The Experts below are selected from a list of 441 Experts worldwide ranked by ideXlab platform
Olli Carpén - One of the best experts on this subject based on the ideXlab platform.
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novel molecular interactions and biological functions of the neurofibromatosis 2 tumor suppressor protein merlin
2008Co-Authors: Olli CarpénAbstract:Abstract : The project has studied the functions of the neurofibromatosis 2 tumor suppressor protein merlin and the related ERM protein ezrin. We identified novel binding partners and functions for both proteins. Merlin was shown to regulate both the microtubule and actin cytoskeleton. Two important kinases, protein kinase A (PKA) and AKT, were shown to phosphorylate merlin at S10. This phosphorylation affects actin dynamics, cell morphology and migration of mouse embryonic fibroblasts (MEF) and Schwann cells. Thus, merlin may serve as a regulator of PKA and AKT induced changes in actin cytoskeleton. We identified a link between merlin and cell cycle control by demonstrating a novel functional interaction between merlin and HEI10. In studies of the biological activities of ezrin we discovered that oncogenic tyrosine kinases Src and c-Met phosphorylate ezrin at Y477. Using reconstituted MEF cells from ezrin -/- mice we studied the biological importance of Y477 phosphorylation. Our results show that ezrin is a key regulator of Src induced malignant behavior in three dimensional culture conditions.
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Protein kinase A-mediated phosphorylation of the NF2 tumor suppressor protein merlin at serine 10 affects the actin cytoskeleton
Oncogene, 2008Co-Authors: M Laulajainen, Olli Carpén, T Muranen, Mikaela GrönholmAbstract:Mutations in the neurofibromatosis 2 tumor suppressor gene ( NF2 ) encoding merlin (moesin–ezrin–radixin like-protein) induce tumors of the nervous system. Merlin localizes to the cell membrane where it links the actin cytoskeleton to membrane proteins. Cell proliferation is regulated by merlin in many cell types, but merlin's tumor suppressor function still remains unclear. Phosphorylation has been suggested to regulate merlin's activity. The C-terminal serine 518 is phosphorylated both by p21-activated kinases (PAKs) and protein kinase A (PKA). In this work, we identify a novel PKA phosphorylation site, serine 10, in the N terminus of merlin. We show that a non-phosphorylatable form of serine 10 (S10A) affects cellular morphology. Regulation of this site also influences actin cytoskeleton organization and dynamics in vivo , as merlin S10A reduces the amount of cellular F-actin and merlin S10D stabilizes F-actin filaments. By using a wound-healing assay and live cell imaging, we demonstrate that dephosphorylation of serine 10 leads to defects in migration, possibly through altered ability of the cells to form lamellipodia. This study suggests a role for merlin in mediating PKA-induced changes of the actin cytoskeleton.
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characterization of the nf2 protein merlin and the erm protein ezrin in human rat and mouse central nervous system
Molecular and Cellular Neuroscience, 2005Co-Authors: Mikaela Grönholm, Olli Carpén, Antti Vaheri, Tambet Teesalu, Jaana Tyynela, Katja M Piltti, Tom Bohling, Kirmo WartiovaaraAbstract:The neurofibromatosis 2 (NF2) protein, merlin, is structurally related to the ERM (ezrin-radixin-moesin) protein family of membrane-cytoskeleton linkers and is mutated in nervous system tumors. Apart from tumor suppressor activity, merlin's functions are poorly understood. We compared the localization and expression of merlin and ezrin in developing and adult brain and in brain-derived progenitor cells. Both proteins were widely but differentially expressed in human, rat, and mouse brain. In brain tissue and neuronal progenitor cell cultures merlin was predominantly found in neurons while ezrin was expressed in astrocytes. Merlin expression was seen from E11 in mouse embryos, whereas ezrin was present earlier. Both proteins were expressed in embryonic mouse neurospheres, where ezrin was specifically localized in filopodia of adherent neuronal progenitor cells. Subcellular analysis demonstrated ezrin in fine filopodial structures in astrocytes, while merlin was detected in neuronal synaptic junctions. The widespread expression of merlin in brain and its association with protein kinase A suggest a role for merlin in brain biology.
