Oncogenic Role of Merlin/NF2 in Glioblastoma

Glioblastoma is the most common and aggressive primary brain tumor in adults, with a poor prognosis because of its resistance to radiotherapy and chemotherapy. Merlin/NF2 (moesin-ezrin-radixin-like protein/neurofibromatosis type 2) is a tumor suppressor found to be mutated in most nervous system tumors; however, it is not mutated in glioblastomas. Merlin associates with several transmembrane receptors and intracellular proteins serving as an anchoring molecule. Additionally, it acts as a key component of cell motility. By selecting sub-populations of U251 glioblastoma cells, we observed that high expression of phosphorylated Merlin at serine 518 (S518-Merlin), NOTCH1 and epidermal growth factor receptor (EGFR) correlated with increased cell proliferation and tumorigenesis. These cells were defective in cell-contact inhibition with changes in Merlin phosphorylation directly affecting NOTCH1 and EGFR expression, as well as downstream targets HES1 (hairy and enhancer of split-1) and CCND1 (cyclin D1). Of note, we identified a function for S518-Merlin, which is distinct from what has been reported when the expression of Merlin is diminished in relation to EGFR and NOTCH1 expression, providing first-time evidence that demonstrates that the phosphorylation of S518-Merlin in glioblastoma promotes oncogenic properties that are not only the result of inactivation of the tumor suppressor role of Merlin but also an independent process implicating a Merlin-driven regulation of NOTCH1 and EGFR.

[1]  D. Brat,et al.  Akt phosphorylation regulates the tumour-suppressor merlin through ubiquitination and degradation , 2007, Nature Cell Biology.

[2]  S. Jhanwar,et al.  The NF2 Tumor Suppressor Gene Product, Merlin, Inhibits Cell Proliferation and Cell Cycle Progression by Repressing Cyclin D1 Expression , 2005, Molecular and Cellular Biology.

[3]  T. Ljungberg,et al.  Dopaminergic supersensitivity in the striatum. , 1975, Advances in neurology.

[4]  K. Ye,et al.  Loss of Tumor Suppressor Merlin in Advanced Breast Cancer Is due to Post-translational Regulation* , 2011, The Journal of Biological Chemistry.

[5]  J. Gusella,et al.  Frequency and distribution of NF2 mutations in schwannomas , 1996, Genes, chromosomes & cancer.

[6]  R. Eldridge.  Central neurofibromatosis with bilateral acoustic neuroma. , 1981, Advances in neurology.

[7]  O. Wiestler,et al.  Notch1 signaling promotes survival of glioblastoma cells via EGFR-mediated induction of anti-apoptotic Mcl-1 , 2012, Oncogene.

[8]  F. Giancotti,et al.  Shedding light on Merlin's wizardry. , 2007, Trends in cell biology.

[9]  Ivan Stamenkovic,et al.  Merlin, a "magic" linker between extracellular cues and intracellular signaling pathways that regulate cell motility, proliferation, and survival. , 2010, Current protein & peptide science.

[10]  T. Muranen,et al.  Cell cycle-dependent nucleocytoplasmic shuttling of the neurofibromatosis 2 tumour suppressor merlin , 2005, Oncogene.

[11]  M. Okada,et al.  Akt phosphorylation of merlin enhances its binding to phosphatidylinositols and inhibits the tumor-suppressive activities of merlin. , 2009, Cancer research.

[12]  Alma Rodenas-Ruano,et al.  Paxillin binds schwannomin and regulates its density-dependent localization and effect on cell morphology , 2002, Nature Genetics.

[13]  X. Yang,et al.  Human homolog of Drosophila expanded, hEx, functions as a putative tumor suppressor in human cancer cell lines independently of the Hippo pathway , 2012, Oncogene.

[14]  N. Pećina-Šlaus.  Merlin, the NF2 Gene Product , 2013, Pathology & Oncology Research.

[15]  C. Haipek,et al.  Effect of merlin phosphorylation on neurofibromatosis 2 (NF2) gene function , 2004, Oncogene.

[16]  H. Jiang,et al.  Suppression of EGFR expression by antisense or small interference RNA inhibits U251 glioma cell growth in vitro and in vivo , 2006, Cancer Gene Therapy.

[17]  Y. Ohmiya,et al.  Hes1 is required for contact inhibition of cell proliferation in 3T3‐L1 preadipocytes , 2011, Genes to cells : devoted to molecular & cellular mechanisms.

