Expression and functional significance of ezrin in human brain astrocytoma

miRNA-204-5p acts as tumor suppressor to influence the invasion and migration of astrocytoma by targeting ezrin and is downregulated by DNA methylation

microRNAs (miRNAs), through their regulation of the expression and activity of numerous proteins, are involved in almost all cellular processes. As a consequence, dysregulation of miRNA expression is closely associated with the development and progression of cancers. Recently, DNA methylation has been shown to play a key role in miRNA expression dysregulation in tumors. miRNA-204-5p commonly acts in the suppression of oncogenes in tumors. In this study, the levels of miRNA-204-5p were found to be down-regulated in the astrocytoma samples. miRNA-204-5p expression was also down-regulated in two astrocytoma cell lines (U87MG and LN382). Examination of online databases showed that the miRNA-204-5p promoter regions exist in CpG islands, which might be subjected to differential methylation. Subsequently, we showed that the miRNA-204-5p promoter region was hypermethylated in the astrocytoma tissue samples and cell lines. Then we found that ezrin expression was down-regulated with an increase in miRNA-204-5p expression in LN382 and U87MG cells after 5-aza-2'-deoxycytidine (5'AZA) treatment compared with control DMSO treatment. In addition, LN382 and U87MG cells treated with 5'AZA exhibited significantly inhibited cell invasion and migration . In a recovery experiment, cell invasion and migration returned to normal levels as miRNA-204-5p and ezrin levels were restored. Overall, our study suggests that miRNA-204-5p acts as a tumor suppressor to influence astrocytoma invasion and migration by targeting ezrin and that miRNA-204-5p expression is downregulated by DNA methylation. This study provides a new potential strategy for astrocytoma treatment.

Urokinase-type plasminogen activator (uPA) protects the tripartite synapse in the ischemic brain via ezrin-mediated formation of peripheral astrocytic processes

Cerebral ischemia has a harmful effect on the synapse associated with neurological impairment. The "tripartite synapse" is assembled by the pre- and postsynaptic terminals, embraced by astrocytic elongations known as peripheral astrocytic processes (PAPs). Ischemic stroke induces the detachment of PAPs from the synapse, leading to synaptic dysfunction and neuronal death. Ezrin is a membrane-associated protein, required for the formation of PAPs, that links the cell surface to the actin cytoskeleton. Urokinase-type plasminogen activator (uPA) is a serine proteinase that upon binding to its receptor (uPAR) promotes neurite growth during development. In the adult brain, neurons release uPA and astrocytes recruit uPAR to the plasma membrane during the recovery phase from an ischemic stroke, and uPA/uPAR binding promotes functional improvement following an ischemic injury. We found that uPA induces the synthesis of ezrin in astrocytes, with the subsequent formation of PAPs that enter in direct contact with the synapse. Furthermore, either the release of neuronal uPA or intravenous treatment with recombinant uPA (ruPA) induces the formation of PAPs in the ischemic brain, and the interaction of these PAPs with the pre- and postsynaptic terminals protects the integrity of the "tripartite synapse" from the harmful effects of the ischemic injury.

Perspectives for Ezrin and Radixin in Astrocytes: Kinases, Functions and Pathology

Astrocytes are increasingly perceived as active partners in physiological brain function and behaviour. The structural correlations of the glia–synaptic interaction are the peripheral astrocyte processes (PAPs), where ezrin and radixin, the two astrocytic members of the ezrin-radixin-moesin (ERM) family of proteins are preferentially localised. While the molecular mechanisms of ERM (in)activation appear universal, at least in mammalian cells, and have been studied in great detail, the actual ezrin and radixin kinases, phosphatases and binding partners appear cell type specific and may be multiplexed within a cell. In astrocytes, ezrin is involved in process motility, which can be stimulated by the neurotransmitter glutamate, through activation of the glial metabotropic glutamate receptors (mGluRs) 3 or 5. However, it has remained open how this mGluR stimulus is transduced to ezrin activation. Knowing upstream signals of ezrin activation, ezrin kinase(s), and membrane-bound binding partners of ezrin in astrocytes might open new approaches to the glial role in brain function. Ezrin has also been implicated in invasive behaviour of astrocytomas, and glial activation. Here, we review data pertaining to potential molecular interaction partners of ezrin in astrocytes, with a focus on PKC and GRK2, and in gliomas and other diseases, to stimulate further research on their potential roles in glia-synaptic physiology and pathology.