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Cyclic AMP-dependent protein kinase phosphorylates merlin at serine 518 independently of p21-activated kinase and promotes merlin-ezrin heterodimerization.
The Journal of biological chemistry, 2004Co-Authors: Kaija Alfthan, Leena Heiska, Mikaela Grönholm, G. Herma Renkema, Olli CarpénAbstract:Abstract Mutations in the NF2 tumor suppressor gene encoding merlin induce the development of tumors of the nervous system. Merlin is highly homologous to the ERM (ezrin-radixin-moesin) family of membrane/cytoskeleton linker proteins. However, the mechanism for the tumor suppressing activity of merlin is not well understood. Previously, we characterized a novel role for merlin as a protein kinase A (PKA)-anchoring protein, which links merlin to the cAMP/PKA signaling pathway. In this study we show that merlin is also a target for PKA-induced phosphorylation. In vitro [γ-33P]ATP labeling revealed that both the merlin N and C termini are phosphorylated by PKA. Furthermore, both in vitro and in vivo phosphorylation studies of the wild-type and mutated C termini demonstrated that PKA can phosphorylate merlin at serine 518, a site that is phosphorylated also by p21-activated kinases (PAKs). Merlin was phosphorylated by PKA in cells in which PAK activity was suppressed, indicating that the two kinases function independently. Both in vitro and in vivo interaction studies indicated that phosphorylation of serine 518 promotes heterodimerization between merlin and ezrin, an event suggested to convert merlin from a growth-suppressive to a growth-permissive state. This study provides further evidence on the connection between merlin and cAMP/PKA signaling and suggests a role for merlin in the cAMP/PKA transduction pathway.
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homotypic and heterotypic interaction of the neurofibromatosis 2 tumor suppressor protein merlin and the erm protein ezrin
Journal of Cell Science, 1999Co-Authors: Mikaela Grönholm, Leena Heiska, Markku Sainio, Fang Zhao, Antti Vaheri, Olli CarpénAbstract:Ezrin, radixin and moesin (ERM) are homologous proteins, which are linkers between plasma membrane components and the actin-containing cytoskeleton. The ERM protein family members associate with each other in a homotypic and heterotypic manner. The neurofibromatosis 2 (NF2) tumor suppressor protein merlin (schwannomin) is structurally related to ERM members. Merlin is involved in tumorigenesis of NF2-associated and sporadic schwannomas and meningiomas, but the tumor suppressor mechanism is poorly understood. We have studied the ability of merlin to self-associate and bind ezrin. Ezrin was coimmunoprecipitated with merlin from lysates of human U251 glioma cells and from COS-1 cells transfected with cDNA encoding for merlin isoform I. The interaction was further studied and the association domains were mapped with the yeast two-hybrid system and with blot overlay and affinity precipitation experiments. The heterotypic binding of merlin and ezrin and the homotypic association of merlin involves interaction between the amino- and carboxy-termini. The amino-terminal association domain of merlin involves residues 1–339 and has similar features with the amino-terminal association domain of ezrin. The carboxy-terminal association domain cannot be mapped as precisely as in ezrin, but it requires residues 585–595 and a more amino-terminal segment. Unlike ezrin, merlin does not require activation for self-association but native merlin molecules can interact with each other. Heterodimerization between merlin and ezrin, however, occurs only following conformational alterations in both proteins. These results biochemically connect merlin to the cortical cytoskeleton and indicate differential regulation of merlin from ERM proteins.
Mikaela Grönholm - One of the best experts on this subject based on the ideXlab platform.
