XBP1S/XBP1U Polyclonal antibody

XBP1 is also named as XBP2, belongs to the bZIP family. The X-box-binding protein-1 (XBP1) is a transcriptional regulator of the ER stress response that lies downstream of inositol-requiring enzyme 1 (IRE1α) activation (PMID: 14559994). IRE1α possesses both kinase and ribonuclease activity and processes XBP1 mRNA to produce an active transcription factor in response to ER stress (PMID: 11779464, 11780124). It has been found that upon accumulation of unfolded proteins in the endoplasmic reticulum, 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. The resulting loss of 26 nt from the spliced mRNA causes a frame-shift and an isoform XBP1S, which is the functionally active transcription factor. The isoform encoded by the unspliced mRNA, XBP1U, is constitutively expressed, and thought to function as a negative feedback regulator of XBP1S, which shuts off transcription of target genes during the recovery phase of ER stress (PMID: 11850408). The unspliced XBP1U isoform is composed of 261 amino acid residues, and the spliced XBP1S isoform is composed of 376 amino acid residues. The XBP1 antibody (24168-1-AP) can detect both XBP1U and XBP1S.