Roles of X-box binding protein 1 (XBP-1) in unfolded protein response and embryonic development in zebrafish

Autor: Meng-Chuen Hu, 胡孟春
Rok vydání: 2007
Druh dokumentu: 學位論文 ; thesis
Popis: 95
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 zebrafish ZF4 embryonic cell line and ZFL liver cell line 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. In addition to the roles in UPR, the function of XBP-1S in zebrafish development was investigated by splicing-inhibition morpholinos to block splicing of XBP-1U mRNA to XBP-1S mRNA. Severe liver and swim bladder shrinkage in company with heart abnormality and edema, and disruption of yolk absorption were easily observed in >83% 5dpf zebrafish, with green fluorescent liver and red fluorescent intestine, induced by both two XBP-1S knockdown morpholinos. It indicates XBP-1S play an essential role in zebrafish development.
Databáze: Networked Digital Library of Theses & Dissertations
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