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Protein kinase A-mediated phosphorylation of the NF2 tumor suppressor protein merlin at serine 10 affects the actin cytoskeleton
Oncogene, 2008Co-Authors: M Laulajainen, Olli Carpén, T Muranen, Mikaela GrönholmAbstract:Mutations in the neurofibromatosis 2 tumor suppressor gene ( NF2 ) encoding merlin (moesin–ezrin–radixin like-protein) induce tumors of the nervous system. Merlin localizes to the cell membrane where it links the actin cytoskeleton to membrane proteins. Cell proliferation is regulated by merlin in many cell types, but merlin's tumor suppressor function still remains unclear. Phosphorylation has been suggested to regulate merlin's activity. The C-terminal serine 518 is phosphorylated both by p21-activated kinases (PAKs) and protein kinase A (PKA). In this work, we identify a novel PKA phosphorylation site, serine 10, in the N terminus of merlin. We show that a non-phosphorylatable form of serine 10 (S10A) affects cellular morphology. Regulation of this site also influences actin cytoskeleton organization and dynamics in vivo , as merlin S10A reduces the amount of cellular F-actin and merlin S10D stabilizes F-actin filaments. By using a wound-healing assay and live cell imaging, we demonstrate that dephosphorylation of serine 10 leads to defects in migration, possibly through altered ability of the cells to form lamellipodia. This study suggests a role for merlin in mediating PKA-induced changes of the actin cytoskeleton.
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characterization of the nf2 protein merlin and the erm protein ezrin in human rat and mouse central nervous system
Molecular and Cellular Neuroscience, 2005Co-Authors: Mikaela Grönholm, Olli Carpén, Antti Vaheri, Tambet Teesalu, Jaana Tyynela, Katja M Piltti, Tom Bohling, Kirmo WartiovaaraAbstract:The neurofibromatosis 2 (NF2) protein, merlin, is structurally related to the ERM (ezrin-radixin-moesin) protein family of membrane-cytoskeleton linkers and is mutated in nervous system tumors. Apart from tumor suppressor activity, merlin's functions are poorly understood. We compared the localization and expression of merlin and ezrin in developing and adult brain and in brain-derived progenitor cells. Both proteins were widely but differentially expressed in human, rat, and mouse brain. In brain tissue and neuronal progenitor cell cultures merlin was predominantly found in neurons while ezrin was expressed in astrocytes. Merlin expression was seen from E11 in mouse embryos, whereas ezrin was present earlier. Both proteins were expressed in embryonic mouse neurospheres, where ezrin was specifically localized in filopodia of adherent neuronal progenitor cells. Subcellular analysis demonstrated ezrin in fine filopodial structures in astrocytes, while merlin was detected in neuronal synaptic junctions. The widespread expression of merlin in brain and its association with protein kinase A suggest a role for merlin in brain biology.
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Cyclic AMP-dependent protein kinase phosphorylates merlin at serine 518 independently of p21-activated kinase and promotes merlin-ezrin heterodimerization.
The Journal of biological chemistry, 2004Co-Authors: Kaija Alfthan, Leena Heiska, Mikaela Grönholm, G. Herma Renkema, Olli CarpénAbstract:Abstract Mutations in the NF2 tumor suppressor gene encoding merlin induce the development of tumors of the nervous system. Merlin is highly homologous to the ERM (ezrin-radixin-moesin) family of membrane/cytoskeleton linker proteins. However, the mechanism for the tumor suppressing activity of merlin is not well understood. Previously, we characterized a novel role for merlin as a protein kinase A (PKA)-anchoring protein, which links merlin to the cAMP/PKA signaling pathway. In this study we show that merlin is also a target for PKA-induced phosphorylation. In vitro [γ-33P]ATP labeling revealed that both the merlin N and C termini are phosphorylated by PKA. Furthermore, both in vitro and in vivo phosphorylation studies of the wild-type and mutated C termini demonstrated that PKA can phosphorylate merlin at serine 518, a site that is phosphorylated also by p21-activated kinases (PAKs). Merlin was phosphorylated by PKA in cells in which PAK activity was suppressed, indicating that the two kinases function independently. Both in vitro and in vivo interaction studies indicated that phosphorylation of serine 518 promotes heterodimerization between merlin and ezrin, an event suggested to convert merlin from a growth-suppressive to a growth-permissive state. This study provides further evidence on the connection between merlin and cAMP/PKA signaling and suggests a role for merlin in the cAMP/PKA transduction pathway.
