Perturbation of cell adhesion and microvilli formation by antisense oligonucleotides to ERM family members

Contribution of radixin and ezrin to the maintenance of hepatocytes' excretory function in health and disease

Background & aims

Excretory liver failure is frequently associated with poor prognosis in critically ill patients. It is characterized by the loss of canalicular membrane export pumps at the hepatocyte membrane. The membrane export pump Multidrug resistant-associated protein (MRP) 2 is pivotal in hepatocytes for brushed membrane morphology and transport of various metabolites. In addition, MRP2 anchoring proteins of the Ezrin/Radixin/Moesin (ERM) family are crucial for the correct MRP2 location, integration, and function in different tissues. In hepatocytes, altered ERM signaling is elementary for developing excretory liver failure.

Methods

Polarized human HepaRG cells, primary human hepatocytes, and hepatocyte-specific Ezrin knockout mice are employed to investigate ERM expression and function in health and the bile duct ligation model of obstructive cholestasis.

Results

ERM-scaffolding protein Ezrin has no relevant function in maintaining the canalicular structure in hepatocytes during health and disease.

Conclusions

Homeostasis of the canalicular pole in hepatocytes is maintained exclusively by Radixin but not Ezrin, and Radixin dysfunction promotes cholestasis.

Ez-Metastasizing: The Crucial Roles of Ezrin in Metastasis

Ezrin is the cytoskeletal organizer and functions in the modulation of membrane-cytoskeleton interaction, maintenance of cell shape and structure, and regulation of cell-cell adhesion and movement, as well as cell survival. Ezrin plays a critical role in regulating tumor metastasis through interaction with other binding proteins. Notably, Ezrin has been reported to interact with immune cells, allowing tumor cells to escape immune attack in metastasis. Here, we review the main functions of Ezrin, the mechanisms through which it acts, its role in tumor metastasis, and its potential as a therapeutic target.

The Immunosuppressive Potential of Cholesterol Sulfate Through T Cell Microvilli Disruption

Cholesterol (CL) is required for various biomolecular production processes, including those of cell membrane components. Therefore, to meet these needs, CL is converted into various derivatives. Among these derivatives is cholesterol sulfate (CS), a naturally produced CL derivative by the sulfotransferase family 2B1 (SULT2B1), which is widely present in human plasma. CS is involved in cell membrane stabilization, blood clotting, keratinocyte differentiation, and TCR nanocluster deformation. This study shows that treatment of T cells with CS resulted in the decreased surface expression of some surface T-cell proteins and reduced IL-2 release. Furthermore, T cells treated with CS significantly reduced lipid raft contents and membrane CLs. Surprisingly, using the electron microscope, we also observed that CS led to the disruption of T-cell microvilli, releasing small microvilli particles containing TCRs and other microvillar proteins. However, in vivo, T cells with CS showed aberrant migration to high endothelial venules and limited infiltrating splenic T-cell zones compared with the untreated T cells. Additionally, we observed significant alleviation of atopic dermatitis in mice injected with CS in the animal model. Based on these results, we conclude that CS is an immunosuppressive natural lipid that impairs TCR signaling by disrupting microvillar function in T cells, suggesting its usefulness as a therapeutic agent for alleviating T-cell-mediated hypersensitivity and a potential target for treating autoimmune diseases.

Role of Ezrin in Asthma-Related Airway Inflammation and Remodeling

Ezrin is an actin binding protein connecting the cell membrane and the cytoskeleton, which is crucial to maintaining cell morphology, intercellular adhesion, and cytoskeleton remodeling. Asthma involves dysfunction of inflammatory cells, cytokines, and airway structural cells. Recent studies have shown that ezrin, whose function is affected by extensive phosphorylation and protein interactions, is closely associated with asthma, may be a therapeutic target for asthma treatment. In this review, we summarize studies on ezrin and discuss its role in asthma-related airway inflammation and remodeling.

Molecular characterization of colorectal cancer related peritoneal metastatic disease

A significant proportion of colorectal cancer (CRC) patients develop peritoneal metastases (PM) in the course of their disease. PMs are associated with a poor quality of life, significant morbidity and dismal disease outcome. To improve care for this patient group, a better understanding of the molecular characteristics of CRC-PM is required. Here we present a comprehensive molecular characterization of a cohort of 52 patients. This reveals that CRC-PM represent a distinct CRC molecular subtype, CMS4, but can be further divided in three separate categories, each presenting with unique features. We uncover that the CMS4-associated structural protein Moesin plays a key role in peritoneal dissemination. Finally, we define specific evolutionary features of CRC-PM which indicate that polyclonal metastatic seeding underlies these lesions. Together our results suggest that CRC-PM should be perceived as a distinct disease entity.

Colorectal cancer can lead to the development of peritoneal metastases, which are associated with worse disease outcome. Here, the authors characterize peritoneal metastases from 52 patients using RNA-seq and mutational sequencing and show a distinct molecular subtype.

Oocyte ERM and EWI Proteins Are Involved in Mouse Fertilization

In mammalian fertilization, the link between the oocyte plasma membrane and underneath cytoskeleton has often been associated to key elements of successful gamete fusion, like microvilli shaping or CD9 function, but its effective role has poorly been studied. EWI-2 and EWI-F as cis partners of CD9, and ERM proteins (Ezrin, Radixin and Moesin) that both attach to the actin cytoskeleton and to the EWI are part of the molecules that make the link between the oocyte membrane and its cytoskeleton. This study aims to assay through siRNA inhibition, the involvement of these ERM and EWI molecules in mouse fertilization, their role in the microvilli morphology of the egg but also their possible contribution to the cortical tension, a parameter that reflects the mechanical behavior of the oocyte cortex. Whereas inhibiting separately the expression of each protein had no effect on fertilization, the combined inhibition of either EWI-2/EWI-F or the three ERM triggered a significant decrease of the fertilization index. This inhibition seems to correlate with an increase in the radius of curvature of the oocyte microvilli. It also causes a decrease of the oocyte cortical tension. These results show the importance of EWI-2 and EWI–F and ERM proteins in the smooth running of a fertilization event and support their involvement in the microvilli architecture of the oocyte and in its mechanical properties.

