PT  - JOURNAL ARTICLE
AU  - PO-HAN CHEN
AU  - Timothy Smith
AU  - Jimin Hu
AU  - Samuel Pan
AU  - Alexander Smith
AU  - Annie Lu
AU  - Jen-Tsan Chi
AU  - Michael Boyce
TI  - Glycosylation of gigaxonin regulates intermediate filaments: Novel molecular insights into giant axonal neuropathy
AID  - 10.1101/530303
DP  - 2019 Jan 01
TA  - bioRxiv
PG  - 530303
4099  - http://biorxiv.org/content/early/2019/01/26/530303.short
4100  - http://biorxiv.org/content/early/2019/01/26/530303.full
AB  - Gigaxonin (also known as KLHL16) is an E3 ligase adaptor protein that promotes the ubiquitination and degradation of intermediate filament (IF) proteins. Mutations in human gigaxonin cause the fatal neurodegenerative disease giant axonal neuropathy (GAN), in which IF proteins accumulate and aggregate in axons throughout the nervous system, impairing neuronal function and viability. Despite this pathophysiological significance, the upstream regulation and downstream effects of normal and aberrant gigaxonin function remain incompletely understood. Here, we report that gigaxonin is modified by O-linked-beta-N-acetylglucosamine (O-GlcNAc), a prevalent form of intracellular glycosylation, in a nutrient- and growth factor-dependent manner. Mass spectrometry analyses of human gigaxonin revealed nine candidate sites of O-GlcNAcylation, two of which - serine 272 and threonine 277 - are required for its ability to mediate IF turnover in novel gigaxonin-deficient human cell models that we created. Taken together, these results suggest that nutrient-responsive gigaxonin O-GlcNAcylation forms a regulatory link between metabolism and IF proteostasis. Our work may have significant implications for understanding the non-genetic modifiers of GAN phenotypes and for the optimization of gene therapy for this disease.