A heparin-binding protein involved in inhibition of smooth-muscle cell proliferation

Pre-organized landscape of T cell surface

T cell activation is initiated by the recognition of specific antigenic peptides and subsequently accomplished by complex signaling cascades. These aspects have been extensively studied for decades as pivotal factors in the establishment of adaptive immunity. However, how receptors or signaling molecules are organized in the resting state prior to encountering antigens has received less attention. Recent advancements in super-resolution microscopy techniques have revealed topographically controlled pre-formed organization of key molecules involved in antigen recognition and signal transduction on microvillar projections of T cells before activation and substantial effort has been dedicated to characterizing the topological structure of resting T cells over the past decade. This review will summarize our current understanding of how key surface receptors are pre-organized on the T-cell plasma membrane and discuss the potential role of these receptors, which are preassembled prior to ligand binding in the early activation events of T cells.

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.

Moesin Serves as Scaffold Protein for PD-L1 in Human Uterine Cervical Squamous Carcinoma Cells

Immune checkpoint blockade (ICB) therapy targeting the programmed death ligand-1 (PD-L1)/PD-1 axis has emerged as a promising treatment for uterine cervical cancer; however, only a small subset of patients with uterine cervical squamous cell carcinoma (SCC) derives clinical benefit from ICB therapies. Thus, there is an urgent unmet medical need for novel therapeutic strategies to block the PD-L1/PD-1 axis in patients with uterine cervical SCC. Here, we investigated the involvement of ezrin/radixin/moesin (ERM) family scaffold proteins, which crosslink several plasma membrane proteins with the actin cytoskeleton, on the plasma membrane localization of PD-L1 in BOKU and HCS-2 cells derived from human uterine cervical SCC. Immunofluorescence analysis showed that PD-L1 colocalized with all three ERM proteins in the plasma membrane. Gene knockdown of moesin, but not ezrin and radixin, substantially reduced the plasma membrane expression of PD-L1, with limited effect on mRNA expression. An immunoprecipitation assay demonstrated the molecular interaction between PD-L1 and moesin. Moreover, phosphorylated, i.e., activated, moesin was highly colocalized with PD-L1 in the plasma membrane. In conclusion, moesin may be a scaffold protein responsible for the plasma membrane expression of PD-L1 in human uterine cervical SCC.

Membrane-organizing extension spike protein and its role as an emerging biomarker in oral squamous cell carcinoma

Oral squamous cell carcinoma (OSCC) is the most malignant tumor worldwide with a relatively poor prognosis. This can be due to lack of using new specific biomarkers as a mode of pristine interventional therapy for detecting the lesions at an early stage, thereby not allowing it to proceed to a severe advanced stage. Biomarkers, being the products of malignant cells, can prove to be promising prognostic factors in understanding the molecular pathogenesis of oral cancer. One such biomarker is membrane-organizing extension spike protein (MOESIN). Belonging to the family of ezrin/radixin/MOESIN proteins, MOESIN acts as a structural linker between plasma membrane and actin filament of the cell moiety and is involved in regulating many fundamental cellular processes such as cell morphology, adhesion and motility. This narrative review is a systematic compilation on MOESIN and its role as an emerging biomarker in OSCC.

Addition of exogenous proteins detected in oviductal secretions to in vitro culture medium does not improve the efficiency of in vitro fertilization in pigs

This work was designed to study whether HSP70-1A, HSP90α, ezrin or PDI4, proteins previously identified in porcine oviductal secretions, have a role in zona pellucida (ZP) resistance to enzymatic digestion, in vitro fertilization (IVF) and sperm viability. In vitro matured porcine cumulus oocyte complexes were denuded and i) incubated for 1 h in TALP medium supplemented or not with each exogenous oviductal protein and in presence or absence of heparin to assess ZP digestion time by pronase; and ii) inseminated with fresh ejaculated boar spermatozoa in medium supplemented or not with each exogenous oviductal protein to assess their effect on fertilization results. Finally, spermatozoa were incubated in Tyrode's medium (0, 1 and 20 h) supplemented or not with HSP-701A, HSP-90α or ezrin, to assess simultaneously sperm viability and acrosome status by means of flow cytometry. Although all proteins increased the ZP digestion time, this increase was lower than 1 min, being ezrin the protein with a stronger effect. Presence of heparin in the medium reinforced the ZP hardening effect of ezrin and HSP-701A up to one more min, but not HSP-90α nor PDI4. Sperm penetration, but not IVF efficiency, increased when gametes were cocultured in medium containing PDIA4 whereas sperm penetration and polyspermy rates decreased in presence of ezrin and HSP proteins. This reduction was not the result of a detrimental effect of proteins on sperm viability or acrosome reaction. In conclusion, addition of exogenous proteins detected in oviductal secretions to artificial media does not reproduce the effect of adding such secretions nor improve the final efficiency of the porcine IVF system.

ERM Proteins at the Crossroad of Leukocyte Polarization, Migration and Intercellular Adhesion

Ezrin, radixin and moesin proteins (ERMs) are plasma membrane (PM) organizers that link the actin cytoskeleton to the cytoplasmic tail of transmembrane proteins, many of which are adhesion receptors, in order to regulate the formation of F-actin-based structures (e.g., microspikes and microvilli). ERMs also effect transmission of signals from the PM into the cell, an action mainly exerted through the compartmentalized activation of the small Rho GTPases Rho, Rac and Cdc42. Ezrin and moesin are the ERMs more highly expressed in leukocytes, and although they do not always share functions, both are mainly regulated through phosphatidylinositol 4,5-bisphosphate (PIP₂) binding to the N-terminal band 4.1 protein-ERM (FERM) domain and phosphorylation of a conserved Thr in the C-terminal ERM association domain (C-ERMAD), exerting their functions through a wide assortment of mechanisms. In this review we will discuss some of these mechanisms, focusing on how they regulate polarization and migration in leukocytes, and formation of actin-based cellular structures like the phagocytic cup-endosome and the immune synapse in macrophages/neutrophils and lymphocytes, respectively, which represent essential aspects of the effector immune response.

The ezrin-radixin-moesin family of proteins in the regulation of B-cell immune response

Dynamic reorganization of the cortical cytoskeleton is essential for numerous cellular processes, including B- and T-cell activation and migration. The ezrin-radixin-moesin (ERM) family of proteins plays structural and regulatory roles in the rearrangement of plasma membrane flexibility and protrusions through its members' reversible interaction with cortical actin filaments and the plasma membrane. Recent studies demonstrated that ERM proteins not only are involved in cytoskeletal organization but also offer a platform for the transmission of signals in response to a variety of extracellular stimuli through their ability to cross-link transmembrane receptors with downstream signaling components. In this review, we summarize present knowledge relating to ERMs and recent progress made toward elucidating a novel role for them in the regulation of B-cell function in health and disease.

FERM family proteins and their importance in cellular movements and wound healing (review)

Motility is a requirement for a number of biological processes, including embryonic development, neuronal development, immune responses, cancer progression and wound healing. Specific to wound healing is the migration of endothelial cells, fibroblasts and other key cellular players into the wound space. Aberrations in wound healing can result in either chronic wounds or abnormally healed wounds. The protein 4.1R, ezrin, radixin, moesin (FERM) superfamily consists of over 40 proteins all containing a three lobed N-terminal FERM domain which binds a variety of cell-membrane associated proteins and lipids. The C-terminal ends of these proteins typically contain an actin-binding domain (ABD). These proteins therefore mediate the linkage between the cell membrane and the actin cytoskeleton, and are involved in cellular movements and migration. Certain FERM proteins have been shown to promote cancer metastasis via this very mechanism. Herein we review the effects of a number of FERM proteins on wound healing and cancer. We show how these proteins typically aid wound healing through their effects on increasing cellular migration and movements, but also typically promote metastasis in cancer. We conclude that FERM proteins play important roles in cellular migration, with markedly different outcomes in the context of cancer and wound healing.