Hepatocyte polarity establishment and apical lumen formation are organized by Par3, Cdc42, and aPKC in conjunction with Lgl

Hepatocytes differ from columnar epithelial cells by their multipolar organization, which follows the initial formation of central lumen-sharing clusters of polarized cells as observed during liver development and regeneration. The molecular mechanism for hepatocyte polarity establishment, however, has been comparatively less studied than those for other epithelial cell types. Here, we show that the tight junction protein Par3 organizes hepatocyte polarization via cooperating with the small GTPase Cdc42 to target atypical protein kinase C (aPKC) to a cortical site near the center of cell-cell contacts. In 3D Matrigel culture of human hepatocytic HepG2 cells, which mimics a process of liver development and regeneration, depletion of Par3, Cdc42, or aPKC results in an impaired establishment of apicobasolateral polarity and a loss of subsequent apical lumen formation. The aPKC activity is also required for bile canalicular (apical) elongation in mouse primary hepatocytes. The lateral membrane-associated proteins Lgl1 and Lgl2, major substrates of aPKC, seem to be dispensable for hepatocyte polarity establishment because Lgl-depleted HepG2 cells are able to form a single apical lumen in 3D culture. On the other hand, Lgl depletion leads to lateral invasion of aPKC, and overexpression of Lgl1 or Lgl2 prevents apical lumen formation, indicating that they maintain proper lateral integrity. Thus, hepatocyte polarity establishment and apical lumen formation are organized by Par3, Cdc42, and aPKC; Par3 cooperates with Cdc42 to recruit aPKC, which plays a crucial role in apical membrane development and regulation of the lateral maintainer Lgl.

Microvilli Adhesion: An Alternative Route for Nanoparticle Cell Internalization

The cellular uptake of nanoparticles (NPs) represents a critical step in nanomedicine and a crucial point for understanding the interaction of nanomaterials with biological systems. No specific mechanism of uptake has been identified so far, as the NPs are generally incorporated by the cells through one of the few well-known endocytotic mechanisms. Here, an alternative internalization route mediated by microvilli adhesion is demonstrated. This microvillus-mediated adhesion (MMA) has been observed using ceria and magnetite NPs with a dimension of <40 nm functionalized with polyacrylic acid but not using NPs with a neutral or positive functionalization. Such an adhesion was not cell specific, as it was demonstrated in three different cell lines. MMA was also reduced by modifications of the microvillus lipid rafts, obtained by depleting cholesterol and altering synthesis of sphingolipids. We found a direct relationship between MAA, cell cycle, and density of microvilli. The evidence suggests that MMA differs from the commonly described uptake mechanisms and might represent an interesting alternative approach for selective NP delivery.

The interaction of ATP11C-b with ezrin contributes to its polarized localization

ATP11C, a member of the P4-ATPase family, translocates phosphatidylserine and phosphatidylethanolamine at the plasma membrane. We previously revealed that its C-terminal splice variant ATP11C-b exhibits polarized localization in motile cell lines, such as MDA-MB-231 and Ba/F3. In the present study, we found that the C-terminal cytoplasmic region of ATP11C-b interacts specifically with ezrin. Notably, the LLxY motif in the ATP11C-b C-terminal region is crucial for its interaction with ezrin as well as its polarized localization on the plasma membrane. A constitutively active, C-terminal phosphomimetic mutant of ezrin was colocalized with ATP11C-b in polarized motile cells. ATP11C-b was partially mislocalized in cells depleted of ezrin alone, and exhibited greater mislocalization in cells simultaneously depleted of the family members ezrin, radixin and moesin (ERM), suggesting that ERM proteins, particularly ezrin, contribute to the polarized localization of ATP11C-b. Furthermore, Atp11c knockout resulted in C-terminally phosphorylated ERM protein mislocalization, which was restored by exogenous expression of ATP11C-b but not ATP11C-a. These observations together indicate that the polarized localizations of ATP11C-b and the active form of ezrin to the plasma membrane are interdependently stabilized.

The cell adhesion molecule TMIGD1 binds to moesin and regulates tubulin acetylation and cell migration

Background

The cell adhesion molecule transmembrane and immunoglobulin (Ig) domain containing1 (TMIGD1) is a novel tumor suppressor that plays important roles in regulating cell–cell adhesion, cell proliferation and cell cycle. However, the mechanisms of TMIGD1 signaling are not yet fully elucidated.

Results

TMIGD1 binds to the ERM family proteins moesin and ezrin, and an evolutionarily conserved RRKK motif on the carboxyl terminus of TMIGD1 mediates the interaction of TMIGD1 with the N-terminal ERM domains of moesin and ezrin. TMIGD1 governs the apical localization of moesin and ezrin, as the loss of TMIGD1 in mice altered apical localization of moesin and ezrin in epithelial cells. In cell culture, TMIGD1 inhibited moesin-induced filopodia-like protrusions and cell migration. More importantly, TMIGD1 stimulated the Lysine (K40) acetylation of α-tubulin and promoted mitotic spindle organization and CRISPR/Cas9-mediated knockout of moesin impaired the TMIGD1-mediated acetylation of α-tubulin and filamentous (F)-actin organization.

Conclusions

TMIGD1 binds to moesin and ezrin, and regulates their cellular localization. Moesin plays critical roles in TMIGD1-dependent acetylation of α-tubulin, mitotic spindle organization and cell migration. Our findings offer a molecular framework for understanding the complex functional interplay between TMIGD1 and the ERM family proteins in the regulation of cell adhesion and mitotic spindle assembly, and have wide-ranging implications in physiological and pathological processes such as cancer progression.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12929-021-00757-z.

Claudins and JAM-A coordinately regulate tight junction formation and epithelial polarity

Tight junctions (TJs) establish the epithelial barrier and are thought to form a membrane fence to regulate epithelial polarity, although the roles of TJs in epithelial polarity remain controversial. Claudins constitute TJ strands in conjunction with the cytoplasmic scaffolds ZO-1 and ZO-2 and play pivotal roles in epithelial barrier formation. However, how claudins and other TJ membrane proteins cooperate to organize TJs remains unclear. Here, we systematically knocked out TJ components by genome editing and show that while ZO-1/ZO-2-deficient cells lacked TJ structures and epithelial barriers, claudin-deficient cells lacked TJ strands and an electrolyte permeability barrier but formed membrane appositions and a macromolecule permeability barrier. Moreover, epithelial polarity was disorganized in ZO-1/ZO-2-deficient cells, but not in claudin-deficient cells. Simultaneous deletion of claudins and a TJ membrane protein JAM-A resulted in a loss of membrane appositions and a macromolecule permeability barrier and in sporadic epithelial polarity defects. These results demonstrate that claudins and JAM-A coordinately regulate TJ formation and epithelial polarity.

Sphingosine 1-phosphate-mediated activation of ezrin-radixin-moesin proteins contributes to cytoskeletal remodeling and changes of membrane properties in epithelial otic vesicle progenitors

Hearing loss is among the most prevalent sensory impairments in humans. Cochlear implantable devices represent the current therapies for hearing loss but have various shortcomings. ERM (ezrin- radixin -moesin) are a family of adaptor proteins that link plasma membrane with actin cytoskeleton, playing a crucial role in cell morphology and in the formation of membrane protrusions. Recently, bioactive sphingolipids have emerged as regulators of ERM proteins. Sphingosine 1-phosphate (S1P) is a pleiotropic sphingolipid which regulates fundamental cellular functions such as proliferation, survival, migration as well as processes such as development and inflammation mainly via ligation to its specific receptors S1PR (S1P_1-5). Experimental findings demonstrate a key role for S1P signaling axis in the maintenance of auditory function. Preservation of cellular junctions is a fundamental function both for S1P and ERM proteins, crucial for the maintenance of cochlear integrity. In the present work, S1P was found to activate ERM in a S1P₂-dependent manner in murine auditory epithelial progenitors US/VOT-E36. S1P-induced ERM activation potently contributed to actin cytoskeletal remodeling and to the appearance of ionic currents and membrane passive properties changes typical of more differentiated cells. Moreover, PKC and Akt activation was found to mediate S1P-induced ERM phosphorylation. The obtained findings contribute to demonstrate the role of S1P signaling pathway in inner ear biology and to disclose potential innovative therapeutical approaches in the field of hearing loss prevention and treatment.

