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Senju Y, Hibino E. Moesin-ezrin-radixin-like protein merlin: Its conserved and distinct functions from those of ERM proteins. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2023; 1865:184076. [PMID: 36302494 DOI: 10.1016/j.bbamem.2022.184076] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/08/2022] [Revised: 10/13/2022] [Accepted: 10/18/2022] [Indexed: 11/06/2022]
Affiliation(s)
- Yosuke Senju
- Research Institute for Interdisciplinary Science (RIIS), Okayama University, Okayama, Japan.
| | - Emi Hibino
- Graduate School of Pharmaceutical Sciences, Nagoya University, Aichi, Japan
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2
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Hennigan RF, Thomson CS, Stachowski K, Nassar N, Ratner N. Merlin tumor suppressor function is regulated by PIP2-mediated dimerization. PLoS One 2023; 18:e0281876. [PMID: 36809290 PMCID: PMC9942953 DOI: 10.1371/journal.pone.0281876] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2022] [Accepted: 01/30/2023] [Indexed: 02/23/2023] Open
Abstract
Neurofibromatosis Type 2 is an inherited disease characterized by Schwann cell tumors of cranial and peripheral nerves. The NF2 gene encodes Merlin, a member of the ERM family consisting of an N-terminal FERM domain, a central α-helical region, and a C-terminal domain. Changes in the intermolecular FERM-CTD interaction allow Merlin to transition between an open, FERM accessible conformation and a closed, FERM-inaccessible conformation, modulating Merlin activity. Merlin has been shown to dimerize, but the regulation and function Merlin dimerization is not clear. We used a nanobody based binding assay to show that Merlin dimerizes via a FERM-FERM interaction, orientated with each C-terminus close to each other. Patient derived and structural mutants show that dimerization controls interactions with specific binding partners, including HIPPO pathway components, and correlates with tumor suppressor activity. Gel filtration experiments showed that dimerization occurs after a PIP2 mediated transition from closed to open conformation monomers. This process requires the first 18 amino acids of the FERM domain and is inhibited by phosphorylation at serine 518. The discovery that active, open conformation Merlin is a dimer represents a new paradigm for Merlin function with implications for the development of therapies designed to compensate for Merlin loss.
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Affiliation(s)
- Robert F. Hennigan
- Division of Experimental Hematology and Cancer Biology, Cincinnati Children’s Hospital Medical Center, Department of Pediatrics, University of Cincinnati, Cincinnati, OH, United States of America
- * E-mail:
| | - Craig S. Thomson
- Division of Experimental Hematology and Cancer Biology, Cincinnati Children’s Hospital Medical Center, Department of Pediatrics, University of Cincinnati, Cincinnati, OH, United States of America
| | - Kye Stachowski
- Division of Experimental Hematology and Cancer Biology, Cincinnati Children’s Hospital Medical Center, Department of Pediatrics, University of Cincinnati, Cincinnati, OH, United States of America
| | - Nicolas Nassar
- Division of Experimental Hematology and Cancer Biology, Cincinnati Children’s Hospital Medical Center, Department of Pediatrics, University of Cincinnati, Cincinnati, OH, United States of America
| | - Nancy Ratner
- Division of Experimental Hematology and Cancer Biology, Cincinnati Children’s Hospital Medical Center, Department of Pediatrics, University of Cincinnati, Cincinnati, OH, United States of America
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3
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A novel NF2 splicing mutant causes neurofibromatosis type 2 via liquid-liquid phase separation with large tumor suppressor and Hippo pathway. iScience 2022; 25:105275. [PMID: 36300003 PMCID: PMC9589172 DOI: 10.1016/j.isci.2022.105275] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2022] [Revised: 06/27/2022] [Accepted: 09/30/2022] [Indexed: 11/24/2022] Open
Abstract
Neurofibromatosis type 2 is an autosomal dominant multiple neoplasia syndrome and is usually caused by mutations in the neurofibromin 2 (NF2) gene, which encodes a tumor suppressor and initiates the Hippo pathway. However, the mechanism by which NF2 functions in the Hippo pathway isn’t fully understood. Here we identified a NF2 c.770-784del mutation from a neurofibromatosis type 2 family. MD simulations showed that this mutation significantly changed the structure of the F3 module of the NF2-FERM domain. Functional assays indicated that the NF2 c.770-784del variant formed LLPS in the cytoplasm with LATS to restrain LATS plasma membrane localization and inactivated the Hippo pathway. Besides, this deletion partly caused a skipping of exon 8 and reduced the protein level of NF2, collectively promoting proliferation and tumorigenesis of meningeal cells. We identified an unrecognized mechanism of LLPS and splicing skipping for the NF2-induced Hippo pathway, which provided new insight into the pathogenesis of neurofibromatosis type 2. NF2 c.770-784 deletion is a novel mutation related to Neurofibromatosis type 2 NF2 variant forms LLPS in the cytoplasm with LATS and inhibits the Hippo pathway NF2 variant causes an aberrant skipping of exon 8 and reduces NF2 protein level NF2 variant promotes proliferation and tumorigenesis of meningeal cells
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4
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Primi MC, Rangarajan ES, Patil DN, Izard T. Conformational flexibility determines the Nf2/merlin tumor suppressor functions. Matrix Biol Plus 2021; 12:100074. [PMID: 34337379 PMCID: PMC8318988 DOI: 10.1016/j.mbplus.2021.100074] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2021] [Revised: 06/14/2021] [Accepted: 06/15/2021] [Indexed: 10/26/2022] Open
Abstract
The Neurofibromatosis type 2 gene encodes the Nf2/merlin tumor suppressor protein that is responsible for the regulation of cell proliferation. Once activated, Nf2/merlin modulates adhesive signaling pathways and thereby inhibits cell growth. Nf2/merlin controls oncogenic gene expression by modulating the Hippo pathway. By responding to several physical and biochemical stimuli, Hippo signaling determines contact inhibition of proliferation as well as organ size. The large tumor suppressor (LATS) serine/threonine-protein kinase is the key enzyme in the highly conserved kinase cascade that negatively regulates the activity and localization of the transcriptional coactivators Yes-associated protein (YAP) and its paralogue transcriptional coactivator with PDZ-binding motif (TAZ). Nf2/merlin belongs to the band 4.1, ezrin, radixin, moesin (FERM) gene family that links the actin cytoskeleton to adherens junctions, remodels adherens junctions during epithelial morphogenesis and maintains organized apical surfaces on the plasma cell membrane. Nf2/merlin and ERM proteins have a globular N-terminal cloverleaf head domain, the FERM domain, that binds to the plasma membrane, a central α-helical domain, and a tail domain that binds to its head domain. Here we present the high-resolution crystal structure of Nf2/merlin bound to LATS1 which shows that LATS1 binding to Nf2/merlin displaces the Nf2/merlin tail domain and causes an allosteric shift in the Nf2/merlin α-helix that extends from its FERM domain. This is consistent with the fact that full-length Nf2/merlin binds LATS1 ~10-fold weaker compared to LATS1 binding to the Nf2/merlin-PIP2 complex. Our data increase our understanding of Nf2/merlin biology by providing mechanistic insights into the Hippo pathway that are relevant to several diseases in particular oncogenic features that are associated with cancers.
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Affiliation(s)
- Marina C Primi
- Cell Adhesion Laboratory, Department of Integrative Structural and Computational Biology, The Scripps Research Institute, Jupiter 33458, FL, United States
| | - Erumbi S Rangarajan
- Cell Adhesion Laboratory, Department of Integrative Structural and Computational Biology, The Scripps Research Institute, Jupiter 33458, FL, United States
| | - Dipak N Patil
- Cell Adhesion Laboratory, Department of Integrative Structural and Computational Biology, The Scripps Research Institute, Jupiter 33458, FL, United States
| | - Tina Izard
- Cell Adhesion Laboratory, Department of Integrative Structural and Computational Biology, The Scripps Research Institute, Jupiter 33458, FL, United States
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5
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Lietha D, Izard T. Roles of Membrane Domains in Integrin-Mediated Cell Adhesion. Int J Mol Sci 2020; 21:ijms21155531. [PMID: 32752284 PMCID: PMC7432473 DOI: 10.3390/ijms21155531] [Citation(s) in RCA: 28] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2020] [Revised: 07/29/2020] [Accepted: 07/31/2020] [Indexed: 12/13/2022] Open
Abstract
The composition and organization of the plasma membrane play important functional and regulatory roles in integrin signaling, which direct many physiological and pathological processes, such as development, wound healing, immunity, thrombosis, and cancer metastasis. Membranes are comprised of regions that are thick or thin owing to spontaneous partitioning of long-chain saturated lipids from short-chain polyunsaturated lipids into domains defined as ordered and liquid-disorder domains, respectively. Liquid-ordered domains are typically 100 nm in diameter and sometimes referred to as lipid rafts. We posit that integrin β senses membrane thickness and that mechanical force on the membrane regulates integrin activation through membrane thinning. This review examines what we know about the nature and mechanism of the interaction of integrins with the plasma membrane and its effects on regulating integrins and its binding partners.