Urokinase-type plasminogen activator (uPA) promotes ezrin-mediated reorganization of the synaptic cytoskeleton in the ischemic brain

Synaptic repair in the ischemic brain is a complex process that requires reorganization of the actin cytoskeleton. Ezrin, radixin, and moesin (ERM) are a group of evolutionarily conserved proteins that link the plasma membrane to the actin cytoskeleton and act as scaffolds for signaling transduction. Urokinase-type plasminogen activator (uPA) is a serine proteinase that upon binding to the urokinase-type plasminogen activator receptor (uPAR) catalyzes the conversion of plasminogen into plasmin on the cell surface and activates intracellular signaling pathways. Early studies indicate that uPA and uPAR expression increase during the recovery phase from an ischemic stroke and that uPA binding to uPAR promotes neurorepair in the ischemic brain. The in vitro and in vivo studies presented here show that either the release of neuronal uPA or treatment with recombinant uPA induces the local synthesis of ezrin in the synapse and the recruitment of β3-integrin to the postsynaptic density (PSD) of cerebral cortical neurons by a plasminogen-independent mechanism. We found that β3-integrin has a double effect on ezrin, inducing its recruitment to the PSD via the intercellular adhesion molecule-5 (ICAM-5) and its subsequent activation by phosphorylation at Thr-567. Finally, our data indicate that by triggering the reorganization of the actin cytoskeleton in the postsynaptic terminal, active ezrin induces the recovery of dendritic spines and synapses that have been damaged by an acute ischemic stroke. In summary, our data show that uPA-uPAR binding promotes synaptic repair in the ischemic brain via ezrin-mediated reorganization of the actin cytoskeleton in the postsynaptic terminal.

Correlation of Ezrin Expression Pattern and Clinical Outcomes in Ewing Sarcoma

Background. Ezrin is a membrane-cytoskeleton linker protein that has been associated with metastasis and poor outcomes in osteosarcoma and high-grade soft tissue sarcomas. The prognostic value of ezrin expression in Ewing sarcoma is unknown. Methods. The relationship between ezrin expression and outcome was analyzed in a cohort of 53 newly diagnosed Ewing sarcoma patients treated between 2000 and 2011. The intensity and proportion of cells with ezrin immunoreactivity were assessed in diagnostic tumor tissue using a semiquantitative scoring system to yield intensity and positivity scores for each tumor. Results. Ezrin expression was detected in 72% (38/53) of tumor samples. The proportion of patients with metastatic disease was equal in the positive and negative ezrin expression groups. There was no significant difference in the 5-year event-free survival (EFS) between patients with positive versus negative ezrin expression. Patients whose tumor sample showed high ezrin intensity had significantly better 5-year EFS when compared to patients with low/no ezrin intensity (78% versus 55%; P = 0.03). Conclusions. Ezrin expression can be detected in the majority of Ewing sarcoma tumor samples. Intense ezrin expression may be correlated with a favorable outcome; however further investigation with a larger cohort is needed to validate this finding.

Prognostic Value of Ezrin in Various Cancers: A Systematic Review and Updated Meta-analysis

More and more studies have investigated the effects of Ezrin expression level on the prognostic role in various tumors. However, the results remain controversial rather than conclusive. Here, we performed a systematic review and meta-analysis to evaluate the correlation of Ezrin expression with the prognosis in various tumors. the pooled hazard ratios (HR) with the corresponding 95% confidence intervals (95% CI) were calculated to evaluate the degree of the association. The overall results of fifty-five studies with 6675 patients showed that elevated Ezrin expression was associated with a worse prognosis in patients with cancers, with the pooled HRs of 1.86 (95% CI: 1.51–2.31, P < 0.001) for over survival (OS), 2.55 (95% CI: 2.14–3.05, P < 0.001) for disease-specific survival (DFS) and 2.02 (95% CI: 1.13–3.63, P = 0.018) for disease-specific survival (DSS)/metastasis-free survival (MFS) by the random, fixed and random effect model respectively. Similar results were also observed in the stratified analyses by tumor types, ethnicity background and sample source. This meta-analysis suggests that Ezrin may be a potential prognostic marker in cancer patients. High Ezrin is associated with a poor prognosis in a variety of solid tumors.

Scaffolding during the cell cycle by A-kinase anchoring proteins

Cell division relies on coordinated regulation of the cell cycle. A process including a well-defined series of strictly regulated molecular mechanisms involving cyclin-dependent kinases, retinoblastoma protein, and polo-like kinases. Dysfunctions in cell cycle regulation are associated with disease such as cancer, diabetes, and neurodegeneration. Compartmentalization of cellular signaling is a common strategy used to ensure the accuracy and efficiency of cellular responses. Compartmentalization of intracellular signaling is maintained by scaffolding proteins, such as A-kinase anchoring proteins (AKAPs). AKAPs are characterized by their ability to anchor the regulatory subunits of protein kinase A (PKA), and thereby achieve guidance to different cellular locations via various targeting domains. Next to PKA, AKAPs also associate with several other signaling elements including receptors, ion channels, protein kinases, phosphatases, small GTPases, and phosphodiesterases. Taking the amount of possible AKAP signaling complexes and their diverse localization into account, it is rational to believe that such AKAP-based complexes regulate several critical cellular events of the cell cycle. In fact, several AKAPs are assigned as tumor suppressors due to their vital roles in cell cycle regulation. Here, we first briefly discuss the most important players of cell cycle progression. After that, we will review our recent knowledge of AKAPs linked to the regulation and progression of the cell cycle, with special focus on AKAP12, AKAP8, and Ezrin. At last, we will discuss this specific AKAP subset in relation to diseases with focus on a diverse subset of cancer.

