title: Ran binding protein 9 interacts with Raf kinase but does not contribute to downstream ERK1/2 activation in skeletal myoblasts.
abstract: Raf kinase is the upstream activator of MEK1/2 leading to phosphorylation and activation of ERK1/2. Sustained activation of Raf represses skeletal muscle-specific reporter gene transcription and formation of multinucleated myofibers. Inhibition of myogenesis by activated Raf involves downstream ERK1/2 as well as undefined mediators. To identify Raf-interacting proteins that may influence repression of muscle formation, a yeast two-hybrid screen was performed using a MEK1-binding defective Raf (RafBXB-T481A) as bait. Twenty cDNAs coding for Raf-interacting proteins were identified including Ran binding protein 9 (RanBP9), a protein previously reported to interact with receptor tyrosine kinases. Forced expression of RanBP9 in myogenic cells did not alter myogenesis. Co-expression of RanBP9 with constitutively active RafBXB, but not RafBXB-T481A, synergistically inhibited MyoD-directed muscle reporter gene transcription. Knockdown of RanBP9 expression did not restore the differentiation program to Raf-expressing myoblasts. Thus, RanBP9 physically associates with Raf but does not substantially contribute to the inhibitory actions of the kinase.
authors.affiliation: Department of Animal Sciences, University of Florida, USA. sjohnson@animal.ufl.edu
authors.forename: Sally E
authors.initials: SE
authors.lastname: Johnson
authors.forename: Dane G
authors.initials: DG
authors.lastname: Winner
authors.forename: Xu
authors.initials: X
authors.lastname: Wang
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D002454:Cell Differentiation / Q000502:physiology; D003598:Cytoskeletal Proteins; D004789:Enzyme Activation / Q000502:physiology; D020868:Gene Silencing / Q000502:physiology; D006801:Humans; D051379:Mice; D008809:Mice, Inbred C3H; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D024510:Muscle Development / Q000502:physiology; D017570:MyoD Protein / Q000037:antagonists & inhibitors / Q000502:physiology; D032448:Myoblasts, Skeletal / Q000166:cytology / Q000201:enzymology*; D009687:Nuclear Proteins / Q000378:metabolism* / Q000502:physiology; D018808:Transcription Factor AP-1 / Q000037:antagonists & inhibitors; D048490:raf Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D020931:ran GTP-Binding Protein / Q000378:metabolism* / Q000502:physiology
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D003598:Cytoskeletal Proteins; D017570:MyoD Protein; D009687:Nuclear Proteins; C116005:Ran binding protein 9; D018808:Transcription Factor AP-1; D048490:raf Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020931:ran GTP-Binding Protein