Necrotizing Enterocolitis in Two Siblings and an Unrelated Infant with Overlapping Chromosome 6q25 Deletions

The pathogenesis of necrotizing enterocolitis (NEC) remains poorly understood but is thought to be multifactorial. There are no specific recurring chromosomal abnormalities previously associated with NEC. We report 3 cases of intestinal necrosis associated with large chromosome 6 deletions. The first patient was found to have a 7.9-Mb deletion of chromosome 6 encompassing over 40 genes, arr[GRCh37] 6q25.3q26(155699183_163554531)×1. The second patient had a 19.5-Mb deletion of chromosome 6 generated by an unbalanced translocation with chromosome 18, 46,XY,der(6)t (6;18)(q25.1;p11.23), arr[GRCh37] 6q25.1q27(151639526_ 171115067)×1, 18p11.32p11.23(131700_7694199)×3, which included the whole 7.9-Mb region deleted in the first patient. The third patient was the younger sibling of the second patient with an identical derivative chromosome 6. The shared abnormal chromosome 6 region includes multiple genes of interest, particularly EZR. Mouse models have demonstrated that Ezr is expressed in microvillar epithelium and helps regulate cell-cell adhesion in the gut. We hypothesize that deletion of this shared region of 6q leads to gastrointestinal vulnerability which may predispose patients to intestinal necrosis.

Role of Polarity Proteins in the Generation and Organization of Apical Surface Protrusions

Protruding from the apical surfaces of epithelial cells are specialized structures, including cilia, microplicae, microvilli, and stereocilia. These contribute to epithelial function by cushioning the apical surface, by amplifying its surface area to facilitate nutrient absorption, and by promoting sensory transduction and barrier function. Despite these important roles, and the diseases that result when their formation is perturbed, there remain significant gaps in our understanding of the biogenesis of apical protrusions, or the pathways that promote their organization and orientation once at the apical surface. Here, I review some general aspects of these apical structures, and then discuss our current understanding of their formation and organization with respect to proteins that specify apicobasolateral polarity and planar cell polarity.

Ezrin regulates skin fibroblast size/mechanical properties and YAP-dependent proliferation

Ezrin acts as a dynamic linkage between plasma membrane and cytoskeleton, and thus involved in many fundamental cellular functions. Yet, its potential role in human skin is virtually unknown. Here we investigate the role of Ezrin in primary skin fibroblasts, the major cells responsible extracellular matrix (ECM) production. We report that Ezrin play an important role in the maintenance of skin fibroblast size/mechanical properties and proliferation. siRNA-mediated Ezrin knockdown decreased fibroblast size and mechanical properties, and thus impaired the nuclear translocation of YAP, a protein commonly response to cell size and mechanical force. Functionally, depletion of Ezrin significantly inhibited YAP target gene expression and fibroblast proliferation. Conversely, restoration of YAP nuclear translocation by overexpression of constitutively active YAP reversed YAP target genes expression and rescued proliferation in Ezrin knockdown cells. These data reveal a novel role for Ezrin in maintenance of fibroblast size/mechanical force and regulating YAP-mediated proliferation.

Expression of ezrin and moesin in primary breast carcinoma and matched lymph node metastases

Ezrin, radixin, moesin (ERM) are important membrane-cytoskeletal crosslinkers and are suggested to play important role in cancer progression and metastasis. Even though ERM proteins were generally considered to be functionally redundant and the most studied was ezrin, recent studies highlight their distinct roles in metastatic process. Little information is available regarding the role of individual ERM proteins and their phosphorylated forms in human breast cancer. Our study is the first to examine expression of ezrin, moesin and their phosphorylated forms in primary breast tumors and matched lymph node metastases (LNMs) and their correlation with clinicopathological variables. A total of 88 primary breast cancer, 91 LNMs, 54 intraductal carcinoma and 26 normal adjacent breast tissue samples from tissue microarrays were studied. Expression was determined by immunohistochemistry, the intensity and number of positive cells was scored. Statistical analysis of protein expression and patients' age, tumor grade and hormonal status was performed. No statistical significant difference was found in ezrin, moesin, p-ezrinTyr353 and pan-p-ezrinThr567/radixinThr564/moesinThr558 expression between primary tumors and LNMs. Even though it was not significant, moesin expression varied between primary tumors, intraductal carcinoma, normal breast adjacent tissue and LNMs. A significant positive correlation between moesin and tumor grade has been proven. Even though primary tumors and matched LNMs did not show different expression patterns, moesin correlated significantly with higher tumor grade. Its positivity in intraductal carcinoma and normal breast tissue adjacent to cancer might indicate its role in tumor intiation/progression.

Hypercalcemia induces targeted autophagic degradation of aquaporin-2 at the onset of nephrogenic diabetes insipidus

Hypercalcemia can cause renal dysfunction such as nephrogenic diabetes insipidus (NDI), but the mechanisms underlying hypercalcemia-induced NDI are not well understood. To elucidate the early molecular changes responsible for this disorder, we employed mass spectrometry-based proteomic analysis of inner medullary collecting ducts (IMCD) isolated from parathyroid hormone-treated rats at onset of hypercalcemia-induced NDI. Forty-one proteins, including the water channel aquaporin-2, exhibited significant changes in abundance, most of which were decreased. Bioinformatic analysis revealed that many of the downregulated proteins were associated with cytoskeletal protein binding, regulation of actin filament polymerization, and cell-cell junctions. Targeted LC-MS/MS and immunoblot studies confirmed the downregulation of 16 proteins identified in the initial proteomic analysis and in additional experiments using a vitamin D treatment model of hypercalcemia-induced NDI. Evaluation of transcript levels and estimated half-life of the downregulated proteins suggested enhanced protein degradation as the possible regulatory mechanism. Electron microscopy showed defective intercellular junctions and autophagy in the IMCD cells from both vitamin D- and parathyroid hormone-treated rats. A significant increase in the number of autophagosomes was confirmed by immunofluorescence labeling of LC3. Colocalization of LC3 and Lamp1 with aquaporin-2 and other downregulated proteins was found in both models. Immunogold electron microscopy revealed aquaporin-2 in autophagosomes in IMCD cells from both hypercalcemia models. Finally, parathyroid hormone withdrawal reversed the NDI phenotype, accompanied by termination of aquaporin-2 autophagic degradation and normalization of both nonphoshorylated and S256-phosphorylated aquaporin-2 levels. Thus, enhanced autophagic degradation of proteins plays an important role in the initial mechanism of hypercalcemic-induced NDI.

