Role of disulfide bridges formed in the luminal domain of ATF6 in sensing endoplasmic reticulum stress.
ATF6 is a membrane-bound transcription factor activated by proteolysis in response to endoplasmic reticulum (ER) stress to induce the transcription of ER chaperone genes. We show here that, owing to the presence of intra- and intermolecular disulfide bridges formed between the two conserved cysteine residues in the luminal domain, ATF6 occurs in unstressed ER in monomer, dimer, and oligomer forms. Disulfide-bonded ATF6 is reduced upon treatment of cells with not only the reducing reagent dithiothreitol but also the glycosylation inhibitor tunicamycin, and the extent of reduction correlates with that of activation. Although reduction is not sufficient for activation, fractionation studies show that only reduced monomer ATF6 reaches the Golgi apparatus, where it is cleaved by the sequential action of the two proteases S1P and S2P. Reduced monomer ATF6 is found to be a better substrate than disulfide-bonded forms for S1P. ER stress-induced reduction is specific to ATF6 as the oligomeric status of a second ER membrane-bound transcription factor, LZIP/Luman, is not changed upon tunicamycin treatment and LZIP/Luman is well cleaved by S1P in the absence of ER stress. This mechanism ensures the strictness of regulation, in that the cell can only process ATF6 which has experienced the changes in the ER.
Nadanaka
Satomi
S
Department of Biophysics, Graduate School of Science, Kyoto University, Kitashirakawa-oiwake, Sakyo-ku, Kyoto 606-8502, Japan.
Okada
Tetsuya
T
Yoshida
Hiderou
H
Mori
Kazutoshi
K
D051702:Activating Transcription Factor 6 / Q000096:biosynthesis / Q000737:chemistry* / Q000378:metabolism*; D000409:Alanine / Q000235:genetics; D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D003545:Cysteine / Q000235:genetics; D004220:Disulfides / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology*; D006056:Golgi Apparatus / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D051379:Mice; D008954:Models, Biological; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction / Q000187:drug effects; D043484:Proprotein Convertases / Q000378:metabolism; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D020836:Protein Structure, Quaternary / Q000187:drug effects; D017434:Protein Structure, Tertiary / Q000187:drug effects; D021381:Protein Transport / Q000187:drug effects; D016415:Sequence Alignment; D012697:Serine Endopeptidases / Q000378:metabolism; D013329:Structure-Activity Relationship; D013379:Substrate Specificity / Q000187:drug effects; D014415:Tunicamycin / Q000494:pharmacology
C497111:ATF6 protein, human; D051702:Activating Transcription Factor 6; D004220:Disulfides; D014415:Tunicamycin; D043484:Proprotein Convertases; D012697:Serine Endopeptidases; C115575:membrane-bound transcription factor peptidase, site 1; D003545:Cysteine; D000409:Alanine