Ran binding protein 9 interacts with Raf kinase but does not contribute to downstream ERK1/2 activation in skeletal myoblasts

• Published in: Biochemical and biophysical research communications 2006-02, Vol.340 (2), p.409-416
• Main Authors: Johnson, Sally E., Winner, Dane G., Wang, Xu
• Format: Article
• Language: English
• Subjects: Adaptor Proteins, Signal Transducing; Animals; Cell Differentiation - physiology; Cytoskeletal Proteins; Enzyme Activation - physiology; ERK1/2; Gene Silencing - physiology; Humans; Inhibition; MEK1; Mice; Mice, Inbred C3H; Mitogen-Activated Protein Kinase 1 - metabolism; Mitogen-Activated Protein Kinase 3 - metabolism; Muscle Development - physiology; Myoblasts, Skeletal - cytology; Myoblasts, Skeletal - enzymology; MyoD Protein - antagonists & inhibitors; MyoD Protein - physiology; Myogenesis; Nuclear Proteins - metabolism; Nuclear Proteins - physiology; Raf; raf Kinases - antagonists & inhibitors; raf Kinases - metabolism; ran GTP-Binding Protein - metabolism; ran GTP-Binding Protein - physiology; RanBP9; Skeletal muscle; Transcription Factor AP-1 - antagonists & inhibitors
• ISSN: 0006-291X; 1090-2104
• DOI: 10.1016/j.bbrc.2005.12.023

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.