Excessive ER-phagy Mediated by the Autophagy Receptor FAM134B Results in ER Stress, the Unfolded Protein Response, and Cell Death in HeLa Cells

J Biol Chem. 2019 Dec 27;294(52):20009-20023. doi: 10.1074/jbc.RA119.008709. Epub 2019 Nov 20.

Abstract

Autophagy is typically a prosurvival cellular process that promotes the turnover of long-lived proteins and damaged organelles, but it can also induce cell death. We have previously reported that the small molecule Z36 induces autophagy along with autophagic cell death in HeLa cells. In this study, we analyzed differential gene expression in Z36-treated HeLa cells and found that Z36-induced endoplasmic reticulum-specific autophagy (ER-phagy) results in ER stress and the unfolded protein response (UPR). This result is in contrast to the common notion that autophagy is generally activated in response to ER stress and the UPR. We demonstrate that Z36 up-regulates the expression levels of FAM134B, LC3, and Atg9, which together mediate excessive ER-phagy, characterized by forming increased numbers of autophagosomes with larger sizes. We noted that the excessive ER-phagy accelerates ER degradation and impairs ER homeostasis and thereby triggers ER stress and the UPR as well as ER-phagy-dependent cell death. Interestingly, overexpression of FAM134B alone in HeLa cells is sufficient to impair ER homeostasis and cause ER stress and cell death. These findings suggest a mechanism involving FAM134B activity for ER-phagy to promote cell death.

Keywords: Bcl-xL inhibitor; ER-phagy; FAM134B; Z36; autophagy; cell death; endoplasmic reticulum (ER); endoplasmic reticulum stress (ER stress); reticulophagy regulator 1 (RETREG1); unfolded protein response (UPR).

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenine / analogs & derivatives
  • Adenine / pharmacology
  • Apoptosis / drug effects
  • Autophagosomes / metabolism
  • Autophagy* / drug effects
  • Autophagy-Related Proteins / genetics
  • Autophagy-Related Proteins / metabolism
  • Endoplasmic Reticulum / metabolism
  • Endoplasmic Reticulum Stress* / drug effects
  • Endoribonucleases / metabolism
  • HeLa Cells
  • Humans
  • Indoles / pharmacology
  • Intracellular Signaling Peptides and Proteins / antagonists & inhibitors
  • Intracellular Signaling Peptides and Proteins / genetics
  • Intracellular Signaling Peptides and Proteins / metabolism*
  • Membrane Proteins / antagonists & inhibitors
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism*
  • Microtubule-Associated Proteins / genetics
  • Microtubule-Associated Proteins / metabolism
  • Protein-Serine-Threonine Kinases / metabolism
  • RNA Interference
  • RNA, Small Interfering / metabolism
  • Unfolded Protein Response* / drug effects
  • Up-Regulation / drug effects
  • Vesicular Transport Proteins / genetics
  • Vesicular Transport Proteins / metabolism

Substances

  • 5-fluoro-1-(3'-dimethylamino)propyl-indolin-2-one
  • Atg9a protein, human
  • Autophagy-Related Proteins
  • Indoles
  • Intracellular Signaling Peptides and Proteins
  • Membrane Proteins
  • Microtubule-Associated Proteins
  • RETREG1 protein, human
  • RNA, Small Interfering
  • Vesicular Transport Proteins
  • light chain 3, human
  • 3-methyladenine
  • ERN1 protein, human
  • Protein-Serine-Threonine Kinases
  • Endoribonucleases
  • Adenine