Tam Arvin B, Koong Albert C, Niwa Maho
Division of Biological Sciences, Section of Molecular Biology, UCSD, La Jolla, CA 92093-0377, USA.
Department of Radiation Oncology, Stanford School of Medicine, Stanford, CA 94305-5152, USA.
Cell Rep. 2014 Nov 6;9(3):850-8. doi: 10.1016/j.celrep.2014.09.016. Epub 2014 Oct 30.
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.
一种进化上保守的未折叠蛋白反应（UPR）组分IRE1，切割XBP1/HAC1内含子以产生剪接的mRNA，这些mRNA被翻译为强效转录因子。IRE1还切割内质网相关RNA导致其降解，这种活性称为受调控的IRE1依赖性降解（RIDD）；然而，IRE1区分内含子切割和RIDD的机制尚不清楚。通过体外实验，我们发现IRE1有两种不同的作用模式：XBP1/HAC1被IRE1亚基在IRE1寡聚体内协同作用切割，而IRE1的单个亚基进行RIDD时无协同作用。此外，这些不同的活性可以通过催化无活性的IRE1核糖核酸酶的互补和寡聚化界面处的突变来分离。使用IRE1核糖核酸酶抑制剂STF-083010，对XBP1剪接的选择性抑制表明XBP1促进细胞存活，而RIDD导致细胞死亡，揭示了调节IRE1活性作为一种药物开发策略。