[18]  D. Gutmann,et al.  Merlin is a potent inhibitor of glioma growth. , 2008, Cancer research.

[19]  D. Gutmann,et al.  Research updateMerlin: hanging tumor suppression on the Rac , 2001 .

[20]  T. Muranen,et al.  Protein kinase A-mediated phosphorylation of the NF2 tumor suppressor protein merlin at serine 10 affects the actin cytoskeleton , 2008, Oncogene.

[21]  Sherry X. Yang,et al.  Targeting notch signaling pathway in cancer: clinical development advances and challenges. , 2014, Pharmacology & therapeutics.

[22]  A. Merlo,et al.  Notch signaling in glioblastoma: a developmental drug target? , 2010, BMC medicine.

[23]  Olli Carpén,et al.  Cyclic AMP-dependent Protein Kinase Phosphorylates Merlin at Serine 518 Independently of p21-activated Kinase and Promotes Merlin-Ezrin Heterodimerization* , 2004, Journal of Biological Chemistry.

[24]  C. Haipek,et al.  The NF2 tumor suppressor gene product, merlin, mediates contact inhibition of growth through interactions with CD44. , 2001, Genes & development.

[25]  R. Fehon,et al.  The Tumor Suppressors Merlin and Expanded Function Cooperatively to Modulate Receptor Endocytosis and Signaling , 2006, Current Biology.

[26]  Jonathan A. Cooper,et al.  Merlin/NF2 Suppresses Tumorigenesis by Inhibiting the E3 Ubiquitin Ligase CRL4DCAF1 in the Nucleus , 2010, Cell.

[27]  C. Haipek,et al.  Neurofibromatosis 2 tumor suppressor protein, merlin, forms two functionally important intramolecular associations , 1999, Journal of neuroscience research.

[28]  T. Muranen,et al.  A functional association between merlin and HEI10, a cell cycle regulator , 2006, Oncogene.

[29]  D. Gutmann,et al.  Interdomain binding mediates tumor growth suppression by the NF2 gene product , 1997, Oncogene.

[30]  D. W. Fry,et al.  G1 cell cycle arrest due to the inhibition of erbB family receptor tyrosine kinases does not require the retinoblastoma protein. , 2004, Experimental cell research.

[31]  C. Hanemann,et al.  Transduction of wild-type merlin into human schwannoma cells decreases schwannoma cell growth and induces apoptosis. , 2002, Human molecular genetics.

[32]  K. Aldape,et al.  Nuclear PKM2 regulates β-catenin transactivation upon EGFR activation , 2011, Nature.

[33]  Kevin W Eliceiri,et al.  NIH Image to ImageJ: 25 years of image analysis , 2012, Nature Methods.

[34]  D. Gutmann,et al.  Merlin: hanging tumor suppression on the Rac. , 2001, Trends in cell biology.

[35]  Jon C. Aster,et al.  Dose-dependent induction of distinct phenotypic responses to Notch pathway activation in mammary epithelial cells , 2010, Proceedings of the National Academy of Sciences.

[36]  J. Gusella,et al.  Mutations in transcript isoforms of the neurofibromatosis 2 gene in multiple human tumour types , 1994, Nature Genetics.

[37]  C. Thaxton,et al.  Phosphorylation of the NF2 tumor suppressor in Schwann cells is mediated by Cdc42-Pak and requires paxillin binding , 2007, Molecular and Cellular Neuroscience.

[38]  S. Pulst,et al.  Alteration in a new gene encoding a putative membrane-organizing protein causes neuro-fibromatosis type 2 , 1993, Nature.

[39]  M. Giovannini,et al.  The Neurofibromatosis 2 Protein, Merlin, Regulates Glial Cell Growth in an ErbB2- and Src-Dependent Manner , 2008, Molecular and Cellular Biology.

[40]  N. Kley,et al.  A novel moesin-, ezrin-, radixin-like gene is a candidate for the neurofibromatosis 2 tumor suppressor. , 1993, Cell.

[41]  J. Haines,et al.  A novel moesin-, ezrin-, radixin-like gene is a candidate for the neurofibromatosis 2 tumor suppressor , 1993, Cell.

[42]  D. Lallemand,et al.  Contact-dependent inhibition of EGFR signaling by Nf2/Merlin , 2007, The Journal of cell biology.