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Affiliation(s)
- Daniel Lietha
- Cell Signaling and Adhesion Group, Structural and Chemical Biology, Margarita Salas Center for Biological Research (CIB-CSIC), E-28040 Madrid, Spain;
| | - Tina Izard
- Cell Adhesion Laboratory, Department of Integrative Structural and Computational Biology, The Scripps Research Institute, Jupiter, FL 33458, USA
- Correspondence:
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6
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Hong AW, Meng Z, Plouffe SW, Lin Z, Zhang M, Guan KL. Critical roles of phosphoinositides and NF2 in Hippo pathway regulation. Genes Dev 2020; 34:511-525. [PMID: 32115406 PMCID: PMC7111263 DOI: 10.1101/gad.333435.119] [Citation(s) in RCA: 36] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2019] [Accepted: 01/27/2020] [Indexed: 12/29/2022]
Abstract
In this study, Hong et al. provide new insights into how NF2 mediates upstream signals to regulate the Hippo pathway. They show that NF2's lipid-binding ability is critical for its function in activating the Hippo pathway in response to osmotic stress in mammalian cells, and identify the PIP5K family as novel regulators upstream of Hippo signaling. The Hippo pathway is a master regulator of tissue homeostasis and organ size. NF2 is a well-established tumor suppressor, and loss of NF2 severely compromises Hippo pathway activity. However, the precise mechanism of how NF2 mediates upstream signals to regulate the Hippo pathway is not clear. Here we report that, in mammalian cells, NF2's lipid-binding ability is critical for its function in activating the Hippo pathway in response to osmotic stress. Mechanistically, osmotic stress induces PI(4,5)P2 plasma membrane enrichment by activating the PIP5K family, allowing for NF2 plasma membrane recruitment and subsequent downstream Hippo pathway activation. An NF2 mutant deficient in lipid binding is unable to activate the Hippo pathway in response to osmotic stress, as measured by LATS and YAP phosphorylation. Our findings identify the PIP5K family as novel regulators upstream of Hippo signaling, and uncover the importance of phosphoinositide dynamics, specifically PI(4,5)P2, in Hippo pathway regulation.
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Affiliation(s)
- Audrey W Hong
- Department of Pharmacology and Moores Cancer Center, University of California at San Diego, La Jolla, California 92093, USA
| | - Zhipeng Meng
- Department of Pharmacology and Moores Cancer Center, University of California at San Diego, La Jolla, California 92093, USA
| | - Steven W Plouffe
- Department of Pharmacology and Moores Cancer Center, University of California at San Diego, La Jolla, California 92093, USA
| | - Zhijie Lin
- Division of Life Science, State Key Laboratory of Molecular Neuroscience, Hong Kong University of Science and Technology, Hong Kong, China
| | - Mingjie Zhang
- Division of Life Science, State Key Laboratory of Molecular Neuroscience, Hong Kong University of Science and Technology, Hong Kong, China.,Center of Systems Biology and Human Health, Hong Kong University of Science and Technology, Kowloon, China
| | - Kun-Liang Guan
- Department of Pharmacology and Moores Cancer Center, University of California at San Diego, La Jolla, California 92093, USA
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7
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Shabardina V, Kashima Y, Suzuki Y, Makalowski W. Emergence and Evolution of ERM Proteins and Merlin in Metazoans. Genome Biol Evol 2020; 12:3710-3724. [PMID: 31851361 PMCID: PMC6978628 DOI: 10.1093/gbe/evz265] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/02/2019] [Indexed: 12/18/2022] Open
Abstract
Ezrin, radixin, moesin, and merlin are cytoskeletal proteins, whose functions are specific to metazoans. They participate in cell cortex rearrangement, including cell-cell contact formation, and play an important role in cancer progression. Here, we have performed a comprehensive phylogenetic analysis of the proteins spanning 87 species. The results describe a possible mechanism for the protein family origin in the root of Metazoa, paralogs diversification in vertebrates, and acquisition of novel functions, including tumor suppression. In addition, a merlin paralog, present in most vertebrates but lost in mammals, has been described here for the first time. We have also highlighted a set of amino acid variations within the conserved motifs as the candidates for determining physiological differences between ERM paralogs.
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Affiliation(s)
| | - Yukie Kashima
- Department of Computational Biology and Medical Sciences, The University of Tokyo, Kashiwa, Japan
| | - Yutaka Suzuki
- Laboratory of Systems Genomics, Department of Computational Biology and Medical Sciences, The University of Tokyo, Kashiwa, Japan
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8
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Hennigan RF, Fletcher JS, Guard S, Ratner N. Proximity biotinylation identifies a set of conformation-specific interactions between Merlin and cell junction proteins. Sci Signal 2019; 12:12/578/eaau8749. [PMID: 31015291 DOI: 10.1126/scisignal.aau8749] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Neurofibromatosis type 2 is an inherited, neoplastic disease associated with schwannomas, meningiomas, and ependymomas and that is caused by inactivation of the tumor suppressor gene NF2 The NF2 gene product, Merlin, has no intrinsic catalytic activity; its tumor suppressor function is mediated through the proteins with which it interacts. We used proximity biotinylation followed by mass spectrometry and direct binding assays to identify proteins that associated with wild-type and various mutant forms of Merlin in immortalized Schwann cells. We defined a set of 52 proteins in close proximity to wild-type Merlin. Most of the Merlin-proximal proteins were components of cell junctional signaling complexes, suggesting that additional potential interaction partners may exist in adherens junctions, tight junctions, and focal adhesions. With mutant forms of Merlin that cannot bind to phosphatidylinositol 4,5-bisphosphate (PIP2) or that constitutively adopt a closed conformation, we confirmed a critical role for PIP2 binding in Merlin function and identified a large cohort of proteins that specifically interacted with Merlin in the closed conformation. Among these proteins, we identified a previously unreported Merlin-binding protein, apoptosis-stimulated p53 protein 2 (ASPP2, also called Tp53bp2), that bound to closed-conformation Merlin predominately through the FERM domain. Our results demonstrate that Merlin is a component of cell junctional mechanosensing complexes and defines a specific set of proteins through which it acts.
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Affiliation(s)
- Robert F Hennigan
- Division of Experimental Hematology and Cancer Biology, Cincinnati Children's Hospital, Cincinnati, OH 45229, USA.
| | - Jonathan S Fletcher
- Division of Experimental Hematology and Cancer Biology, Cincinnati Children's Hospital, Cincinnati, OH 45229, USA
| | - Steven Guard
- Department of Molecular, Cellular & Developmental Biology, University of Colorado Boulder, Boulder, CO 80309, USA
| | - Nancy Ratner
- Division of Experimental Hematology and Cancer Biology, Cincinnati Children's Hospital, Cincinnati, OH 45229, USA
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9
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Lipid binding promotes the open conformation and tumor-suppressive activity of neurofibromin 2. Nat Commun 2018; 9:1338. [PMID: 29626191 PMCID: PMC5889391 DOI: 10.1038/s41467-018-03648-4] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2017] [Accepted: 03/02/2018] [Indexed: 01/29/2023] Open
Abstract
Neurofibromatosis type 2 (NF2) is a tumor-forming disease of the nervous system caused by deletion or by loss-of-function mutations in NF2, encoding the tumor suppressing protein neurofibromin 2 (also known as schwannomin or merlin). Neurofibromin 2 is a member of the ezrin, radixin, moesin (ERM) family of proteins regulating the cytoskeleton and cell signaling. The correlation of the tumor-suppressive function and conformation (open or closed) of neurofibromin 2 has been subject to much speculation, often based on extrapolation from other ERM proteins, and controversy. Here we show that lipid binding results in the open conformation of neurofibromin 2 and that lipid binding is necessary for inhibiting cell proliferation. Collectively, our results provide a mechanism in which the open conformation is unambiguously correlated with lipid binding and localization to the membrane, which are critical for the tumor-suppressive function of neurofibromin 2, thus finally reconciling the long-standing conformation and function debate. Neurofibromin 2 (NF2) is a tumour suppressor that inhibits cell growth. Here the authors combine functional, biochemical, and structural studies and show that lipid-bound NF2 adopts an open conformation and that NF2 lipid binding is required for inhibition of cell proliferation.
