title: Acute Endoplasmic Reticulum Stress-Independent Unconventional Splicing of XBP1 mRNA in the Nucleus of Mammalian Cells.
abstract: The regulation of expression of X-box-binding protein-1 (XBP1), a transcriptional factor, involves an unconventional mRNA splicing that removes the 26 nucleotides intron. In contrast to the conventional splicing that exclusively takes place in the nucleus, determining the location of unconventional splicing still remains controversial. This study was designed to examine whether the unconventional spicing of XBP1 mRNA could occur in the nucleus and its possible biological relevance. We use RT-PCR reverse transcription system and the expand high fidelity PCR system to detect spliced XBP1 mRNA, and fraction cells to determine the location of the unconventional splicing of XBP1 mRNA. We employ reporter constructs to show the presence of unconventional splicing machinery in mammal cells independently of acute endoplasmic reticulum (ER) stress. Our results reveal the presence of basal unconventional splicing of XBP1 mRNA in the nucleus that also requires inositol-requiring transmembrane kinase and endonuclease 1α (IRE1α) and can occur independently of acute ER stress. Furthermore, we confirm that acute ER stress induces the splicing of XBP1 mRNA predominantly occurring in the cytoplasm, but it also promotes the splicing in the nucleus. The deletion of 5'-nucleotides in XBP1 mRNA significantly increases its basal unconventional splicing, suggesting that the secondary structure of XBP1 mRNA may determine the location of unconventional splicing. These results suggest that the unconventional splicing of XBP1 mRNA can take place in the nucleus and/or cytoplasm, which possibly depends on the elaborate regulation. The acute ER stress-independent unconventional splicing in the nucleus is most likely required for the maintaining of day-to-day folding protein homeostasis.
authors.affiliation: Laboratory of Cancer Cell Biology, National Clinical Research Center for Cancer, Tianjin Key Laboratory of Cancer Prevention and Therapy, Tianjin Medical University Cancer Institute and Hospital, Tianjin 300060, China. cristinaup@163.com.|The First Department of Breast Tumor, National Clinical Research Center for Cancer, Tianjin Key Laboratory of Cancer Prevention and Therapy, Tianjin Medical University Cancer Institute and Hospital, Tianjin 300060, China. cristinaup@163.com.
authors.forename: Yuanyuan
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Laboratory of Cancer Cell Biology, National Clinical Research Center for Cancer, Tianjin Key Laboratory of Cancer Prevention and Therapy, Tianjin Medical University Cancer Institute and Hospital, Tianjin 300060, China. xingpan1314@126.com.
authors.forename: Pan
authors.initials: P
authors.lastname: Xing
authors.affiliation: Laboratory of Cancer Cell Biology, National Clinical Research Center for Cancer, Tianjin Key Laboratory of Cancer Prevention and Therapy, Tianjin Medical University Cancer Institute and Hospital, Tianjin 300060, China. zuiaisuxueer@126.com.|The First Department of Breast Tumor, National Clinical Research Center for Cancer, Tianjin Key Laboratory of Cancer Prevention and Therapy, Tianjin Medical University Cancer Institute and Hospital, Tianjin 300060, China. zuiaisuxueer@126.com.
authors.forename: Wenjing
authors.initials: W
authors.lastname: Cui
authors.affiliation: Laboratory of Cancer Cell Biology, National Clinical Research Center for Cancer, Tianjin Key Laboratory of Cancer Prevention and Therapy, Tianjin Medical University Cancer Institute and Hospital, Tianjin 300060, China. wangwenwen.1988@163.com.|The First Department of Breast Tumor, National Clinical Research Center for Cancer, Tianjin Key Laboratory of Cancer Prevention and Therapy, Tianjin Medical University Cancer Institute and Hospital, Tianjin 300060, China. wangwenwen.1988@163.com.
authors.forename: Wenwen
authors.initials: W
authors.lastname: Wang
authors.affiliation: Laboratory of Cancer Cell Biology, National Clinical Research Center for Cancer, Tianjin Key Laboratory of Cancer Prevention and Therapy, Tianjin Medical University Cancer Institute and Hospital, Tianjin 300060, China. cuiyanfen@163.com.
authors.forename: Yanfen
authors.initials: Y
authors.lastname: Cui
authors.affiliation: Laboratory of Cancer Cell Biology, National Clinical Research Center for Cancer, Tianjin Key Laboratory of Cancer Prevention and Therapy, Tianjin Medical University Cancer Institute and Hospital, Tianjin 300060, China. yingguoguang@163.com.
authors.forename: Guoguang
authors.initials: G
authors.lastname: Ying
authors.affiliation: The First Department of Breast Tumor, National Clinical Research Center for Cancer, Tianjin Key Laboratory of Cancer Prevention and Therapy, Tianjin Medical University Cancer Institute and Hospital, Tianjin 300060, China. xinwangse@126.com.
authors.forename: Xin
authors.initials: X
authors.lastname: Wang
authors.affiliation: Laboratory of Cancer Cell Biology, National Clinical Research Center for Cancer, Tianjin Key Laboratory of Cancer Prevention and Therapy, Tianjin Medical University Cancer Institute and Hospital, Tianjin 300060, China. binghuililab@163.com.
authors.forename: Binghui
authors.initials: B
authors.lastname: Li
mesh_terms: D016475:3T3 Cells; D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D059865:Endoplasmic Reticulum Stress; D004722:Endoribonucleases / Q000235:genetics / Q000378:metabolism; D061986:MCF-7 Cells; D051379:Mice; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D012326:RNA Splicing; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D000071701:Regulatory Factor X Transcription Factors; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism; D056811:Unfolded Protein Response; D000071717:X-Box Binding Protein 1
chemical_list: D004268:DNA-Binding Proteins; D012333:RNA, Messenger; D000071701:Regulatory Factor X Transcription Factors; D014157:Transcription Factors; D000071717:X-Box Binding Protein 1; C000605543:XBP1 protein, human; C000605544:Xbp1 protein, mouse; C528229:ERN1 protein, human; D017346:Protein Serine-Threonine Kinases; D004722:Endoribonucleases
keywords: ER stress; IRE1α; XBP1; unconventional splicing; unfolded protein response