Necroptosis activates UPR sensors without disrupting their binding with GRP78

• Published in: Proceedings of the National Academy of Sciences - PNAS 2021-09, Vol.118 (39), p.1-8
• Main Authors: Liang, Wei, Qi, Weiwei, Geng, Yang, Wang, Linhan, Zhao, Jing, Zhu, Kezhou, Wu, Guowei, Zhang, Zairong, Pan, Heling, Qian, Lihui, Yuan, Junying
• Format: Article
• Language: English
• Subjects: Apoptosis; Binding; Biological Sciences; eIF-2 Kinase - genetics; eIF-2 Kinase - metabolism; Endoplasmic Reticulum; Endoplasmic Reticulum Chaperone BiP; Endoplasmic Reticulum Stress; Endoribonucleases - genetics; Endoribonucleases - metabolism; Heat-Shock Proteins - genetics; Heat-Shock Proteins - metabolism; HT29 Cells; Humans; mRNA; Necroptosis; Necrosis; Protein folding; Protein Serine-Threonine Kinases - genetics; Protein Serine-Threonine Kinases - metabolism; Receptor-Interacting Protein Serine-Threonine Kinases - genetics; Receptor-Interacting Protein Serine-Threonine Kinases - metabolism; RNA Splicing; Sensors; Signal transduction; Signaling; Splicing; Unfolded Protein Response; X-Box Binding Protein 1 - genetics
• ISSN: 0027-8424; 1091-6490
• 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.