The function of Ensembl gene identifier ENSG00000178607 (ERN1, endoplasmic reticulum to nucleus signaling 1) is as follows. Serine/threonine-protein kinase and endoribonuclease that acts as a key sensor for the endoplasmic reticulum unfolded protein response (UPR) (PubMed:11175748, PubMed:11779464, PubMed:12637535, PubMed:19328063, PubMed:21317875, PubMed:28128204, PubMed:30118681, PubMed:36739529, PubMed:9637683). In unstressed cells, the endoplasmic reticulum luminal domain is maintained in its inactive monomeric state by binding to the endoplasmic reticulum chaperone HSPA5/BiP (PubMed:21317875). Accumulation of misfolded proteins 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:21317875). The endoribonuclease activity is specific for XBP1 mRNA and excises 26 nucleotides from XBP1 mRNA (PubMed:11779464, PubMed:21317875, PubMed:24508390). The resulting spliced transcript of XBP1 encodes a transcriptional activator protein that up-regulates expression of UPR target genes (PubMed:11779464, PubMed:21317875, PubMed:24508390). 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 (PubMed:21884936, PubMed:28067262). {ECO:0000269|PubMed:11175748, ECO:0000269|PubMed:11779464, ECO:0000269|PubMed:12637535, ECO:0000269|PubMed:19328063, ECO:0000269|PubMed:21317875, ECO:0000269|PubMed:21884936, ECO:0000269|PubMed:28067262, ECO:0000269|PubMed:28128204, ECO:0000269|PubMed:30118681, ECO:0000269|PubMed:36739529, ECO:0000269|PubMed:9637683, ECO:0000305|PubMed:24508390}.