapeutic strategies for asthma treatment.

MARCKS regulates tonic and chronic active B cell receptor signaling

Tonic or chronic active B-cell receptor (BCR) signaling is essential for the survival of normal or some malignant B cells, respectively. However, the molecular mechanism regulating the strength of these two types of BCR signaling remains unknown. Here, using high-speed high-resolution single-molecule tracking in live cells, we identified that PKCβ, STIM1, and IP3R1/2/3 molecules affected the lateral Brownian mobile behavior of BCRs on the plasma membrane of quiescent B cells, which was correlated to the strength of BCR signaling. Further mechanistic studies revealed that these three molecules influenced BCR mobility by regulating the membrane tethering of MARCKS to the inner leaflet of the plasma membrane. Indeed, membrane-untethered or deficiency of MARCKS significantly decreased, while membrane-tethered or overexpression of MARCKS drastically increased the lateral mobility of BCRs. Functional experiments indicated that the membrane-tethered MARCKS suppressed the survival and/or proliferation in both B-cell tumor cells and mouse primary splenic B cells in vitro and in vivo. Mechanistically, we found that membrane-tethered MARCKS increased BCR lateral mobility, and thus decreased BCR nanoclustering by disturbing the interaction between cortical F-actin and the inner leaflet of the plasma membrane, resulting in the suppression of the strength of both tonic and chronic active BCR signaling. Conclusively, MARCKS is a newly identified molecule regulating the strength of BCR signaling by modulating cytoskeleton and plasma membrane interactions, both in the physiological and pathological conditions, suggesting that MARCKS is a putative target for drug design.

The Coordination Between B Cell Receptor Signaling and the Actin Cytoskeleton During B Cell Activation

B-cell activation plays a crucial part in the immune system and is initiated via interaction between the B cell receptor (BCR) and specific antigens. In recent years with the help of modern imaging techniques, it was found that the cortical actin cytoskeleton changes dramatically during B-cell activation. In this review, we discuss how actin-cytoskeleton reorganization regulates BCR signaling in different stages of B-cell activation, specifically when stimulated by antigens, and also how this reorganization is mediated by BCR signaling molecules. Abnormal BCR signaling is associated with the progression of lymphoma and immunological diseases including autoimmune disorders, and recent studies have proved that impaired actin cytoskeleton can devastate the normal activation of B cells. Therefore, to figure out the coordination between the actin cytoskeleton and BCR signaling may reveal an underlying mechanism of B-cell activation, which has potential for new treatments for B-cell associated diseases.

Kallikrein-related peptidases 4, 5, 6 and 7 regulate tumour-associated factors in serous ovarian cancer

BACKGROUND

Tissue kallikrein-related peptidases 4, 5, 6 and 7 (KLK4-7) strongly increase the malignancy of ovarian cancer cells. Deciphering their downstream effectors, we aimed at finding new potential prognostic biomarkers and treatment targets for ovarian cancer patients. KLK4-7-transfected (OV-KLK4-7) and vector-control OV-MZ-6 (OV-VC) ovarian cancer cells were established to select differentially regulated factors.

METHODS

With three independent approaches, PCR arrays, genome-wide microarray and proteome analyses, we identified 10 candidates (MSN, KRT19, COL5A2, COL1A2, BMP5, F10, KRT7, JUNB, BMP4, MMP1). To determine differential protein expression, we performed western blot analyses, immunofluorescence and immunohistochemistry for four candidates (MSN, KRT19, KRT7, JUNB) in cells, tumour xenograft and patient-derived tissues.

RESULTS

We demonstrated that KLK4-7 clearly regulates expression of MSN, KRT19, KRT7 and JUNB at the mRNA and protein levels in ovarian cancer cells and tissues. Protein expression of the top-upregulated effectors, MSN and KRT19, was investigated by immunohistochemistry in patients afflicted with serous ovarian cancer and related to KLK4-7 immunoexpression. Significant positive associations were found for KRT19/KLK4, KRT19/KLK5 and MSN/KLK7.

CONCLUSION

These findings imply that KLK4-7 exert key modulatory effects on other cancer-related genes and proteins in ovarian cancer. These downstream effectors of KLK4-7, MSN and KRT19 may represent important therapeutic targets in serous ovarian cancer.

Cutting Edge: Deletion of Ezrin in B Cells of Lyn-Deficient Mice Downregulates Lupus Pathology

Genetic deletion of the Src family tyrosine kinase Lyn in mice recapitulates human systemic lupus erythematosus, characterized by hyperactive BCR signaling, splenomegaly, autoantibody generation, and glomerulonephritis. However, the molecular regulators of autoimmunity in Lyn-deficient mice and in human lupus remain poorly characterized. In this study, we report that conditional deletion of the membrane-cytoskeleton linker protein ezrin in B cells of Lyn-deficient mice (double knockout [DKO] mice) ameliorates B cell activation and lupus pathogenesis. B cells from DKO mice respond poorly to BCR stimulation, with severe downregulation of major signaling pathways. DKO mice exhibit reduced splenomegaly as well as significantly lower levels of autoantibodies against a variety of autoantigens, including dsDNA, histone, and chromatin. Leukocyte infiltration and deposition of IgG and complement component C3 in the kidney glomeruli of DKO mice are markedly reduced. Our data demonstrate that ezrin is a novel molecular regulator of B cell-associated lupus pathology.

