title: The unfolded protein response transducer ATF6 represents a novel transmembrane-type endoplasmic reticulum-associated degradation substrate requiring both mannose trimming and SEL1L protein.
abstract: Proteins misfolded in the endoplasmic reticulum (ER) are cleared by the ubiquitin-dependent proteasome system in the cytosol, a series of events collectively termed ER-associated degradation (ERAD). It was previously shown that SEL1L, a partner protein of the E3 ubiquitin ligase HRD1, is required for degradation of misfolded luminal proteins (ERAD-Ls substrates) but not misfolded transmembrane proteins (ERAD-Lm substrates) in both mammalian and chicken DT40 cells. Here, we analyzed ATF6, a type II transmembrane glycoprotein that serves as a sensor/transducer of the unfolded protein response, as a potential ERAD-Lm substrate in DT40 cells. Unexpectedly, degradation of endogenous ATF6 and exogenously expressed chicken and human ATF6 by the proteasome required SEL1L. Deletion analysis revealed that the luminal region of ATF6 is a determinant for SEL1L-dependent degradation. Chimeric analysis showed that the luminal region of ATF6 confers SEL1L dependence on type I transmembrane protein as well. In contrast, degradation of other known type I ERAD-Lm substrates (BACE457, T-cell receptor-α, CD3-δ, and CD147) did not require SEL1L. Thus, ATF6 represents a novel type of ERAD-Lm substrate requiring SEL1L for degradation despite its transmembrane nature. In addition, endogenous ATF6 was markedly stabilized in wild-type cells treated with kifunensine, an inhibitor of α1,2-mannosidase in the ER, indicating that degradation of ATF6 requires proper mannose trimming. Our further analyses revealed that the five ERAD-Lm substrates examined are classified into three subgroups based on their dependence on mannose trimming and SEL1L. Thus, ERAD-Lm substrates are degraded through much more diversified mechanisms in higher eukaryotes than previously thought.
authors.affiliation: From the Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Horimoto
authors.forename: Satoshi
authors.initials: S
authors.lastname: Ninagawa
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Okada
authors.forename: Hibiki
authors.initials: H
authors.lastname: Koba
authors.forename: Takehiro
authors.initials: T
authors.lastname: Sugimoto
authors.forename: Yukiko
authors.initials: Y
authors.lastname: Kamiya
authors.forename: Koichi
authors.initials: K
authors.lastname: Kato
authors.forename: Shunichi
authors.initials: S
authors.lastname: Takeda
authors.forename: Kazutoshi
authors.initials: K
authors.lastname: Mori
mesh_terms: D051702:Activating Transcription Factor 6 / Q000235:genetics / Q000378:metabolism*; D000470:Alkaloids / Q000494:pharmacology; D000818:Animals; D000928:Antidepressive Agents / Q000494:pharmacology; D002460:Cell Line; D002645:Chickens; D060746:Endoplasmic Reticulum-Associated Degradation / Q000187:drug effects / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D008358:Mannose / Q000235:genetics / Q000378:metabolism*; D008361:Mannosidases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D010624:Phenelzine / Q000494:pharmacology; D055550:Protein Stability / Q000187:drug effects; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D059748:Proteolysis / Q000187:drug effects; D013379:Substrate Specificity / Q000187:drug effects / Q000502:physiology
chemical_list: C497111:ATF6 protein, human; D051702:Activating Transcription Factor 6; D000470:Alkaloids; D000928:Antidepressive Agents; D004791:Enzyme Inhibitors; D011506:Proteins; C117384:SEL1L protein, human; C065629:kifunensine; D008361:Mannosidases; C046090:mannosyl-oligosaccharide 1,2-alpha-mannosidase; D010624:Phenelzine; D008358:Mannose
keywords: Endoplasmic Reticulum (ER); Membrane Proteins; Protein Degradation; Ubiquitin Ligase; Unfolded Protein Response
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