title: iRhom1 regulates proteasome activity via PAC1/2 under ER stress.
abstract: Proteasome is a protein degradation complex that plays a major role in maintaining cellular homeostasis. Despite extensive efforts to identify protein substrates that are degraded through ubiquitination, the regulation of proteasome activity itself under diverse signals is poorly understood. In this study, we have isolated iRhom1 as a stimulator of proteasome activity from genome-wide functional screening using cDNA expression and an unstable GFP-degron. Downregulation of iRhom1 reduced enzymatic activity of proteasome complexes and overexpression of iRhom1 enhanced it. Native-gel and fractionation analyses revealed that knockdown of iRhom1 expression impaired the assembly of the proteasome complexes. The expression of iRhom1 was increased by endoplasmic reticulum (ER) stressors, such as thapsigargin and tunicamycin, leading to the enhancement of proteasome activity, especially in ER-containing microsomes. iRhom1 interacted with the 20S proteasome assembly chaperones PAC1 and PAC2, affecting their protein stability. Moreover, knockdown of iRhom1 expression impaired the dimerization of PAC1 and PAC2 under ER stress. In addition, iRhom1 deficiency in D. melanogaster accelerated the rough-eye phenotype of mutant Huntingtin, while transgenic flies expressing either human iRhom1 or Drosophila iRhom showed rescue of the rough-eye phenotype. Together, these results identify a novel regulator of proteasome activity, iRhom1, which functions via PAC1/2 under ER stress.
authors.affiliation: Global Research Laboratory, School of Biological Science/N-bio Institute, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 151-747, Korea.
authors.forename: WonJae
authors.initials: W
authors.lastname: Lee
authors.affiliation: Global Research Laboratory, School of Biological Science/N-bio Institute, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 151-747, Korea.
authors.forename: YoungDoo
authors.initials: Y
authors.lastname: Kim
authors.affiliation: Global Research Laboratory, School of Biological Science/N-bio Institute, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 151-747, Korea.
authors.forename: Jisu
authors.initials: J
authors.lastname: Park
authors.affiliation: Global Research Laboratory, School of Biological Science/N-bio Institute, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 151-747, Korea.
authors.forename: SangMi
authors.initials: S
authors.lastname: Shim
authors.affiliation: Global Research Laboratory, School of Biological Science/N-bio Institute, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 151-747, Korea.
authors.forename: Jieun
authors.initials: J
authors.lastname: Lee
authors.affiliation: Global Research Laboratory, School of Biological Science/N-bio Institute, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 151-747, Korea.
authors.forename: Se-hoon
authors.initials: SH
authors.lastname: Hong
authors.affiliation: Global Research Laboratory, School of Biological Science/N-bio Institute, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 151-747, Korea.
authors.forename: Hye-Hyun
authors.initials: HH
authors.lastname: Ahn
authors.affiliation: Global Research Laboratory, School of Biological Science/N-bio Institute, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 151-747, Korea.
authors.forename: Huikyong
authors.initials: H
authors.lastname: Lee
authors.affiliation: Global Research Laboratory, School of Biological Science/N-bio Institute, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 151-747, Korea.
authors.forename: Yong-Keun
authors.initials: YK
authors.lastname: Jung
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D019281:Dimerization; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism; D004331:Drosophila melanogaster / Q000378:metabolism; D054641:Dual Specificity Phosphatase 2 / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects; D066246:ErbB Receptors / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D000071058:Huntingtin Protein; D008565:Membrane Proteins; D018832:Molecular Chaperones / Q000737:chemistry / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D055550:Protein Stability; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D019284:Thapsigargin / Q000494:pharmacology; D014415:Tunicamycin / Q000494:pharmacology; D054875:Ubiquitination / Q000187:drug effects; D015854:Up-Regulation / Q000187:drug effects
chemical_list: D029721:Drosophila Proteins; C086055:HTT protein, human; D000071058:Huntingtin Protein; D008565:Membrane Proteins; D018832:Molecular Chaperones; D009419:Nerve Tissue Proteins; C081962:RHBDF1 protein, human; D034741:RNA, Small Interfering; D014415:Tunicamycin; D019284:Thapsigargin; D066246:ErbB Receptors; C517032:DUSP2 protein, human; D054641:Dual Specificity Phosphatase 2; D046988:Proteasome Endopeptidase Complex