Ezrin mediates both HGF/Met autocrine and non-autocrine signaling-induced metastasis in melanoma

Development of Personalized Strategies for Precisely Battling Malignant Melanoma

Melanoma is the most severe and fatal form of skin cancer, resulting from multiple gene mutations with high intra-tumor and inter-tumor molecular heterogeneity. Treatment options for patients whose disease has progressed beyond the ability for surgical resection rely on currently accepted standard therapies, notably immune checkpoint inhibitors and targeted therapies. Acquired resistance to these therapies and treatment-associated toxicity necessitate exploring novel strategies, especially those that can be personalized for specific patients and/or populations. Here, we review the current landscape and progress of standard therapies and explore what personalized oncology techniques may entail in the scope of melanoma. Our purpose is to provide an up-to-date summary of the tools at our disposal that work to circumvent the common barriers faced when battling melanoma.

Myoglobin Inhibits Breast Cancer Cell Fatty Acid Oxidation and Migration via Heme-dependent Oxidant Production and Not Fatty Acid Binding

The monomeric heme protein myoglobin (Mb), traditionally thought to be expressed exclusively in cardiac and skeletal muscle, is now known to be expressed in approximately 40% of breast tumors. While Mb expression is associated with better patient prognosis, the molecular mechanisms by which Mb limits cancer progression are unclear. In muscle, Mb's predominant function is oxygen storage and delivery, which is dependent on the protein's heme moiety. However, prior studies demonstrate that the low levels of Mb expressed in cancer cells preclude this function. Recent studies propose a novel fatty acid binding function for Mb via a lysine residue (K46) in the heme pocket. Given that cancer cells can upregulate fatty acid oxidation (FAO) to maintain energy production for cytoskeletal remodeling during cell migration, we tested whether Mb-mediated fatty acid binding modulates FAO to decrease breast cancer cell migration. We demonstrate that the stable expression of human Mb in MDA-MB-231 breast cancer cells decreases cell migration and FAO. Site-directed mutagenesis of Mb to disrupt Mb fatty acid binding did not reverse Mb-mediated attenuation of FAO or cell migration in these cells. In contrast, cells expressing Apo-Mb, in which heme incorporation was disrupted, showed a reversal of Mb-mediated attenuation of FAO and cell migration, suggesting that Mb attenuates FAO and migration via a heme-dependent mechanism rather than through fatty acid binding. To this end, we show that Mb's heme-dependent oxidant generation propagates dysregulated gene expression of migratory genes, and this is reversed by catalase treatment. Collectively, these data demonstrate that Mb decreases breast cancer cell migration, and this effect is due to heme-mediated oxidant production rather than fatty acid binding. The implication of these results will be discussed in the context of therapeutic strategies to modulate oxidant production and Mb in tumors.

Highlights

Myoglobin (Mb) expression in MDA-MB-231 breast cancer cells slows migration.Mb expression decreases mitochondrial respiration and fatty acid oxidation.Mb-dependent fatty acid binding does not regulate cell migration or respiration.Mb-dependent oxidant generation decreases mitochondrial metabolism and migration.Mb-derived oxidants dysregulate migratory gene expression.

Using the single-cell imaging system and orthotropic footpad injection to establish mouse models for experimental and spontaneous melanoma metastasis

Metastasis, a complex process, is responsible for most deaths in patients with cancer. Clinically relevant research models are indispensable to advancing our understanding of metastatic mechanisms and developing new treatments. We here describe detailed protocols to establish mouse models for melanoma metastasis using the single-cell imaging system and orthotropic footpad injection. The single-cell imaging system permits the tracking and quantification of early metastatic cell survival, while the orthotropic footpad transplantation mimics aspects of the complex metastatic process. For complete details on the use and execution of this protocol, please refer to Yu et al.1,2.

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.

