LC3 and STRAP regulate actin filament assembly by JMY during autophagosome formation

J Cell Biol. 2019 Jan 7;218(1):251-266. doi: 10.1083/jcb.201802157. Epub 2018 Nov 12.

Abstract

During autophagy, actin filament networks move and remodel cellular membranes to form autophagosomes that enclose and metabolize cytoplasmic contents. Two actin regulators, WHAMM and JMY, participate in autophagosome formation, but the signals linking autophagy to actin assembly are poorly understood. We show that, in nonstarved cells, cytoplasmic JMY colocalizes with STRAP, a regulator of JMY's nuclear functions, on nonmotile vesicles with no associated actin networks. Upon starvation, JMY shifts to motile, LC3-containing membranes that move on actin comet tails. LC3 enhances JMY's de novo actin nucleation activity via a cryptic actin-binding sequence near JMY's N terminus, and STRAP inhibits JMY's ability to nucleate actin and activate the Arp2/3 complex. Cytoplasmic STRAP negatively regulates autophagy. Finally, we use purified proteins to reconstitute LC3- and JMY-dependent actin network formation on membranes and inhibition of network formation by STRAP. We conclude that LC3 and STRAP regulate JMY's actin assembly activities in trans during autophagy.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Actin Cytoskeleton / metabolism*
  • Actin Cytoskeleton / ultrastructure
  • Actins / genetics*
  • Actins / metabolism
  • Adaptor Proteins, Signal Transducing / genetics*
  • Adaptor Proteins, Signal Transducing / metabolism
  • Animals
  • Autophagosomes / metabolism*
  • Autophagosomes / ultrastructure
  • Autophagy / genetics
  • Cell Line, Tumor
  • Gene Expression Regulation
  • Genes, Reporter
  • Green Fluorescent Proteins / genetics
  • Green Fluorescent Proteins / metabolism
  • HEK293 Cells
  • Humans
  • Luminescent Proteins / genetics
  • Luminescent Proteins / metabolism
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism
  • Mice
  • Microtubule-Associated Proteins / genetics*
  • Microtubule-Associated Proteins / metabolism
  • Nuclear Proteins / genetics*
  • Nuclear Proteins / metabolism
  • Osteoblasts / metabolism
  • Osteoblasts / ultrastructure
  • RNA-Binding Proteins
  • Recombinant Fusion Proteins / genetics
  • Recombinant Fusion Proteins / metabolism
  • Sf9 Cells
  • Signal Transduction
  • Spodoptera
  • Trans-Activators / genetics*
  • Trans-Activators / metabolism

Substances

  • Actins
  • Adaptor Proteins, Signal Transducing
  • JMY protein, human
  • Luminescent Proteins
  • MAP1LC3A protein, human
  • Membrane Proteins
  • Microtubule-Associated Proteins
  • Nuclear Proteins
  • RNA-Binding Proteins
  • Recombinant Fusion Proteins
  • STRAP protein, mouse
  • Trans-Activators
  • WHAMM protein, human
  • red fluorescent protein
  • Green Fluorescent Proteins