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10
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Ruggieri M, Praticò AD, Serra A, Maiolino L, Cocuzza S, Di Mauro P, Licciardello L, Milone P, Privitera G, Belfiore G, Di Pietro M, Di Raimondo F, Romano A, Chiarenza A, Muglia M, Polizzi A, Evans DG. Childhood neurofibromatosis type 2 (NF2) and related disorders: from bench to bedside and biologically targeted therapies. ACTA OTORHINOLARYNGOLOGICA ITALICA 2017; 36:345-367. [PMID: 27958595 PMCID: PMC5225790 DOI: 10.14639/0392-100x-1093] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/10/2016] [Accepted: 04/29/2016] [Indexed: 12/22/2022]
Abstract
Neurofibromatosis type 2 [NF2; MIM # 101000] is an autosomal dominant disorder characterised by the occurrence of vestibular schwannomas (VSs), schwannomas of other cranial, spinal and cutaneous nerves, cranial and spinal meningiomas and/or other central nervous system (CNS) tumours (e.g., ependymomas, astrocytomas). Additional features include early onset cataracts, optic nerve sheath meningiomas, retinal hamartomas, dermal schwannomas (i.e., NF2-plaques), and (few) café-au-lait spots. Clinically, NF2 children fall into two main groups: (1) congenital NF2 - with bilateral VSs detected as early as the first days to months of life, which can be stable/asymptomatic for one-two decades and suddenly progress; and (2) severe pre-pubertal (Wishart type) NF2- with multiple (and rapidly progressive) CNS tumours other-than-VS, which usually present first, years before VSs [vs. the classical adult (Gardner type) NF2, with bilateral VSs presenting in young adulthood, sometimes as the only disease feature]. Some individuals can develop unilateral VS associated with ipsilateral meningiomas or multiple schwannomas localised to one part of the peripheral nervous system [i.e., mosaic NF2] or multiple non-VS, non-intradermal cranial, spinal and peripheral schwannomas (histologically proven) [schwannomatosis]. NF2 is caused by mutations in the NF2 gene at chromosome 22q12.1, which encodes for a protein called merlin or schwannomin, most similar to the exrin-readixin-moesin (ERM) proteins; mosaicNF2 is due to mosaic phenomena for the NF2 gene, whilst schwannomatosis is caused by coupled germ-line and mosaic mutations either in the SMARCB1 gene [SWNTS1; MIM # 162091] or the LZTR1 gene [SWNTS2; MIM # 615670] both falling within the 22q region and the NF2 gene. Data driven from in vitro and animal studies on the merlin pathway [e.g., post-translational and upstream/downstream regulation] allowed biologically targeted treatment strategies [e.g., Lapatinib, Erlotinib, Bevacizumab] aimed to multiple tumour shrinkage and/or regression and tumour arrest of progression with functional improvement.
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Affiliation(s)
- M Ruggieri
- Unit of Rare Diseases of the Nervous System in Childhood, Department of Clinical and Experimental Medicine, Section of Pediatrics and Child Neuropsychiatry, University of Catania, Italy
| | - A D Praticò
- Unit of Rare Diseases of the Nervous System in Childhood, Department of Clinical and Experimental Medicine, Section of Pediatrics and Child Neuropsychiatry, University of Catania, Italy.,Department of Biomedical and Biotechnological Sciences, University of Catania, Italy
| | - A Serra
- Department of Medical and Surgical Sciences and Advanced Technologies "G. Ingrassia", Institute of Otorhinolaryngology, University of Catania, Italy
| | - L Maiolino
- Department of Medical and Surgical Sciences and Advanced Technologies "G. Ingrassia", Institute of Otorhinolaryngology, University of Catania, Italy
| | - S Cocuzza
- Department of Medical and Surgical Sciences and Advanced Technologies "G. Ingrassia", Institute of Otorhinolaryngology, University of Catania, Italy
| | - P Di Mauro
- Department of Medical and Surgical Sciences and Advanced Technologies "G. Ingrassia", Institute of Otorhinolaryngology, University of Catania, Italy
| | - L Licciardello
- Department of Medical and Surgical Sciences and Advanced Technologies "G. Ingrassia", Institute of Otorhinolaryngology, University of Catania, Italy
| | - P Milone
- Department of Medical and Surgical Sciences and Advanced Technologies "G. Ingrassia", Institute of Radiology, University of Catania, Italy
| | - G Privitera
- Department of Medical and Surgical Sciences and Advanced Technologies "G. Ingrassia", Institute of Radiology, University of Catania, Italy
| | - G Belfiore
- Unit of Paediatric Radiology, AOU "Policlinico-Vittorio Emanuele", Catania, Italy
| | - M Di Pietro
- Department of Medical and Surgical Sciences and Advanced Technologies "G. Ingrassia", Institute of Ophthalmology, University of Catania, Italy
| | - F Di Raimondo
- Division of Hematology, AOU "Policlinico-Vittorio Emanuele", University of Catania, Italy
| | - A Romano
- Division of Hematology, AOU "Policlinico-Vittorio Emanuele", University of Catania, Italy
| | - A Chiarenza
- Division of Hematology, AOU "Policlinico-Vittorio Emanuele", University of Catania, Italy
| | - M Muglia
- Unit of Genetics, Institute of Neurological Sciences, National Research Council, Piano Lago di Mangone, Italy
| | - A Polizzi
- National Centre for Rare Disease, Istituto Superiore di Sanità, Rome, Italy.,Institute of Neurological Sciences, National Research Council, Catania, Italy
| | - D G Evans
- Genomic Medicine, University of Manchester, Manchester Academic Health Science Centre, Institute of Human Development, Central Manchester NHS Foundation Trust, Manchester Royal Infirmary, Manchester, UK
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11
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Huang X, Schurman N, Handa K, Hakomori S. Functional role of glycosphingolipids in contact inhibition of growth in a human mammary epithelial cell line. FEBS Lett 2017; 591:1918-1928. [DOI: 10.1002/1873-3468.12709] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2017] [Revised: 05/22/2017] [Accepted: 05/24/2017] [Indexed: 11/08/2022]
Affiliation(s)
- Xiaohua Huang
- Division of Biomembrane Research; Pacific Northwest Research Institute; Seattle WA USA
| | - Nathan Schurman
- Division of Biomembrane Research; Pacific Northwest Research Institute; Seattle WA USA
| | - Kazuko Handa
- Division of Biomembrane Research; Pacific Northwest Research Institute; Seattle WA USA
| | - Senitiroh Hakomori
- Division of Biomembrane Research; Pacific Northwest Research Institute; Seattle WA USA
- Department of Pathobiology and Global Health; University of Washington; Seattle WA USA
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12
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Shah AD, Inder KL, Shah AK, Cristino AS, McKie AB, Gabra H, Davis MJ, Hill MM. Integrative Analysis of Subcellular Quantitative Proteomics Studies Reveals Functional Cytoskeleton Membrane-Lipid Raft Interactions in Cancer. J Proteome Res 2016; 15:3451-3462. [PMID: 27384440 DOI: 10.1021/acs.jproteome.5b01035] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Lipid rafts are dynamic membrane microdomains that orchestrate molecular interactions and are implicated in cancer development. To understand the functions of lipid rafts in cancer, we performed an integrated analysis of quantitative lipid raft proteomics data sets modeling progression in breast cancer, melanoma, and renal cell carcinoma. This analysis revealed that cancer development is associated with increased membrane raft-cytoskeleton interactions, with ∼40% of elevated lipid raft proteins being cytoskeletal components. Previous studies suggest a potential functional role for the raft-cytoskeleton in the action of the putative tumor suppressors PTRF/Cavin-1 and Merlin. To extend the observation, we examined lipid raft proteome modulation by an unrelated tumor suppressor opioid binding protein cell-adhesion molecule (OPCML) in ovarian cancer SKOV3 cells. In agreement with the other model systems, quantitative proteomics revealed that 39% of OPCML-depleted lipid raft proteins are cytoskeletal components, with microfilaments and intermediate filaments specifically down-regulated. Furthermore, protein-protein interaction network and simulation analysis showed significantly higher interactions among cancer raft proteins compared with general human raft proteins. Collectively, these results suggest increased cytoskeleton-mediated stabilization of lipid raft domains with greater molecular interactions as a common, functional, and reversible feature of cancer cells.
