Dual IRE1 targets: Determinants of the cell fate?

IRE1α (hereafter referred to as IRE1) is one of the sensors implicated in the unfolded protein response that controls the ER protein homeostasis (also known as proteostasis). Alteration of proteostasis is observed in many diseases, making IRE1 a central element of cell adaptability upon disease onset and progression. Upon ER stress, IRE1 initially promotes cell adaptation. Conversely, when proteostasis cannot be restored, IRE1 activation can lead to cell death. IRE1 activity mainly regulates two pathways: the formation of the transcription factor XBP1s; and the regulated IRE1-dependent decay (RIDD) of RNA, which can contribute to both cell adaptation and death. Hence, on one hand, IRE1 favors gene expression, while on the other hand it induces transcript degradation. We have recently identified two genes, CD95 and UBE2D3, which are targeted by both signaling branches downstream of IRE1 RNase's activity, resulting in a dual and opposing regulation of their expression. We propose naming these targets 'DIT' for Dual IRE1 Targets. Interestingly, other IRE1 targets, such as BiP and DGAT2, have previously been reported to be regulated by XBP1s and RIDD in separate studies. We hypothesize that regulation of DIT could be crucial to tilt the balance between the pro-adaptative and pro-death outcomes of IRE1, especially in pathological contexts. Therefore, understanding this regulation could be key to unraveling the IRE1/XBP1s/RIDD signaling network. Here, we explore these hypotheses by highlighting various aspects of the regulation of IRE1 branches, and reviewing the DIT identified in the literature so far.