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merlin links to the camp neuronal signaling pathway by anchoring the riβ subunit of protein kinase a
Journal of Biological Chemistry, 2003Co-Authors: Mikaela Grönholm, Kaija Alfthan, Antti Vaheri, Tambet Teesalu, Lutz Vossebein, Cathrine R Carlson, Juha Kujapanula, Heikki Rauvala, Friedrich W Herberg, Kjetil TaskenAbstract:The cAMP-protein kinase A (PKA) pathway, important in neuronal signaling, is regulated by molecules that bind and target PKA regulatory subunits. Of four regulatory subunits, RIbeta is most abundantly expressed in brain. The RIbeta knockout mouse has defects in hippocampal synaptic plasticity, suggesting a role for RIbeta in learning and memory-related functions. Molecules that interact with or regulate RIbeta are still unknown. We identified the neurofibromatosis 2 tumor suppressor protein merlin (schwannomin), a molecule related to the ezrin-radixin-moesin family of membrane-cytoskeleton linker proteins, as a binding partner for RIbeta. Merlin and RIbeta demonstrated a similar expression pattern in central nervous system neurons and an overlapping subcellular localization in cultured hippocampal neurons and transfected cells. The proteins were coprecipitated from brain lysates by cAMP-agarose and coimmunoprecipited from cellular lysates with specific antibodies. In vitro binding studies verified that the interaction is direct. The interaction appeared to be under conformational regulation and was mediated via the alpha-helical region of merlin. Sequence comparison between merlin and known PKA anchoring proteins identified a conserved alpha-helical PKA anchoring protein motif in merlin. These results identify merlin as the first neuronal binding partner for PKA-RIbeta and suggest a novel function for merlin in connecting neuronal cytoskeleton to PKA signaling.
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homotypic and heterotypic interaction of the neurofibromatosis 2 tumor suppressor protein merlin and the erm protein ezrin
Journal of Cell Science, 1999Co-Authors: Mikaela Grönholm, Leena Heiska, Markku Sainio, Fang Zhao, Antti Vaheri, Olli CarpénAbstract:Ezrin, radixin and moesin (ERM) are homologous proteins, which are linkers between plasma membrane components and the actin-containing cytoskeleton. The ERM protein family members associate with each other in a homotypic and heterotypic manner. The neurofibromatosis 2 (NF2) tumor suppressor protein merlin (schwannomin) is structurally related to ERM members. Merlin is involved in tumorigenesis of NF2-associated and sporadic schwannomas and meningiomas, but the tumor suppressor mechanism is poorly understood. We have studied the ability of merlin to self-associate and bind ezrin. Ezrin was coimmunoprecipitated with merlin from lysates of human U251 glioma cells and from COS-1 cells transfected with cDNA encoding for merlin isoform I. The interaction was further studied and the association domains were mapped with the yeast two-hybrid system and with blot overlay and affinity precipitation experiments. The heterotypic binding of merlin and ezrin and the homotypic association of merlin involves interaction between the amino- and carboxy-termini. The amino-terminal association domain of merlin involves residues 1–339 and has similar features with the amino-terminal association domain of ezrin. The carboxy-terminal association domain cannot be mapped as precisely as in ezrin, but it requires residues 585–595 and a more amino-terminal segment. Unlike ezrin, merlin does not require activation for self-association but native merlin molecules can interact with each other. Heterodimerization between merlin and ezrin, however, occurs only following conformational alterations in both proteins. These results biochemically connect merlin to the cortical cytoskeleton and indicate differential regulation of merlin from ERM proteins.
Helen Morrison - One of the best experts on this subject based on the ideXlab platform.