Activated Ezrin controls MISP levels to ensure correct NuMA polarization and spindle orientation

Correct spindle orientation is achieved through signaling pathways that provide a molecular link between the cell cortex and spindle microtubules in an F-actin dependent manner. A conserved cortical protein complex, composed of LGN, NuMA, dynein-dynactin, plays a key role in establishing proper spindle orientation. It has also been shown that the actin-binding protein MISP and the ERM family, that are activated by LOK/SLK in mitosis, regulate spindle orientation. Here, we report that MISP functions between the ERM family member Ezrin and NuMA to allow optimal spindle positioning. We show that MISP directly interacts with Ezrin and that SLK/LOK-activated Ezrin ensures appropriate cortical MISP levels in mitosis by competing with MISP for actin-binding sites at the cell cortex. Furthermore, we found that regulation of proper cortical MISP levels by preventing its excessive accumulation is essential for crescent-like polarized NuMA localization at the cortex and as a consequence for highly dynamic astral microtubules. Our results uncover how appropriate MISP levels at the cortex are required for proper NuMA polarization and therefore an optimal placement of the mitotic spindle within the cell.

A glimpse of the ERM proteins

In all eukaryotes, the plasma membrane is critically important as it maintains the architectural integrity of the cell. Proper anchorage and interaction between the plasma membrane and the cytoskeleton is critical for normal cellular processes. The ERM (ezrin-radixin-moesin) proteins are a class of highly homologous proteins involved in linking the plasma membrane to the cortical actin cytoskeleton. This review takes a succinct look at the biology of the ERM proteins including their structure and function. Current reports on their regulation that leads to activation and deactivation was examined before taking a look at the different interacting partners. Finally, emerging roles of each of the ERM family members in cancer was highlighted.

Caspase Cleavages of the Lymphocyte-oriented Kinase Prevent Ezrin, Radixin, and Moesin Phosphorylation during Apoptosis

The lymphocyte-oriented kinase (LOK), also called serine threonine kinase 10 (STK10), is synthesized mainly in lymphocytes. It is involved in lymphocyte migration and polarization and can phosphorylate ezrin, radixin, and moesin (the ERM proteins). In a T lymphocyte cell line and in purified human lymphocytes, we found LOK to be cleaved by caspases during apoptosis. The first cleavage occurs at aspartic residue 332, located between the kinase domain and the coiled-coil regulation domain. This cleavage generates an N-terminal fragment, p50 N-LOK, containing the kinase domain and a C-terminal fragment, which is further cleaved during apoptosis. Although these cleavages preserve the entire kinase domain, p50 N-LOK displays no kinase activity. In apoptotic lymphocytes, caspase cleavages of LOK are concomitant with a decrease in ERM phosphorylation. When non-apoptotic lymphocytes from mice with homozygous and heterozygous LOK knockout were compared, the latter showed a higher level of ERM phosphorylation, but when apoptosis was induced, LOK(-/-) and LOK(+/-) lymphocytes showed the same low level, confirming in vivo that LOK-induced ERM phosphorylation is prevented during lymphocyte apoptosis. Our results demonstrate that cleavage of LOK during apoptosis abolishes its kinase activity, causing a decrease in ERM phosphorylation, crucial to the role of the ERM proteins in linking the plasma membrane to actin filaments.

Cutting Edge: Ezrin Regulates Inflammation by Limiting B Cell IL-10 Production

IL-10 produced by B cells is important for controlling inflammation, thus underscoring the need to identify mechanisms regulating its production. In this study, we demonstrate that conditional deletion of ezrin in B cells increases IL-10 production induced by TLR4 ligation. The MyD88-independent Toll/IL-1R domain-containing adapter inducing IFN-β-IFN regulatory factor 3 pathway is required for Ezrin-deficient B cells to produce higher IL-10 upon LPS stimulation. Treatment of B cells with a novel small-molecule inhibitor of ezrin induces its dephosphorylation and increases LPS-induced NF-κB and IFN regulatory factor 3 activation and IL-10 secretion, indicating a role for threonine 567 phosphorylation of ezrin in limiting IL-10. Loss of ezrin in B cells results in dampened proinflammatory response to a sublethal dose of LPS in vivo, which is dependent on increased IL-10 production. Taken together, our data yield new insights into molecular and membrane-cytoskeletal regulation of B cell IL-10 production and reveal ezrin as a potential therapeutic target in inflammatory diseases.

Functional role of regulatory T cells in B cell lymphoma and related mechanisms

B cell lymphoma (BCL) has a higher degree of malignancy and complicated pathogenic mechanism. Regulatory T cells (Treg cells) are known to exert certain immune suppression functions, in addition to immune mediating effects. Recent studies have revealed the role of Treg cells in pathogenesis and progression of multiple malignant tumors. This study therefore investigated the functional role and related mechanism of Treg cells in BCL. A cohort of thirty patients who were diagnosed with BCL in our hospital between January 2013 and December 2014. Another thirty healthy individuals were recruited. Peripheral blood mononuclear cells (PBMCs) were separated and analyzed for the ratio of CD4+/CD25+ Treg cells. The mRNA expression levels of Foxp3, transforming growth factor (TGF)-β1 and interleukin (IL)-10 genes were quantified by real-time PCR, while their serum levels were determined by enzyme-linked immunosorbent assay (ELISA). Meanwhile all laboratory indexes for patients were monitored during the complete remission (CR) stage. BCL patients significantly elevated ratio of CD4+/CD25+ Treg cells, which were decreased at CR stage. mRNA levels of Foxp3, TGF-β1 and IL-10, in addition to protein levels of TGF-β1 and IL-10 were potentiated in lymphoma patients but decreased in CR patients (P<0.05 in all cases). CD4+/CD25+ Treg cells exert immune suppressing functions in BCL via regulating cytokines, thereby facilitating the pathogenesis and progression of lymphoma.