Necroptosis activates UPR sensors without disrupting their binding with GRP78

Proc Natl Acad Sci U S A. 2021 Sep 28;118(39):e2110476118. doi: 10.1073/pnas.2110476118.


Necroptosis is a form of regulated necrosis mediated by the formation of the necrosome, composed of the RIPK1/RIPK3/MLKL complex. Here, we developed a proximity ligation assay (PLA) that allows in situ visualization of necrosomes in necroptotic cells and in vivo. Using PLA assay, we show that necrosomes can be found in close proximity to the endoplasmic reticulum (ER). Furthermore, we show that necroptosis activates ER stress sensors, PERK, IRE1α, and ATF6 in a RIPK1-RIPK3-MLKL axis-dependent manner. Activated MLKL can be translocated to the ER membrane to directly initiate the activation of ER stress signaling. The activation of IRE1α in necroptosis promotes the splicing of XBP1, and the subsequent incorporation of spliced XBP1 messenger RNA (mRNA) into extracellular vesicles (EVs). Finally, we show that unlike that of a conventional ER stress response, necroptosis promotes the activation of unfolded protein response (UPR) sensors without affecting their binding of GRP78. Our study reveals a signaling pathway that links MLKL activation in necroptosis to an unconventional ER stress response.

Keywords: ER stress; IRE1α; PERK; UPR sensors; necroptosis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Apoptosis
  • Endoplasmic Reticulum
  • Endoplasmic Reticulum Stress
  • Endoribonucleases / genetics
  • Endoribonucleases / metabolism*
  • HT29 Cells
  • Heat-Shock Proteins / genetics
  • Heat-Shock Proteins / metabolism*
  • Humans
  • Necroptosis*
  • Protein-Serine-Threonine Kinases / genetics
  • Protein-Serine-Threonine Kinases / metabolism*
  • RNA Splicing
  • Receptor-Interacting Protein Serine-Threonine Kinases / genetics
  • Receptor-Interacting Protein Serine-Threonine Kinases / metabolism*
  • Unfolded Protein Response*
  • X-Box Binding Protein 1 / genetics
  • eIF-2 Kinase / genetics
  • eIF-2 Kinase / metabolism*


  • Heat-Shock Proteins
  • X-Box Binding Protein 1
  • XBP1 protein, human
  • EIF2AK3 protein, human
  • ERN1 protein, human
  • Protein-Serine-Threonine Kinases
  • RIPK1 protein, human
  • RIPK3 protein, human
  • Receptor-Interacting Protein Serine-Threonine Kinases
  • eIF-2 Kinase
  • Endoribonucleases
  • molecular chaperone GRP78