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Noncanonical mRNA decay by the endoplasmic-reticulum stress sensor IRE1-alpha promotes cancer cell survival [GRO-seq]

ABSTRACT: Eukaryotic IRE1 mitigates endoplasmic-reticulum (ER) stress by orchestrating the unfolded-protein response (UPR). IRE1 spans the ER membrane, and signals through a cytosolic kinase-endoribonuclease module. The endoribonuclease generates the transcription factor XBP1s by intron excision between similar RNA stem-loop endomotifs, and depletes select cellular mRNAs through regulated IRE1-dependent decay (RIDD). Paradoxically, mammalian RIDD seemingly targets only mRNAs with XBP1-like endomotifs, while in flies RIDD exhibits little sequence restriction. By comparing nascent and total IRE1α-controlled mRNAs in human breast cancer cells, we discovered not only canonical endomotif-containing RIDD substrates, but also many targets lacking recognizable motifs—degraded by a process we coin RIDDLE, for RIDD lacking endomotif. IRE1α displayed two basic endoribonuclease modalities: endomotif-specific cleavage, minimally requiring dimers; and endomotif-independent promiscuous processing, requiring phospho-oligomers. An oligomer-deficient mutant that did not support RIDDLE failed to rescue cancer-cell viability. These results link IRE1α oligomers, RIDDLE, and cell survival, advancing mechanistic understanding of the UPR.

ORGANISM(S): Homo sapiens

PROVIDER: GSE169583 | GEO | 2021/06/01

REPOSITORIES: GEO

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Noncanonical mRNA decay by the endoplasmic-reticulum stress sensor IRE1-alpha promotes cancer cell survival [RNA-seq]

Project description:Eukaryotic IRE1 mitigates endoplasmic-reticulum (ER) stress by orchestrating the unfolded-protein response (UPR). IRE1 spans the ER membrane, and signals through a cytosolic kinase-endoribonuclease module. The endoribonuclease generates the transcription factor XBP1s by intron excision between similar RNA stem-loop endomotifs, and depletes select cellular mRNAs through regulated IRE1-dependent decay (RIDD). Paradoxically, mammalian RIDD seemingly targets only mRNAs with XBP1-like endomotifs, while in flies RIDD exhibits little sequence restriction. By comparing nascent and total IRE1α-controlled mRNAs in human breast cancer cells, we discovered not only canonical endomotif-containing RIDD substrates, but also many targets lacking recognizable motifs—degraded by a process we coin RIDDLE, for RIDD lacking endomotif. IRE1α displayed two basic endoribonuclease modalities: endomotif-specific cleavage, minimally requiring dimers; and endomotif-independent promiscuous processing, requiring phospho-oligomers. An oligomer-deficient mutant that did not support RIDDLE failed to rescue cancer-cell viability. These results link IRE1α oligomers, RIDDLE, and cell survival, advancing mechanistic understanding of the UPR.

2021-06-01 | GSE169584 | GEO

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Project description:Endoplasmic Reticulum (ER) stress is a hallmark of various diseases, which is dealt with through the activation of an adaptive signaling pathway named the Unfolded Protein Response (UPR). This response is mediated by three ER-resident sensors and the most evolutionary conserved, IRE1α signals through its cytosolic kinase and endoribonuclease (RNase) activities. IRE1α RNase activity can either catalyze the initial step of XBP1 mRNA unconventional splicing or degrade a number of RNAs through Regulated IRE1-Dependent Decay (RIDD). The balance between these two activities plays an instrumental role in cells’ life and death decisions upon ER stress. Until now, the biochemical and biological outputs of IRE1α RNase activity have been well documented, however, the precise mechanisms controlling whether IRE1 signaling is adaptive or pro-death (terminal) remain unclear. This prompted us to further investigate those mechanisms and we hypothesized that XBP1 mRNA splicing and RIDD activity could be co-regulated by the IRE1α RNase regulatory network. We showed that a key nexus in this pathway is the tRNA ligase RtcB which, together with IRE1α, is responsible for XBP1 mRNA splicing. We demonstrated that RtcB is tyrosine phosphorylated by c-Abl and dephosphorylated by PTP1B. Moreover, we identified RtcB Y306 as a key residue which, when phosphorylated, perturbs RtcB interaction with IRE1α, thereby attenuating XBP1 mRNA splicing and favoring RIDD. Our results demonstrate that the IRE1α RNase regulatory network is dynamically fine-tuned by tyrosine kinases and phosphatases upon various stresses and that the nature of the stress determines cell adaptive or death outputs.

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RNA sequencing identifies novel regulated IRE1-dependent decay targets that affect multiple myeloma survival and proliferation

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Expression data from IRE1a or XBP1 deficient mouse liver

2012-10-17 | GSE40515 | GEO

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2022-02-15 | PXD030594 | Pride

A role for the ribosome-associated complex in activation of the IRE1 branch of UPR

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2021-06-14 | GSE173852 | GEO

A novel blood brain barrier-permeable IRE1 inhibitor prevents Glioblastoma relapse in mice

Project description:Inositol Requiring Enzyme 1 (IRE1) is a bifunctional serine/threonine kinase and endoribonuclease that is a major mediator of the Unfolded Protein Response (UPR) during endoplasmic reticulum (ER) stress. Tumor cells experience ER stress due to adverse environmental cues such as hypoxia or nutrient shortage and high metabolic/protein folding demand. To cope with those stresses, cancer cells utilize IRE1 signaling as an adaptive mechanism. Here we report the discovery of novel family of compounds as IRE1 inhibitors identified through a structural exploration of the IRE1 kinase domain. All the inhibitors were tested for their ability to sensitize glioblastoma (GBM) cells to chemotherapy. We show that all molecules identified inhibit IRE1 signaling and sensitize glioblastoma cells to the standard of care chemotherapy temozolomide (TMZ). From these inhibitors we selected one that was able to cross the Brain Blood Barrier (BBB) and evaluated its capacity to inhibit tumor growth and avoid relapse in vivo. These results support the attractiveness of IRE1 as an adjuvant therapeutic target in GBM; a common and wholly fatal diagnosis. In addition, they provide scope for quickly testing IRE1 inhibitor suitability in GBM as adjuvant therapy due to their current status for clinical use.

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