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Affiliation(s)
- Anup D Shah
- The University of Queensland Diamantina Institute, The University of Queensland , Translational Research Institute, Brisbane, Queensland 4102, Australia
| | - Kerry L Inder
- The University of Queensland Diamantina Institute, The University of Queensland , Translational Research Institute, Brisbane, Queensland 4102, Australia
| | - Alok K Shah
- The University of Queensland Diamantina Institute, The University of Queensland , Translational Research Institute, Brisbane, Queensland 4102, Australia
| | - Alexandre S Cristino
- The University of Queensland Diamantina Institute, The University of Queensland , Translational Research Institute, Brisbane, Queensland 4102, Australia
| | - Arthur B McKie
- Ovarian Cancer Action Research Centre, Department of Surgery and Cancer, Imperial College London Hammersmith Campus , London W12 0NN, United Kingdom
| | - Hani Gabra
- Ovarian Cancer Action Research Centre, Department of Surgery and Cancer, Imperial College London Hammersmith Campus , London W12 0NN, United Kingdom
| | - Melissa J Davis
- Division of Bioinformatics, The Walter and Eliza Hall Institute of Medical Research , 1G Royal Parade, Parkville Victoria 3052, Australia
| | - Michelle M Hill
- The University of Queensland Diamantina Institute, The University of Queensland , Translational Research Institute, Brisbane, Queensland 4102, Australia
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13
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Chinthalapudi K, Patil DN, Rangarajan ES, Rader C, Izard T. Lipid-directed vinculin dimerization. Biochemistry 2015; 54:2758-68. [PMID: 25880222 DOI: 10.1021/acs.biochem.5b00015] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Vinculin localizes to cellular adhesions where it regulates motility, migration, development, wound healing, and response to force. Importantly, vinculin loss results in cancer phenotypes, cardiovascular disease, and embryonic lethality. At the plasma cell membrane, the most abundant phosphoinositide, phosphatidylinositol 4,5-bisphosphate (PIP2), binds the vinculin tail domain, Vt, and triggers homotypic and heterotypic interactions that amplify binding of vinculin to the actin network. Binding of PIP2 to Vt is necessary for maintaining optimal focal adhesions, for organizing stress fibers, for cell migration and spreading, and for the control of vinculin dynamics and turnover of focal adhesions. While the recently determined Vt/PIP2 crystal structure revealed the conformational changes occurring upon lipid binding and oligomerization, characterization of PIP2-induced vinculin oligomerization has been challenging in the adhesion biology field. Here, via a series of novel biochemical assays not performed in previous studies that relied on chemical cross-linking, we characterize the PIP2-induced vinculin oligomerization. Our results show that Vt/PIP2 forms a tight dimer with Vt or with the muscle-specific vinculin isoform, metavinculin, at sites of adhesion at the cell membrane. Insight into how PIP2 regulates clustering and into mechanisms that regulate cell adhesion allows the development for a more definite sensor for PIP2, and our developed techniques can be applied generally and thus open the door for the characterization of many other protein/PIP2 complexes under physiological conditions.
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Affiliation(s)
- Krishna Chinthalapudi
- †Cell Adhesion Laboratory, ‡Department of Cancer Biology, and §Department of Molecular Therapeutics, The Scripps Research Institute, Jupiter, Florida 33458, United States
| | - Dipak N Patil
- †Cell Adhesion Laboratory, ‡Department of Cancer Biology, and §Department of Molecular Therapeutics, The Scripps Research Institute, Jupiter, Florida 33458, United States
| | - Erumbi S Rangarajan
- †Cell Adhesion Laboratory, ‡Department of Cancer Biology, and §Department of Molecular Therapeutics, The Scripps Research Institute, Jupiter, Florida 33458, United States
| | - Christoph Rader
- †Cell Adhesion Laboratory, ‡Department of Cancer Biology, and §Department of Molecular Therapeutics, The Scripps Research Institute, Jupiter, Florida 33458, United States
| | - Tina Izard
- †Cell Adhesion Laboratory, ‡Department of Cancer Biology, and §Department of Molecular Therapeutics, The Scripps Research Institute, Jupiter, Florida 33458, United States
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Lipid rafts and raft-mediated supramolecular entities in the regulation of CD95 death receptor apoptotic signaling. Apoptosis 2015; 20:584-606. [DOI: 10.1007/s10495-015-1104-6] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
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15
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Molecular insights into NF2/Merlin tumor suppressor function. FEBS Lett 2014; 588:2743-52. [PMID: 24726726 DOI: 10.1016/j.febslet.2014.04.001] [Citation(s) in RCA: 128] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2014] [Revised: 04/01/2014] [Accepted: 04/02/2014] [Indexed: 02/07/2023]
Abstract
The FERM domain protein Merlin, encoded by the NF2 tumor suppressor gene, regulates cell proliferation in response to adhesive signaling. The growth inhibitory function of Merlin is induced by intercellular adhesion and inactivated by joint integrin/receptor tyrosine kinase signaling. Merlin contributes to the formation of cell junctions in polarized tissues, activates anti-mitogenic signaling at tight-junctions, and inhibits oncogenic gene expression. Thus, inactivation of Merlin causes uncontrolled mitogenic signaling and tumorigenesis. Merlin's predominant tumor suppressive functions are attributable to its control of oncogenic gene expression through regulation of Hippo signaling. Notably, Merlin translocates to the nucleus where it directly inhibits the CRL4(DCAF1) E3 ubiquitin ligase, thereby suppressing inhibition of the Lats kinases. A dichotomy in NF2 function has emerged whereby Merlin acts at the cell cortex to organize cell junctions and propagate anti-mitogenic signaling, whereas it inhibits oncogenic gene expression through the inhibition of CRL4(DCAF1) and activation of Hippo signaling. The biochemical events underlying Merlin's normal function and tumor suppressive activity will be discussed in this Review, with emphasis on recent discoveries that have greatly influenced our understanding of Merlin biology.
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Li W, Cooper J, Karajannis MA, Giancotti FG. Merlin: a tumour suppressor with functions at the cell cortex and in the nucleus. EMBO Rep 2012; 13:204-15. [PMID: 22482125 DOI: 10.1038/embor.2012.11] [Citation(s) in RCA: 98] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Inhibition of proliferation by cell-to-cell contact is essential for tissue organization, and its disruption contributes to tumorigenesis. The FERM domain protein Merlin, encoded by the NF2 tumour suppressor gene, is an important mediator of contact inhibition. Merlin was thought to inhibit mitogenic signalling and activate the Hippo pathway by interacting with diverse target-effectors at or near the plasma membrane. However, recent studies highlight that Merlin pleiotropically affects signalling by migrating into the nucleus and inducing a growth-suppressive programme of gene expression through its direct inhibition of the CRL4DCAF1 E3 ubiquitin ligase. In addition, Merlin promotes the establishment of epithelial adhesion and polarity by recruiting Par3 and aPKC to E-cadherin-dependent junctions, and by ensuring the assembly of tight junctions. These recent advances suggest that Merlin acts at the cell cortex and in the nucleus in a similar, albeit antithetic, manner to the oncogene β-catenin.
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Affiliation(s)
- Wei Li
- Cell Biology Program, Sloan–Kettering Institute for Cancer Research, Memorial Sloan–Kettering Cancer Center, 1275 York Avenue, Box 216, New York, New York 10065, USA
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FERM domain phosphoinositide binding targets merlin to the membrane and is essential for its growth-suppressive function. Mol Cell Biol 2011; 31:1983-96. [PMID: 21402777 DOI: 10.1128/mcb.00609-10] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
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.
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Abstract
Membrane rafts (MRs) are specialized microdomains in the cell membrane with an altered lipid composition. Upon various stimulations, MRs can be clustered to aggregate or recruit NADPH oxidase sub-units and related proteins to form MR redox signalosomes in the membrane of cells like vascular endothelial cells (ECs). Multiple protein complexes, like MR redox signalosomes, are now considered to play a crucial role in the regulation of cell function and in the development of different cell dysfunctions. To form such redox signalosomes, ceramide will be generated from the hydrolysis of sphingomyelin by lysosomal acid sphingomyelinase that has been translocated via lysosome fusion to the MR area. In this brief review, current information is provided to help understand the occurrence and function of MR redox signalosomes. This may increase enthusiasm of the scientific community for further studies on the molecular mechanisms and the functional significance of forming such MR redox signalosomes.