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Merlin cooperates with neurofibromin and Spred1 to suppress the Ras-Erk pathway
Human molecular genetics, 2020Co-Authors: Yan Cui, Hongchuan Jin, Stephan Schacke, Jiani C Yin, Yi-ping Hsueh, Helen MorrisonAbstract:The Ras-Erk pathway is frequently over-activated in human tumors. Neurofibromatosis type 1 and 2 (NF1, NF2) are characterized by multiple tumors of Schwann cell origin. The NF1 tumor suppressor neurofibromin is a principal Ras-GAP accelerating Ras inactivation, whereas the NF2 tumor suppressor merlin is a scaffold protein coordinating multiple signaling pathways. We have previously reported that merlin interacts with Ras and p120RasGAP. Here, we show that merlin can also interact with the neurofibromin/Spred1 complex via merlin-binding sites present on both proteins. Further, merlin can directly bind to the Ras-binding domain and the kinase domain of Raf1. As the third component of the neurofibromin/Spred1 complex, merlin cannot increase the Ras-GAP activity; rather, it blocks Ras binding to Raf1 by functioning as a 'selective Ras barrier'. Merlin-deficient Schwann cells require the Ras-Erk pathway activity for proliferation. Accordingly, suppression of the Ras-Erk pathway likely contributes to merlin's tumor suppressor activity. Taken together, our results, and studies by others, support targeting or co-targeting of this pathway as a therapy for NF2 inactivation-related tumors.
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the nf2 tumor suppressor merlin interacts with ras and rasgap which may modulate ras signaling
Oncogene, 2019Co-Authors: Yan Cui, Susann Groth, Scott Troutman, Annemarie Carlstedt, Tobias Sperka, Lars Bjorn Riecken, Joseph L Kissil, Hongchuan Jin, Helen MorrisonAbstract:Inactivation of the tumor suppressor NF2/merlin underlies neurofibromatosis type 2 (NF2) and some sporadic tumors. Previous studies have established that merlin mediates contact inhibition of proliferation; however, the exact mechanisms remain obscure and multiple pathways have been implicated. We have previously reported that merlin inhibits Ras and Rac activity during contact inhibition, but how merlin regulates Ras activity has remained elusive. Here we demonstrate that merlin can directly interact with both Ras and p120RasGAP (also named RasGAP). While merlin does not increase the catalytic activity of RasGAP, the interactions with Ras and RasGAP may fine-tune Ras signaling. In vivo, loss of RasGAP in Schwann cells, unlike the loss of merlin, failed to promote tumorigenic growth in an orthotopic model. Therefore, modulation of Ras signaling through RasGAP likely contributes to, but is not sufficient to account for, merlin's tumor suppressor activity. Our study provides new insight into the mechanisms of merlin-dependent Ras regulation and may have additional implications for merlin-dependent regulation of other small GTPases.
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Expression of Merlin and phospho-Merlin in oligodendrocyte cell lines.
2018Co-Authors: Andrea Toledo, Elena Grieger, Khalad Karram, Helen Morrison, Stephan L. BaaderAbstract:RT4, OLN93 and TC620 cell lines were stably transfected with pcNF2hflag (Merlin) and pcDNA3.1 (control). Representative Western blots of gels loaded with 15 μg of total protein extracts are shown in A. The densitometric determination of Merlin and phospho-Merlin in the cell lines was performed by normalizing with cyclophilin B (mean ± SEM, n = 3, ***p < 0.001, Wilcoxon rank-sum test). Immunofluorescent staining of Merlin and phalloidin staining of actin in Nf2 stably transfected cell lines demonstrates the preferred localization of Merlin in the cytoplasm (B). Single confocal planes of transfected cells are shown using the same microscope parameters. Scale bars: 10μm.
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Quantification of Merlin expression in cerebellar tissue, cell lines and primary cell cultures.
2018Co-Authors: Andrea Toledo, Elena Grieger, Khalad Karram, Helen Morrison, Stephan L. BaaderAbstract:(A) Merlin expression is demonstrated by Western blotting loading 30 μg of total protein extract. Merlin was expressed as a 70kDa sized protein in RT4, OLN93, TC620 and Oli-neu cell lines; it was absent in SC4 cells. Western blots have been repeated three times with different samples and densitometrically evaluated (B). Expression levels have been related to the expression of Merlin in RT4 cells marked by the dashed line. Significant differences in expression of Merlin in oligodendrocyte cell lines vs. RT4 are marked by asterisks (mean ± SEM, n = 3; *** p < 0.001, ** p < 0.05 t-test).
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merlin neurofibromatosis type 2 suppresses growth by inhibiting the activation of ras and rac
Cancer Research, 2007Co-Authors: Helen Morrison, Marco Giovannini, Tobias Sperka, Jan Manent, Helmut Ponta, Peter HerrlichAbstract:The small G-protein Ras is a tightly controlled regulator of cell fate. Prolonged or persistent arrest in the activated GTP-loaded state by mutation of Ras as in lung cancer or in a Ras-GTPase-activating protein as in neurofibromatosis type 1 promotes tumorigenesis. We now show that the tumor-suppressor protein merlin (mutated in neurofibromatosis type 2) also controls Ras activity. Systematic analysis of growth factor signaling located the step of merlin interference to the activation of Ras and Rac. Merlin independently uncouples both Ras and Rac from growth factor signals. In the case of Ras, merlin acts downstream of the receptor tyrosine kinase-growth factor receptor binding protein 2 (Grb2)-SOS complex. However, merlin does not bind either SOS or Ras, but it counteracts the ERM (ezrin, radixin, moesin)-dependent activation of Ras, which correlates with the formation of a complex comprising ERM proteins, Grb2, SOS, Ras, and filamentous actin. Because efficient signaling from Ras requires Rac-p21-activated kinase-dependent phosphorylations of Raf and mitogen-activated protein/extracellular signal-regulated kinase kinase, merlin can also inhibit signal transfer from dominantly active Ras mutants. We propose that the interference of merlin with Ras- and Rac-dependent signal transfer represents part of the tumor-suppressive action of merlin.
Tyler Jacks - One of the best experts on this subject based on the ideXlab platform.
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merlin the product of the nf2 tumor suppressor gene is an inhibitor of the p21 activated kinase pak1
Molecular Cell, 2003Co-Authors: Joseph L Kissil, Erik Wilker, Kristen C Johnson, Matthew S Eckman, Michael B Yaffe, Tyler JacksAbstract:The Nf2 tumor suppressor gene codes for merlin, a protein whose function has been elusive. We describe a novel interaction between merlin and p21-activated kinase 1 (Pak1), which is dynamic and facilitated upon increased cellular confluence. Merlin inhibits the activation of Pak1, as the loss of merlin expression results in the inappropriate activation of Pak1 under conditions associated with low basal activity. Conversely, the overexpression of merlin in cells that display a high basal activity of Pak1 resulted in the inhibition of Pak1 activation. This inhibitory function of merlin is mediated through its binding to the Pak1 PBD and by inhibiting Pak1 recruitment to focal adhesions. This link provides a possible mechanism for the effect of loss of merlin expression in tumorigenesis.
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Merlin phosphorylation by p21-activated kinase 2 and effects of phosphorylation on merlin localization.
The Journal of biological chemistry, 2002Co-Authors: Joseph L Kissil, Kristen C Johnson, Matthew S Eckman, Tyler JacksAbstract:The Nf2 tumor suppressor gene product merlin is related to the membrane-cytoskeleton linker proteins of the band 4.1 superfamily, including ezrin, radixin, and moesin (ERMs). Merlin is regulated by phosphorylation in a Rac/cdc42-dependent fashion. We report that the phosphorylation of merlin at serine 518 is induced by the p21-activated kinase PAK2. This is demonstrated by biochemical fractionation, use of active and dominant-negative mutants of PAK2, and immunodepletion. By using wild-type and mutated forms of merlin and phospho-directed antibodies, we show that phosphorylation of merlin at serine 518 leads to dramatic protein relocalization.
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regulation of the neurofibromatosis type 2 tumor suppressor protein merlin by adhesion and growth arrest stimuli
Journal of Biological Chemistry, 1998Co-Authors: Reuben J. Shaw, Andrea I. Mcclatchey, Tyler JacksAbstract:The neurofibromatosis type 2 tumor suppressor gene is inactivated in the development of familial and sporadic schwannomas and meningiomas. The encoded protein, Merlin, is closely related to the Ezrin, Radixin, and Moesin family of membrane/cytoskeletal linker proteins. Examination of Merlin in several cell lines revealed that the protein migrates as two distinct species near 70 kDa. Phosphatase treatment and orthophosphate labeling demonstrated that the species with decreased mobility is phosphorylated. Given Merlin's localization to cortical actin structures, we examined the effect of cell-cell contact or other forms of growth arrest on Merlin expression and post-translational modification. Under conditions of confluency or serum deprivation, the levels of phosphorylated and unphosphorylated Merlin species increased significantly. Cells arrested in G1 by other methods or other phases of the cell cycle did not show changes in Merlin levels. Furthermore, loss of adhesion resulted in a nearly complete dephosphorylation of Merlin, which was reversed upon re-plating of cells, suggesting Merlin phosphorylation may be responsive to cell spreading or changes in cell shape. Thus, the tumor suppressor function of Merlin may involve the regulation of cellular responses to cues such as cell-cell contact, growth factor microenvironment, or changes in cell shape.
David H. Gutmann - One of the best experts on this subject based on the ideXlab platform.
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the neurofibromatosis 2 protein merlin regulates glial cell growth in an erbb2 and src dependent manner
Molecular and Cellular Biology, 2009Co-Authors: Sean S Houshmandi, Ryan J Emnett, David H. GutmannAbstract:Individuals with the inherited cancer predisposition syndrome neurofibromatosis 2 (NF2) develop several central nervous system (CNS) malignancies, including glial cell neoplasms (ependymomas). Recent studies have suggested that the NF2 protein, merlin (or schwannomin), may regulate receptor tyrosine kinase signaling, intracellular mitogenic growth control pathways, or adherens junction organization in non-nervous-system cell types. For this report, we used glial fibrillary acidic protein conditional knockout mice and derivative glia to determine how merlin regulates CNS glial cell proliferation. We show that the loss of merlin in glial cells results in increased proliferation in vitro and in vivo. Merlin regulation of glial cell growth reflects deregulated Src activity, such that pharmacologic or genetic inhibition of Src activation reduces Nf2(-/-) glial cell growth to wild-type levels. We further show that Src regulates Nf2(-/-) glial cell growth by sequentially regulating FAK and paxillin phosphorylation/activity. Next, we demonstrate that Src activation results from merlin regulation of ErbB2 activation and that genetic or pharmacologic ErbB2 inhibition reduces Nf2(-/-) glial cell Src/Src effector activation and proliferation to wild-type levels. Lastly, we show that merlin competes with Src for direct binding to ErbB2 and present a novel molecular mechanism for merlin regulation of ErbB2-dependent Src signaling and growth control.
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the neurofibromatosis 2 tumor suppressor gene product merlin regulates human meningioma cell growth by signaling through yap
Neoplasia, 2008Co-Authors: Katherine Striedinger, David H. Gutmann, Gilson S. Baia, Scott R Vandenberg, Michael W Mcdermott, Anita LalAbstract:Neurofibromatosis type 2 (NF2) is an autosomal dominant disorder characterized by the occurrence of schwannomas and meningiomas. Several studies have examined the ability of the NF2 gene product, merlin, to function as a tumor suppressor in diverse cell types; however, little is known about merlin growth regulation in meningiomas. In Drosophila, merlin controls cell proliferation and apoptosis by signaling through the Hippo pathway to inhibit the function of the transcriptional coactivator Yorkie. The Hippo pathway is conserved in mammals. On the basis of these observations, we developed human meningioma cell lines matched for merlin expression to evaluate merlin growth regulation and investigate the relationship between NF2 status and Yes-associated protein (YAP), the mammalian homolog of Yorkie. NF2 loss in meningioma cells was associated with loss of contact-dependent growth inhibition, enhanced anchorage-independent growth and increased cell proliferation due to increased S-phase entry. In addition, merlin loss in both meningioma cell lines and primary tumors resulted in increased YAP expression and nuclear localization. Finally, siRNA-mediated reduction of YAP in NF2-deficient meningioma cells rescued the effects of merlin loss on cell proliferation and S-phase entry. Collectively, these results represent the first demonstration that merlin regulates cell growth in human cancer cells by suppressing YAP.
