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XBP1

This gene encodes a transcription factor that regulates MHC class II genes by binding to a promoter element referred to as an X box. This gene product is a bZIP protein, which was also identified as a cellular transcription factor that binds to an enhancer in the promoter of the T cell leukemia virus type 1 promoter. It may increase expression of viral proteins by acting as the DNA binding partner of a viral transactivator. It has been found that upon accumulation of unfolded proteins in the endoplasmic reticulum (ER), the mRNA of this gene is processed to an active form by an unconventional splicing mechanism that is mediated by the endonuclease inositol-requiring enzyme 1 (IRE1). The resulting loss of 26 nt from the spliced mRNA causes a frame-shift and an isoform XBP1(S), which is the functionally active transcription factor. The isoform encoded by the unspliced mRNA, XBP1(U), is constitutively expressed, and thought to function as a negative feedback regulator of XBP1(S), which shuts off transcription of target genes during the recovery phase of ER stress. A pseudogene of XBP1 has been identified and localized to chromosome 5. [provided by RefSeq, Jul 2008]
Protein class

Cancer-related genes, Disease related genes, Transcription factors

Predicted location

Intracellular, Membrane (different isoforms)

Single cell type specificity

Cell type enhanced (Plasma cells, Breast glandular cells)

Immune cell specificity

Low immune cell specificity

Cell line specificity

Cell line enhanced (MCF7, SK-BR-3, T-47d)

Interaction

Isoform 2 interacts with SIRT1. Isoform 2 interacts with PIK3R1 and PIK3R2; the interactions are direct and induce translocation of XBP1 isoform 2 into the nucleus and the unfolded protein response (UPR) XBP1-dependent target genes activation in a ER stress- and/or insulin-dependent but PI3K-independent manner. Isoform 2 interacts with FOXO1; the interaction is direct and leads to FOXO1 ubiquitination and degradation via the proteasome pathway in hepatocytes (By similarity). Isoform 1 interacts with HM13 (PubMed:25239945). Isoform 1 interacts with RNF139; the interaction induces ubiquitination and degradation of isoform 1 (PubMed:25239945). Isoform 1 interacts (via luminal domain) with DERL1; the interaction obviates the need for ectodomain shedding prior HM13/SPP-mediated XBP1 isoform 1 cleavage (PubMed:25239945). Isoform 1 interacts with isoform 2; the interaction sequesters isoform 2 from the nucleus and enhances isoform 2 degradation in the cytoplasm (PubMed:16461360, 25239945). Isoform 1 interacts with HDAC3 and AKT1; the interactions occur in endothelial cell (EC) under disturbed flow (PubMed:25190803). Isoform 1 interacts with the oncoprotein FOS (PubMed:1903538). Isoform 2 interacts with ATF6; the interaction occurs in a ER stress-dependent manner and is required for DNA binding to the unfolded protein response element (UPRE) (PubMed:17765680). Isoform 2 interacts with PIK3R1; the interaction is direct and induces translocation of XBP1 isoform 2 into the nucleus and the unfolded protein response (UPR) XBP1-dependent target genes activation in a ER stress- and/or insulin-dependent but PI3K-independent manner (PubMed:20348923).

Molecular function

Activator, Developmental protein, DNA-binding

More Types Infomation

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