title: Endoplasmic Reticulum Stress Response and Mutant Protein Degradation in CHO Cells Accumulating Antithrombin (C95R) in Russell Bodies.
abstract: Newly synthesized secretory proteins are folded and assembled in the endoplasmic reticulum (ER), where an efficient protein quality control system performs a critically important function. When unfolded or aggregated proteins accumulate in the ER, certain signaling pathways such as the unfolded protein response (UPR) and ER-overload response (EOR) are functionally active in maintaining cell homeostasis. Recently we prepared Chinese hamster ovary (CHO) cells expressing mutant antithrombin (AT)(C95R) under control of the Tet-On system and showed that AT(C95R) accumulated in Russell bodies (RB), large distinctive structures derived from the ER. To characterize whether ER stress takes place in CHO cells, we examined characteristic UPR and EOR in ER stress responses. We found that the induction of ER chaperones such as Grp97, Grp78 and protein disulfide isomerase (PDI) was limited to a maximum of approximately two-fold. The processing of X-box-binding protein-1 (XBP1) mRNA and the phosphorylation of eukaryotic translation initiation factor 2α (eIF2α) subunit were not induced. Furthermore, the activation of nuclear factor-kappa B (NF-κB) was not observed. In contrast, CHO cells displayed UPR and EOR when the cells were treated with thapsigargin and tumor necrosis factor (TNF)-α, respectively. In addition, a portion of the mutant AT(C95R) was degraded through proteasomes and autophagy. CHO cells do respond to ER stress but the folding state of mutant AT(C95R) does not appear to activate the ER stress signal pathway.
authors.affiliation: Department of Biological Chemistry, University of Toyama.
authors.forename: Koji
authors.initials: K
authors.lastname: Kimura
authors.forename: Kengo
authors.initials: K
authors.lastname: Inoue
authors.forename: Jun
authors.initials: J
authors.lastname: Okubo
authors.forename: Yumiko
authors.initials: Y
authors.lastname: Ueda
authors.forename: Kosuke
authors.initials: K
authors.lastname: Kawaguchi
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Sakurai
authors.forename: Ikuo
authors.initials: I
authors.lastname: Wada
authors.forename: Masashi
authors.initials: M
authors.lastname: Morita
authors.forename: Tsuneo
authors.initials: T
authors.lastname: Imanaka
mesh_terms: D000818:Animals; D000991:Antithrombins / Q000378:metabolism*; D016466:CHO Cells; D003412:Cricetulus; D004721:Endoplasmic Reticulum; D000091342:Endoplasmic Reticulum Chaperone BiP; D059865:Endoplasmic Reticulum Stress; D006360:Heat-Shock Proteins / Q000378:metabolism; D006801:Humans; D051379:Mice; D018832:Molecular Chaperones / Q000378:metabolism*; D050505:Mutant Proteins / Q000378:metabolism*; D016328:NF-kappa B / Q000378:metabolism; D059748:Proteolysis; D012333:RNA, Messenger / Q000378:metabolism; D011817:Rabbits; D015398:Signal Transduction; D014157:Transcription Factors / Q000378:metabolism; D056811:Unfolded Protein Response
chemical_list: D000991:Antithrombins; D000091342:Endoplasmic Reticulum Chaperone BiP; C000717247:HSPA5 protein, human; D006360:Heat-Shock Proteins; C000717248:Hspa5 protein, mouse; D018832:Molecular Chaperones; D050505:Mutant Proteins; D016328:NF-kappa B; D012333:RNA, Messenger; D014157:Transcription Factors