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neurofibromatosis 2 nf2 tumor suppressor merlin inhibits phosphatidylinositol 3 kinase through binding to pike l
Proceedings of the National Academy of Sciences of the United States of America, 2004Co-Authors: Rong Rong, Xiaoling Tang, David H. GutmannAbstract:Neurofibromatosis 2 (NF2) is a tumor suppressor, although the molecular mechanism accounting for this effect remains unknown. Here, we show that merlin exerts its activity by inhibiting phosphatidylinositol 3-kinase (PI3-kinase), through binding to PIKE-L. Wild-type merlin, but not patient-derived mutant (L64P), binds PIKE-L and inhibits PI3-kinase activity. This suppression of PI3-kinase activity results from merlin disrupting the binding of PIKE-L to PI3-kinase. In addition, merlin suppression of PI3-kinase activity as well as schwannoma cell growth is abrogated by a single PIKE-L point mutation (P187L) that cannot bind merlin but can still activate PI3-kinase. Knocking down PIKE-L with RNA interference abolishes merlin's tumor-suppressive activity. Our data support the hypothesis that PIKE-L is an important mediator of merlin growth suppression.
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the nf2 tumor suppressor gene product merlin mediates contact inhibition of growth through interactions with cd44
Genes & Development, 2001Co-Authors: Helen Morrison, Carrie A. Haipek, David H. Gutmann, Helmut Ponta, Larry S Sherman, James Legg, Fatima Banine, Clare M Isacke, Peter HerrlichAbstract:The neurofibromatosis-2 (NF2) gene encodes merlin, an ezrin-radixin-moesin-(ERM)-related protein that functions as a tumor suppressor. We found that merlin mediates contact inhibition of growth through signals from the extracellular matrix. At high cell density, merlin becomes hypo-phosphorylated and inhibits cell growth in response to hyaluronate (HA), a mucopolysaccharide that surrounds cells. Merlin’s growth-inhibitoryactivitydepends on specific interaction with the cy toplasmic tail of CD44, a transmembrane HA receptor. At low cell density, merlin is phosphorylated, growth permissive, and exists in a complex with ezrin, moesin, and CD44. These data indicate that merlin and CD44 form a molecular switch that specifies cell growth arrest or proliferation.
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the nf2 tumor suppressor gene product merlin mediates contact inhibition of growth through interactions with cd44
Genes & Development, 2001Co-Authors: Helen Morrison, Carrie A. Haipek, David H. Gutmann, Helmut Ponta, Larry S Sherman, James Legg, Fatima Banine, Clare M Isacke, Peter HerrlichAbstract:The neurofibromatosis-2 (NF2) gene encodes merlin, an ezrin-radixin-moesin-(ERM)-related protein that functions as a tumor suppressor. We found that merlin mediates contact inhibition of growth through signals from the extracellular matrix. At high cell density, merlin becomes hypo-phosphorylated and inhibits cell growth in response to hyaluronate (HA), a mucopolysaccharide that surrounds cells. Merlin’s growth-inhibitoryactivitydepends on specific interaction with the cy toplasmic tail of CD44, a transmembrane HA receptor. At low cell density, merlin is phosphorylated, growth permissive, and exists in a complex with ezrin, moesin, and CD44. These data indicate that merlin and CD44 form a molecular switch that specifies cell growth arrest or proliferation.