Directional Fluid Transport across Organ-Blood Barriers: Physiology and Cell Biology

Directional fluid flow is an essential process for embryo development as well as for organ and organism homeostasis. Here, we review the diverse structure of various organ-blood barriers, the driving forces, transporters, and polarity mechanisms that regulate fluid transport across them, focusing on kidney-, eye-, and brain-blood barriers. We end by discussing how cross talk between barrier epithelial and endothelial cells, perivascular cells, and basement membrane signaling contribute to generate and maintain organ-blood barriers.

The difference in Ezrin-pAkt signaling axis between lepidic and papillary predominant invasive adenocarcinomas of the lung

PURPOSE

Histologic classification of invasive lung adenocarcinomas by predominant subtype has prognostic value. Papillary predominant adenocarcinoma (PPA) reportedly shows poorer prognosis than lepidic predominant adenocarcinoma (LPA); however, biological differences between PPA and LPA are unclear. The purpose of this study was to clarify biological differences between PPA and LPA.

METHODS

Clinicopathological characteristics of invasive 62 PPAs and 117 LPAs smaller than 30 mm were investigated. Furthermore, we compared immunochemical staining scores of 9 molecular markers (E-cadherin, S100A4, fibronectin, integrinβ1, ezrin, GLUT1, ALDH1, SOX2 and Nanog) between PPA and LPA. We performed Western blot analysis using ezrin shRNA-knockdown lung adenocarcinoma cell lines to examine whether molecules that are highly expressed in PPA, such as ezrin, affect pAkt. Finally, we performed immunochemical staining to compare pAkt expression level in PPA and LPA.

RESULTS

Lymphovascular and pleural invasion and lymph node metastasis were significantly more often detected in PPA than in LPA (lymphatic permeation: 31 vs 3 %, vascular invasion: 35 vs 3 %, pleural invasion: 29 vs 5 %, lymph node metastasis: 18 vs 1 %; all P < 0.01). Immunohistochemical (IHC) study revealed that expression score of ezrin was significantly higher in PPA than in LPA (38.3 vs 15.0; P < 0.01). The level of pAkt decreased in shEzrin-induced PC-9 and A549 cancer cells. Moreover, the IHC staining score of pAkt was significantly higher in PPA than in LPA (13.3 vs 0.0; P < 0.01).

CONCLUSIONS

Our results show that the activation of the ezrin-pAkt signaling axis is associated with the more aggressive clinicopathological features of PPA compared with LPA.

Loss of ezrin in human intrahepatic cholangiocarcinoma is associated with ectopic expression of E-cadherin

AIMS

Ezrin connects proteins from the plasma membrane to the subcortical cytoskeleton, and contributes to epithelial integrity by interacting with the cell-cell adhesion molecule E-cadherin. In the liver, ezrin is restricted to cholangiocytes, where it regulates biliary secretory functions. During carcinogenesis, ezrin expression is impaired and associated with enhancement of cell migratory activity in cancer cells; therefore, we aimed to analyse ezrin in cholangiocarcinogenesis.

METHODS AND RESULTS

Ezrin expression was evaluated by immunohistochemistry on tissue microarrays from 94 surgical specimens of intrahepatic cholangiocarcinoma (CCA), and correlated with clinicopathological factors and E-cadherin expression. Ezrin function was also analysed in human CCA cell lines. In CCA, ezrin was negative/weakly expressed in 49 cases (52%) and moderately/strongly expressed in 45 cases (48%), mostly in cell cytoplasm. The negative/weak expression of ezrin was more frequent in peripheral than in perihilar CCA (P = 0.002), and was associated with high tumour size (P = 0.001), low mucus secretion (P = 0.042), the presence of satellite nodules (P = 0.024), and ectopic cytoplasmic expression of E-cadherin (P = 0.005). In vitro, silencing of ezrin in CCA cells caused internalization of E-cadherin and favoured cell migration.

CONCLUSIONS

Ezrin is down-regulated during cholangiocarcinogenesis, and its loss results in a more aggressive phenotype.

A Three-Dimensional Cell Culture Model To Study Enterovirus Infection of Polarized Intestinal Epithelial Cells

Despite serving as the primary entry portal for coxsackievirus B (CVB), little is known about CVB infection of the intestinal epithelium, owing at least in part to the lack of suitable in vivo models and the inability of cultured cells to recapitulate the complexity and structure associated with the gastrointestinal (GI) tract. Here, we report on the development of a three-dimensional (3-D) organotypic cell culture model of Caco-2 cells to model CVB infection of the gastrointestinal epithelium. We show that Caco-2 cells grown in 3-D using the rotating wall vessel (RWV) bioreactor recapitulate many of the properties of the intestinal epithelium, including the formation of well-developed tight junctions, apical-basolateral polarity, brush borders, and multicellular complexity. In addition, transcriptome analyses using transcriptome sequencing (RNA-Seq) revealed the induction of a number of genes associated with intestinal epithelial differentiation and/or intestinal processes in vivo when Caco-2 cells were cultured in 3-D. Applying this model to CVB infection, we found that although the levels of intracellular virus production were similar in two-dimensional (2-D) and 3-D Caco-2 cell cultures, the release of infectious CVB was enhanced in 3-D cultures at early stages of infection. Unlike CVB, the replication of poliovirus (PV) was significantly reduced in 3-D Caco-2 cell cultures. Collectively, our studies show that Caco-2 cells grown in 3-D using the RWV bioreactor provide a cell culture model that structurally and transcriptionally represents key aspects of cells in the human GI tract and can thus be used to expand our understanding of enterovirus-host interactions in intestinal epithelial cells. IMPORTANCE Coxsackievirus B (CVB), a member of the enterovirus family of RNA viruses, is associated with meningitis, pericarditis, diabetes, dilated cardiomyopathy, and myocarditis, among other pathologies. CVB is transmitted via the fecal-oral route and encounters the epithelium lining the gastrointestinal tract early in infection. The lack of suitable in vivo and in vitro models to study CVB infection of the gastrointestinal epithelium has limited our understanding of the events that surround infection of these specialized cells. Here, we report on the development of a three-dimensional (3-D) organotypic cell culture model of human intestinal epithelial cells that better models the gastrointestinal epithelium in vivo. By applying this 3-D model, which recapitulates many aspects of the gastrointestinal epithelium in vivo, to the study of CVB infection, our work provides a new cell system to model the mechanisms by which CVB infects the intestinal epithelium, which may have a profound impact on CVB pathogenesis. Podcast: A podcast concerning this article is available.