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Affiliation(s)
- Chun Zhang
- Department of Pharmacology & Toxicology, Medical College of Virginia, Virginia Commonwealth University, Richmond, VA 23298, USA
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Lee MH, Padmashali R, Koria P, Andreadis ST. JNK regulates binding of alpha-catenin to adherens junctions and cell-cell adhesion. FASEB J 2010; 25:613-23. [PMID: 21030692 DOI: 10.1096/fj.10-161380] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
We recently reported that c-Jun N-terminal kinase (JNK) is associated with adherens junctions and phosphorylates β-catenin at serine 33/37 and threonine 41. Here, we report that inhibition of JNK led to formation of adherens junctions, which was accompanied by dissociation of α-catenin from the β-catenin/E-cadherin complex and increased association of α-catenin with the cytoskeleton. Conversely, activation of JNK increased binding of α-catenin to β-catenin, which was blocked by the JNK inhibitor SP600125 or JNK siRNA. In addition, inhibition of JNK failed to lead to adherens junction formation in cells where α-catenin was absent or knocked down. Conversely, introduction of α-catenin restored the responsiveness of cells to JNK inhibition and led to cell-cell adhesion. Experiments with domain deletion mutants showed that binding of α-catenin to β-catenin was required for transport of adherens junction complexes to the cell surface, while binding to actin was required for translocation to the cell-cell contact sites. Collectively, our results suggest that JNK affects the association of α-catenin with the adherens junction complex and regulates adherens junctions.
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Affiliation(s)
- Meng-Horng Lee
- Bioengineering Laboratory, Department of Chemical and Biological Engineering, University at Buffalo, State University of New York, Amherst, NY 14260-4200, USA
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Microtubule-mediated transport of the tumor-suppressor protein Merlin and its mutants. Proc Natl Acad Sci U S A 2010; 107:7311-6. [PMID: 20368450 DOI: 10.1073/pnas.0907389107] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The neurofibromatosis type 2 (NF2) tumor-suppressor protein Merlin is a member of the ERM family of proteins that links the cytoskeleton to the plasma membrane. In humans, mutations in the NF2 gene cause neurofibromatosis type-2 (NF2), a cancer syndrome characterized by the development of tumors of the nervous system. Previous reports have suggested that the subcellular distribution of Merlin is critical to its function, and that several NF2 mutants that lack tumor-suppressor activity present improper localization. Here we used a Drosophila cell culture model to study the distribution and mechanism of intracellular transport of Merlin and its mutants. We found that Drosophila Merlin formed cytoplasmic particles that move bidirectionally along microtubules. A single NF2-causing amino acid substitution in the FERM domain dramatically inhibited Merlin particle movement. Surprisingly, the presence of this immotile Merlin mutant also inhibited trafficking of the WT protein. Analysis of the movement of WT protein using RNAi and pull-downs showed that Merlin particles are associated with and moved by microtubule motors (kinesin-1 and cytoplasmic dynein), and that binding of motors and movement is regulated by Merlin phosphorylation. Inhibition of Merlin transport by expression of the dominant-negative mutant or depletion of kinesin-1 results in increased nuclear accumulation of the transcriptional coactivator Yorkie. These results demonstrate the requirement of microtubule-dependent transport for Merlin function.
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Lin SL, Chien CW, Han CL, Chen ESW, Kao SH, Chen YJ, Liao F. Temporal proteomics profiling of lipid rafts in CCR6-activated T cells reveals the integration of actin cytoskeleton dynamics. J Proteome Res 2010; 9:283-97. [PMID: 19928914 DOI: 10.1021/pr9006156] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Chemokines orchestrate leukocyte migration toward sites of inflammation and infection and target leukocytes via chemokine receptors such as CCR6, a subfamily of the seven-transmembrane G-protein-coupled receptors. Lipid rafts are cholesterol and sphingolipid-enriched liquid-ordered membrane microdomains thought to serve as scaffolding platforms for signal transduction. To globally understand the dynamic changes of proteins within lipid rafts upon CCR6 activation in T cells, we quantitatively analyzed the time-dependent changes of lipid raft proteome using our recently reported membrane proteomics strategy combining gel-assisted digestion, iTRAQ labeling and LC-MS/MS. To our knowledge, the error-free identification of 852 proteins represents the first data set of the raft proteome in T cells upon chemokine receptor activation, including 354 previously annotated raft proteins and 85 dynamically recruited proteins that are potential raft-associated proteins. The temporal profiles revealed that many proteins involved in the actin cytoskeleton rearrangement are actively recruited into lipid rafts upon CCR6 activation. We further confirmed the proteomics results by Western blotting and used small interfering RNA-mediated knockdown to evaluate their roles upon CCR6 activation. In sum, we employed quantitative proteomic strategy to analyze raft proteome and identified many molecules actively involved in the control of actin assembly and disassembly regulating CCR6 activation-induced cell migration.
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Affiliation(s)
- Shu-Ling Lin
- Institute of Biomedical Sciences, Academia Sinica, Taipei 11529, Taiwan
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23
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Moulding the shape of a metastatic cell. Leuk Res 2010; 34:843-7. [PMID: 20189645 DOI: 10.1016/j.leukres.2010.02.006] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2010] [Revised: 02/06/2010] [Accepted: 02/07/2010] [Indexed: 11/23/2022]
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McClatchey AI, Fehon RG. Merlin and the ERM proteins--regulators of receptor distribution and signaling at the cell cortex. Trends Cell Biol 2009; 19:198-206. [PMID: 19345106 DOI: 10.1016/j.tcb.2009.02.006] [Citation(s) in RCA: 148] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2008] [Revised: 02/16/2009] [Accepted: 02/19/2009] [Indexed: 11/19/2022]
Abstract
Recent studies highlight the importance of the distribution of membrane receptors in controlling receptor output and in contributing to complex biological processes. The cortical cytoskeleton is known to affect membrane protein distribution but the molecular basis of this is largely unknown. Here, we discuss the functions of Merlin and the ERM proteins both in linking membrane proteins to the underlying cortical cytoskeleton and in controlling the distribution of and signaling from membrane receptors. We also propose a model that could account for the intricacies of Merlin function across model organisms.
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Affiliation(s)
- Andrea I McClatchey
- Massachusetts General Hospital Center for Cancer Research and Harvard Medical School Department of Pathology, 149 13th Street, Charlestown, MA 02129, USA
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Moh MC, Tian Q, Zhang T, Lee LH, Shen S. The immunoglobulin-like cell adhesion molecule hepaCAM modulates cell adhesion and motility through direct interaction with the actin cytoskeleton. J Cell Physiol 2009; 219:382-91. [PMID: 19142852 DOI: 10.1002/jcp.21685] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Previously, we reported the identification of a novel immunoglobulin-like cell adhesion molecule hepaCAM that promotes cell-extracellular matrix (ECM) interactions including cell adhesion and motility. Cell-ECM interactions are known to be directed by the actin cytoskeleton. In this study, we examined the association of hepaCAM with the actin cytoskeleton. We found that hepaCAM was partially insoluble in Triton X-100 and colocalized with the actin cytoskeleton on the plasma membrane. Disruption of F-actin decreased the detergent insolubility and disturbed the subcellular localization of hepaCAM. Coimmunoprecipitation and F-actin cosedimentation assays revealed that hepaCAM directly bound to F-actin. In addition, we constructed three N- and C-terminal domain-deleted mutants of hepaCAM to determine the actin-binding region as well as to evaluate the effect of the domains on the biological function of hepaCAM. Detergent solubility assays showed that the cytoplasmic domain of hepaCAM might be required for actin association. However, deletion of either the extracellular or the cytoplasmic domain of hepaCAM abolished actin coprecipitation as well as delayed cell-ECM adhesion and cell motility. The data suggest that an intact hepaCAM protein is critical for establishing a stable physical association with the actin cytoskeleton; and such association is important for modulating hepaCAM-mediated cell adhesion and motility.
