XBP1

XBP1

A gene on chromosome 22q12.1 that encodes a bZIP protein transcription factor, which regulates MHC class-II genes by binding to a promoter element or X box.
 
Molecular pathology
XBP1 binds to a T-cell leukaemia virus type-1 promoter, and may increase expression of viral proteins by acting as the DNA binding partner of a viral transactivator.
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Among them, IRE1[alpha]-X-box protein 1 (XBP1) is the most conserved machinery utilised in the UPR.
XBP-1 is normally kept in its inactive form, but under ERS, the endoRNase domain of IRE-1 splices the mRNA of downstream sensor XBP-1, removing a 26-bp segment from the full-length XBP1 mRNA that generates a translational frameshift, leading to the expression of the active protein XBP-1s.[25],[26],[27] XBP-1s binds to intranuclear mRNA directly to regulate protein transcription, thereby affecting subsequent physiological activities.[28],[29] Lee et al .'s study[30] showed for the first time that XBP-1 regulates hepatic lipid metabolism, because XBP1 -knockout mice manifested hypotriglyceridemia and hypocholesterolemia.
XBP1 is required for the differentiation of plasma cells, dendritic cells, CD[8.sup.+] T cells, and eosinophils, as well as the production of several cytokines in macrophages [9, 10].
Recently, the promoter regions of GPR43 were determined in human monocytes, showing transcription factors including XBP1 were key transcription factors for the regulation of GPR43 expression [11].
Apart from low expression of proliferation and cell cycle-related genes, luminal A tumors are distinguished by higher expression of PR and FOXA1, GATA3, and XBP1, whereas the ESR1 gene is expressed at comparable levels as in luminal B tumors [5], [11].
Activated IRE1 induces the splicing of XBP1 (X-box-binding protein 1) mRNA by cleaving off its intron [12].
And their downstream transcription factors include eukaryotic initiation factor 2-[alpha] (eIF2-[alpha]) for PERK, fragmented ATF6 for ATF6, and spliced X-box binding protein 1 (XBP1) for IRE1.
In model systems, UPR is activated by a set of transcription factors including activating transcription factor 6 (ATF6 (N)), X-box binding protein 1 (XBP1), and activating transcription factor 4 (ATF4) (Walter and Ron, 2011).
Lugea and colleagues (2011) examined this protective effect in mice with and without the gene for the X-box binding protein 1 (XBP1), a transcription factor that promotes synthesis of cellular components for protein transport and secretion.
This gene is transcriptionally suppressed by MSX1 and XBP1 [35].
Treadmill exercise can improve cardiac function and reduce cardiac infarction by attenuating the expression of GRP78, DERLIN1, p-PERK, p-eIF2a, ATF4/6, XBP1, CHOP, and cleaved caspase-3 [11, 87].
In the 5% [O.sub.2] group, there was a higher abundance of ATF4, CDX2, DDIT3, KEAP1, HSF1, OTX2, PAF1, POU5F1 (OCT4), REST, SREBF1, and XBP1 factors that are related to several cell cycle processes.