title: IRE1 couples endoplasmic reticulum load to secretory capacity by processing the XBP-1 mRNA.
abstract: The unfolded protein response (UPR), caused by stress, matches the folding capacity of endoplasmic reticulum (ER) to the load of client proteins in the organelle. In yeast, processing of HAC1 mRNA by activated Ire1 leads to synthesis of the transcription factor Hac1 and activation of the UPR. The responses to activated IRE1 in metazoans are less well understood. Here we demonstrate that mutations in either ire-1 or the transcription-factor-encoding xbp-1 gene abolished the UPR in Caenorhabditis elegans. Mammalian XBP-1 is essential for immunoglobulin secretion and development of plasma cells, and high levels of XBP-1 messenger RNA are found in specialized secretory cells. Activation of the UPR causes IRE1-dependent splicing of a small intron from the XBP-1 mRNA both in C. elegans and mice. The protein encoded by the processed murine XBP-1 mRNA accumulated during the UPR, whereas the protein encoded by unprocessed mRNA did not. Purified mouse IRE1 accurately cleaved XBP-1 mRNA in vitro, indicating that XBP-1 mRNA is a direct target of IRE1 endonucleolytic activity. Our findings suggest that physiological ER load regulates a developmental decision in higher eukaryotes.
authors.affiliation: Skirball Institute of Biomolecular Medicine, New York University School of Medicine, New York, NY 10016, USA.
authors.forename: Marcella
authors.initials: M
authors.lastname: Calfon
authors.forename: Huiqing
authors.initials: H
authors.lastname: Zeng
authors.forename: Fumihiko
authors.initials: F
authors.lastname: Urano
authors.forename: Jeffery H
authors.initials: JH
authors.lastname: Till
authors.forename: Stevan R
authors.initials: SR
authors.lastname: Hubbard
authors.forename: Heather P
authors.initials: HP
authors.lastname: Harding
authors.forename: Scott G
authors.initials: SG
authors.lastname: Clark
authors.forename: David
authors.initials: D
authors.lastname: Ron
mesh_terms: D000818:Animals; D001483:Base Sequence; D017173:Caenorhabditis elegans / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D029742:Caenorhabditis elegans Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D005347:Fibroblasts; D007438:Introns / Q000235:genetics; D008565:Membrane Proteins; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D009690:Nucleic Acid Conformation; D011489:Protein Denaturation; D017510:Protein Folding; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D012326:RNA Splicing; D018510:RNA, Helminth / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000071701:Regulatory Factor X Transcription Factors; D013234:Stem Cells / Q000378:metabolism; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D000071717:X-Box Binding Protein 1
chemical_list: D029742:Caenorhabditis elegans Proteins; D004268:DNA-Binding Proteins; D008565:Membrane Proteins; D018510:RNA, Helminth; D012333:RNA, Messenger; D000071701:Regulatory Factor X Transcription Factors; D014157:Transcription Factors; D000071717:X-Box Binding Protein 1; C000605544:Xbp1 protein, mouse; C486556:Ern2 protein, mouse; D017346:Protein Serine-Threonine Kinases