Expression of moesin and CD44 is associated with poor prognosis in gastric adenocarcinoma

AIMS

CD44 has been reported as a negative prognostic marker in gastric cancer. It interacts with moesin in epithelial-mesenchymal transition. To date, to our knowledge, there has been no clinical study dealing with the relationship between moesin and gastric adenocarcinoma. We analysed the expression of moesin and CD44 in gastric adenocarcinoma tissue, and correlations with clinicopathological factors.

METHODS AND RESULTS

A retrospective analysis was made of 430 patients who had undergone gastrectomy at the Korea University Guro Hospital between 2002 and 2005 for gastric adenocarcinoma. Using tissue microarray and immunohistochemical staining, moesin expression was observed in 192 (44.7%) cases; it was associated significantly with poorly differentiated histology, invasion depth, lymph node metastasis, lymphatic invasion and advanced pathological TNM stage. CD44 expression was not correlated with clinicopathological features or moesin expression. Moesin expression was a strong predictor of lymph node metastasis in logistic regression analysis. Both moesin expression and CD44 expression were associated significantly with poor overall survival in univariate analysis. Furthermore, in multivariate analysis, moesin and CD44 were independent markers of poor prognosis, along with pathological TNM stage and older patient age.

CONCLUSION

Moesin expression and CD44 expression might be useful markers of poor prognosis in gastric adenocarcinoma.

Anti-moesin antibodies derived from patients with aplastic anemia stimulate monocytic cells to secrete TNF-alpha through an ERK1/2-dependent pathway

Antibodies specific to moesin, which are frequently detectable in the serum of patients with aplastic anemia (AA), can induce tumor necrosis factor-alpha (TNF-alpha) secretion from monocytes and a human monocytic leukemia cell line THP-1. We investigated the mechanisms responsible for TNF-alpha secretion from monocytic cells induced by the auto-antibodies that are purified from the sera of AA patients. TNF-alpha induction by anti-moesin antibodies depended on the amount of cell surface moesin expressed by THP-1 cells. F(ab')(2) fragments prepared from the anti-moesin antibodies were able to stimulate THP-1 cells to secrete TNF-alpha and this stimulatory effect was enhanced by cross-linking of moesins with anti-human IgG F(ab')(2) fragment antibodies. Anti-moesin antibodies as well as their F(ab')(2) fragments induced the phosphorylation of ERK1/2 in monocytic cells and this effect was suppressed by the addition of an ERK1/2 inhibitor. Moreover, anti-moesin antibody treatment induced the phosphorylation of moesin proteins in the monocytes and THP-1 cells within 30 min. These results indicate that anti-moesin antibodies induce TNF-alpha secretion from monocytes through the activation of the ERK1/2 pathway provoked by direct binding to moesin on the cells.

Moesin-dependent cytoskeleton remodelling is associated with an anaplastic phenotype of pancreatic cancer

Cell motility is controlled by the dynamic cytoskeleton and its related proteins, such as members of the ezrin/radixin/moesin (ERM) family, which act as signalling molecules inducing cytoskeleton remodelling. Although ERM proteins have been identified as important factors in various malignancies, functional redundancy between these proteins has hindered the dissection of their individual contribution. The aim of the present study was to analyse the functional role of moesin in pancreatic malignancies. Cancer cells of different malignant lesions of human and transgenic mice pancreata were evaluated by immunohistochemistry. For functional analysis, cell growth, adhesion and invasion assays were carried out after transient and stable knock-down of moesin expression in pancreatic cancer cells. In vivo tumourigenicity was determined using orthotopic and metastatic mouse tumour models. We now show that moesin knock-down increases migration, invasion and metastasis and influences extracellular matrix organization of pancreatic cancer. Moesin-regulated migratory activities of pancreatic cancer cells were in part promoted through cellular translocation of β-catenin, and re-distribution and organization of the cytoskeleton. Analysis of human and different transgenic mouse pancreatic cancers demonstrated that moesin is a phenotypic marker for anaplastic carcinoma, suggesting that this ERM protein plays a specific role in pancreatic carcinogenesis.

The preventive effects of heparin-superoxide dismutase on carbon tetrachloride-induced acute liver failure and hepatic fibrosis in mice

In this study, the effects of heparin-superoxide dismutase conjugate (heparin-SOD) on carbon tetrachloride (CCl4)-induced acute liver failure and hepatic fibrosis were evaluated. To investigate the effects of heparin-SOD on acute liver failure, heparin-SOD was administered to CCl4-treated mice by intravenous injection. Biochemical indicators, such as glutamic oxaloacetic transaminase/glutamic pyruvic transaminase (GOT/GPT), GSH (glutathione), lactate dehydrogenase (LDH), and malondialdehyde (MDA) were determined 24 h after CCl4 treatment. The development of CCl4-induced acute liver failure altered the redox state with a decreased hepatic GSH and increased formation of lipid peroxidative products, which were partially normalized by treatment with heparin-SOD or heparin + SOD. Compared with other groups, the acute liver injury of heparin-SOD group was significantly lessened (reduced activities of GOT/GPT, MDA, and increased activities of GSH). To investigate the effects of heparin-SOD on hepatic fibrosis, heparin-SOD and CCl4 were co-administered by intraperitoneal injection twice a week for 12 weeks. Histological and hepatic hydroxyproline examination revealed that heparin-SOD could significantly prevent the progression of hepatic fibrosis. Moreover, real-time PCR was used to determine transforming growth factor-beta1 (TGF-beta1), metalloproteinase-2 (MMP-2), fibronectin, and collagen-I expression. Significantly, greater fibrosis and TGF-beta1, MMP-2, fibronectin, and collagen-I expression were found in the liver of CCl4-induced mice at the end of 12th week. Heparin-SOD could markedly attenuate the mRNA expression of TGF-beta1, MMP-2, and collagen-I. Western blots of tissue homogenates revealed that the protein expression of TGF-beta1 was substantially reduce also by heparin-SOD treatment. These results demonstrate that administration of heparin-SOD may be useful in the treatment and prevention of acute liver failure and hepatic fibrosis.

Disturbed colocalization of multidrug resistance protein 2 and radixin in human cholestatic liver diseases

BACKGROUND AND AIM

Endocytic retrieval of multidrug resistance protein 2 (MRP2) is closely associated with cholestasis and may be attributed to the disturbed linking of MRP2 and radixin, a cross-linker between actin filaments and membrane proteins. This study aimed to investigate the role of radixin in the altered localization of MRP2 in various human cholestatic liver diseases.

METHODS

Using immunofluorescence microscopy, we investigated the localization and expression of MRP2 and radixin in various cholestatic liver diseases, such as drug-induced liver injury, obstructive jaundice, primary sclerosing cholangitis and autoimmune hepatitis. Changes in localization and expression were analyzed using Scion Image (software).

RESULTS

In the icteric drug-induced liver injury, MRP2 was localized outside as well as inside of ZO-1 staining, indicating endocytic retrieval from the canalicular membrane into the pericanalicular compartments of the hepatocytes. The colocalization of MRP2 and radixin observed in the controls was disturbed, and MRP2 fluorescence disappeared in the canaliculi with disrupted radixin staining. Disturbed colocalization of MRP2 and radixin as well as endocytic retrieval of MRP2 was found in the poorly drained obstructive jaundice. When drainage was good, MRP2 was exclusively colocalized with radixin. Similar findings were observed in autoimmune hepatitis and primary sclerosing cholangitis. In the controls, the immunostaining intensity curves for MRP2 and radixin were steeply elevated in the canaliculi. The intensity curves for MRP2 and radixin were broadened in the icteric drug-induced liver injury and poorly drained obstructive jaundice, indicating endocytic retrieval into the hepatocytes. The peak fluorescence intensities for MRP2 and radixin decreased in the icteric liver.

