High impact information on XBP1

• We propose that nuclear-localized IRE1alpha and cytoplasmic-localized ATF6 signaling pathways merge through regulation of XBP1 activity to induce downstream gene expression [1].
• Whereas ATF6 increases the amount of XBP1 mRNA, IRE1alpha removes an unconventional 26-nucleotide intron that increases XBP1 transactivation potential [1].
• Furthermore, the deletion of XBP1 prevents the drop in Clb2 levels and inhibits cellular elongation in nitrogen-limited chemostat cultures as well as inhibiting pseudohyphal growth on nitrogen-limited agar media [2].
• During meiosis, XBP1 is highly induced and its mRNA appears at the same time as DIT1 mRNA, but its expression remains high for up to 24 h [3].
• Furthermore, Xbp1 target genes are normally repressed late in meiosis, and loss of XBP1 results in their derepression [3].

Biological context of XBP1

• Overexpression of XBP1 results in a slow-growth phenotype, lengthening of G1, an increase in cell volume, and a repression of G1 cyclin expression [4].
• The XBP1 promoter contains several stress-regulated elements, and its expression is induced by heat shock, high osmolarity, oxidative stress, DNA damage, and glucose starvation [4].
• Transcriptional activation of the XBP1 gene and the subsequent repression of CLB gene expression are thus key responses of yeast cells to nitrogen limitation [2].
• These observations suggest that Xbp1 may contribute to the repression of specific transcripts and cause a transient cell cycle delay under stress conditions [4].
• The consensus binding site of Xbp1, GcCTCGA(G/A)G(C/A)g(a/g), is a palindromic sequence, with an XhoI restriction enzyme recognition site at its center [4].

Anatomical context of XBP1

• Xbp1-deficient cells are capable of forming viable gametes, although ascus formation is delayed by several hours [3].

Regulatory relationships of XBP1

• Ire1 regulated XBP1 mRNA splicing is essential for the unfolded protein response (UPR) in Drosophila melanogaster [5].

Other interactions of XBP1

• CLN1 and its repression by Xbp1 are important for efficient sporulation in budding yeast [3].
• Xbp1, a transcriptional repressor of Saccharomyces cerevisiae with homology to Swi4 and Mbp1, is induced by stress and starvation during the mitotic cycle [3].
• When fused to the LexA DNA-binding domain, Xbp1 acts as transcriptional repressor, defining it as the first repressor in the Swi4/Mbp1 family and the first potential negative regulator of transcription induced by stress [4].

References