IRE1 RNase controls CD95-mediated cell death.

Signalling by the Unfolded Protein Response (UPR) or by the Death Receptors (DR) are frequently activated towards pro-tumoral outputs in cancer. Herein, we demonstrate that the UPR sensor IRE1 controls the expression of the DR CD95/Fas, and its cell death-inducing ability. Both genetic and pharmacologic blunting of IRE1 activity increased CD95 expression and exacerbated CD95L-induced cell death in glioblastoma (GB) and Triple-Negative Breast Cancer (TNBC) cell lines. In accordance, CD95 mRNA was identified as a target of Regulated IRE1-Dependent Decay of RNA (RIDD). Whilst CD95 expression is elevated in TNBC and GB human tumours exhibiting low RIDD activity, it is surprisingly lower in XBP1s-low human tumour samples. We show that IRE1 RNase inhibition limited CD95 expression and reduced CD95-mediated hepatic toxicity in mice. In addition, overexpression of XBP1s increased CD95 expression and sensitized GB and TNBC cells to CD95L-induced cell death. Overall, these results demonstrate the tight IRE1-mediated control of CD95-dependent cell death in a dual manner through both RIDD and XBP1s, and they identify a novel link between IRE1 and CD95 signalling. Synopsis: Dual regulation of Cell Death Receptor CD95 signalling by ER stress sensor IRE1. IRE1, a mediator of the unfolded protein response (UPR), governs CD95/Fas expression and CD95L-induced cell death in opposing ways. IRE1 can induce CD95 expression to promote CD95L-induced cell death via the transcription factor XBP1s in triple-negative breast cancer (TNBC) and glioblastoma (GB) cells. IRE1 can also repress CD95 expression to limit CD95L-induced cell death through RIDD activity, which cleaves CD95 mRNA in both TNBC and GB cells. The net effect of these opposing mechanisms depends on the cellular context. IRE1 controls CD95 signalling in vivo. Activation of RIDD or XBP1s downstream of IRE1 dually correlates with CD95 mRNA expression in human TNBC and GB tumours. Dual regulation of Cell Death Receptor CD95 signaling by ER stress sensor IRE1. IRE1, a mediator of the unfolded protein response (UPR), governs CD95/Fas expression and CD95L-induced cell death in opposing ways. [ABSTRACT FROM AUTHOR]