CONCLUSION

Disturbed colocalization of MRP2 and radixin was common in various cholestatic liver diseases, which may be associated with endocytic retrieval of MRP2 due to failure in anchoring MRP2 in the canalicular membrane.

The role of radixin in altered localization of canalicular conjugate export pump Mrp2 in cholestatic rat liver

AIM

Cholestasis has been associated with the endocytic retrieval of multidrug resistance protein 2 (Mrp2), but its mechanism is still unclear. Recent studies have indicated that radixin, a cross-linker between the actin filaments and membrane proteins, may be activated by phosphorylation and may be required for the canalicular localization of Mrp2.

METHODS

We investigated the role of radixin in the altered localization of Mrp2 in rat models of intrahepatic (ethinyl estradiol treatment) and extrahepatic (bile duct ligation) cholestasis using immunofluorescence microscopy. The changes in localization and expression were analyzed using Scion Image for Windows.

RESULTS

In both models, Mrp2 was localized outside as well as inside the ZO-1 staining, indicating partial dislocation from the canalicular membrane. In contrast to the steep elevation of the immunostaining intensity curves for Mrp2 in the controls, the corresponding curves in both models were broadened and flattened, confirming endocytic retrieval into the hepatocytes. Mrp2 and radixin were colocalized at the canalicular domain in the controls, whereas in both cholestatic rats they were dissociated at some canaliculi, indicating the disturbed colocalization of Mrp2 and radixin in cholestasis. The fluorescence of phosphorylated radixin, an active form of radixin, markedly decreased in both cholestatic models, which was supported by the reduced peak fluorescence intensities.

CONCLUSION

The disturbed colocalization of Mrp2 and radixin may contribute to the endocytic retrieval of Mrp2 in cholestasis due to the failure to anchor Mrp2 in the canalicular membrane, in which the phosphorylated radixin may play a major role.

Identification of proteins released by mammalian cells that mediate DNA internalization through proteoglycan-dependent macropinocytosis

Naked DNA plasmid represents the simplest vehicle for gene therapy and DNA-based vaccination purposes; however, the molecular mechanisms of DNA uptake in mammalian cells are poorly understood. Here, we show that naked DNA uptake occurs via proteoglycan-dependent macropinocytosis, thus challenging the concept of a specific DNA-internalizing receptor. Cells genetically deficient in proteoglycans, which constitute a major source of cell-surface polyanions, exhibited substantially decreased uptake of likewise polyanionic DNA. The apparent paradox was explained by the action of DNA-transporting proteins present in conditioned medium. Complexes between these proteins and DNA require proteoglycans for cellular entry. Mass spectrometry analysis of cell medium components identified several proteins previously shown to associate with DNA and to participate in membrane transport of macromolecular cargo. The major pathway for proteoglycan-dependent DNA uptake was macropinocytosis, whereas caveolae-dependent and clathrin-dependent pathways were not involved, as determined by using caveolin-1 knock-out cells, dominant-negative constructs for dynamin and Eps15, and macropinocytosis-disruptive drugs, as well as confocal fluorescence co-localization studies. Importantly, a significant fraction of internalized DNA was translocated to the nucleus for expression. Our results provide novel insights into the mechanism of DNA uptake by mammalian cells and extend the emerging role of proteoglycans in macromolecular transport.

The expression of ezrin in NPC and its interaction with NGX6, a novel candidate suppressor

Ezrin, the linker between membrane protein and cytoskeleton, plays an important role in the cellular morphology, cytoskeleton reorganization, adhesion, invasion and metastasis. In this study, ezrin was found to express in high levels either in nasopharyngeal carcinoma tissues or in nasopharyngeal carcinoma 5-8F cells and the knockdown of ezrin expression in the 5-8F cells by RNA interferance could reduce invasive ability, suggesting that ezrin is involved in the progression and invasion of nasopharyngeal carcinoma. Nasopharyngeal carcinoma-associated gene 6 is a novel candidate suppressor gene of tumor metastasis, which was originally cloned in nasopharyngeal carcinoma high-frequency heterozygosity loss region 9p21-22 and is down-regulated in nasopharyngeal carcinoma. In the present study, we hypothesize that nasopharyngeal carcinoma-associated gene 6 plays an inhibitory role in the migration and invasion of nasopharyngeal carcinoma cells via modulating the function of ezrin. Firstly, different mutants of NGX6 were constructed and transfected into nasopharyngeal carcinoma 5-8F cells. The invasion and migration of 5-8F cells overexpressing nasopharyngeal carcinoma-associated gene 6 or mutants were measured. The results showed that enhanced expression of nasopharyngeal carcinoma-associated gene 6 could reduce invasive and migratory abilities of 5-8F cells, and the cytoplasmic domain was essential for nasopharyngeal carcinoma-associated gene 6 to modulate cell migration and invasion. Further experiment results showed that nasopharyngeal carcinoma-associated gene 6 protein was associated with ezrin by its cytoplasm region, and it could down-regulate the expression level of ezrin. These results demonstrated that nasopharyngeal carcinoma-associated gene 6 was probably involved in the modulation of invasive and adhesive ability of nasopharyngeal carcinoma cells by down-regulating the expression level of ezrin.

The nuclear receptor hepatocyte nuclear factor 4alpha acts as a morphogen to induce the formation of microvilli

Microvilli are actin-based organelles found on apical plasma membranes that are involved in nutrient uptake and signal transduction. Numerous components, including ezrin/radixin/moesin (ERM) proteins, have been identified that link filamentous actins to transmembrane proteins, but the signals driving microvillus biogenesis are not known. In this study, we show that the conditional and/or ectopic expression of a nuclear receptor, hepatocyte nuclear factor 4α (HNF4α), triggers microvillus morphogenesis. We also demonstrate that HNF4α expression induces ERM-binding phosphoprotein 50 (EBP50) expression and that attenuation of EBP50 using RNA interference inhibits microvillus development. We conclude that HNF4α acts as a morphogen to trigger microvillus formation.

Identification of a novel Ezrin-binding site in syndecan-2 cytoplasmic domain

ERM (Ezrin/Radixin/Moesin) proteins are crosslinkers between plasma membrane proteins and the actin cytoskeleton, thereby involved in the formation of cell adhesion sites. Earlier work showed that Ezrin links syndecan-2 to the actin cytoskeleton. Here we provide evidence that the Ezrin N-terminal domain binds to the syndecan-2 cytoplasmic domain with an estimated K(D) of 0.71 microM and without the requirement of other proteins. We also studied the regions in the syndecan-2 cytoplasmic domain implicated in the binding to Ezrin. By truncating the syndecan-2 cytoplasmic domain and by oligopeptide competition assays we show that the Ezrin-binding sequence is not located in the positively charged juxtamembrane region (RMRKK), but in the neighboring sequence DEGSYD. We therefore conclude that the consensus sequence for Ezrin binding is unique among membrane proteins, suggesting a distinct regulation.

Shifts in cellular localization of moesin in normal oral epithelium, oral epithelial dysplasia, verrucous carcinoma and oral squamous cell carcinoma

BACKGROUND

Moesin, a member of ERM (ezrin/radixin/moesin) family, links actin filaments of cell surface structure to the cell membrane. The purpose of the study is to assess the shifts in cellular distribution of moesin in normal oral epithelium, oral epithelial dysplasia (OED), verrucous carcinoma (VC), and oral squamous cell carcinoma (OSCC).

METHODS

The expression of moesin was evaluated immunohistochemically in paraffin-embedded tissues of 59 specimens of OSCC, 35 specimens of OED, 17 specimens of VC, and five specimens of normal oral epithelium.