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Affiliation(s)
- Mei Chung Moh
- Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore
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26
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Moh MC, Lee LH, Zhang T, Shen S. Interaction of the immunoglobulin-like cell adhesion molecule hepaCAM with caveolin-1. Biochem Biophys Res Commun 2008; 378:755-60. [PMID: 19059381 DOI: 10.1016/j.bbrc.2008.11.119] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2008] [Accepted: 11/21/2008] [Indexed: 10/21/2022]
Abstract
Subsequent to our identification of the novel immunoglobulin-like cell adhesion molecule hepaCAM, we demonstrated that hepaCAM is capable of modulating cell growth and cell-extracellular matrix interactions. In this study, we examined the localization of hepaCAM in lipid rafts/caveolae as well as the interaction of hepaCAM with the caveolar structural protein caveolin-1 (Cav-1). Our results revealed that a portion of hepaCAM resided in detergent-resistant membranes and co-partitioned with Cav-1 to low buoyant density fractions characteristic of lipid rafts/caveolae. In addition, co-localization and coimmunoprecipitation assays confirmed the association of hepaCAM with Cav-1. Deletion analysis of hepaCAM showed that the extracellular first immunoglobulin domain of hepaCAM was required for binding Cav-1. Furthermore, when co-expressed, Cav-1 induced the expression of hepaCAM as well as distributed hepaCAM to intracellular Cav-1-positive caveolar structures. Taken together, our findings indicate that hepaCAM is partially localized in the lipid rafts/caveolae and interacts with Cav-1 through its first immunoglobulin domain.
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Affiliation(s)
- Mei Chung Moh
- Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore
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27
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Tewari R, Sharma V, Koul N, Sen E. Involvement of miltefosine-mediated ERK activation in glioma cell apoptosis through Fas regulation. J Neurochem 2008; 107:616-27. [DOI: 10.1111/j.1471-4159.2008.05625.x] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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Tumor suppressor schwannomin/merlin is critical for the organization of Schwann cell contacts in peripheral nerves. J Neurosci 2008; 28:10472-81. [PMID: 18923024 DOI: 10.1523/jneurosci.2537-08.2008] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
Schwannomin/merlin is the product of a tumor suppressor gene mutated in neurofibromatosis type 2 (NF2). Although the consequences of NF2 mutations on Schwann cell proliferation are well established, the physiological role of schwannomin in differentiated cells is not known. To unravel this role, we studied peripheral nerves in mice overexpressing in Schwann cells schwannomin with a deletion occurring in NF2 patients (P0-SCH-Delta39-121) or a C-terminal deletion. The myelin sheath and nodes of Ranvier were essentially preserved in both lines. In contrast, the ultrastructural and molecular organization of contacts between Schwann cells and axons in paranodal and juxtaparanodal regions were altered, with irregular juxtaposition of normal and abnormal areas of contact. Similar but more severe alterations were observed in mice with conditional deletion of the Nf2 gene in Schwann cells. The number of Schmidt-Lanterman incisures, which are cytoplasmic channels interrupting the compact myelin and characterized by distinct autotypic contacts, was increased in the three mutant lines. P0-SCH-Delta39-121 and conditionally deleted mice displayed exuberant wrapping of nonmyelinated fibers and short internodes, an abnormality possibly related to altered control of Schwann cell proliferation. In support of this hypothesis, Schwann cell number was increased along fibers before myelination in P0-SCH-Delta39-121 mice but not in those with C-terminal deletion. Schwann cell numbers were also more numerous in mice with conditional deletion. Thus, schwannomin plays an important role in the control of Schwann cell number and is necessary for the correct organization and regulation of axoglial heterotypic and glio-glial autotypic contacts.
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Bénéteau M, Pizon M, Chaigne-Delalande B, Daburon S, Moreau P, De Giorgi F, Ichas F, Rebillard A, Dimanche-Boitrel MT, Taupin JL, Moreau JF, Legembre P. Localization of Fas/CD95 into the lipid rafts on down-modulation of the phosphatidylinositol 3-kinase signaling pathway. Mol Cancer Res 2008; 6:604-13. [PMID: 18403639 DOI: 10.1158/1541-7786.mcr-07-0331] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Activation of the phosphatidylinositol 3-kinase (PI3K) signaling pathway is known to protect tumor cells from apoptosis and more specifically from the Fas-mediated apoptotic signal. The antitumoral agent edelfosine sensitizes leukemic cells to death by inducing the redistribution of the apoptotic receptor Fas into plasma membrane subdomains called lipid rafts. Herein, we show that inhibition of the PI3K signal by edelfosine triggers a Fas-mediated apoptotic signal independently of the Fas/FasL interaction. Furthermore, similarly to edelfosine, blockade of the PI3K activity, using specific inhibitors LY294002 and wortmannin, leads to the clustering of Fas whose supramolecular complex is colocalized within the lipid rafts. These findings indicate that the antitumoral agent edelfosine down-modulates the PI3K signal to sensitize tumor cells to death through the redistribution of Fas into large platform of membrane rafts.
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Affiliation(s)
- Marie Bénéteau
- Centre National de la Recherche Scientifique-Unite Mixte de Recherche 5164, 33076 Bordeaux, France
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Delacour D, Koch A, Ackermann W, Parco IEL, Elsässer HP, Poirier F, Jacob R. Loss of galectin-3 impairs membrane polarisation of mouse enterocytes in vivo. J Cell Sci 2008; 121:458-65. [DOI: 10.1242/jcs.020800] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Epithelial cells are characterised by distinct apical and basolateral membrane domains that are separated by tight junctions. Establishment and maintenance of this polarity depend on specific gene expression and protein targeting to their correct location. Our former studies, performed with renal epithelial MDCK cells, revealed a new function for galectin-3, a member of a conserved family of lectins. There, galectin-3 is required for intracellular sorting and correct targeting of non-raft-associated glycoproteins to the apical plasma membrane. In the present study, we found transport defects of the intestinal brush border hydrolases lactase-phlorizin hydrolase (LPH) and dipeptidylpeptidase IV (DPPIV) in galectin-3-null mutant mice. We could show that, in enterocytes of wild-type mice, both glycoproteins directly interact with galectin-3 and transit through non-raft-dependent apical transport platforms. Therefore, this genetic analysis provides definitive evidence for the involvement of galectin-3 in protein intracellular trafficking in vivo. Further investigations revealed that gal3-null enterocytes also exhibit striking cytoarchitecture defects, with the presence of numerous and regular protrusions located along basolateral membranes. Moreover, β-actin and villin, two characteristic markers of brush borders, become abnormally distributed along these atypical basolateral membranes in gal3–/– mice. Taken together, our results demonstrate that, in addition to a pivotal role in apical trafficking, galectin-3 also participates in epithelial morphogenesis in mouse enterocytes.
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Affiliation(s)
- Delphine Delacour
- Department of Cell Biology and Cell Pathology, Philipps University, D-35037 Marburg, Germany
| | - Annett Koch
- Department of Cell Biology and Cell Pathology, Philipps University, D-35037 Marburg, Germany
| | - Waltraud Ackermann
- Department of Cell Biology and Cell Pathology, Philipps University, D-35037 Marburg, Germany
| | - Isabelle Eude-Le Parco
- Department of Development, Institut Jacques Monod, CNRS UMR 7592, Universités Paris 6 and Paris 7, Cedex 05 Paris, France
| | - Hans-Peter Elsässer
- Department of Cell Biology and Cell Pathology, Philipps University, D-35037 Marburg, Germany
| | - Francoise Poirier
- Department of Development, Institut Jacques Monod, CNRS UMR 7592, Universités Paris 6 and Paris 7, Cedex 05 Paris, France
| | - Ralf Jacob
- Department of Cell Biology and Cell Pathology, Philipps University, D-35037 Marburg, Germany
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Localization to the cortical cytoskeleton is necessary for Nf2/merlin-dependent epidermal growth factor receptor silencing. Mol Cell Biol 2007; 28:1274-84. [PMID: 18086884 DOI: 10.1128/mcb.01139-07] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Merlin, the product of the NF2 tumor suppressor gene, is closely related to the ERM (ezrin, radixin, moesin) proteins, which provide anchorage between membrane proteins and the underlying cortical cytoskeleton; all four proteins are members of the band 4.1 superfamily. Despite their similarity, the subcellular distributions and functional properties of merlin and the ERM proteins are largely distinct. Upon cell-cell contact merlin prevents internalization of and signaling from the epidermal growth factor receptor (EGFR) by sequestering it into an insoluble membrane compartment. Here we show that the extreme amino (N) terminus directs merlin biochemically to an insoluble membrane compartment and physically to the cortical actin network, with a marked concentration along cell-cell boundaries. This insoluble-membrane distribution is required for the growth-suppressing function of merlin and for the functional association of merlin with EGFR and other membrane receptors. Our data support a model whereby locally activated merlin sequesters membrane receptors such as EGFR at the cortical network, contributing to the long-held observation that the cortical actin cytoskeleton can control the lateral mobility of and signaling from certain membrane receptors.