PTEN phosphatase inhibits metastasis by negatively regulating the Entpd5/IGF1R pathway through ATF6

PTEN encodes a tumor suppressor with lipid and protein phosphatase activities whose dysfunction has been implicated in melanomagenesis; less is known about how its phosphatases regulate melanoma metastasis. We demonstrate that PTEN expression negatively correlates with metastatic progression in human melanoma samples and a PTEN-deficient mouse melanoma model. Wildtype PTEN expression inhibited melanoma cell invasiveness and metastasis in a dose-dependent manner, behaviors that specifically required PTEN protein phosphatase activity. PTEN phosphatase activity regulated metastasis through Entpd5. Entpd5 knockdown reduced metastasis and IGF1R levels while promoting ER stress. In contrast, Entpd5 overexpression promoted metastasis and enhanced IGF1R levels while reducing ER stress. Moreover, Entpd5 expression was regulated by the ER stress sensor ATF6. Altogether, our data indicate that PTEN phosphatase activity inhibits metastasis by negatively regulating the Entpd5/IGF1R pathway through ATF6, thereby identifying novel candidate therapeutic targets for the treatment of PTEN mutant melanoma.

Ezrin expression in female reproductive tissues: A review of regulation and pathophysiological implications

Ezrin, a plasma membrane-microfilament linker, is a cytoskeletal organizer involved in many cellular activities by binding to the membrane protein-ezrin-cytoskeletal protein complex and regulating downstream signal transduction. Increasing evidence demonstrates that ezrin plays an important role in regulating cell polarity, proliferation and invasion. In this study, we analyzed the effects of ezrin on oocytes, follicle development, embryo development and embryo implantation. We reviewed the recent studies on the modalities of ezrin regulation and its involvement in the biological processes of female reproductive physiology and summarized the current research advances in ezrin inhibitors. These studies will provide new strategies and insights for the treatment of diseases.

Ezrin gone rogue in cancer progression and metastasis: An enticing therapeutic target

Cancer metastasis is the primary cause of morbidity and mortality in cancer as it remains the most complicated, devastating, and enigmatic aspect of cancer. Several decades of extensive research have identified several key players closely associated with metastasis. Among these players, cytoskeletal linker Ezrin (the founding member of the ERM (Ezrin-Radixin-Moesin) family) was identified as a critical promoter of metastasis in pediatric cancers in the early 21st century. Ezrin was discovered 40 years ago as a aminor component of intestinal epithelial microvillus core protein, which is enriched in actin-containing cell surface structures. It controls gastric acid secretion and plays diverse physiological roles including maintaining cell polarity, regulating cell adhesion, cell motility and morphogenesis. Extensive research for more than two decades evinces that Ezrin is frequently dysregulated in several human cancers. Overexpression, altered subcellular localization and/or aberrant activation of Ezrin are closely associated with higher metastatic incidence and patient mortality, thereby justifying Ezrin as a valuable prognostic biomarker in cancer. Ezrin plays multifaceted role in multiple aspects of cancer, with its significant contribution in the complex metastatic cascade, through reorganizing the cytoskeleton and deregulating various cellular signaling pathways. Current preclinical studies using genetic and/or pharmacological approaches reveal that inactivation of Ezrin results in significant inhibition of Ezrin-mediated tumor growth and metastasis as well as increase in the sensitivity of cancer cells to various chemotherapeutic drugs. In this review, we discuss the recent advances illuminating the molecular mechanisms responsible for Ezrin dysregulation in cancer and its pleiotropic role in cancer progression and metastasis. We also highlight its potential as a prognostic biomarker and therapeutic target in various cancers. More importantly, we put forward some potential questions, which we strongly believe, will stimulate both basic and translational research to better understand Ezrin-mediated malignancy, ultimately leading to the development of Ezrin-targeted cancer therapy for the betterment of human life.

