title: XBP-1, a key regulator of unfolded protein response, activates transcription of IGF1 and Akt phosphorylation in zebrafish embryonic cell line.
abstract: The unfolded protein response (UPR) is a conserved and adaptive cellular response to increase cell survival during ER stress. XBP-1 spliced form (XBP-1S) generated by IRE1 endoribonuclease is a key transcriptional regulator in UPR to activate genes involved in protein folding and degradation to restore ER function. Although Akt activation was suggested to be a pro-survival pathway activated during ER stress, the signal to trigger Akt is still not clear. In this study, we report IGF1 transcription and Akt phosphorylation are enhanced in XBP-1S stably overexpressed clone of zebrafish embryonic cell line (ZF4). In addition, zebrafish IGF1 intron1 with predicted UPRE (XBP-1S binding sites) and ERSE (ATF6/XBP-1S binding site) linked with basal promoter could be activated by XBP-1S, not by XBP-1 unspliced form (XBP-1U). Furthermore, we demonstrate that expression of endogenous IGF1 is transiently induced as XBP-1 splicing during ER stress in parallel to ER chaperone GRP78/Hspa5 and ER resided E3 ubiquitin ligase Synoviolin in ZF4 cells by quantitative PCR. Our results suggest zebrafish XBP-1S not only activates genes responsible for protein folding, transporting, glycosylation and ER associated degradation but also activates anti-apoptosis signal via IGF1/Akt pathway in unfolded protein response to cope with ER stress.
authors.affiliation: Graduate Institute of Life Sciences, National Defense Medical Center, Taipei, Taiwan.
authors.forename: Meng-Chuen
authors.initials: MC
authors.lastname: Hu
authors.forename: Hong-Yi
authors.initials: HY
authors.lastname: Gong
authors.forename: Gen-Hwa
authors.initials: GH
authors.lastname: Lin
authors.forename: Shao-Yang
authors.initials: SY
authors.lastname: Hu
authors.forename: Mark Hung-Chih
authors.initials: MH
authors.lastname: Chen
authors.forename: Shin-Jie
authors.initials: SJ
authors.lastname: Huang
authors.forename: Ching-Fong
authors.initials: CF
authors.lastname: Liao
authors.forename: Jen-Leih
authors.initials: JL
authors.lastname: Wu
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism; D000091342:Endoplasmic Reticulum Chaperone BiP; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000235:genetics*; D008969:Molecular Sequence Data; D020411:Oligonucleotide Array Sequence Analysis; D010766:Phosphorylation; D017510:Protein Folding; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D000071701:Regulatory Factor X Transcription Factors; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D013997:Time Factors; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic / Q000235:genetics*; D015854:Up-Regulation; D000071717:X-Box Binding Protein 1; D015027:Zebrafish / Q000196:embryology / Q000235:genetics* / Q000378:metabolism*
chemical_list: D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D000091342:Endoplasmic Reticulum Chaperone BiP; C000717247:HSPA5 protein, human; D012333:RNA, Messenger; D000071701:Regulatory Factor X Transcription Factors; D014157:Transcription Factors; D000071717:X-Box Binding Protein 1; C000605543:XBP1 protein, human; D007334:Insulin-Like Growth Factor I; D051057:Proto-Oncogene Proteins c-akt