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Abstract
In response to various stimuli, membrane lipid rafts (LRs) are clustered to aggregate or recruit NADPH oxidase subunits and related proteins in vascular endothelial cells (ECs), forming redox signaling platforms. These LR signaling platforms may play important roles in the normal regulation of endothelial function and in the development of endothelial dysfunction or injury under pathological conditions. This LR-mediated mechanism now takes center stage in cell signaling for the regulation of many cellular activities or cell function such as ECs redox signaling, phagosomal activity of phagocytes, and cell apopotosis of lymphocytes. This brief review summarizes current evidence that relates to the formation of LR redox signaling platforms and their features in ECs, the functional significance of these signaling platforms in mediating death receptor activation-induced endothelial dysfunction, and the mechanisms initiating or promoting the formation of these platforms. It is expected that information provided here will help readers to understand this new signaling mechanism and perhaps extend the LR signaling platform concept to other research areas related to death receptors, redox signaling, endothelial biology, and cell/molecular biology of the cardiovascular system.
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Affiliation(s)
- Pin-Lan Li
- Department of Pharmacology and Toxicology, Medical College of Virginia, Virginia Commonwealth University, Richmond, Virginia, USA
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Lepont P, Stickney JT, Foster LA, Meng JJ, Hennigan RF, Ip W. Point mutation in the NF2 gene of HEI-193 human schwannoma cells results in the expression of a merlin isoform with attenuated growth suppressive activity. Mutat Res 2007; 637:142-51. [PMID: 17868749 PMCID: PMC2233940 DOI: 10.1016/j.mrfmmm.2007.07.015] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2007] [Revised: 07/26/2007] [Accepted: 07/31/2007] [Indexed: 10/23/2022]
Abstract
Neurofibromatosis type 2 (NF2) is a genetic disorder characterized by the formation of bilateral schwannomas of the eighth cranial nerve. Although the protein product of the NF2 gene (merlin) is a classical tumor suppressor, the mechanism by which merlin suppresses cell proliferation is not fully understood. The availability of isolated tumor cells would facilitate a better understanding of the molecular function of merlin, but primary schwannoma cells obtained from patients grow slowly and do not yield adequate numbers for biochemical analysis. In this study, we have examined the NF2 mutation in HEI-193 cells, an immortalized cell line derived from the schwannoma of an NF2 patient. Previous work showed that the NF2 mutation in HEI-193 cells causes a splicing defect in the NF2 transcript. We have confirmed this result and further identified the resultant protein product as an isoform of merlin previously designated as isoform 3. The level of isoform 3 proteins in HEI-193 cells is comparable to the levels of merlin isoforms 1 and 2 in normal human Schwann cells and several other immortalized cell lines. In contrast to many mutant forms of merlin, isoform 3 is as resistant to proteasomal degradation as isoforms 1 and 2 and can interact with each of these isoforms in vivo. Cell proliferation assays showed that, in NF2(-/-) mouse embryonic fibroblasts, exogenously expressed merlin isoform 3 does exhibit growth suppressive activity although it is significantly lower than that of identically expressed merlin isoform 1. These results indicate that, although HEI-193 cells have undetectable levels of merlin isoforms 1 and 2, they are, in fact, not a merlin-null model because they express the moderately active growth suppressive merlin isoform 3.
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Affiliation(s)
- Pierig Lepont
- Department of Cell and Cancer Biology, Vontz Center for Molecular Studies, University of Cincinnati College of Medicine, Cincinnati, OH 45267-0521, USA
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Curto M, Cole BK, Lallemand D, Liu CH, McClatchey AI. Contact-dependent inhibition of EGFR signaling by Nf2/Merlin. ACTA ACUST UNITED AC 2007; 177:893-903. [PMID: 17548515 PMCID: PMC2064288 DOI: 10.1083/jcb.200703010] [Citation(s) in RCA: 257] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The neurofibromatosis type 2 (NF2) tumor suppressor, Merlin, is a membrane/cytoskeleton-associated protein that mediates contact-dependent inhibition of proliferation. Here we show that upon cell-cell contact Merlin coordinates the processes of adherens junction stabilization and negative regulation of epidermal growth factor receptor (EGFR) signaling by restraining the EGFR into a membrane compartment from which it can neither signal nor be internalized. In confluent Nf2(-/-) cells, EGFR activation persists, driving continued proliferation that is halted by specific EGFR inhibitors. These studies define a new mechanism of tumor suppression, provide mechanistic insight into the poorly understood phenomenon of contact-dependent inhibition of proliferation, and suggest a therapeutic strategy for NF2-mutant tumors.
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Affiliation(s)
- Marcello Curto
- MGH Center for Cancer Research, Harvard Medical School Department of Pathology, Charlestown, MA 02129, USA
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Okada T, You L, Giancotti FG. Shedding light on Merlin's wizardry. Trends Cell Biol 2007; 17:222-9. [PMID: 17442573 DOI: 10.1016/j.tcb.2007.03.006] [Citation(s) in RCA: 85] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2006] [Revised: 02/14/2007] [Accepted: 03/23/2007] [Indexed: 12/21/2022]
Abstract
Inactivation of the tumor suppressor Merlin, encoded by the NF2 (Neurofibromatosis type 2) gene, contributes to malignant conversion in many cell types. Merlin is an Ezrin-Radixin-Moesin protein and localizes underneath the plasma membrane at cell-cell junctions and other actin-rich sites. Recent studies indicate that Merlin mediates contact inhibition of proliferation by blocking recruitment of Rac to the plasma membrane. In mitogen-stimulated cells, p21-activated kinase phosphorylates Ser518 in the C-terminus of Merlin, inactivating the growth suppressive function of the protein. Furthermore, the myosin phosphatase MYPT1-PP1delta, has been identified as a direct activator of Merlin and its inhibition has been linked to malignant transformation. Finally, studies in the fruit fly Drosophila melanogaster have revealed that Merlin functions together with the band 4.1 protein Expanded to promote [corrected] the endocytosis of many signaling receptors, limiting [corrected] their accumulation at the plasma membrane, and to activate [corrected] the Hippo signaling pathway. Here, we review these recent findings and their relevance to the tumor suppressor function of Merlin.
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Affiliation(s)
- Tomoyo Okada
- Cell Biology Program, Sloan-Kettering Institute for Cancer Research, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA
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Tyler DM, Baker NE. Expanded and fat regulate growth and differentiation in the Drosophila eye through multiple signaling pathways. Dev Biol 2007; 305:187-201. [PMID: 17359963 PMCID: PMC2075468 DOI: 10.1016/j.ydbio.2007.02.004] [Citation(s) in RCA: 89] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2006] [Revised: 02/06/2007] [Accepted: 02/06/2007] [Indexed: 12/29/2022]
Abstract
Mutations in the expanded gene act as hyperplastic tumor suppressors, interfere with cell competition and elevate Dpp signaling. Unlike Dpp overexpression, ex causes few patterning defects. Our data suggest that patterning effects are partly masked by antagonistic roles of other signaling pathways that are also activated. ex causes proliferation of cells in the posterior eye disc that are normally postmitotic. ex mutations elevate Wg signaling, but Dpp signaling antagonizes patterning effects of Wg. By contrast, if Dpp signaling is blocked in ex mutant cells, the elevated Wg signaling preserves an immature developmental state and prevents retinal differentiation. An effect of ex mutations on vesicle transport is suggested by evidence for altered sterol distribution. Mutations in ft show effects on proliferation, Wg signaling and sterols very similar to those of ex mutations. During disc growth, ex was largely epistatic to ft, and the Warts pathway mutation hippo largely epistatic to ex. Our data suggest that ft and ex act partially through the Warts pathway.
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Affiliation(s)
- David M. Tyler
- Correspondence to : ,, Tel 718-430-2854, Fax 718-430-8778
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Affiliation(s)
- Andrea I. McClatchey
- Center for Cancer Research, Massachusetts General Hospital, Charlestown, Massachusetts 02129 and Department of Pathology, Harvard Medical School, Boston, Massachusetts 02115;
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Thankamony SP, Knudson W. Acylation of CD44 and its association with lipid rafts are required for receptor and hyaluronan endocytosis. J Biol Chem 2006; 281:34601-9. [PMID: 16945930 PMCID: PMC3039921 DOI: 10.1074/jbc.m601530200] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
CD44 is a cell surface receptor for the extracellular matrix macromolecule hyaluronan. In addition, CD44 mediates the endocytosis of hyaluronan leading to its subsequent degradation within lysosomes. Using model systems of COS-7 and Flp-293 cells, we demonstrate that the association of CD44 with lipid rafts is essential for the endocytosis of hyaluronan but not the extracellular binding. Further, we demonstrate that palmitoylation of CD44 on two highly conserved cysteine residues is essential for the association with lipid rafts as determined by density gradient ultracentrifugation. Mutations of either cysteine residues or pretreatment of cells with the palmitic acid analog 2-bromopalmitate, reduced the [3H]palmitic acid incorporation into CD44 and prevented CD44-lipid rafts association. Preventing CD44 palmitoylation had no effect on the binding of hyaluronan but inhibited hyaluronan internalization. The turnover of the CD44 receptor itself was also affected by blocking its association with lipid rafts. Using cycloheximide to prevent de novo protein synthesis, palmitoylation-deficient cysteine mutants underwent slower turnover from cell surface compared with the palmitoylation-intact wild type, as determined by immunofluorescence and Western blotting. These results indicate that palmitoylation of CD44 is a critical driving determinant to CD44 association with lipid rafts and, concomitantly, the rates of hyaluronan endocytosis and CD44 turnover from cell surface.
