Sterol biosensor reveals LAM-family Ltc1-dependent sterol flow to endosomes upon Arp2/3 inhibition

J Cell Biol. 2020 Jun 1;219(6):e202001147. doi: 10.1083/jcb.202001147.

Abstract

Sterols are crucial components of biological membranes, which are synthetized in the ER and accumulate in the plasma membrane (PM). Here, by applying a genetically encoded sterol biosensor (D4H), we visualize a sterol flow between PM and endosomes in the fission yeast Schizosaccharomyces pombe. Using time-lapse and correlative light-electron microscopy, we found that inhibition of Arp2/3-dependent F-actin assembly promotes the reversible relocalization of D4H from the PM to internal sterol-rich compartments (STRIC) labeled by synaptobrevin Syb1. Retrograde sterol internalization to STRIC is independent of endocytosis or an intact Golgi, but depends on Ltc1, a LAM/StARkin-family protein localized to ER-PM contact sites. The PM in ltc1Δ cells over-accumulates sterols and upon Arp2/3 inhibition forms extended ER-interacting invaginations, indicating that sterol transfer contributes to PM size homeostasis. Anterograde sterol movement from STRIC is independent of canonical vesicular trafficking but requires Arp2/3, suggesting a novel role for this complex. Thus, transfer routes orthogonal to vesicular trafficking govern the flow of sterols in the cell.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Actin-Related Protein 2-3 Complex / antagonists & inhibitors*
  • Actin-Related Protein 2-3 Complex / metabolism
  • Actins / metabolism
  • Antiporters / genetics
  • Antiporters / metabolism*
  • Biosensing Techniques
  • Cell Membrane / drug effects
  • Cell Membrane / genetics
  • Cell Membrane / metabolism*
  • Endocytosis / drug effects
  • Endocytosis / genetics
  • Endoplasmic Reticulum / genetics
  • Endoplasmic Reticulum / metabolism
  • Endosomes / drug effects
  • Endosomes / metabolism*
  • Endosomes / ultrastructure
  • Genes, Reporter
  • Golgi Apparatus / metabolism
  • Microscopy, Electron, Transmission
  • Mixed Function Oxygenases / genetics
  • Mixed Function Oxygenases / metabolism
  • Mutation
  • R-SNARE Proteins / metabolism
  • Schizosaccharomyces / metabolism*
  • Sterols / metabolism*

Substances

  • Actin-Related Protein 2-3 Complex
  • Actins
  • Antiporters
  • R-SNARE Proteins
  • Sterols
  • Mixed Function Oxygenases
  • hyoscyamine (6S)-dioxygenase