Tumor-suppression functions of merlin are independent of its role as an organizer of the actin cytoskeleton in Schwann cells

Lallemand, Dominique; Saint-Amaux, Aurelie Lampin; Giovannini, Marco

doi:10.1242/jcs.045914

Cited by 48 publications

(56 citation statements)

References 58 publications

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“…In SC4 cells transfected with Cerulean-merlin-Venus (WT and 6N), merlin WT fluorescence localized to the cortical membrane and colocalized with phalloidin (actin) staining. This colocalization was dependent on intact actin cytoskeleton/ cellular architecture as treatment with cytochalasin D resulted in loss of merlin WT and actin colocalization and accumulation of merlin WT as large aggregates, as previously described (10,33). In contrast, merlin 6N fluorescence was largely cytoplas- (Fig.…”

Section: Vol 31 2011 Merlin Regulation By Phosphoinositide Binding supporting

confidence: 77%

“…SC4 cells were transfected with either Cerulean-merlin WT-Venus or Cerulean-merlin 6N-Venus and plated onto coverslips. Cells were washed in PBS three times, followed by simultaneous fixation and permeabilization in 4% paraformaldehyde containing 0.2% TX-100 for 20 min at room temperature as previously described (33). Coverslips were blocked for 30 min in the dark at room temperature in PBS containing 1% fatty acid-free BSA followed by counterstaining with Alexa Fluor 633-phalloidin at a final concentration of 5U/ml (for actin) and with 4Ј,6Ј-diamidino-2-phenylindole (DAPI; for nuclei) for 30 min in the dark at room temperature in blocking buffer.…”

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confidence: 99%

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FERM Domain Phosphoinositide Binding Targets Merlin to the Membrane and Is Essential for Its Growth-Suppressive Function

Mani

Hennigan

Foster

et al. 2011

Molecular and Cellular Biology

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The neurofibromatosis type 2 tumor suppressor protein, merlin, is related to the ERM (ezrin, radixin, and moesin) family of plasma membrane-actin cytoskeleton linkers. For ezrin, phosphatidylinositol 4,5-bisphosphate (PIP 2 ) binding to the amino-terminal FERM domain is required for its conformational activation, proper subcellular localization, and function, but less is known about the role of phosphoinositide binding for merlin. Current evidence indicates that association with the membrane is important for merlin to function as a growth regulator; however, the mechanisms by which merlin localizes to the membrane are less clear. Here, we report that merlin binds phosphoinositides, including PIP 2 , via a conserved binding motif in its FERM domain. Abolition of FERM domain-mediated phosphoinositide binding of merlin displaces merlin from the membrane and releases it into the cytosol without altering the folding of merlin. Importantly, a merlin protein whose FERM domain cannot bind phosphoinositide is defective in growth suppression. Retargeting the mutant merlin into the membrane using a dual-acylated amino-terminal decapeptide from Fyn is sufficient to restore the growth-suppressive properties to the mutant merlin. Thus, FERM domain-mediated phosphoinositide binding and membrane association are critical for the growth-regulatory function of merlin.Merlin, the neurofibromatosis type 2 (NF2) tumor suppressor protein, is a member of the band 4.1/ERM family of plasma membrane-actin cytoskeleton linkers (6). Like other members of this family, merlin has a globular amino-terminal FERM (four point one, ezrin, radixin, and moesin) domain followed by an ␣-helical coiled-coil domain and a carboxy-terminal domain (28, 58). The amino and carboxy termini of merlin and ERM proteins can bind one another; thus, these proteins can exist in two states, open and closed (6,57). Interconversion between the two states is regulated by phosphorylation near the carboxy terminus. For ERM, the best-studied phosphorylated residue is a conserved threonine (ezrin T567, radixin T564, and moesin T558) (42). Likewise, for merlin, the phosphorylated residue is S518 (56); only the dephosphorylated, closed conformation is believed to be growth suppressive (44,55,57).For ezrin, phosphorylation and the ability to undergo conformational changes are regulated by the binding of the FERM domain to the membrane lipid, phosphoinositide-(4,5)-bisphosphate (PIP 2 ) (3, 14). PIP 2 facilitates the binding of ERM proteins to membrane proteins (21, 24). Recent studies showed that even after ezrin is phosphorylated, PIP 2 binding is the primary regulator of ERM membrane association (19).The residues implicated in PIP 2 binding are conserved among the ERM proteins (17,36,58), and sequence homology suggests that there are potential PIP 2 binding motifs in the merlin FERM domain. Exogenous addition of PIP 2 enhances the binding of a regulatory cofactor for Na ϩ -H ϩ exchange (NHE-RF) to merlin in vitro (16), suggesting that PIP 2 binding might play an important ro...