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Affiliation(s)
- Sai P. Thankamony
- Department of Biochemistry, Rush Medical College, Rush University Medical Center, Chicago, Illinois 60612
| | - Warren Knudson
- Department of Biochemistry, Rush Medical College, Rush University Medical Center, Chicago, Illinois 60612
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Bai Y, Liu YJ, Wang H, Xu Y, Stamenkovic I, Yu Q. Inhibition of the hyaluronan-CD44 interaction by merlin contributes to the tumor-suppressor activity of merlin. Oncogene 2006; 26:836-50. [PMID: 16953231 DOI: 10.1038/sj.onc.1209849] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Mutation or loss of expression of merlin is responsible for neurofibromatosis type 2 (NF2), which is characterized by the development of schwannomas and other tumors of the nervous system. Like the ERM (ezrin-radixin-moesin) proteins, merlin interacts with CD44, a cell-surface receptor for hyaluronan (HA) that promotes tumorigenesis. However, the relationship between merlin and CD44 and the mechanism by which merlin exerts its tumor-suppressor function have not been elucidated. In the present study, we show that increased expression of wild-type merlin in Tr6BC1 schwannoma cells inhibits HA binding to CD44. Furthermore, we demonstrate that the residues required for this inhibitory effect and the interaction between CD44 and merlin lie within the first 50 amino acids of merlin. Overexpression of merlin inhibited subcutaneous growth of Tr6BC1 cells in immunocompromised Rag1 mice. In contrast, knocking down expression of endogenous merlin promoted tumor cell growth, as did overexpression of a merlin deletion mutant (merlinDel-1) that lacks the first 50 amino acids but not of other NH(2)-terminal deletion mutants. Together, our results demonstrate that inhibition of the CD44-HA interaction contributes to the tumor-suppressor function of merlin, and they suggest that merlin inhibits tumor growth, at least in part, by negatively regulating CD44 function.
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Affiliation(s)
- Y Bai
- Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
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Schachter KA, Du Y, Lin A, Gallo KA. Dynamic positive feedback phosphorylation of mixed lineage kinase 3 by JNK reversibly regulates its distribution to Triton-soluble domains. J Biol Chem 2006; 281:19134-44. [PMID: 16687404 DOI: 10.1074/jbc.m603324200] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
MLK3 (mixed lineage kinase 3) is a widely expressed, mammalian serine/threonine protein kinase that activates multiple MAPK pathways. Previously our laboratory used in vivo labeling/mass spectrometry to identify phosphorylation sites of activated MLK3. Seven of 11 identified sites correspond to the consensus motif for phosphorylation by proline-directed kinases. Based on these results, we hypothesized that JNK, or another proline-directed kinase, phosphorylates MLK3 as part of a feedback loop. Herein we provide evidence that MLK3 can be phosphorylated by JNK in vitro and in vivo. Blockade of JNK results in dephosphorylation of MLK3. The hypophosphorylated form of MLK3 is inactive and redistributes to a Triton-insoluble fraction. Recovery from JNK inhibition restores MLK3 solubility and activity, indicating that the redistribution process is reversible. This work describes a novel mode of regulation of MLK3, by which JNK-mediated feedback phosphorylation of MLK3 regulates its activation and deactivation states by cycling between Triton-soluble and Triton-insoluble forms.
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Affiliation(s)
- Karen A Schachter
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing 48824, USA
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Okada T, Lopez-Lago M, Giancotti FG. Merlin/NF-2 mediates contact inhibition of growth by suppressing recruitment of Rac to the plasma membrane. ACTA ACUST UNITED AC 2006; 171:361-71. [PMID: 16247032 PMCID: PMC2171182 DOI: 10.1083/jcb.200503165] [Citation(s) in RCA: 138] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Introduction of activated p21-activated kinase (PAK) is sufficient to release primary endothelial cells from contact inhibition of growth. Confluent cells display deficient activation of PAK and translocation of Rac to the plasma membrane at matrix adhesions. Targeting Rac to the plasma membrane rescues these cells from contact inhibition. PAK's ability to release human umbilical vein endothelial cells from contact inhibition is blocked by an unphosphorylatable form of its target Merlin, suggesting that PAK promotes mitogenesis by phosphorylating, and thus inactivating, Merlin. Merlin mutants, which are presumed to exert a dominant-negative effect, enable recruitment of Rac to matrix adhesions and promote mitogenesis in confluent cells. Small interference RNA–mediated knockdown of Merlin exerts the same effects. Dominant-negative Rac blocks PAK-mediated release from contact inhibition, implying that PAK functions upstream of Rac in this signaling pathway. These results provide a framework for understanding the tumor suppressor function of Merlin and indicate that Merlin mediates contact inhibition of growth by suppressing recruitment of Rac to matrix adhesions.
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Affiliation(s)
- Tomoyo Okada
- Cell Biology Program, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA.
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McClatchey AI, Giovannini M. Membrane organization and tumorigenesis--the NF2 tumor suppressor, Merlin. Genes Dev 2005; 19:2265-77. [PMID: 16204178 DOI: 10.1101/gad.1335605] [Citation(s) in RCA: 190] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
The NF2 tumor-suppressor gene was cloned more than a decade ago, but the function of its encoded protein, Merlin, remains elusive. Merlin, like the closely related ERM proteins, appears to provide regulated linkage between membrane-associated proteins and the actin cytoskeleton and is therefore poised to function in receiving and interpreting signals from the extracellular milieu. Recent studies suggest that Merlin may coordinate the processes of growth-factor receptor signaling and cell adhesion. Varying use of this organizing activity by different types of cells could provide an explanation for the unique spectrum of tumors associated with NF2 deficiency in mammals.
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Affiliation(s)
- Andrea I McClatchey
- Massachusetts General Hospital, Center for Cancer Research and Harvard Medical School, Department of Pathology, Charlestown, Massachusetts 02129, USA.
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Schleicher M, Brundin F, Gross S, Müller-Esterl W, Oess S. Cell cycle-regulated inactivation of endothelial NO synthase through NOSIP-dependent targeting to the cytoskeleton. Mol Cell Biol 2005; 25:8251-8. [PMID: 16135813 PMCID: PMC1234313 DOI: 10.1128/mcb.25.18.8251-8258.2005] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Nitric oxide (NO) plays a key role in vascular function, cell proliferation, and apoptosis. Proper subcellular localization of endothelial NO synthase (eNOS) is crucial for its activity; however, the role of eNOS trafficking for NO biosynthesis remains to be defined. Overexpression of NOS-interacting protein (NOSIP) induces translocation of eNOS from the plasma membrane to intracellular compartments, thereby impairing NO production. Here we report that endogenous NOSIP reduces the enzymatic capacity of eNOS, specifically in the G(2) phase of the cell cycle by targeting eNOS to the actin cytoskeleton. This regulation is critically dependent on the nucleocytoplasmic shuttling of NOSIP and its cytoplasmic accumulation in the G(2) phase. The predominant nuclear localization of NOSIP depends on a bipartite nuclear localization sequence (NLS) mediating interaction with importin alpha. Mutational destruction of the NLS abolishes nuclear import and interaction with importin alpha. Nuclear export is insensitive to leptomycin B and hence different from the CRM1-dependent default mechanism. Inhibition of NOSIP expression by RNA interference completely abolishes G(2)-specific cytoskeletal association and inhibition of eNOS. These findings describe a novel cell cycle-dependent modulation of endogenous NO levels that are critical to the cell cycle-related actions of NO such as apoptosis or cell proliferation.
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Affiliation(s)
- Michael Schleicher
- Institute for Biochemistry II, University of Frankfurt Medical School, Theodor-Stern-Kai 7, 60590 Frankfurt/Main, Germany
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