Ern1
Function
Serine/threonine-protein kinase and endoribonuclease that acts as a key sensor for the endoplasmic reticulum unfolded protein response (UPR) (PubMed:11850408, PubMed:25164867). In unstressed cells, the endoplasmic reticulum luminal domain is maintained in its inactive monomeric state by binding to the endoplasmic reticulum chaperone HSPA5/BiP. Accumulation of misfolded protein in the endoplasmic reticulum causes release of HSPA5/BiP, allowing the luminal domain to homodimerize, promoting autophosphorylation of the kinase domain and subsequent activation of the endoribonuclease activity (PubMed:25164867). The endoribonuclease activity is specific for XBP1 mRNA and excises 26 nucleotides from XBP1 mRNA (PubMed:11850408, PubMed:25164867). The resulting spliced transcript of XBP1 encodes a transcriptional activator protein that up-regulates expression of UPR target genes (PubMed:11850408, PubMed:25164867). Acts as an upstream signal for ER stress-induced GORASP2-mediated unconventional (ER/Golgi-independent) trafficking of CFTR to cell membrane by modulating the expression and localization of SEC16A (By similarity).
Post-translational modifications
Autophosphorylated following homodimerization. Autophosphorylation promotes activation of the endoribonuclease domain (PubMed:25164867). In response to ER stress, phosphorylated at Ser-724, Ser-729 and possibly Ser-726; phosphorylation promotes oligomerization and endoribonuclease activity (PubMed:30118681). Dephosphorylated at Ser-724, Ser-729 and possibly Ser-726 by RPAP2 to abort failed ER-stress adaptation and trigger apoptosis (By similarity).
ADP-ribosylated by PARP16 upon ER stress, which increases both kinase and endonuclease activities.
Sequence Similarities
Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.
Tissue Specificity
Expressed in liver (at protein level) (PubMed:30118681). Ubiquitously expressed (PubMed:11146108). High levels in thymus, liver and lung. In the brain, preferentially expressed in cortical, hippocampal and olfactory neurons (PubMed:11146108).
Cellular localization
- Endoplasmic reticulum membrane
- Single-pass type I membrane protein
Alternative names
Ire1, Ern1, Serine/threonine-protein kinase/endoribonuclease IRE1, Endoplasmic reticulum-to-nucleus signaling 1, Inositol-requiring protein 1, Ire1-alpha, IRE1a