title: Gigaxonin-controlled degradation of MAP1B light chain is critical to neuronal survival.
abstract: Giant axonal neuropathy (GAN) is a devastating sensory and motor neuropathy caused by mutations in the GAN gene, which encodes the ubiquitously expressed protein gigaxonin. Cytopathological features of GAN include axonal degeneration, with accumulation and aggregation of cytoskeletal components. Little is currently known about the molecular mechanisms underlying this recessive disorder. Here we show that gigaxonin controls protein degradation, and is essential for neuronal function and survival. We present evidence that gigaxonin binds to the ubiquitin-activating enzyme E1 through its amino-terminal BTB domain, while the carboxy-terminal kelch repeat domain interacts directly with the light chain (LC) of microtubule-associated protein 1B (MAP1B). Overexpression of gigaxonin leads to enhanced degradation of MAP1B-LC, which can be antagonized by proteasome inhibitors. Ablation of gigaxonin causes a substantial accumulation of MAP1B-LC in GAN-null neurons. Moreover, we show that overexpression of MAP1B in wild-type cortical neurons leads to cell death characteristic of GAN-null neurons, whereas reducing MAP1B levels significantly improves the survival rate of null neurons. Our results identify gigaxonin as a ubiquitin scaffolding protein that controls MAP1B-LC degradation, and provide insight into the molecular mechanisms underlying human neurodegenerative disorders.
authors.affiliation: Department of Neurology and Neurological Sciences, Stanford University School of Medicine, 1201 Welch Road, Stanford, California 94305-5489, USA.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Allen
authors.forename: Jianqing
authors.initials: J
authors.lastname: Ding
authors.forename: Wei
authors.initials: W
authors.lastname: Wang
authors.forename: Suneet
authors.initials: S
authors.lastname: Pramanik
authors.forename: Jonathan
authors.initials: J
authors.lastname: Chou
authors.forename: Vincent
authors.initials: V
authors.lastname: Yau
authors.forename: Yanmin
authors.initials: Y
authors.lastname: Yang
mesh_terms: D000818:Animals; D002470:Cell Survival; D002478:Cells, Cultured; D003598:Cytoskeletal Proteins / Q000737:chemistry / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D051379:Mice; D008869:Microtubule-Associated Proteins / Q000737:chemistry* / Q000378:metabolism*; D009474:Neurons / Q000166:cytology* / Q000378:metabolism*; D016716:PC12 Cells; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D051381:Rats; D025801:Ubiquitin / Q000378:metabolism; D044764:Ubiquitin-Activating Enzymes / Q000235:genetics / Q000378:metabolism
chemical_list: D003598:Cytoskeletal Proteins; C501171:Gan protein, mouse; D008869:Microtubule-Associated Proteins; D025801:Ubiquitin; C085284:microtubule-associated protein 1B; D044764:Ubiquitin-Activating Enzymes