title: Activation of mammalian IRE1alpha upon ER stress depends on dissociation of BiP rather than on direct interaction with unfolded proteins.
abstract: IRE1, an ER-localized transmembrane protein, plays a central role in the unfolded protein response. Upon ER stress, IRE1 senses the accumulation of unfolded proteins in the ER, and transfers signal from the ER to the cytosol. Recently, it was reported that the luminal domain of yeast Ire1 senses the unfolded proteins via a two-step mechanism, namely dissociation of BiP and direct interaction with unfolded proteins. However, it has been unclear whether a similar mechanism is applicable to mammalian IRE1alpha. To address this point, we analyzed luminal-domain mutants of mammalian IRE1alpha in cells, and evaluated the anti-aggregation activity of the luminal fragment of IRE1alpha in vitro. We generated a mutant that has low affinity for BiP, and this mutant was significantly activated even under normal conditions. Moreover, the luminal fragments of mammalian IRE1alpha did not exhibit anti-aggregation activity. These results suggest that in contrast to yeast Ire1, the regulation of mammalian IRE1alpha strongly depends on the dissociation of BiP.
authors.affiliation: Iwawaki Initiative Research Unit, Advanced Science Institute, RIKEN, 2-1 Hirosawa, Wako, Saitama, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Oikawa
authors.forename: Yukio
authors.initials: Y
authors.lastname: Kimata
authors.forename: Kenji
authors.initials: K
authors.lastname: Kohno
authors.forename: Takao
authors.initials: T
authors.lastname: Iwawaki
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D004722:Endoribonucleases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D005347:Fibroblasts / Q000166:cytology / Q000502:physiology; D005816:Genetic Complementation Test; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D009842:Oligopeptides / Q000235:genetics / Q000378:metabolism*; D011487:Protein Conformation; D017510:Protein Folding; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D013312:Stress, Physiological
chemical_list: C539791:Bax-inhibiting peptide, BIP; D009842:Oligopeptides; D011994:Recombinant Proteins; C528229:ERN1 protein, human; D017346:Protein Serine-Threonine Kinases; D004722:Endoribonucleases