The Journal of Neuroscience, May 9, 2007, 27(19):5163-5171; doi:10.1523/JNEUROSCI.0206-07.2007
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Neurobiology of Disease
Selective Cochlear Degeneration in Mice Lacking the F-Box Protein, Fbx2, a Glycoprotein-Specific Ubiquitin Ligase Subunit
Rick F. Nelson,1,2,3
Kevin A. Glenn,4
Yuzhou Zhang,5
Hsiang Wen,3
Tina Knutson,3
Cynthia M. Gouvion,3
Barbara K. Robinson,5
Zouping Zhou,3
Baoli Yang,3,6
Richard J. H. Smith,5,7 and
Henry L. Paulson2,3,7
1Medical Scientist Training Program, 2Graduate Program in Neuroscience, Departments of 3Neurology, 4Internal Medicine, 5OtolaryngologyHead and Neck Surgery, and 6Pediatrics, and 7Graduate Program in Genetics, University of Iowa Roy J. and Lucille A. Carver College of Medicine, Iowa City, Iowa 52242
Correspondence should be addressed to Henry L. Paulson, Department of Neurology, University of Iowa College of Medicine, 2007 RCP, Iowa City, IA 52242. Email: henry-paulson{at}uiowa.edu
Little is known about the role of protein quality control in the inner ear. We now report selective cochlear degeneration in mice deficient in Fbx2, a ubiquitin ligase F-box protein with specificity for high-mannose glycoproteins (Yoshida et al., 2002). Originally described as a brain-enriched protein (Erhardt et al., 1998), Fbx2 is also highly expressed in the organ of Corti, in which it has been called organ of Corti protein 1 (Thalmann et al., 1997). Mice with targeted deletion of Fbxo2 develop age-related hearing loss beginning at 2 months. Cellular degeneration begins in the epithelial support cells of the organ of Corti and is accompanied by changes in cellular membrane integrity and early increases in connexin 26, a cochlear gap junction protein previously shown to interact with Fbx2 (Henzl et al., 2004). Progressive degeneration includes hair cells and the spiral ganglion, but the brain itself is spared despite widespread CNS expression of Fbx2. Cochlear Fbx2 binds Skp1, the common binding partner for F-box proteins, and is an unusually abundant inner ear protein. Whereas cochlear Skp1 levels fall in parallel with the loss of Fbx2, other components of the canonical SCF (Skp1, Cullin1, F-box, Rbx1) ubiquitin ligase complex remain unchanged and show little if any complex formation with Fbx2/Skp1, suggesting that cochlear Fbx2 and Skp1 form a novel, heterodimeric complex. Our findings demonstrate that components of protein quality control are essential for inner ear homeostasis and implicate Fbx2 and Skp1 as potential genetic modifiers in age-related hearing loss.
Key words: deafness; ubiquitin; Fbx2; glycoprotein; Skp1; degradation
Received Jan. 17, 2007;
revised April 2, 2007;
accepted April 4, 2007.
Correspondence should be addressed to Henry L. Paulson, Department of Neurology, University of Iowa College of Medicine, 2007 RCP, Iowa City, IA 52242. Email: henry-paulson{at}uiowa.edu
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K. A. Glenn, R. F. Nelson, H. M. Wen, A. J. Mallinger, and H. L. Paulson
Diversity in Tissue Expression, Substrate Binding, and SCF Complex Formation for a Lectin Family of Ubiquitin Ligases
J. Biol. Chem.,
May 9, 2008;
283(19):
12717 - 12729.
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