title: Ire1 has distinct catalytic mechanisms for XBP1/HAC1 splicing and RIDD.
abstract: An evolutionarily conserved unfolded protein response (UPR) component, IRE1, cleaves XBP1/HAC1 introns in order to generate spliced mRNAs that are translated into potent transcription factors. IRE1 also cleaves endoplasmic-reticulum-associated RNAs leading to their decay, an activity termed regulated IRE1-dependent decay (RIDD); however, the mechanism by which IRE1 differentiates intron cleavage from RIDD is not well understood. Using in vitro experiments, we found that IRE1 has two different modes of action: XBP1/HAC1 is cleaved by IRE1 subunits acting cooperatively within IRE1 oligomers, whereas a single subunit of IRE1 performs RIDD without cooperativity. Furthermore, these distinct activities can be separated by complementation of catalytically inactive IRE1 RNase and mutations at oligomerization interfaces. Using an IRE1 RNase inhibitor, STF-083010, selective inhibition of XBP1 splicing indicates that XBP1 promotes cell survival, whereas RIDD leads to cell death, revealing modulation of IRE1 activities as a drug-development strategy.
authors.affiliation: Division of Biological Sciences, Section of Molecular Biology, UCSD, La Jolla, CA 92093-0377, USA.
authors.forename: Arvin B
authors.initials: AB
authors.lastname: Tam
authors.affiliation: Department of Radiation Oncology, Stanford School of Medicine, Stanford, CA 94305-5152, USA.
authors.forename: Albert C
authors.initials: AC
authors.lastname: Koong
authors.affiliation: Division of Biological Sciences, Section of Molecular Biology, UCSD, La Jolla, CA 92093-0377, USA. Electronic address: niwa@ucsd.edu.
authors.forename: Maho
authors.initials: M
authors.lastname: Niwa
mesh_terms: D000818:Animals; D055162:Biocatalysis; D016923:Cell Death; D019070:Cell Lineage; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004722:Endoribonucleases; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000378:metabolism*; D051379:Mice; D008958:Models, Molecular; D055503:Protein Multimerization; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D012326:RNA Splicing; D020871:RNA Stability; D012331:RNA, Fungal / Q000378:metabolism; D000071701:Regulatory Factor X Transcription Factors; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000378:metabolism*; D013329:Structure-Activity Relationship; D013379:Substrate Specificity; D014157:Transcription Factors / Q000378:metabolism*; D000071717:X-Box Binding Protein 1
chemical_list: D004268:DNA-Binding Proteins; D008562:Membrane Glycoproteins; D012331:RNA, Fungal; D000071701:Regulatory Factor X Transcription Factors; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D000071717:X-Box Binding Protein 1; C000605543:XBP1 protein, human; C000605544:Xbp1 protein, mouse; C082863:IRE1 protein, S cerevisiae; C528229:ERN1 protein, human; D017346:Protein Serine-Threonine Kinases; D004722:Endoribonucleases