RESULTS

In the normal oral epithelia, all specimens showed a pattern of membranous expression against the anti-moesin antibody in the basal layer cells. In the OED specimens, moesin was dominantly expressed in the cell membrane except for the cornified layer. In VC and OSCC specimens, almost the whole of the carcinoma cells were stained with anti-moesin antibody. However, in OSCC samples, moesin was markedly expressed increasingly in the cytoplasm and decreasingly in the cell membrane, as compared with OED and VC. In addition, there was a significant correlation between the pattern of moesin expression and tumor differentiation in OSCC.

CONCLUSIONS

Our results suggest that it is useful to detect the moesin expression as adjunct to screening mucosal lesions in the oral cavity.

Kidney Na+,K(+)-ATPase is associated with moesin

Na+,K(+)-ATPase is a ubiquitous plasmalemmal membrane protein essential for generation and maintenance of transmembrane Na+ and K+ gradients in virtually all animal cell types. Activity and polarized distribution of renal Na+,(+)-ATPase appears to depend on connection of ankyrin to the spectrin-based membrane cytoskeleton as well as on association with actin filaments. In a previous study we showed copurification and codistribution of renal Na+,K(+)-ATPase not only with ankyrin, spectrin and actin, but also with two further peripheral membrane proteins, pasin 1 and pasin 2. In this paper we show by sequence analysis through mass spectrometry as well as by immunoblotting that pasin 2 is identical to moesin, a member of the FERM (protein 4.1, ezrin, radixin, moesin) protein family, all members of which have been shown to serve as cytoskeletal adaptor molecules. Moreover, we show that recombinant full-length moesin as well as its FERM domain bind to Na+,K(+)-ATPase and that this binding can be inhibited by an antibody specific for the ATPase activity-containing cytoplasmic loop (domain 3) of the Na+,K(+)-ATPase alpha-subunit. This loop has been previously shown to be a site essential for ankyrin binding. These observations indicate that moesin might not only serve as direct linker molecule of Na+,K(+)-ATPase to actin filaments but also modify ankyrin binding at domain 3 of Na+,K(+)-ATPase in a way similar to protein 4.1 modifying the binding of ankyrin to the cytoplasmic domain of the erythrocyte anion exchanger (AE1).

Membrane-bound heparin binding proteins from HL-60 cells purified in a two-step affinity chromatography differentially eluted with divalent cations

Solubilized membrane proteins from HL-60 cells were separated by two-step affinity chromatography. Proteins eluted with MgCl2 in the first heparin-gel were applied to the second heparin-gel and eluted with CaCl2. The eluted proteins were analysed and purified by electrophoresis. N-terminal amino acid sequences of eight proteins on the characteristic bands were determined. Homology search for the sequences indicated that three microsomal proteins, two nuclear proteins and a glycolytic enzyme were eluted with divalent cations, whereas a nuclear ribonucleoprotein and a membrane-cytoskelton linker protein were not dissociated with divalent cations, but with 2 M NaCl. Heparin affinity chromatography combined with differential elution with divalent cations can be a useful method for separation of membrane proteins.

ERM proteins and merlin: integrators at the cell cortex

A fundamental property of many plasma-membrane proteins is their association with the underlying cytoskeleton to determine cell shape, and to participate in adhesion, motility and other plasma-membrane processes, including endocytosis and exocytosis. The ezrin-radixin-moesin (ERM) proteins are crucial components that provide a regulated linkage between membrane proteins and the cortical cytoskeleton, and also participate in signal-transduction pathways. The closely related tumour suppressor merlin shares many properties with ERM proteins, yet also provides a distinct and essential function.

Characterization of a novel intracellular heparanase that has a FERM domain

The catabolism of cell-surface heparan sulphate proteoglycans is initiated by endosomal heparanases, which are endoglycosidases that cleave the glycosaminoglycans off core proteins and degrade them to shorter oligosaccharides. We have purified previously four intracellular heparanase activities from Chinese hamster ovary (CHO) cells [Bame, Hassall, Sanderson, Venkatesan and Sun (1998) Biochem. J. 336, 191-200], and in the present study we characterize further the most abundant activity (C1A heparanase). This enzyme purifies as a family of 37-48 kDa proteins from both CHO cells and the rat liver, with the major species being 37 and 40 kDa. Amino acid sequence analysis shows the purified C1A heparanase protein is highly homologous with the N-terminal domain, or FERM domain, of the approximately 80 kDa proteins ezrin, radixin and moesin (ERM proteins, after ezrin-radixin-moesin). This domain, which is also found in erythrocyte protein 4.1, links cytoplasmic proteins to membranes. Antibodies against the FERM domain recognize all the C1A heparanase proteins on Western blots, suggesting that the smaller species are derived from a larger protein. Activity binds to, and is affected by, molecules known to interact with FERM domains, supporting the hypothesis that the intracellular C1A heparanase is the purified FERM domain protein. Since bacterially expressed FERM domains of radixin and moesin lack heparanase activity, and some tryptic peptides generated from the enzyme do not have a match in any ERM protein, it appears that, rather than being derived from ezrin, radixin or moesin, C1A heparanase may be a new member of the FERM domain family.

Distinct cell type-specific expression of scaffolding proteins EBP50 and E3KARP: EBP50 is generally expressed with ezrin in specific epithelia, whereas E3KARP is not

The ezrin/radixin/moesin (ERM) proteins are regulated microfilament membrane linking proteins. Previous tissue localization studies have revealed that the three related proteins show distinct tissue distributions, with ezrin being found predominantly in polarized epithelial cells, whereas moesin is enriched in endothelial cells and lymphocytes. EBP50 and E3KARP are two related scaffolding proteins that bind to the activated form of ERM proteins in vitro, and through their PDZ domains to the cytoplasmic domains of specific membrane proteins, including the Na+/H+ exchanger isoform (NHE3) present in kidney proximal tubules and the beta2-adrenergic receptor. Using specific antibodies to EBP50 and E3KARP for localization in murine tissues, we find that the cellular distribution of EBP50 and E3KARP is mutually exclusive. Epithelial cells expressing ezrin generally co-express EBP50, such as intestinal epithelial cells, gastric parietal cells, the epithelial cells of the kidney proximal tubule, the terminal bronchiole of the lung, and in mesothelia. This correlation is not absolute as cells of the mucous epithelium of the stomach and in the renal corpuscle, express ezrin but no detectable EBP50, whereas the bile canaliculi of hepatocytes express EBP50 and not ezrin. E3KARP has a restricted tissue distribution with the highest expression being found in lung. It is largely colocalized with moesin and radixin, especially in the alveoli of the lung, as well as being highly enriched in the renal corpuscle. These results document a preference for co-expression of EBP50, but not E3KARP, with ezrin in polarized epithelia. These results place constraints on the physiological roles that can be proposed for these scaffolding molecules.

Localized Activation of m-Calpain in Human Umbilical Vein Endothelial Cells Upon Hypoxia

Bleb formation is an early event of cellular damage observed in a variety of cell types upon hypoxia. Although we previously found the appearance of the localized cytoplasmic ionized Ca(2+) concentration ([Ca(2+)](i)) rise before bleb formation at the same loci of human umbilical vein endothelial cell (HUVEC) upon hypoxia, the mode of [Ca(2+)](i)-rise-induced cytoskeletal alteration remains ill-defined. The aim of this study is to clarify the mechanisms causing bleb formation after localized [Ca(2+)](i) rise. We studied the activation of m-calpain associated with the alteration of cytoskeleton-related proteins, F-actin, mu-actin, or ezrin by employing specific antibodies in conjunction with a confocal laser scanning microscopy (CLSM). Specific antibodies against 80-kDa-preactivated and 78-kDa-activated m-calpain clearly demonstrated redistribution of 80-kDa m-calpain followed by autoproteolytic activation of m-calpain to the 78-kDa form at the same loci of [Ca(2+)](i) rise in hypoxia-treated HUVECs, which was associated with the decrease of ezrin and the localized appearance of beta-actin at the same loci. In conclusion, hypoxia-induced localized [Ca(2+)](i) rise causes bleb formation at the same loci through m-calpain-catalyzed destruction of cross-linking between plasma membrane and actin filaments.

