Eukaryotic translation initiation factor 2-alpha kinase 1 (EIF2AK1) (HRI)

Eukaryotic translation initiation factor 2-alpha kinase 1 (EIF2AK1), commonly known as Heme-regulated inhibitor (HRI), is a critical signaling enzyme that coordinates protein synthesis with cellular conditions, particularly heme availability [UniProt: Q9BQI3]. Primarily expressed in the erythroid lineage, HRI senses heme deficiency to inhibit globin translation, thereby preventing the accumulation of toxic, heme-free globin chains that cause oxidative damage [PubMed: 29439114]. Beyond its role in red blood cells, HRI is activated by diverse stimuli including heat shock, oxidative stress, and mitochondrial dysfunction as part of the integrated stress response (ISR) [PubMed: 31064770]. