Identification of a post-translationally myristoylated autophagy-inducing domain released by caspase cleavage of huntingtin.
Huntington disease (HD) is a debilitating neurodegenerative disease characterized by the loss of motor control and cognitive ability that ultimately leads to death. It is caused by the expansion of a polyglutamine tract in the huntingtin (HTT) protein, which leads to aggregation of the protein and eventually cellular death. Both the wild-type and mutant form of the protein are highly regulated by post-translational modifications including proteolysis, palmitoylation and phosphorylation. We now demonstrate the existence of a new post-translational modification of HTT: the addition of the 14 carbon fatty acid myristate to a glycine residue exposed on a caspase-3-cleaved fragment (post-translational myristoylation) and that myristoylation of this fragment is altered in a physiologically relevant model of mutant HTT. Myristoylated HTT553-585-EGFP, but not its non-myristoylated variant, initially localized to the ER, induced the formation of autophagosomes and accumulated in abnormally large autophagolysosomal/lysosomal structures in a variety of cell types, including neuronal cell lines under nutrient-rich conditions. Our results suggest that accumulation of myristoylated HTT553-586 in cells may alter the rate of production of autophagosomes and/or their clearance through the heterotypic autophagosomal/lysosomal fusion process. Overall, our novel observations establish a role for the post-translational myristoylation of a caspase-3-cleaved fragment of HTT, highly similar to the Barkor/ATG14L autophagosome-targeting sequence domain thought to sense, maintain and/or promote membrane curvature in the regulation of autophagy. Abnormal processing or production of this myristoylated HTT fragment might be involved in the pathophysiology of HD.
Department of Cell Biology, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada Department of Medical Genetics and Centre for Molecular Medicine and Therapeutics, Child and Family Research Institute, University of British Columbia, 950 West 28th Avenue, Vancouver, BC, Canada.
Dale D O
DD
Martin
Department of Cell Biology, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada.
Ryan J
RJ
Heit
Department of Cell Biology, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada.
Megan C
MC
Yap
National High Magnetic Field Laboratory and Department of Biological Science, Florida State University, 1800 East Paul Dirac Drive, Tallahassee, FL 32310, USA.
Michael W
MW
Davidson
Department of Medical Genetics and Centre for Molecular Medicine and Therapeutics, Child and Family Research Institute, University of British Columbia, 950 West 28th Avenue, Vancouver, BC, Canada.
Michael R
MR
Hayden
Department of Cell Biology, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, Canada luc.berthiaume@ualberta.ca.
Luc G
LG
Berthiaume
D033942:Adaptor Proteins, Vesicular Transport / Q000378:metabolism; D001343:Autophagy; D000071183:Autophagy-Related Proteins; D053148:Caspase 3 / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005998:Glycine / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D000071058:Huntingtin Protein; D008247:Lysosomes / Q000378:metabolism; D019814:Myristic Acid / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000378:metabolism*; D010588:Phagosomes / Q000378:metabolism; D011499:Protein Processing, Post-Translational
C539000:ATG14 protein, human; D033942:Adaptor Proteins, Vesicular Transport; D000071183:Autophagy-Related Proteins; C086055:HTT protein, human; D000071058:Huntingtin Protein; D009419:Nerve Tissue Proteins; D019814:Myristic Acid; C505407:CASP3 protein, human; D053148:Caspase 3; D005998:Glycine