Pathophysiological Roles of Actin-Binding Scaffold Protein, Ezrin

Ezrin is one of the members of the ezrin/radixin/moesin (ERM) family of proteins. It was originally discovered as an actin-binding protein in the microvilli structure about forty years ago. Since then, it has been revealed as a key protein with functions in a variety of fields including cell migration, survival, and signal transduction, as well as functioning as a structural component. Ezrin acts as a cross-linker of membrane proteins or phospholipids in the plasma membrane and the actin cytoskeleton. It also functions as a platform for signaling molecules at the cell surface. Moreover, ezrin is regarded as an important target protein in cancer diagnosis and therapy because it is a key protein involved in cancer progression and metastasis, and its high expression is linked to poor survival in many cancers. Small molecule inhibitors of ezrin have been developed and investigated as candidate molecules that suppress cancer metastasis. Here, we wish to comprehensively review the roles of ezrin from the pathophysiological points of view.

Modulation of membrane-cytoskeleton interactions: ezrin as key player

Membrane-cytoskeleton interactions (MCIs) are mediated by actin-binding proteins (ABPs). Ezrin is a crucial ABP that links membranes to actin filaments during lamellipodia formation, cell polarization, and migration. We discuss the concept of MCI and the potential of ezrin as a druggable target for treating inflammatory diseases and cancers.

PERK mediates resistance to BRAF inhibition in melanoma with impaired PTEN

Targeting mutant BRAF in patients with melanomas harboring this oncogene has been highly successful as a first-line treatment, but other mutations may affect its efficacy and alter the route of acquired resistance resulting in recurrence and poor prognosis. As an evolving strategy, melanoma treatment needs to be expanded to include targets based on newly discovered emerging molecules and pathways. We here show that PERK plays a critical role in BRAF inhibitor-acquired resistance in melanoma with impaired PTEN. Inhibition of PERK by either shRNA or a pharmacological inhibitor blocked the growth of BRAF inhibitor-resistant melanoma with impaired PTEN in vitro and in vivo, suggesting an effective approach against melanomas with mutant BRAF and PTEN deficiency. Our current findings, along with our previous discovery that the AXL/AKT axis mediates resistance to BRAF inhibition in melanoma with wild-type PTEN, provide new insights toward a strategy for combating BRAF inhibition-acquired resistance in BRAF mutant melanoma with different PTEN statuses.

Phosphorylated Ezrin (Thr567) Regulates Hippo Pathway and Yes-Associated Protein (Yap) in Liver

The activation of CD81 [the portal of entry of hepatitis C virus (HCV)] by agonistic antibody results in phosphorylation of Ezrin via Syk kinase and is associated with inactivation of the Hippo pathway and increase in yes-associated protein (Yap1). The opposite occurs when glypican-3 or E2 protein of HCV binds to CD81. Hepatocyte-specific glypican-3 transgenic mice have decreased levels of phosphorylated (p)-Ezrin (Thr567) and Yap, increased Hippo activity, and suppressed liver regeneration. The role of Ezrin in these processes has been speculated, but not proved. We show that Ezrin has a direct role in the regulation of Hippo pathway and Yap. Forced expression of plasmids expressing mutant Ezrin (T567D) that mimics p-Ezrin (Thr567) suppressed Hippo activity and activated Yap signaling in hepatocytes in vivo and enhanced activation of pathways of β-catenin and leucine rich repeat containing G protein-coupled receptor 4 (LGR4) and LGR5 receptors. Hepatoma cell lines JM1 and JM2 have decreased CD81 expression and Hippo activity and up-regulated p-Ezrin (T567). NSC668394, a p-Ezrin (Thr567) antagonist, significantly decreased hepatoma cell proliferation. We additionally show that p-Ezrin (T567) is controlled by epidermal growth factor receptor and MET. Ezrin phosphorylation, mediated by CD81-associated Syk kinase, is directly involved in regulation of Hippo pathway, Yap levels, and growth of normal and neoplastic hepatocytes. The finding has mechanistic and potentially therapeutic applications in hepatocyte growth biology, hepatocellular carcinoma, and HCV pathogenesis.