On the Role of the Blood Vessel Endothelial Microvilli in the Blood Flow in Small Capillaries

Endothelial microvilli that protrude into the capillary lumen, although invisible in the optical microscopy, may play an important role in the blood flow control in the capillaries. Because of the plug effects, the width of the gap between the capillary wall and the blood cell is especially critical for the blood flow dynamics in capillaries, while microvilli located on the capillary wall can easily control the velocity of the blood flow. We report that microvilli in the capillaries of different vertebrate species have similar characteristics and density, suggesting similarities between the respective regulation mechanisms. A simplified physical model of the capillary effective diameter control by the microvilli is presented.

Moesin expression in fibrosis in the mouse cornea after sterile mechanical trauma or infection

PURPOSE

The aim of this study was to compare the expression patterns of 3 important biochemical characteristics of fibrosis-moesin, transforming growth factor (TGF)-β1, and α-smooth muscle actin (SMA) in the mouse cornea with fibrosis induced by common etiologies-sterile mechanical injury and infection.

METHODS

Corneas of 8-week-old C57BL6 mice were either wounded after an anterior keratectomy or were infected by Pseudomonas aeruginosa, and the animals were killed on days 2 and 7, and on weeks 2 and 4 after the procedure. Western blot and immunofluorescence were used to analyze the expression of moesin and phospho-moesin, and the presence of myofibroblasts identified by the expression of α-SMA in the corneal stroma. The expression of TGF-β1 was analyzed by immunofluorescence.

RESULTS

By immunofluorescent analysis, TGF-β1, α-SMA, and phospho-moesin were not detected in the normal corneal stroma. However, after either treatment, TGF-β1 expression increased, along with phospho-moesin in the wounded corneal stroma until day 7, and decreased after week 2. No expression of TGF-β1 and phospho-moesin was found at postoperative week 4. Moesin expression increased until week 2. Myofibroblasts positive for α-SMA were detected on day 2 until week 4 and peaked at week 2. Western blot analysis confirmed the immunofluorescent data for moesin, phospho-moesin, and α-SMA.

CONCLUSIONS

The similar expression pattern of moesin, phospho-moesin, TGF-β1, and α-SMA in the mouse cornea with fibrosis caused by sterile mechanical injury or infection indicated a role for moesin signaling in corneal fibrosis. Interference with the action of moesin may be a potential approach for intervention strategies to avert fibrosis after infection or mechanical injury.

Desmoglein 3: a help or a hindrance in cancer progression?

Desmoglein 3 is one of seven desmosomal cadherins that mediate cell-cell adhesion in desmosomes. Desmosomes are the intercellular junctional complexes that anchor the intermediate filaments of adjacent cells and confer strong cell adhesion thus are essential in the maintenance of tissue architecture and structural integrity. Like adherens junctions, desmosomes function as tumour suppressors and are down regulated in the process of epithelial-mesenchymal transition and in tumour cell invasion and metastasis. However, recently several studies have shown that various desmosomal components, including desmoglein 3, are up-regulated in cancer with increased levels of expression correlating with the clinical stage of malignancy, implicating their potentiality to serve as a diagnostic and prognostic marker. Furthermore, in vitro studies have demonstrated that overexpression of desmoglein 3 in cancer cell lines activates several signal pathways that have an impact on cell morphology, adhesion and locomotion. These additional signalling roles of desmoglein 3 may not be associated to its adhesive function in desmosomes but rather function outside of the junctions, acting as a key regulator in the control of actin based cellular processes. This review will discuss recent advances which support the role of desmoglein 3 in cancer progression.

Active calpain in phagocytically competent human neutrophils: electroinjection of fluorogenic calpain substrate

Calpain has been implicated in the apparent expansion of neutrophil plasma membrane that accompanies cell spreading and phagocytosis. In order to test this hypothesis, an internally quenched fluorescent peptide substrate of calpain-1 which increased in fluorescence on cleavage, was micro-electroinjected into neutrophils. The fluorescence intensity increased in a significant number of neutrophils, including those which appeared to be in a morphologically resting (spherical) state. In order to test whether calpain was activated by an elevation of cytosolic Ca(2+) during the injection, Ca(2+) chelators were added to the injectate and cytosolic free Ca(2+) in the receiving neutrophil was simultaneously monitored. It was shown that this approach could be used without raising Ca(2+) within the injected cell. Despite this, approximately 75% of individual neutrophils had calpain activity which consumed the substrate within approx. 100 s. It was found that all neutrophils had elevated calpain activity were phagocytically competent; whereas neutrophils with low or undetectable calpain activity failed to undergo phagocytosis. This association was consistent with the hypothesis that calpain activity within neutrophils was necessary for them to undergo efficient phagocytosis.

Clustered PI(4,5)P₂ accumulation and ezrin phosphorylation in response to CLIC5A

CLIC5A (encoded by CLIC5) is a component of the ezrin-NHERF2-podocalyxin complex in renal glomerular podocyte foot processes. We explored the mechanism(s) by which CLIC5A regulates ezrin function. In COS-7 cells, CLIC5A augmented ezrin phosphorylation without changing ezrin abundance, increased the association of ezrin with the cytoskeletal fraction and enhanced actin polymerization and the formation of cell surface projections. CLIC5A caused the phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2] reporter RFP-PH-PLC to translocate from the cytosol to discrete plasma membrane clusters at the cell surface, where it colocalized with CLIC5A. Transiently expressed HA-PIP5Kα colocalized with GFP-CLIC5A and was pulled from cell lysates by GST-CLIC5A, and silencing of endogenous PIP5Kα abrogated CLIC5A-dependent ERM phosphorylation. N- and C-terminal deletion mutants of CLIC5A, which failed to associate with the plasma membrane, failed to colocalize with PIP5Kα, did not alter the abundance of PI(4,5)P2 plasma membrane clusters and failed to enhance ezrin phosphorylation. Relative to wild-type mice, in CLIC5-deficient mice, the phosphorylation of glomerular ezrin was diminished and the cytoskeletal association of both ezrin and NHERF2 was reduced. Therefore, the mechanism of CLIC5A action involves clustered plasma membrane PI(4,5)P2 accumulation through an interaction of CLIC5A with PI(4,5)P2-generating kinases, in turn facilitating ezrin activation and actin-dependent cell surface remodeling.

ERM proteins in cancer progression

Members of the ezrin-radixin-moesin (ERM) family of proteins are involved in multiple aspects of cell migration by acting both as crosslinkers between the membrane, receptors and the actin cytoskeleton, and as regulators of signalling molecules that are implicated in cell adhesion, cell polarity and migration. Increasing evidence suggests that the regulation of cell signalling and the cytoskeleton by ERM proteins is crucial during cancer progression. Thus, both their expression levels and subcellular localisation would affect tumour progression. High expression of ERM proteins has been shown in a variety of cancers. Mislocalisation of ERM proteins reduces the ability of cells to form cell-cell contacts and, therefore, promotes an invasive phenotype. Similarly, mislocalisation of ERM proteins impairs the formation of receptor complexes and alters the transmission of signals in response to growth factors, thereby facilitating tumour progression. In this Commentary, we address the structure, function and regulation of ERM proteins under normal physiological conditions as well as in cancer progression, with particular emphasis on cancers of epithelial origin, such as those from breast, lung and prostate. We also discuss any recent developments that have added to the understanding of the underlying molecular mechanisms and signalling pathways these proteins are involved in during cancer progression.

