a transcription factor essential for hepatocyte growth, the differentiation of plasma cells, immunoglobulin secretion, and the unfolded protein response (UPR). XBP1 mRNA is spliced by IRE1 during the UPR to generate a new C-terminus, converting it into a potent unfolded-protein response transcriptional activator and triggering growth arrest and apoptosis. Only the spliced form of XBP1 can activate the UPR efficiently. Activates UPR target genes via direct binding to the UPR element (UPRE). Binds DNA preferably to the CRE-like element 5'-GATGACGTG[TG]N(3)[AT]T-3', and also to some TPA response elements (TRE). Binds to the HLA DR-alpha promoter. Binds to the Tax-responsive element (TRE) of HTLV-I. Up-regulated by ATF6 via direct binding to the ERSE in response to endoplasmic reticulum stress. Genetic variations in XBP1 could be associated with susceptibility to major affective disorder type 7 (MAFD7). Major affective disorders represent a class of mental disorders characterized by a disturbance in mood as their predominant feature. Two human isoforms are produced by alternative splicing. Isoform 1 is also known as XBP-1U. Isoform 2, also known as XBP-1S, is produced by IRE1 in response to endoplasmic reticulum stress. IRE1 cleaves a 26-bp fragment causing a frameshift of the mRNA transcript. Note: This description may include information from UniProtKB.
Molecular Function: DNA binding; protein binding; protein heterodimerization activity; transcription factor activity
Biological Process: angiogenesis; cellular response to glucose starvation; cellular response to insulin stimulus; cellular response to nutrient; cholesterol homeostasis; fatty acid biosynthetic process; fatty acid homeostasis; immune response; liver development; negative regulation of apoptosis; neuron development; positive regulation of angiogenesis; positive regulation of B cell differentiation; positive regulation of cell migration; positive regulation of cell proliferation; positive regulation of fat cell differentiation; positive regulation of immunoglobulin production; positive regulation of immunoglobulin secretion; positive regulation of MHC class II biosynthetic process; positive regulation of T cell differentiation; positive regulation of transcription from RNA polymerase II promoter; positive regulation of transcription of target genes involved in unfolded protein response; sterol homeostasis; transcription from RNA polymerase II promoter; ubiquitin-dependent protein catabolic process; unfolded protein response