LOXL2 Upregulates Phosphorylation of Ezrin to Promote Cytoskeletal Reorganization and Tumor Cell Invasion

Lysyl oxidase-like 2 (LOXL2), a copper-dependent enzyme of the lysyl oxidase family and its nonsecreted, catalytically dead spliced isoform L2Δ13, enhance cell migration and invasion, stimulate filopodia formation, modulate the expression of cytoskeletal genes, and promote tumor development and metastasis in vivo. We previously showed that LOXL2 reorganizes the actin cytoskeleton in esophageal squamous cell carcinoma (ESCC) cells, however, the underlying molecular mechanisms were not identified. Here, using interactome analysis, we identified ezrin (EZR), fascin (FSCN1), heat shock protein beta-1 (HSPB1), and tropomodulin-3 (TMOD3) as actin-binding proteins that associate with cytoplasmic LOXL2, as well as with its L2Δ13 variant. High levels of LOXL2 and L2Δ13 and their cytoskeletal partners correlated with poor clinical outcome in patients with ESCC. To better understand the significance of these interactions, we focused on the interaction of LOXL2 with ezrin. Phosphorylation of ezrin at T567 was greatly reduced following depletion of LOXL2 and was enhanced following LOXL2/L2Δ13 reexpression. Furthermore, LOXL2 depletion inhibited the ability of ezrin to promote tumor progression. These results suggest that LOXL2-induced ezrin phosphorylation, which also requires PKCα, is critical for LOXL2-induced cytoskeletal reorganization that subsequently promotes tumor cell invasion and metastasis in ESCC. In summary, we have characterized a novel molecular mechanism that mediates, in part, the protumorigenic activity of LOXL2. These findings may enable the future development of therapeutic agents targeting cytoplasmic LOXL2. SIGNIFICANCE: LOXL2 and its spliced isoform L2Δ13 promote cytoskeletal reorganization and invasion of esophageal cancer cells by interacting with cytoplasmic actin-binding proteins such as ezrin.

The clinical prognostic significance of ezrin in patients with bone and soft tissue sarcomas: a meta-analysis

Ezrin is a member of the ezrin–radixin–moesin (ERM) protein family and has been shown to be associated with poor prognosis in patients with a variety of solid tumors. However, the clinical prognostic significance of ezrin in patients with bone and soft tissue sarcomas remains unclear. Here, we performed a systematic meta‐analysis by searching PubMed, the Cochrane Library Database, EMBASE, the Web of Science, and the CBM, WanFang Med Online and CNKI databases. In total, 19 studies with a total of 1316 bone and soft tissue sarcoma patients were included. Pooled analyses showed that ezrin overexpression was correlated with a higher rate of tumor metastasis (OR 6.59, 95% CI: 2.84–15.33, P < 0.01, P_FDR < 0.01) and recurrence (OR 3.18, 95% CI: 1.88–5.37, P < 0.01, P_FDR < 0.01) and a more advanced tumor grade (OR 3.252, 95% CI: 1.371–7.715, P = 0.01, P_FDR = 0.03). Moreover, elevated ezrin expression could predict poor OS (HR 3.02, 95% CI: 2.35–3.89, P < 0.01, P_FDR < 0.01), MFS (HR 5.22, 95% CI: 2.08–13.08, P < 0.01, P_FDR < 0.01), and EFS (HR 1.07, 95% CI: 1.03–1.11, P < 0.01, P_FDR < 0.01). Subgroup analyses revealed the underlying sources of heterogeneity. Publication bias was observed in the analysis of metastasis. Sensitivity analysis revealed that the results were robust. Our findings indicated that ezrin overexpression was significantly correlated with poor survival and more advanced tumor progression in bone and soft tissue sarcomas, which suggests that ezrin might be a valuable prognostic biomarker and a potential therapeutic target.

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.

Ezrin promotes pancreatic cancer cell proliferation and invasion through activating the Akt/mTOR pathway and inducing YAP translocation

Background

Ezrin and YAP are abnormally expressed in various cancers, and play pivotal roles in cancer initiation and development. However, the mechanisms of Ezrin in pancreatic cancer have not been fully elucidated. In this study, we aimed to elucidate the functions and mechanisms of Ezrin in the pathogenesis of pancreatic cancer.

