Abstract
IRE1 couples endoplasmic reticulum unfolded protein load to RNA cleavage events that culminate in the sequence-specific splicing of the Xbp1 mRNA and in the regulated degradation of diverse membrane-bound mRNAs. We report on the identification of a small molecule inhibitor that attains its selectivity by forming an unusually stable Schiff base with lysine 907 in the IRE1 endonuclease domain, explained by solvent inaccessibility of the imine bond in the enzyme-inhibitor complex. The inhibitor (abbreviated 4μ8C) blocks substrate access to the active site of IRE1 and selectively inactivates both Xbp1 splicing and IRE1-mediated mRNA degradation. Surprisingly, inhibition of IRE1 endonuclease activity does not sensitize cells to the consequences of acute endoplasmic reticulum stress, but rather interferes with the expansion of secretory capacity. Thus, the chemical reactivity and sterics of a unique residue in the endonuclease active site of IRE1 can be exploited by selective inhibitors to interfere with protein secretion in pathological settings.
Publication types
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Research Support, N.I.H., Extramural
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Research Support, Non-U.S. Gov't
MeSH terms
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Animals
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Binding Sites
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Coumarins / chemistry
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Coumarins / pharmacology*
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DNA-Binding Proteins / metabolism
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Endoplasmic Reticulum Stress
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Endoribonucleases / antagonists & inhibitors
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Endoribonucleases / metabolism*
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Humans
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Lysine / metabolism
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Membrane Proteins / antagonists & inhibitors
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Membrane Proteins / metabolism*
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Mice
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Protein Binding / drug effects
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Protein Serine-Threonine Kinases / antagonists & inhibitors
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Protein Serine-Threonine Kinases / metabolism*
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Proteolysis / drug effects
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RNA Splicing* / drug effects
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RNA, Messenger / genetics
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RNA, Messenger / metabolism
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Regulatory Factor X Transcription Factors
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Ribonucleases / antagonists & inhibitors
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Ribonucleases / metabolism
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Schiff Bases / chemistry
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Schiff Bases / metabolism
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Secretory Pathway / drug effects
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Transcription Factors / metabolism
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X-Box Binding Protein 1
Substances
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Coumarins
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DNA-Binding Proteins
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Membrane Proteins
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RNA, Messenger
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Regulatory Factor X Transcription Factors
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Schiff Bases
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Transcription Factors
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X-Box Binding Protein 1
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XBP1 protein, human
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Xbp1 protein, mouse
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ERN2 protein, human
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Ern2 protein, mouse
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Protein Serine-Threonine Kinases
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Endoribonucleases
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Ribonucleases
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Lysine