NGX6a is degraded through a proteasome-dependent pathway without ubiquitination mediated by ezrin, a cytoskeleton-membrane linker

Our previous study demonstrated that the NGX6b gene acts as a suppressor in the invasion and migration of nasopharyngeal carcinoma (NPC). Recently, we identified the novel isoform NGX6a, which is longer than NGX6b. In this study, we first found that NGX6a was degraded in NPC cells and that this degradation was mediated by ezrin, a linker between membrane proteins and the cytoskeleton. Specific siRNAs against ezrin increase the protein level of NGX6a in these cells. During degradation, NGX6a is not ubiquitinated but is degraded through a proteasome-dependent pathway. The distribution pattern of ezrin was negatively associated with NGX6a in an immunochemistry analysis of a nasopharyngeal carcinoma tissue microarray and fetus multiple organ tissues and Western blot analysis in nasopharyngeal and NPC cell lines, suggesting that ezrin and NGX6a are associated and are involved in the progression and invasion of NPC. By mapping the interacting binding sites, the seven-transmembrane domain of NGX6a was found to be the critical region for the degradation of NGX6a, and the amino terminus of ezrin is required for the induction of NGX6a degradation. The knockdown of ezrin or transfection of the NGX6a mutant CO, which has an EGF-like domain and a transmembrane 1 domain, resulted in no degradation, significantly reducing the ability of invasion and migration of NPC cells. This study provides a novel molecular mechanism for the low expression of NGX6a in NPC cells and an important molecular event in the process of invasion and metastasis of nasopharyngeal carcinoma cells.

MicroRNA-204, a direct negative regulator of ezrin gene expression, inhibits glioma cell migration and invasion

Ezrin is overexpressed in a variety of neoplastic cells and involved in the later stages of tumor progression and metastasis. Ezrin expression can be regulated at both the transcriptional and post-transcriptional levels. We used a combination of bioinformatics and experimental techniques to demonstrate that the miR-204 is a direct negative regulator of ezrin. Overexpression of miR-204 mimics decreased the activity of a luciferase reporter containing the ezrin 3' UTR and led to repression of ezrin protein. In contrast, ectopic expression of miR-204 inhibitor elevated ezrin expression. We also show that miR-204 is down-regulated in a panel of glioma tissues and in high invasive glioma cell lines we examined. Moreover, miR-204 mimics significantly reduced glioma cell migration and invasion, while miR-204 inhibitor generated the opposite results. Finally, overexpression of miR-204 and knockdown of ezrin reduced glioma cell invasion, and these effects could be rescued by re-expression of ezrin. These findings reveal that miR-204 could be partly due to its inhibitory effects on glioma cell migration and invasion through regulating ezrin expression.

Role of ezrin in osteosarcoma metastasis

The cause of death for the vast majority of cancer patients is the development of metastases at sites distant from that of the primary tumor. For most pediatric sarcoma patients such as those with osteosarcoma (OS), despite successful management of the primary tumor through multimodality approaches, the development of metastases, commonly to the lungs, is the cause of death. Significant improvements in long-term outcome for these patients have not been seen in more than 30 years. Furthermore, the long-term outcome for patients who present with metastatic disease is grave [1-5]. New treatment options are needed.Opportunities to improve outcomes for patients who present with metastases and those at-risk for progression and metastasis require an improved understanding of cancer progression and metastasis. With this goal in mind we and others have identified ezrin as a metastasis-associated protein that associated with OS and other cancers. Ezrin is the prototypical ERM (Ezrin/Radixin/Moesin) protein family member. ERMs function as linker proteins connecting the actin cytoskeleton and the plasma membrane. Since our initial identification of ezrin in pediatric sarcoma, an increasing understanding the role of ezrin in metastasis has emerged. Briefly, ezrin appears to allow metastatic cells to overcome a number of stresses experienced during the metastatic cascade, most notably the stress experienced as cells interact with the microenvironment of the secondary site. Cells must rapidly adapt to this environment in order to survive. Evidence now suggests a connection between ezrin expression and a variety of mechanisms linked to this important cellular adaptation including the ability of metastatic cells to initiate the translation of new proteins and to allow the efficient generation of ATP through a variety of sources. This understanding of the role of ezrin in the biology of metastasis is now sufficient to consider ezrin as an important therapeutic target in osteosarcoma patients. This chapter reviews our understanding of ezrin and the related ERM proteins in normal tissues and physiology, summarizes the expression of ezrin in human cancers and associations with clinical parameters of disease progression, reviews reports that detail a biological understanding of ezrin's role in metastatic progression, and concludes with a rationale that may be considered to target ezrin and ezrin biology in osteosarcoma.