ERM-Merlin and EBP50 protein families in plasma membrane organization and function

The ezrin-radixin-moesin (ERM) family of proteins have emerged as key regulatory molecules in linking F-actin to specific membrane proteins, especially in cell surface structures. Merlin, the product of the NF2 tumor suppressor gene, has sequence similarity to ERM proteins and binds to some of the same membrane proteins, but lacks a C-terminal F-actin binding site. In this review we discuss how ERM proteins and merlin are negatively regulated by an intramolecular association between their N- and C-terminal domains. Activation of at least ERM proteins can be accomplished by C-terminal phosphorylation in the presence of PIP2. We also discuss membrane proteins to which ERM and merlin bind, including those making an indirect linkage through the PDZ-containing adaptor molecules EBP50 and E3KARP. Finally, the function of these proteins in cortical structure, endocytic traffic, signal transduction, and growth control is discussed.

Cell surface-expressed moesin-like receptor regulates T cell interactions with tissue components and binds an adhesion-modulating IL-2 peptide generated by elastase

The adhesion of leukocytes to the extracellular matrix (ECM) depends on their responses to variations in the chemotactic signals in their milieu, as well as on the functioning of cytoskeletal and context-specific receptors. Ezrin, radixin, and moesin constitute a family of proteins that link the plasma membrane to the actin cytoskeleton. The surface expression of moesin on T cells and its role in cell adhesion has not been fully elucidated. Recently, we found that IL-2 peptides generated by elastase modified the adhesion of activated T cells to ECM ligands. Here, we further examined the adhesion regulatory effects of EFLNRWIT, one of the IL-2 peptides, as well as the existence and putative function of its receptor on T cells. We found that when presented to T cells in the absence of another activator, the EFLNRWIT peptide induced cell adhesion to vessel wall and ECM components. Binding of a radiolabeled peptide to T cells, precipitation with the immobilized peptide, and amino acid sequencing of the precipitated protein revealed that EFLNRWIT exerts its function via a cell surface-expressed moesin-like moiety, whose constitutive expression on T cells was increased after activation. This notion was further supported by our findings that: 1) anti-moesin mAb inhibited the binding of T cells to the immobilized EFLNRWIT peptide, 2) immobilized recombinant moesin bound the IL-2 peptide, and 3) soluble moesin inhibited the EFLNRWIT-induced T cell adhesion to fibronectin. Interestingly, moesin appears to be generally involved in T cell responses to adhesion-regulating signals. Thus, the IL-2 peptide EFLNRWIT appears to exert its modulating capacities via an adhesion-regulating moesin-like receptor.

Regulation of the cytoskeleton and cell adhesion by the Rho family GTPases in mammalian cells

Members of the Rho family of small Ras-like GTPases--including RhoA, -B, and -C, Rac1 and -2, and Cdc42--exhibit guanine nucleotide-binding activity and function as molecular switches, cycling between an inactive GDP-bound state and an active GTP-bound state. The Rho family GTPases participate in regulation of the actin cytoskeleton and cell adhesion through specific targets. Identification and characterization of these targets have begun to clarify how the Rho family GTPases act to regulate cytoskeletal structure and cell-cell and cell-substratum contacts in mammalian cells. The Rho family GTPases are also involved in regulation of smooth muscle contraction, cell morphology, cell motility, neurite retraction, and cytokinesis. However, the molecular mechanisms by which the Rho family GTPases participate in the regulation of such processes are not well established.

Activities of the EM10 protein from Echinococcus multilocularis in cultured mammalian cells demonstrate functional relationships to ERM family members

The ezrin-radixin-moesin (ERM) homolog EM10 is expressed by the larval stage of the parasite E. multilocularis and shows 46.9% overall identity in the primary structure with human ezrin. To determine whether EM10 has similar activities to ERM proteins, we investigated properties of the protein expressed in mammalian cells. In particular, we transiently expressed haemagglutinin-tagged (HA-tagged) versions of the full-length EM10 as well as the amino- and the carboxy-terminal halves of EM10 in HtTA-1 cells. In addition we stably transfected NIH-3T3 cells with untagged full-length EM10. The data demonstrate that EM10 polypeptides behave like their corresponding portions of radixin when transiently expressed in mammalian cells. The full-length and amino-terminal EM10 polypeptides were localized to cortical structures. Cells expressing the carboxy-terminal polypeptide of EM10 showed long actin-filled protrusions. Cells expressing full-length EM10 showed a reduction in endogenous moesin-staining at cortical structures. In stably transfected NIH-3T3 cells EM10 was not crisply localized but rather was diffuse throughout the cytoplasm. These cells showed a conspicuous loss of stress-fibers, a phenotype that was not seen in analogous experiments with ERM proteins. The results demonstrate both similarities and differences between the functional properties of EM10 and ERM proteins expressed in vertebrate cells.

The tyrosine kinase PYK-2/RAFTK regulates natural killer (NK) cell cytotoxic response, and is translocated and activated upon specific target cell recognition and killing

The compartmentalization of plasma membrane proteins has a key role in regulation of lymphocyte activation and development of immunity. We found that the proline-rich tyrosine kinase-2 (PYK-2/RAFTK) colocalized with the microtubule-organizing center (MTOC) at the trailing edge of migrating natural killer (NK) cells. When polyclonal NK cells bound to K562 targets, PYK-2 translocated to the area of NK-target cell interaction. The specificity of this process was assessed with NK cell clones bearing activatory or inhibitory forms of CD94/NKG2. The translocation of PYK-2, MTOC, and paxillin to the area of NK-target cell contact was regulated upon specific recognition of target cells through NK cell receptors, controlling target cell killing. Furthermore, parallel in vitro kinase assays showed that PYK-2 was activated in response to signals that specifically triggered its translocation and NK cell mediated cytotoxicity. The overexpression of both the wt and a dominant-negative mutant of PYK-2, but not ZAP-70 wt, prevented the specific translocation of the MTOC and paxillin, and blocked the cytotoxic response of NK cells. Our data indicate that subcellular compartmentalization of PYK-2 correlates with effective signal transduction. Furthermore, they also suggest an important role for PYK-2 on the assembly of the signaling complexes that regulate the cytotoxic response.

Polarization and interaction of adhesion molecules P-selectin glycoprotein ligand 1 and intercellular adhesion molecule 3 with moesin and ezrin in myeloid cells

In response to the chemoattractants interleukin 8, C5a,N-formyl-methionyl-leucyl-phenylalanine, and interleukin 15, adhesion molecules P-selectin glycoprotein ligand 1 (PSGL-1), intercellular adhesion molecule 3 (ICAM-3), CD43, and CD44 are redistributed to a newly formed uropod in human neutrophils. The adhesion molecules PSGL-1 and ICAM-3 were found to colocalize with the cytoskeletal protein moesin in the uropod of stimulated neutrophils. Interaction of PSGL-1 with moesin was shown in HL-60 cell lysates by isolating a complex with glutathione S-transferase fusions of the cytoplasmic domain of PSGL-1. Bands of 78- and 81-kd were identified as moesin and ezrin by Western blot analysis. ICAM-3 and moesin also coeluted from neutrophil lysates with an anti-ICAM-3 immunoaffinity assay. Direct interaction of the cytoplasmic domains of ICAM-3 and PSGL-1 with the amino-terminal domain of recombinant moesin was demonstrated by protein-protein binding assays. These results suggest that the redistribution of PSGL-1 and its association with intracellular molecules, including the ezrin-radixin-moesin actin-binding proteins, regulate functions mediated by PSGL-1 in leukocytes stimulated by chemoattractants.

