Tandem reporter assay for myristoylated proteins post-translationally (TRAMPP) identifies novel substrates for post-translational myristoylation: PKCε, a case study

FASEB J. 2012 Jan;26(1):13-28. doi: 10.1096/fj.11-182360. Epub 2011 Sep 29.

Abstract

Myristoylation, the addition of a 14-carbon fatty acid to the N-terminal glycine of a protein, is key to protein-membrane and protein-protein interactions. Typically, myristoylation occurs cotranslationally; however, post-translational myristoylation of caspase-cleaved proteins is now emerging as a well-established protein modification and as a novel regulator of apoptosis. To identify additional post-translationally myristoylated proteins, we engineered a plasmid vector encoding for a caspase-cleavable reporter protein named tandem reporter assay for myristoylation of proteins post-translationally (TRAMPP). pTRAMPP consists of tdTomato-DEVD-"test myristoylation sequence"-enhanced green fluorescent protein (EGFP). After induction of apoptosis, the reporter protein is cleaved by caspases, which frees a new N-terminal glycine residue attached to EGFP that can be myristoylated. We used pTRAMPP in appropriately transfected cells to identify 7 post-translationally myristoylated proteins. First, we confirmed the post-translational myristoylation of two previously identified putative substrates, cytoplasmic dynein intermediate chain 2A and PKCε (ctPKCε), and identified 5 more caspase-cleaved potential substrates for myristoylation that include the antiapoptotic regulator of apoptosis, Mcl-1, and the causative agent of Huntington's disease, huntingtin protein. Further investigation revealed that post-translationally myristoylated ctPKCε localized to membranes and increased Erk signaling and degradation of the proapoptotic protein Bim, which prevented a significant loss of mitochondrial potential of 17% over nonmyristoylated ctPKCε in HeLa cells in the presence of apoptotic stimuli. Taken together, these findings suggest a possible antiapoptotic role for post-translationally myristoylated caspase-cleaved ctPKCε.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis / physiology
  • COS Cells
  • Caspases / metabolism
  • Chlorocebus aethiops
  • Cloning, Molecular / methods*
  • Genes, Reporter / genetics
  • Genetic Vectors / genetics
  • Green Fluorescent Proteins / genetics*
  • HeLa Cells
  • Humans
  • Myristic Acid / metabolism*
  • Plasmids / genetics*
  • Protein Kinase C-epsilon / metabolism*
  • Protein Processing, Post-Translational / genetics
  • Protein Processing, Post-Translational / physiology*
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Signal Transduction / physiology
  • Transfection / methods
  • p21-Activated Kinases / metabolism

Substances

  • Recombinant Proteins
  • enhanced green fluorescent protein
  • Myristic Acid
  • Green Fluorescent Proteins
  • PAK2 protein, human
  • p21-Activated Kinases
  • Protein Kinase C-epsilon
  • Caspases