Identification of a post-translationally myristoylated autophagy-inducing domain released by caspase cleavage of huntingtin

Hum Mol Genet. 2014 Jun 15;23(12):3166-79. doi: 10.1093/hmg/ddu027. Epub 2014 Jan 23.

Abstract

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Vesicular Transport / metabolism
  • Autophagy
  • Autophagy-Related Proteins
  • Caspase 3 / metabolism*
  • Endoplasmic Reticulum / metabolism
  • Glycine / metabolism*
  • HeLa Cells
  • Humans
  • Huntingtin Protein
  • Lysosomes / metabolism
  • Myristic Acid / metabolism*
  • Nerve Tissue Proteins / chemistry
  • Nerve Tissue Proteins / metabolism*
  • Phagosomes / metabolism
  • Protein Processing, Post-Translational*

Substances

  • ATG14 protein, human
  • Adaptor Proteins, Vesicular Transport
  • Autophagy-Related Proteins
  • HTT protein, human
  • Huntingtin Protein
  • Nerve Tissue Proteins
  • Myristic Acid
  • CASP3 protein, human
  • Caspase 3
  • Glycine