Polarization and interaction of adhesion molecules P-selectin glycoprotein ligand 1 and intercellular adhesion molecule 3 with moesin and ezrin in myeloid cells

In response to the chemoattractants interleukin 8, C5a,N-formyl-methionyl-leucyl-phenylalanine, and interleukin 15, adhesion molecules P-selectin glycoprotein ligand 1 (PSGL-1), intercellular adhesion molecule 3 (ICAM-3), CD43, and CD44 are redistributed to a newly formed uropod in human neutrophils. The adhesion molecules PSGL-1 and ICAM-3 were found to colocalize with the cytoskeletal protein moesin in the uropod of stimulated neutrophils. Interaction of PSGL-1 with moesin was shown in HL-60 cell lysates by isolating a complex with glutathione S-transferase fusions of the cytoplasmic domain of PSGL-1. Bands of 78- and 81-kd were identified as moesin and ezrin by Western blot analysis. ICAM-3 and moesin also coeluted from neutrophil lysates with an anti-ICAM-3 immunoaffinity assay. Direct interaction of the cytoplasmic domains of ICAM-3 and PSGL-1 with the amino-terminal domain of recombinant moesin was demonstrated by protein-protein binding assays. These results suggest that the redistribution of PSGL-1 and its association with intracellular molecules, including the ezrin-radixin-moesin actin-binding proteins, regulate functions mediated by PSGL-1 in leukocytes stimulated by chemoattractants.

Rho GTPases control migration and polarization of adhesion molecules and cytoskeletal ERM components in T lymphocytes

Motile lymphocytes adopt a polarized morphology with different adhesion molecules (ICAM, CD43 and CD44) and ERM actin-binding proteins concentrated on the uropod, a slender posterior appendage with important functions in cell-cell interactions and lymphocyte recruitment. We have studied the role of Rho family of GTPases (Rho, Rac and Cdc42) in the control of lymphocyte polarity and migration by analyzing the effects of exogenously introduced Rho GTPase mutants. Transfection of T cell lines that constitutively display a polarized motile morphology with activated mutants of RhoA, Rac1 and Cdc42 impaired cell polarization. A guanosine nucleotide exchange factor for Rac, Tiam-1, induced the same effect as activated Rac1. Conversely, dominant negative forms of the three GTP-binding proteins induced a polarized phenotype in constitutively round-shaped T cells with redistribution of ICAM-3 and moesin to the uropod in an integrin-dependent manner. On the other hand, overexpression of dominant negative Cdc42 and activated mutants of all three Rho GTPases significantly inhibited SDF-1alpha-induced T cell chemotaxis. Together, these data demonstrate that Rho GTPases regulate lymphocyte polarization and chemokine-induced migration, and underscore the key role of Cdc42 in lymphocyte directional migration.

C, Mérida I, Sánchez-Madrid F. Involvement of Phosphatidylinositol 3-Kinase in Stromal Cell-Derived Factor-1α-Induced Lymphocyte Polarization and Chemotaxis

The role of phosphatidylinositol 3-kinase (PI3-kinase), an important enzyme involved in signal transduction events, has been studied in the polarization and chemotaxis of lymphocytes induced by the chemokine stromal cell-derived factor-1α (SDF-1α). This chemokine was able to directly activate p85/p110 PI3-kinase in whole human PBL and to induce the association of PI3-kinase to the SDF-1α receptor, CXCR4, in a pertussis toxin-sensitive manner. Two unrelated chemical inhibitors of PI3-kinase, wortmannin and Ly294002, prevented ICAM-3 and ERM protein moesin polarization as well as the chemotaxis of PBL in response to SDF-1α. However, they did not interfere with the reorganization of either tubulin or the actin cytoskeleton. Moreover, the transient expression of a dominant negative form of the PI3-kinase 85-kDa regulatory subunit in the constitutively polarized Peer T cell line inhibited ICAM-3 polarization and markedly reduced SDF-1α-induced chemotaxis. Conversely, overexpression of a constitutively activated mutant of the PI3-kinase 110-kDa catalytic subunit in the round-shaped PM-1 T cell line induced ICAM-3 polarization. These results underline the role of PI3-kinase in the regulation of lymphocyte polarization and motility and indicate that PI3-kinase plays a selective role in the regulation of adhesion and ERM proteins redistribution in the plasma membrane of lymphocytes.

Regulation of F-actin binding to platelet moesin in vitro by both phosphorylation of threonine 558 and polyphosphatidylinositides

Activation of human platelets with thrombin transiently increases phosphorylation at (558)threonine of moesin as determined with phosphorylation state-specific antibodies. This specific modification is completely inhibited by the kinase inhibitor staurosporine and maximally promoted by the phosphatase inhibitor calyculin A, making it possible to purify the two forms of moesin to homogeneity. Blot overlay assays with F-actin probes labeled with either [32P]ATP or 125I show that only phosphorylated moesin interacts with F-actin in total platelet lysates, in moesin antibody immunoprecipitates, and when purified. In the absence of detergents, both forms of the isolated protein are aggregated. Phosphorylated, purified moesin co-sediments with alpha- or beta/gamma-actin filaments in cationic, but not in anionic, nonionic, or amphoteric detergents. The interaction affinity is high (Kd, approximately 1.5 nM), and the maximal moesin:actin stoichiometry is 1:1. This interaction is also observed in platelets extracted with cationic but not with nonionic detergents. In 0.1% Triton X-100, F-actin interacts with phosphorylated moesin only in the presence of polyphosphatidylinositides. Thus, both polyphosphatidylinositides and phosphorylation can activate moesin's high-affinity F-actin binding site in vitro. Dual regulation by both mechanisms may be important for proper cellular control of moesin-mediated linkages between the actin cytoskeleton and the plasma membrane.

Immunofluorescence detection of ezrin/radixin/moesin (ERM) proteins with their carboxyl-terminal threonine phosphorylated in cultured cells and tissues

Ezrin/radixin/moesin (ERM) proteins are thought to play an important role in organizing cortical actin-based cytoskeletons through cross-linkage of actin filaments with integral membrane proteins. Recent in vitro biochemical studies have revealed that ERM proteins phosphorylated on their COOH-terminal threonine residue (CPERMs) are active in their cross-linking activity, but this has not yet been evaluated in vivo. To immunofluorescently visualize CPERMs in cultured cells as well as tissues using a mAb specific for CPERMs, we developed a new fixation protocol using trichloroacetic acid (TCA) as a fixative. Immunoblotting analyses in combination with immunofluorescence microscopy showed that TCA effectively inactivated soluble phosphatases, which maintained the phosphorylation level of CPERMs during sample processing for immunofluorescence staining. Immunofluorescence microscopy with TCA-fixed samples revealed that CPERMs were exclusively associated with plasma membranes in a variety of cells and tissues, whereas total ERM proteins were distributed in both the cytoplasm and plasma membranes. Furthermore, the amounts of CPERMs were shown to be regulated in a cell and tissue type-dependent manner. These findings favored the notion that phosphorylation of the COOH-terminal threonine plays a key role in the regulation of the cross-linking activity of ERM proteins in vivo.

