title: XBP1U inhibits the XBP1S-mediated upregulation of the iNOS gene expression in mammalian ER stress response.
abstract: Upregulation of the inducible nitric oxide synthase (iNOS) gene is associated with many pathological conditions such as endoplasmic reticulum (ER) stress, and X-box binding protein 1 (XBP1) is critical in mediating ER-stress responsive genes, including iNOS. Nonetheless, the mechanism by which XBP1 regulates iNOS during ER stress remains unexplored. Here we show that the active/spliced form of XBP1 protein, XBP1S, directly binds to the AABS (A-activator-binding site) in the iNOS promoter in vitro and in living cells. XBP1S exhibits dose-dependent activation of iNOS-specific reporter gene activity and endogenous iNOS expression. XBP1S is elevated whereas the unspliced form of XBP1, XBP1U, reduced in ER stress in HepG2 cells. In addition, XBP1U binds to XBP1S and this complex is associated with the iNOS promoter in response to ER stress. Furthermore, XBP1U acts as a negative mediator and suppresses XBP1S-mediated induction of iNOS. Collectively, we present the first evidence demonstrating the regulation of iNOS gene induction by the interaction between the spliced and unspliced forms of XBP1 in response to ER stress.
authors.affiliation: Department of Cell Biology and Genetics, ChongQing Medical University, ChongQing 400016, P.R. China. guo.fengjin@gmail.com
authors.forename: Fengjin
authors.initials: F
authors.lastname: Guo
authors.forename: Edward A
authors.initials: EA
authors.lastname: Lin
authors.forename: Ping
authors.initials: P
authors.lastname: Liu
authors.forename: Jianwei
authors.initials: J
authors.lastname: Lin
authors.forename: Chuanju
authors.initials: C
authors.lastname: Liu
mesh_terms: D000818:Animals; D001665:Binding Sites; D006528:Carcinoma, Hepatocellular / Q000378:metabolism; D045744:Cell Line, Tumor; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression; D017930:Genes, Reporter; D006801:Humans; D008113:Liver Neoplasms / Q000378:metabolism; D008322:Mammals / Q000235:genetics / Q000378:metabolism; D052247:Nitric Oxide Synthase Type II / Q000235:genetics / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D012326:RNA Splicing; D000071701:Regulatory Factor X Transcription Factors; D013312:Stress, Physiological; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D015854:Up-Regulation; D000071717:X-Box Binding Protein 1
chemical_list: D004268:DNA-Binding Proteins; D000071701:Regulatory Factor X Transcription Factors; D014157:Transcription Factors; D000071717:X-Box Binding Protein 1; C000605543:XBP1 protein, human; D052247:Nitric Oxide Synthase Type II