A PKA-ezrin-Cx43 signaling complex controls gap junction communication and thereby trophoblast cell fusion

Cell fusion occurs as part of the differentiation of some cell types, including myotubes in muscle and osteoclasts in remodeling bone. In the human placenta, mononuclear cytotrophoblasts in a human chorionic gonadotropin (hCG)-driven process fuse to form multinucleated syncytia that allow the exchange of nutrients and gases between the maternal and fetal circulation. Experiments in which protein kinase A (PKA) is displaced from A-kinase anchoring proteins (AKAPs), or in which specific AKAPs are depleted by siRNA-mediated knockdown, point to ezrin as a scaffold required for hCG-, cAMP- and PKA-mediated regulation of the fusion process. By a variety of immunoprecipitation and immunolocalization experiments, we show that ezrin directs PKA to a molecular complex of connexin 43 (Cx43, also known as GJA1) and zona occludens-1 (ZO-1, also known as TJP1). A combination of knockdown experiments and reconstitution with ezrin or Cx43 with or without the ability to bind to its interaction partner or to PKA demonstrate that ezrin-mediated coordination of the localization of PKA and Cx43 is necessary for discrete control of Cx43 phosphorylation and hCG-stimulated gap junction communication that triggers cell fusion in cytotrophoblasts.

Regulation of cell shape and adhesion by CD34

We previously reported that expression of CD43/leukosialin induces cell rounding and microvillus formation via inhibition of cell adhesion. Here, we found that CD34, a cell surface sialomucin and marker for hematopoietic progenitor cells, also inhibited cell adhesion and induced cell rounding and microvillus formation. Forced expression of CD34-induced cell rounding, microvillus formation, and phosphorylation of ezrin/radixin/moesin (ERM) proteins in HEK293T cells, while inhibiting integrin-mediated cell re-attachment. Furthermore, CD34+ blood cells and KG-1 cells, which express endogenous CD34 on their surface, were spherical in shape, surrounded by microvilli, and non-adherent to substrata. In addition, cleavage of O-sialomucin augmented integrin-mediated cell adhesion of KG-1 cells. These results suggest the involvement of CD34 in the inhibition of integrin-mediated cell adhesion and formation of the cell surface structure. The inhibitory function of CD34 in cell adhesion may affect cell shape organization via phosphorylation of ERM proteins. Cellular structures such as the spherical shape and microvilli of CD34+ cells may also contribute to regulation of cell adhesion.

Ezrin is required for the functional regulation of the epithelial sodium proton exchanger, NHE3

The sodium hydrogen exchanger isoform 3 (NHE3) mediates absorption of sodium, bicarbonate and water from renal and intestinal lumina. This activity is fundamental to the maintenance of a physiological plasma pH and blood pressure. To perform this function NHE3 must be present in the apical membrane of renal tubular and intestinal epithelia. The molecular determinants of this localization have not been conclusively determined, although linkage to the apical actin cytoskeleton through ezrin has been proposed. We set out to evaluate this hypothesis. Functional studies of NHE3 activity were performed on ezrin knockdown mice (Vil2^kd/kd) and NHE3 activity similar to wild-type animals detected. Interpretation of this finding was difficult as other ERM (ezrin/radixin/moesin) proteins were present. We therefore generated an epithelial cell culture model where ezrin was the only detectable ERM. After knockdown of ezrin expression with siRNA, radixin and moesin expression remained undetectable. Consistent with the animal ultrastructural data, cells lacking ezrin retained an epithelial phenotype but had shortened and thicker microvilli. NHE3 localization was identical to cells transfected with non-targeting siRNA. The attachment of NHE3 to the apical cytoskeleton was unaltered as assessed by fluorescent recovery after photobleaching (FRAP) and the solubility of NHE3 in Triton X-100. Baseline NHE3 activity was unaltered, however, cAMP-dependent inhibition of NHE3 was largely lost even though NHE3 was phosphorylated at serines 552 and 605. Thus, ezrin is not necessary for the apical localization, attachment to the cytoskeleton, baseline activity or cAMP induced phosphrylation of NHE3, but instead is required for cAMP mediated inhibition.

Depletion of PtdIns(4,5)P₂ underlies retinal degeneration in Drosophila trp mutants

The prototypical transient receptor potential (TRP) channel is the major light-sensitive, and Ca(2+)-permeable channel in the microvillar photoreceptors of Drosophila. TRP channels are activated following hydrolysis of phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P₂] by the key effector enzyme phospholipase C (PLC). Mutants lacking TRP channels undergo light-dependent retinal degeneration, as a consequence of the reduced Ca(2+) influx. It has been proposed that degeneration is caused by defects in the Ca(2+)-dependent visual pigment cycle, which result in accumulation of toxic phosphorylated metarhodopsin-arrestin complexes (MPP-Arr2). Here we show that two interventions, which prevent accumulation of MPP-Arr2, namely rearing under red light or eliminating the C-terminal rhodopsin phosphorylation sites, failed to rescue degeneration in trp mutants. Instead, degeneration in trp mutants reared under red light was rescued by mutation of PLC. Degeneration correlated closely with the light-induced depletion of PtdIns(4,5)P₂ that occurs in trp mutants due to failure of Ca(2+)-dependent inhibition of PLC. Severe retinal degeneration was also induced in the dark in otherwise wild-type flies by overexpression of a bacterial PtdInsPn phosphatase (SigD) to deplete PtdIns(4,5)P₂. In degenerating trp photoreceptors, phosphorylated Moesin, a PtdIns(4,5)P₂-regulated membrane-cytoskeleton linker essential for normal microvillar morphology, was found to delocalize from the rhabdomere and there was extensive microvillar actin depolymerisation. The results suggest that compromised light-induced Ca(2+) influx, due to loss of TRP channels, leads to PtdIns(4,5)P₂ depletion, resulting in dephosphorylation of Moesin, actin depolymerisation and disintegration of photoreceptor structure.

Model membranes to shed light on the biochemical and physical properties of ezrin/radixin/moesin

Ezrin, radixin and moesin (ERM) proteins are now more and more recognized to play a key role in a large number of important physiological processes such as morphogenesis, cancer metastasis and virus infection. Several recent reviews extensively discuss their biological functions [1 -4 ]. In this review, we will first remind the main features of this family of proteins, which are now known as linkers and regulators of the plasma membrane/cytoskeleton linkage. We will then briefly review their implication in pathological processes such as cancer and viral infection. In a second part, we will focus on biochemical and biophysical approaches to study ERM interaction with lipid membranes and conformational change in well-defined environments. In vitro studies using biomimetic lipid membranes, especially large unilamellar vesicles (LUVs), giant unilamellar vesicles (GUVs) and supported lipid bilayers (SLBs) and recombinant proteins help to understand the molecular mechanism of conformational activation of ERM proteins. These tools are aimed to decorticate the different steps of the interaction, to simplify the experiments performed in vivo in much more complex biological environments.