Methods

Effects of Ezrin deregulation on pancreatic cancer phenotype were determined in Capan-1 and BxPC-3 cells using MTT, colony formation, transwell, wound-healing, and chick chorioallantoic membrane assays. To find out the underlying mechanism of Ezrin, multiple assays were performed to detect the effect of Ezrin on Akt pathway activation and YAP expression. Then, Ezrin and YAP expression was analyzed in pancreatic cancer and normal pancreas samples. Finally, the prognostic value of Ezrin and YAP was evaluated in pancreatic cancer patients.

Results

Ezrin promoted proliferation, invasion, epithelial–mesenchymal transition (EMT) progression, and angiogenesis of pancreatic cancers. Mechanistically, Ezrin activated Akt/mTOR pathways and induced YAP phosphorylation and nucleus translocation. The PI3K/Akt pathway inhibitor, rapamycin, and LY294002 could partially attenuate the effect of Ezrin on cell proliferation, invasion, EMT progression, and YAP phosphorylation and translocation. Moreover, both Ezrin and YAP were significantly overexpressed in pancreatic cancer tissues compared with adjacent normal pancreas, and correlated with poor prognosis in pancreatic cancer patients. Multivariate survival analysis showed that Ezrin was an independent prognostic marker for pancreatic cancer. Furthermore, the expression status of Ezrin and YAP had positive correlations in pancreatic cancer tissues.

Conclusion

Ezrin promoted pancreatic cancer proliferation, invasion, migration, and EMT progression, partially through activating the PI3K/Akt pathway, and also regulated YAP phosphorylation and translocation, partially through the PI3K/Akt pathway. Ezrin and YAP were significantly overexpressed in pancreatic cancers, and correlated with poor prognosis in pancreatic cancer patients.

microRNA-211 regulates cell proliferation, apoptosis and migration/invasion in human osteosarcoma via targeting EZRIN

Background

In recent years, microRNA-211 (miR211) has been considered as a tumor suppressor in multiple malignancies. However, the function of miR211 in human osteosarcoma has not been explored intensively so far. In this study, the relationship between miR211 and EZRIN was analyzed in human osteosarcoma.

Methods

The expression levels of miR211 and EZRIN were measured in both human osteosarcoma cells and tissues. The direct regulatory relationship between miR211 and EZRIN was evaluated using dual-luciferase assay. The effect of miR211 and EZRIN overexpression on cell proliferation, migration/invasion, and apoptosis was detected.

Results

The expression of miR211 was obviously lower in osteosarcoma tissues than paracancerous tissues. EZRIN was identified as the direct target of miR211, and up-regulation of miR211 increased the percentage of cell apoptosis, and suppressed cell proliferation as well as cell migration/invasion via directly regulating EZRIN.

Conclusions

Our study indicated that miR211 has an important role in the development and progress of osteosarcoma, and it might become a novel target in the diagnosis and treatment of human osteosarcoma.

Electronic supplementary material

The online version of this article (10.1186/s11658-019-0173-x) contains supplementary material, which is available to authorized users.

MicroRNA-622 is a novel mediator of tumorigenicity in melanoma by targeting Kirsten rat sarcoma

The network of molecular players is similar when comparing neural crest-derived, actively migrating melanoblasts to melanoma cells. However, melanoblasts are sensitive to differentiation-initiating signals at their target site (epidermis), while melanoma cells maintain migratory and undifferentiated features. We aimed at identifying downregulated genes in melanoma that are particularly upregulated in melanoblasts. Loss of such genes could contribute to stabilization of a dedifferentiated, malignant phenotype in melanoma. We determined that microRNA-622 (miR-622) expression was strongly downregulated in melanoma cells and tissues compared to melanocytes and melanoblast-related cells. miR-622 expression correlated with survival of patients with melanoma. miR-622 re-expression inhibited clonogenicity, proliferation, and migration in melanoma. Inhibition of miR-622 in melanocytes induced enhanced migration. Kirsten rat sarcoma (KRAS) was identified as a major functional target of miR-622 in melanoma. We conclude that miR-622 is a novel tumor suppressor in melanoma and identify the miR-622-KRAS axis as potential therapeutic target.