How is Xbp1 mRNA related to the Unfolded Protein Response?
The UPR is activated when there is an accumulation of misfolded or unfolded proteins in the ER. Xbp1 mRNA undergoes an unconventional splicing event mediated by the ER stress sensor IRE1 (Inositol-Requiring Enzyme 1). This splicing converts the unspliced form of Xbp1 mRNA (Xbp1u) into its spliced form (Xbp1s), which encodes a potent transcription factor that upregulates UPR target genes.