Local phosphocycling mediated by LOK/SLK restricts ezrin function to the apical aspect of epithelial cells

Local cycling of LOK/SLK-dependent phosphorylation of ezrin is required for its apical localization and for microvillus formation.

In this paper, we describe how a dynamic regulatory process is necessary to restrict microvilli to the apical aspect of polarized epithelial cells. We found that local phosphocycling regulation of ezrin, a critical plasma membrane–cytoskeletal linker of microvilli, was required to restrict its function to the apical membrane. Proteomic approaches and ribonucleic acid interference knockdown identified lymphocyte-oriented kinase (LOK) and SLK as the relevant kinases. Using drug-resistant LOK and SLK variants showed that these kinases were sufficient to restrict ezrin function to the apical domain. Both kinases were enriched in microvilli and locally activated there. Unregulated kinase activity caused ezrin mislocalization toward the basolateral domain, whereas expression of the kinase regulatory regions of LOK or SLK resulted in local inhibition of ezrin phosphorylation by the endogenous kinases. Thus, the domain-specific presence of microvilli is a dynamic process requiring a localized kinase driving the phosphocycling of ezrin to continually bias its function to the apical membrane.

Phosphorylation of ezrin/radixin/moesin (ERM) protein in spinal microglia following peripheral nerve injury and lysophosphatidic acid administration

Peripheral nerve injury activates spinal glial cells, which may contribute to the development of pain behavioral hypersensitivity. There is growing evidence that activated microglia show dynamic changes in cell morphology; however, the molecular mechanisms that underlie the modification of the membrane and cytoskeleton of microglia are not known. Here, we investigated the phosphorylation of ezrin, radixin, and moesin (ERM) proteins in the spinal cord after peripheral nerve injury. ERM is known to function as membrane-cytoskeletal linkers and be localized at filopodia- and microvilli-like structures. ERM proteins must be phosphorylated at a specific C-terminal threonine residue to be in the active state. The nature of ERM proteins in the spinal cord of animals in a neuropathic pain model has not been investigated and characterized. In the present study, we observed an increase in the phosphorylated ERM in the spinal microglia following spared nerve injury. The intrathecal administration of lysophosphatidic acid induced the phosphorylation of ERM proteins in microglia along with the development of mechanical pain hypersensitivity. Intrathecal administration of ERM antisense locked nucleic acid suppressed nerve injury-induced tactile allodynia and decreased the phosphorylation of ERM, but not the Iba1 staining pattern, in spinal glial cells. These findings suggest that lysophosphatidic acid induced the phosphorylation of ERM proteins in spinal microglia and may be involved in the emergence of neuropathic pain. These findings may underlie the pathological mechanisms of nerve injury-induced neuropathic pain.

Knockdown of ERM family member moesin in host cells increases HIV type 1 replication

Moesin is a member of the ERM (ezrin, radixin, moesin) family of cytoskeleton/membrane structure organizing and signal transduction proteins. Previously, we found an increased expression of moesin during HIV-1 infection. Moesin was also reported to be incorporated into HIV-1 virions. To analyze whether moesin is a host factor affecting the replication cycle of human immunodeficiency virus type 1 (HIV-1), we used small interfering RNAs (siRNAs) to evaluate the effect of moesin knockdown on HIV-1 replication in P4-CCR5 cells. Moesin's knockdown did not affect the cell viability or cell phenotype. Interestingly, we observed a marked increase in viral replication, as demonstrated by enhanced HIV-1 RNA, p24 antigen, and ß-galactosidase reporter expression. Moesin-dependent enhancement of HIV-1 replication was confirmed in lymphocytic host cells (Jurkat). These results suggest an overall rather restrictive role of moesin for HIV-1 replication in host cells in vitro.

Differential involvement of ezrin/radixin/moesin proteins in sphingosine 1-phosphate-induced human pulmonary endothelial cell barrier enhancement

Endothelial cell (EC) barrier dysfunction induced by inflammatory agonists is a frequent pathophysiologic event in multiple diseases. The platelet-derived phospholipid sphingosine-1 phosphate (S1P) reverses this dysfunction by potently enhancing the EC barrier through a process involving Rac GTPase-dependent cortical actin rearrangement as an integral step. In this study we explored the role of the ezrin, radixin, and moesin (ERM) family of actin-binding linker protein in modulating S1P-induced human pulmonary EC barrier enhancement. S1P induces ERM translocation to the EC periphery and promotes ERM phosphorylation on a critical threonine residue (Ezrin-567, Radixin-564, Moesin-558). This phosphorylation is dependent on activation of PKC isoforms and Rac1. The majority of ERM phosphorylation on these critical threonine residues after S1P occurs in moesin and ezrin. Baseline radixin phosphorylation is higher than in the other two ERM proteins but does not increase after S1P. S1P-induced moesin and ezrin threonine phosphorylation is not mediated by the barrier enhancing receptor S1PR1 because siRNA downregulation of S1PR1 fails to inhibit these phosphorylation events, while stimulation of EC with the S1PR1-specific agonist SEW2871 fails to induce these phosphorylation events. Silencing of either all ERM proteins or radixin alone (but not moesin alone) reduced S1P-induced Rac1 activation and phosphorylation of the downstream Rac1 effector PAK1. Radixin siRNA alone, or combined siRNA for all three ERM proteins, dramatically attenuates S1P-induced EC barrier enhancement (measured by transendothelial electrical resistance (TER), peripheral accumulation of di-phospho-MLC, and cortical cytoskeletal rearrangement. In contrast, moesin depletion has the opposite effects on these parameters. Ezrin silencing partially attenuates S1P-induced EC barrier enhancement and cytoskeletal changes. Thus, despite structural similarities and reported functional redundancy, the ERM proteins differentially modulate S1P-induced alterations in lung EC cytoskeleton and permeability. These results suggest that ERM activation is an important regulatory event in EC barrier responses to S1P.

