Functional analysis of the neurofibromatosis type 2 protein by means of disease-causing point mutations.
Despite intense study of the neurofibromatosis type 2 (NF2) tumor-suppressor protein merlin, the biological properties and tumor-suppressor functions of merlin are still largely unknown. In this study, we examined the molecular activities of NF2-causing mutant merlin proteins in transfected mammalian cells, to elucidate the merlin properties that are critical for tumor-suppressor function. Most important, we found that 80% of the merlin mutants studied significantly altered cell adhesion, causing cells to detach from the substratum. This finding implies a function for merlin in regulating cell-matrix attachment, and changes in cell adhesion caused by mutant protein expression may be an initial step in the pathogenesis of NF2. In addition, five different mutations in merlin caused a significant increase in detergent solubility of merlin compared to wild type, indicating a decreased ability to interact with the cytoskeleton. Although not correlated to the cell-adhesion phenotype, four missense mutations decreased the binding of merlin to the ERM-interacting protein EBP-50, implicating this interaction in merlin inhibition of cell growth. Last, we found that some NF2 point mutations in merlin most closely resembled gain-of-function alleles in their cellular phenotype, which suggests that mutant NF2 alleles may not always act in a loss-of-function manner, as had been assumed, but may include a spectrum of allelic types with different phenotypic effects on the function of the protein. In aggregate, these cellular phenotypes provide a useful assay for identifying the functional domains and molecular partners necessary for merlin tumor-suppressor activity.
Stokowski
R P
RP
Department of Genetics, School of Medicine, Stanford University, Palo Alto, CA 94305-5120, USA.
Cox
D R
DR
D000483:Alleles; D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D002448:Cell Adhesion / Q000235:genetics; D002455:Cell Division / Q000235:genetics; D002460:Cell Line; D048429:Cell Size / Q000235:genetics; D003599:Cytoskeleton / Q000378:metabolism; D004331:Drosophila melanogaster / Q000235:genetics; D016515:Genes, Neurofibromatosis 2 / Q000235:genetics* / Q000502:physiology; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009363:Neoplasm Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016518:Neurofibromatosis 2 / Q000235:genetics*; D025581:Neurofibromin 2; D010641:Phenotype; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D017354:Point Mutation / Q000235:genetics*; D011485:Protein Binding; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017384:Sequence Deletion / Q000235:genetics; D017923:Sodium-Hydrogen Exchangers; D012995:Solubility; D014162:Transfection
D002352:Carrier Proteins; D008565:Membrane Proteins; D009363:Neoplasm Proteins; D025581:Neurofibromin 2; D010750:Phosphoproteins; D011993:Recombinant Fusion Proteins; D017923:Sodium-Hydrogen Exchangers; C093376:sodium-hydrogen exchanger regulatory factor