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Section: Vol 31 2011 Merlin Regulation By Phosphoinositide Binding supporting

confidence: 77%

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confidence: 99%

FERM Domain Phosphoinositide Binding Targets Merlin to the Membrane and Is Essential for Its Growth-Suppressive Function

Mani

Hennigan

Foster

et al. 2011

Molecular and Cellular Biology

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“…5B, lane 10), highlighting the possible need for an actin link to achieve CD44 cleavage. Interestingly, in respect to its inability to bind to actin, ezrin R579A mimics the cleavage inhibitory merlin whose Cterminus also cannot interact with F-actin (28,29). These observations propose that disrupting F-actin would exert a similar inhibitory effect.…”

Section: Resultsmentioning

confidence: 97%

Tumor Suppressor NF2 Blocks Cellular Migration by Inhibiting Ectodomain Cleavage of CD44

Hartmann

Parra

Ruschel

et al. 2015

Molecular Cancer Research

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Ectodomain cleavage (shedding) of transmembrane proteins by metalloproteases (MMP) generates numerous essential signaling molecules, but its regulation is not totally understood. CD44, a cleaved transmembrane glycoprotein, exerts both antiproliferative or tumor-promoting functions, but whether proteolysis is required for this is not certain. CD44-mediated contact inhibition and cellular proliferation are regulated by counteracting CD44 C-terminal interacting proteins, the tumor suppressor protein merlin (NF2) and ERM proteins (ezrin, radixin, moesin). We show here that activation or overexpression of constitutively active merlin or downregulation of ERMs inhibited 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced [as well as serum, hepatocyte growth factor (HGF), or plateletderived growth factor (PDGF)] CD44 cleavage by the metalloprotease ADAM10, whereas overexpressed ERM proteins promoted cleavage. Merlin-and ERM-modulated Ras or Rac activity was not required for this function. However, latrunculin (an actin-disrupting toxin) or an ezrin mutant which is unable to link CD44 to actin, inhibited CD44 cleavage, identifying a cytoskeletal C-terminal link as essential for induced CD44 cleavage. Cellular migration, an important tumor property, depended on CD44 and its cleavage and was inhibited by merlin. These data reveal a novel function of merlin and suggest that CD44 cleavage products play a tumor-promoting role. Neuregulin, an EGF ligand released by ADAM17 from its proform NRG1, is predominantly involved in regulating cellular differentiation. In contrast to CD44, release of neuregulin from its pro-form was not regulated by merlin or ERM proteins. Disruption of the actin cytoskeleton however, also inhibited NRG1 cleavage. This current study presents one of the first examples of substrate-selective cleavage regulation.

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“…In support of this notion, the F2 subdomain was recently shown to be essential for merlin to suppress the proliferation of primary Nf2-deficient Schwann cells. 38 The merlin F2 domain also harbors a submotif called the blue box (177-YQMTPEM-183), which is conserved in other species but not in ERM proteins. 39 In Drosophila, a blue box mutant acts as a dominant negative, underscoring the importance of this region in merlin functions.…”

Section: Discussionmentioning

confidence: 99%

Unfurling of the band 4.1, ezrin, radixin, moesin (FERM) domain of the merlin tumor suppressor

et al. 2011

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The merlin-1 tumor suppressor is encoded by the Neurofibromatosis-2 (Nf2) gene and loss-of-function Nf2 mutations lead to nervous system tumors in man and to several tumor types in mice. Merlin is an ERM (ezrin, radixin, moesin) family cytoskeletal protein that interacts with other ERM proteins and with components of cell-cell adherens junctions (AJs). Merlin stabilizes the links of AJs to the actin cytoskeleton. Thus, its loss destabilizes AJs, promoting cell migration and invasion, which in Nf2 1/-mice leads to highly metastatic tumors. Paradoxically, the ''closed'' conformation of merlin-1, where its N-terminal four-point-one, ezrin, radixin, moesin (FERM) domain binds to its C-terminal tail domain, directs its tumor suppressor functions. Here we report the crystal structure of the human merlin-1 head domain when crystallized in the presence of its tail domain. Remarkably, unlike other ERM head-tail interactions, this structure suggests that binding of the tail provokes dimerization and dynamic movement and unfurling of the F2 motif of the FERM domain. We conclude the ''closed'' tumor suppressor conformer of merlin-1 is in fact an ''open'' dimer whose functions are disabled by Nf2 mutations that disrupt this architecture.

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Tumor-suppression functions of merlin are independent of its role as an organizer of the actin cytoskeleton in Schwann cells

Abstract: Merlin is the product of the

Cited by 48 publications

References 58 publications

FERM Domain Phosphoinositide Binding Targets Merlin to the Membrane and Is Essential for Its Growth-Suppressive Function

FERM Domain Phosphoinositide Binding Targets Merlin to the Membrane and Is Essential for Its Growth-Suppressive Function

Tumor Suppressor NF2 Blocks Cellular Migration by Inhibiting Ectodomain Cleavage of CD44

Unfurling of the band 4.1, ezrin, radixin, moesin (FERM) domain of the merlin tumor suppressor

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