Normal development of mice and unimpaired cell adhesion/cell motility/actin-based cytoskeleton without compensatory up-regulation of ezrin or radixin in moesin gene knockout

Ezrin/radixin/moesin (ERM) proteins are general cross-linkers between the plasma membrane and actin filaments. Because their expression is regulated in a tissue-specific manner, each ERM protein has been proposed to have unique functions. On the other hand, experiments at the cellular level and in vitro have suggested their functional redundancy. To assess the possible unique functions of ERM proteins in vivo, the moesin gene located on the X chromosome was disrupted by gene targeting in embryonic stem cells. Male mice hemizygous for the mutation as well as homozygous females were completely devoid of moesin but developed normally and were fertile, with no obvious histological abnormalities in any of the tissues examined. In the tissues of the mutant mice, moesin completely disappeared without affecting the expression levels or subcellular distribution of ezrin and radixin. Also, in platelets, fibroblasts, and mast cells isolated from moesin-deficient mice, targeted disruption of the moesin gene did not affect their ERM-dependent functions, i.e. platelet aggregation, stress fiber/focal contact formation of fibroblasts, and microvillar formation of mast cells, without compensatory up-regulation of ezrin or radixin. These findings favor the notion that ERM proteins are functionally redundant at the cellular as well as the whole body level.

Animal virus receptors

The term 'receptor' is generally accepted as the cell-surface component that participates in virus binding and facilitates subsequent viral infection. Recent advances in technology have permitted the identification of several virus receptors, increasing our understanding of the significance of this initial virus-cell and virus-host interaction. Virus binding was previously considered to involve simple recognition and attachment to a single cell surface molecule by virus attachment proteins. The classical concept of these as single entities that participate in a lock-and-key-type process has been superseded by new data indicating that binding can be a multistep process, often involving different virus-attachment proteins and more than one host-cell receptor.

CD43 Interacts With Moesin and Ezrin and Regulates Its Redistribution to the Uropods of T Lymphocytes at the Cell-Cell Contacts

Chemokines as well as the signaling through the adhesion molecules intercellular adhesion molecule (ICAM)-3 and CD43 are able to induce in T lymphocytes their switching from a spherical to a polarized motile morphology, with the formation of a uropod at the rear of the cell. We investigated here the role of CD43 in the regulation of T-cell polarity, CD43-cytoskeletal interactions, and lymphocyte aggregation. Pro-activatory anti-CD43 monoclonal antibody (MoAb) induced polarization of T lymphocytes with redistribution of CD43 to the uropod and the CCR2 chemokine receptor to the leading edge of the cell. Immunofluorescence analysis showed that all three ezrin-radixin-moesin (ERM) actin-binding proteins localized in the uropod of both human T lymphoblasts stimulated with anti-CD43 MoAb and tumor-infiltrating T lymphocytes. Radixin localized at the uropod neck, whereas ezrin and moesin colocalized with CD43 in the uropod. Biochemical analyses showed that ezrin and moesin coimmunoprecipitated with CD43 in T lymphoblasts. Furthermore, in these cells, the CD43-associated moesin increased after stimulation through CD43. The interaction of moesin and ezrin with CD43 was specifically mediated by the cytoplasmic domain of CD43, as shown by precipitation of both ERM proteins with a GST-fusion protein containing the CD43 cytoplasmic tail. Videomicroscopy analysis of homotypic cell aggregation induced through CD43 showed that cellular uropods mediate cell-cell contacts and lymphocyte recruitment. Immunofluorescence microscopy performed in parallel showed that uropods enriched in CD43 and moesin localized at the cell-cell contact areas of cell aggregates. The polarization and homotypic cell aggregation induced through CD43 was prevented by butanedione monoxime, indicating the involvement of myosin cytoskeleton in these phenomena. Altogether, these data indicate that CD43 plays an important regulatory role in remodeling T-cell morphology, likely through its interaction with actin-binding proteins ezrin and moesin. In addition, the redistribution of CD43 to the uropod region of migrating lymphocytes and during the formation of cell aggregates together with the enhancing effect of anti-CD43 antibodies on lymphocyte cell recruitment suggest that CD43 plays a key role in the regulation of cell-cell interactions during lymphocyte traffic.

CD43 Interacts With Moesin and Ezrin and Regulates Its Redistribution to the Uropods of T Lymphocytes at the Cell-Cell Contacts

Chemokines as well as the signaling through the adhesion molecules intercellular adhesion molecule (ICAM)-3 and CD43 are able to induce in T lymphocytes their switching from a spherical to a polarized motile morphology, with the formation of a uropod at the rear of the cell. We investigated here the role of CD43 in the regulation of T-cell polarity, CD43-cytoskeletal interactions, and lymphocyte aggregation. Pro-activatory anti-CD43 monoclonal antibody (MoAb) induced polarization of T lymphocytes with redistribution of CD43 to the uropod and the CCR2 chemokine receptor to the leading edge of the cell. Immunofluorescence analysis showed that all three ezrin-radixin-moesin (ERM) actin-binding proteins localized in the uropod of both human T lymphoblasts stimulated with anti-CD43 MoAb and tumor-infiltrating T lymphocytes. Radixin localized at the uropod neck, whereas ezrin and moesin colocalized with CD43 in the uropod. Biochemical analyses showed that ezrin and moesin coimmunoprecipitated with CD43 in T lymphoblasts. Furthermore, in these cells, the CD43-associated moesin increased after stimulation through CD43. The interaction of moesin and ezrin with CD43 was specifically mediated by the cytoplasmic domain of CD43, as shown by precipitation of both ERM proteins with a GST-fusion protein containing the CD43 cytoplasmic tail. Videomicroscopy analysis of homotypic cell aggregation induced through CD43 showed that cellular uropods mediate cell-cell contacts and lymphocyte recruitment. Immunofluorescence microscopy performed in parallel showed that uropods enriched in CD43 and moesin localized at the cell-cell contact areas of cell aggregates. The polarization and homotypic cell aggregation induced through CD43 was prevented by butanedione monoxime, indicating the involvement of myosin cytoskeleton in these phenomena. Altogether, these data indicate that CD43 plays an important regulatory role in remodeling T-cell morphology, likely through its interaction with actin-binding proteins ezrin and moesin. In addition, the redistribution of CD43 to the uropod region of migrating lymphocytes and during the formation of cell aggregates together with the enhancing effect of anti-CD43 antibodies on lymphocyte cell recruitment suggest that CD43 plays a key role in the regulation of cell-cell interactions during lymphocyte traffic.

Expression of moesin and its associated molecule CD44 in epithelial skin tumors

Moesin, one of the ERM (ezrin; radixin; moesin) family members, is directly associated with the cytoplasmic domain of CD44, which is now thought to be related to the metastatic potential of tumor cells. Using immunohistochemistry we investigated the expression of moesin in normal epidermis and various kinds of epithelial skin tumors: squamous cell carcinoma, verrucous carcinoma, Bowen's disease, solar keratosis, keratoacanthoma, basal cell carcinoma, and extramammary Paget's disease. Normal skin showed positive epidermal staining for moesin with the exception of the stratum corneum. The expression of moesin varied with the type of skin tumor. In basal cell carcinoma, Bowen's disease, and extramammary Paget's disease, moesin expression was either faint or negative. In contrast to Bowen's disease, invasive squamous cell carcinoma showed more intense and heterogeneous staining of the cytoplasm and the cell membrane. Verrucous carcinoma was weakly positive, with a tendency for the moesin to be distributed in the cell membrane. The staining pattern of moesin varied among the different kinds of epithelial skin tumors, and its expression was generally similar to that of the standard form of CD44. These results suggest that moesin is closely inter-related with CD44 in epithelial skin cells as seen in other cellular systems, and that the variable pattern of moesin staining among the skin tumor cells could reflect expression disorders associated with the transformation.