Ezrin is required for efficient Rap1-induced cell spreading

The Rap family of small GTPases regulate the adhesion of cells to extracellular matrices. Several Rap-binding proteins have been shown to function as effectors that mediate Rap-induced adhesion. However, little is known regarding the relationships between these effectors, or about other proteins that are downstream of or act in parallel to the effectors. To establish whether an array of effectors was required for Rap-induced cell adhesion and spreading, and to find new components involved in Rap-signal transduction, we performed a small-scale siRNA screen in A549 lung epithelial cells. Of the Rap effectors tested, only Radil blocked Rap-induced spreading. Additionally, we identified a novel role for Ezrin downstream of Rap1. Ezrin was necessary for Rap-induced cell spreading, but not Rap-induced cell adhesion or basal adhesion processes. Furthermore, Ezrin depletion inhibited Rap-induced cell spreading in several cell lines, including primary human umbilical vein endothelial cells. Interestingly, Radixin and Moesin, two proteins with high homology to Ezrin, are not required for Rap-induced cell spreading and cannot compensate for loss of Ezrin to rescue Rap-induced cell spreading. Here, we present a novel function for Ezrin in Rap1-induced cell spreading and evidence of a non-redundant role of an ERM family member.

Drosophila PI4KIIIalpha is required in follicle cells for oocyte polarization and Hippo signaling

In a genetic screen we isolated mutations in CG10260, which encodes a phosphatidylinositol 4-kinase (PI4KIIIalpha), and found that PI4KIIIalpha is required for Hippo signaling in Drosophila ovarian follicle cells. PI4KIIIalpha mutations in the posterior follicle cells lead to oocyte polarization defects similar to those caused by mutations in the Hippo signaling pathway. PI4KIIIalpha mutations also cause misexpression of well-established Hippo signaling targets. The Merlin-Expanded-Kibra complex is required at the apical membrane for Hippo activity. In PI4KIIIalpha mutant follicle cells, Merlin fails to localize to the apical domain. Our analysis of PI4KIIIalpha mutants provides a new link in Hippo signal transduction from the cell membrane to its core kinase cascade.

Formation of microvilli and phosphorylation of ERM family proteins by CD43, a potent inhibitor for cell adhesion: cell detachment is a potential cue for ERM phosphorylation and organization of cell morphology

CD43/sialophorin/leukosialin, a common leukocyte antigen, is known as an inhibitor for cell adhesion. The ectodomain of CD43 is considered as a molecular barrier for cell adhesion, while the cytoplasmic domain has a binding site for Ezrin/Radixin/Moesin (ERM). We found expression of CD43 induced cell rounding, inhibition of cell re-attachment, augmentation of microvilli, and phosphorylation of ERM in HEK293T cells. Mutant studies revealed the ectodomain of CD43, but not the intracellular domain, essential and sufficient for all these phenomena. We also found that forced cell detachment by itself induced phosphorylation of ERM in HEK293T cells. Taken together, these findings indicate that inhibition of cell adhesion by the ectodomain of CD43 induces phosphorylation of ERM, microvilli formation, and eventual cell rounding. Furthermore, our study suggests a novel possibility that cell detachment itself induces activation of ERM and modification of cell shape.

Emerging role for ERM proteins in cell adhesion and migration

The highly related ERM (Ezrin, Radixin, Moesin) proteins provide a regulated linkage between the membrane and the underlying actin cytoskeleton. They also provide a platform for the transmission of signals in responses to extracellular cues. Studies in different model organisms and in cultured cells have highlighted the importance of ERM proteins in the generation and maintenance of specific domains of the plasma membrane. A central question is how do ERM proteins coordinate actin filament organization and membrane protein transport/stability with signal transduction pathways to build up complex structures? Through their interaction with numerous partners including membrane proteins, actin cytoskeleton and signaling molecules, ERM proteins have the ability to organize multiprotein complexes in specific cellular compartments. Likewise, ERM proteins participate in diverse functions including cell morphogenesis, endocytosis/exocytosis, adhesion and migration. This review focuses on aspects still poorly understood related to the function of ERM proteins in epithelial cell adhesion and migration.

Differential expression of CD44 variants among meningioma subtypes

Aims/background-CD44 is a widely distributed cell surface molecule which has numerous isoforms generated by alternative splicing. The diverse functions related to the CD44 variants (CD44v) have been reported in various physiological and pathological conditions. The pattern of expression of CD44v among meningioma subtypes was investigated to ascertain whether CD44 variants play a role in a variety of biological processes, such as epithelial differentiation and extracranial metastasis.Methods-Twenty three meningiomas were studied immunohistochemically using novel antibodies directed against CD44 isoforms. Six of the 23 samples were analysed by reverse transcription polymerase chain reaction (RT-PCR), followed by Southern blotting with CD44v specific probes.Results-In meningothelial, fibrous and anaplastic meningiomas, a standard form of CD44 was detected by RT-PCR and was homogeneously expressed in tumour cells when studied immunohistochemically. CD44v was not detected in these subtypes. In secretory meningiomas, however, CD44v isoforms were strongly expressed in the cell clusters that produce secretory granules and also accumulated in the granules. The population of tumour cells immunopositive for CD44v was similar to that which stained with antibodies directed against carcinoembryonic antigen, epithelial membrane antigen and ezrin. On RT-PCR with Southern blotting, only the secretory type showed high level expression of CD44v.Conclusions-CD44v in meningiomas is expressed in relation to tumour cell differentiation towards the epithelial type.

Estrogen regulation of placental angiogenesis and fetal ovarian development during primate pregnancy

During human and nonhuman primate pregnancy, an extensive blood vessel network is established within the villous placenta to support fetal growth and follicles develop within the fetal ovary to provide a pool of oocytes for reproductive function in adulthood. These two important developmental events occur in association with a progressive increase in placental estrogen production and levels. This review will describe the developmental processes required for placental vascularization and fetal follicular maturation and recent studies which show that estrogen has an important role in regulating these events.

A congenital activating mutant of WASp causes altered plasma membrane topography and adhesion under flow in lymphocytes

Leukocytes rely on dynamic actin-dependent changes in cell shape to pass through blood vessels, which is fundamental to immune surveillance. Wiskott-Aldrich Syndrome protein (WASp) is a hematopoietic cell-restricted cytoskeletal regulator important for modulating cell shape through Arp2/3-mediated actin polymerization. A recently identified WASp(I294T) mutation was shown to render WASp constitutively active in vivo, causing increased filamentous (F)-actin polymerization, high podosome turnover in macrophages, and myelodysplasia. The aim of this study was to determine the effect of WASp(I294T) expression in lymphocytes. Here, we report that lymphocytes isolated from a patient with WASp(I294T), and in a cellular model of WASp(I294T), displayed abnormal microvillar architecture, associated with an increase in total cellular F-actin. Microvillus function was additionally altered as lymphocytes bearing the WASp(I294T) mutation failed to roll normally on L-selectin ligand under flow. This was not because of defects in L-selectin expression, shedding, cytoskeletal anchorage, or membranal positioning; however, under static conditions of adhesion, WASp(I294T)-expressing lymphocytes exhibited altered dynamic interaction with L-selectin ligand, with a significantly reduced rate of adhesion turnover. Together, our results demonstrate that WASp(I294T) significantly affects lymphocyte membrane topography and L-selectin-dependent adhesion, which may be linked to defective hematopoiesis and leukocyte function in affected patients.