title: Activation of the unfolded protein response during anoxia exposure in the turtle Trachemys scripta elegans.
abstract: Red-eared slider turtles, Trachemys scripta elegans, can survive for several weeks without oxygen when submerged in cold water. We hypothesized that anaerobiosis is aided by adaptive up-regulation of the unfolded protein response (UPR), a stress-responsive pathway that is activated by accumulation of unfolded proteins in the endoplasmic reticulum (ER) and functions to restore ER homeostasis. RT-PCR, western immunoblotting and DNA-binding assays were used to quantify the responses and/or activation status of UPR-responsive genes and proteins in turtle tissues after animal exposure to 5 or 20 h of anoxic submergence at 4 °C. The phosphorylation state of protein kinase-like ER kinase (PERK) (a UPR-regulated kinase) and eukaryotic initiation factor 2 (eIF2α) increased by 1.43-2.50 fold in response to anoxia in turtle heart, kidney, and liver. Activation of the PERK-regulated transcription factor, activating transcription factor 4 (ATF4), during anoxia was documented by elevated atf4 transcripts and total ATF4 protein (1.60-2.43 fold), increased nuclear ATF4 content, and increased DNA-binding activity (1.44-2.32 fold). ATF3 and GADD34 (downstream targets of ATF4) also increased by 1.38-3.32 fold in heart and liver under anoxia, and atf3 transcripts were also elevated in heart. Two characteristic chaperones of the UPR, GRP78, and GRP94, also responded positively to anoxia with strong increases in both the transcript and protein levels. The data demonstrate that the UPR is activated in turtle heart, kidney, and liver in response to anoxia, suggesting that this pathway mediates an integrated stress response to protect tissues during oxygen deprivation.
authors.affiliation: Department of Biology, Institute of Biochemistry, Carleton University, 1125 Colonel By Drive, Ottawa, ON, K1S 5B6, Canada. krivoruchko@gmail.com
authors.forename: Anastasia
authors.initials: A
authors.lastname: Krivoruchko
authors.forename: Kenneth B
authors.initials: KB
authors.lastname: Storey
mesh_terms: D051700:Activating Transcription Factor 3 / Q000378:metabolism; D051701:Activating Transcription Factor 4 / Q000235:genetics / Q000378:metabolism; D000693:Anaerobiosis / Q000502:physiology; D000818:Animals; D001483:Base Sequence; D004268:DNA-Binding Proteins / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D000091342:Endoplasmic Reticulum Chaperone BiP; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006321:Heart; D006360:Heat-Shock Proteins / Q000378:metabolism; D000860:Hypoxia; D007668:Kidney; D008099:Liver; D008565:Membrane Proteins / Q000378:metabolism; D008969:Molecular Sequence Data; D010100:Oxygen / Q000378:metabolism; D010766:Phosphorylation; D017510:Protein Folding; D017422:Sequence Analysis, DNA; D015398:Signal Transduction; D014426:Turtles / Q000378:metabolism*; D056811:Unfolded Protein Response; D019892:eIF-2 Kinase / Q000378:metabolism
chemical_list: D051700:Activating Transcription Factor 3; D051701:Activating Transcription Factor 4; D004268:DNA-Binding Proteins; D000091342:Endoplasmic Reticulum Chaperone BiP; D015852:Eukaryotic Initiation Factor-2; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D008565:Membrane Proteins; D010100:Oxygen; D019892:eIF-2 Kinase; C018551:glucose-regulated proteins