Moesin and CD44 expression in cutaneous melanocytic tumours

The ERM (ezrin, radixin and moesin) family members, located just beneath the plasma membranes, are thought to be involved in the association of action filaments with the plasma membrane. One of the family members, moesin, is reported to bind to CD44. Splice variants of CD44 are thought to be associated with tumour progression or differentiation. Our aim was to investigate immunohistochemically the expression of moesin together with CD44 on paraffin tissue sections of a series of melanocytic tumours. The material included 12 ordinary melanocytic naevi, six Spitz naevi, eight dysplastic naevi, six blue naevi, seven malignant melanomas in situ, 15 primary malignant melanomas, five metastatic melanomas to the skin and five lymph node metastases. In the normal skin and the melanocytic tumours the expression of moesin was largely similar to that of CD44 standard. Strong moesin staining was observed in benign melanocytic lesions and melanomas in situ. However, the expression was decreased in advanced malignant melanomas. The moesin labelling in melanoma cells was downregulated with the depth of dermal invasion. The immunoreactivity was also diminished in the skin metastases and the lymph node metastases of melanoma. These results suggest that in melanocytic tumours, the alternation in the expression of moesin may be involved in the progression of malignancy.

Association of the myosin-binding subunit of myosin phosphatase and moesin: dual regulation of moesin phosphorylation by Rho-associated kinase and myosin phosphatase

The small GTPase Rho is believed to regulate the actin cytoskeleton and cell adhesion through its specific targets. We previously identified the Rho targets: protein kinase N, Rho-associated kinase (Rho-kinase), and the myosin-binding subunit (MBS) of myosin phosphatase. We found that in MDCK epithelial cells, MBS accumulated at the tetradecanoylphorbol-13-acetate (TPA)-induced membrane ruffling area, where moesin, a member of the ERM (ezrin, radixin, and moesin) family, was localized. Neither membrane ruffling nor an accumulation of moesin and MBS at the free-end plasma membrane was induced when MDCK cells were stimulated with TPA after the microinjection of C3, which ADP-ribosylates and inactivates Rho. MBS was colocalized with moesin at the cell-cell contact sites in MDCK cells. We also found that moesin was coimmunoprecipitated with MBS from MDCK cells. Recombinant MBS interacted with the amino-terminal domains of moesin and ezrin. Myosin phosphatase composed of the catalytic subunit and MBS showed phosphatase activity toward moesin, which was phosphorylated by Rho-kinase. The phosphatase activity was inhibited when MBS was phosphorylated by Rho-kinase. These results suggest that MBS is recruited with moesin to the plasma membrane and that myosin phosphatase and Rho-kinase regulate the phosphorylation state of moesin downstream of Rho.

A peptide sequence of heparin/heparan sulfate (HP/HS)-interacting protein supports selective, high affinity binding of HP/HS and cell attachment

We previously have identified a novel cell surface heparan sulfate/heparin (HS/HP)-interacting protein (HIP) found in human uterine epithelia and a variety of other human epithelial and endothelial cells and cell lines (Liu, S., Smith, S. E., Julian, J., Rohde, L. H., Karin, N. J., and Carson, D. D. (1996) J. Biol. Chem. 271, 11817-11823; Rohde, L. H., Julian, J., Babaknia, A., and Carson, D. D. (1996) J. Biol. Chem. 271, 11824-11830). The amino acid sequence predicted for HIP revealed a potential HS/HP-binding motif. In the present studies, a synthetic peptide corresponding to this putative HS/HP-binding motif, HIP peptide, was synthesized and examined with regard to its HS/HP binding and cell attachment promoting activity. Results using solid phase binding assays demonstrate that HIP peptide binds HS/HP with high selectivity and has high affinity for bulk HP (50% saturation congruent with 300 nM) and even higher affinity for a subset of polysaccharides found in commercial [3H]HP (half-saturation congruent with 10 nM). Moreover, HIP peptide binds subsets of cell and extracellular matrix-associated HS and dermatan sulfate expressed by RL95 cells, a human uterine adenocarcinoma cell line. HIP peptide also binds a similar fraction of HS as well as dermatan sulfate expressed by JAR cells, a human choriocarcinoma cell line. In contrast to binding of cell- or extracellular matrix-associated HS, HIP peptide does not bind secreted or released forms of HS or DS from either RL95 or JAR cells to a significant extent. HS species that bind to HIP peptide are generally larger, have a higher negative charge density, and have a larger proportion of di- and trisulfated disaccharide units than HS species that do not bind to HIP peptide, demonstrating structural differences among these polysaccharides. This same peptide supports HS-dependent JAR cell attachment. Collectively, these data demonstrate that a linear peptide sequence found within HIP can account, at least in part, for the HS/HP binding and cell adhesion promoting activities of this protein.

Protein kinase C-theta phosphorylation of moesin in the actin-binding sequence

Moesin, a member of the ezrin-radixin-moesin (ERM) family of membrane/cytoskeletal linkage proteins, is known to be threonine-phosphorylated at Thr558 in activated platelets within its conserved putative actin-binding domain. The pathway leading to this phosphorylation step and its control have not been previously elucidated. We have detected and characterized reactions leading to moesin phosphorylation in human leukocyte extracts. In vitro phosphorylation of endogenous moesin, which was identified by peptide microsequencing, was dependent on phosphatidylglycerol (PG) or to a lesser extent, phosphatidylinositol (PI), but not phosphatidylserine (PS) and diacylglycerol (DAG). Analysis of charge shifts, phosphoamino acid analysis, and stoichiometry was consistent with a single phosphorylation site. By using mass spectroscopy and direct microsequencing of CNBr fragments of phospho-moesin, the phosphorylation site was identified as KYKT*LRQIR (where * indicates the phosphorylation site) (Thr558), which is conserved in the ERM family. Recombinant moesin demonstrated similar in vitro phospholipid-dependent phosphorylation compared with the endogenous protein. The phosphorylation site sequence of moesin displays a high degree of conservation with the pseudosubstrate sequences of the protein kinase C (PKC) family. We identified the kinase activity as PKC-theta on the basis of immunodepletion of the moesin kinase activity and copurification of PKC-theta with the enzymic activity. We further demonstrate that PKC-theta displays a preference for PG vesicles over PI or PS/DAG, with minimal activation by DAG, as well as specificity for moesin compared with myelin basic protein, histone H1, or other cellular proteins. Expression of a human His6-tagged PKC-theta in Jurkat cells and purification by Ni2+ chelate chromatography yield an active enzyme that phosphorylates moesin. PG vesicle binding experiments with expressed PKC-theta and moesin demonstrate that both bind to vesicles independently of one another. Thus, PKC-theta is identified as a major kinase within cells with specificity for moesin and with activation under non-classical PKC conditions. It appears likely that this activity corresponds to a specific intracellular pathway controlling the function of moesin as well as other ERM proteins.

High-performance affinity chromatography for the purification of heparin-binding proteins from detergent-solubilized smooth muscle cell membranes

Heparin and heparan sulfates are regulators of cellular events including adhesion, proliferation and migration. In particular, the antiproliferative effect of heparin on smooth muscle cell (SMC) growth is well described. However, its mechanism of action remains unclear. Numerous results suggest an endocytosis mediated by a still unknown heparin receptor on vascular SMCs. In order to identify a putative heparin receptor on SMCs that could be involved in heparin signalling, affinity chromatography supports were developed. In this paper, we describe high-performance liquid affinity chromatography (HPLAC) supports obtained from silica beads coated with dextran polymer substituted by a calculated amount of diethylaminoethyl functions. With a polysaccharide dextran layer, this type of support can be grafted with specific ligands, such as heparin, using conventional coupling methods. In a previous work, we demonstrated, using butanedioldiglycidyl ether, that silica stationary phases coupled to heparin could be used for the fast elution and good peak resolution of heparin-binding proteins. In the present work, an affinity chromatographic fraction of SMC membrane extracts was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and six heparin-binding proteins from dodecyloctaethyleneglycol monoether-solubilized SMCs were observed. Their Mr values were between 40 and 70 kDa, with three major protein bands at 66, 45 and 41 kDa. These results indicate the usefulness of the chromatographic method for purifying heparin binding proteins from SMC membrane.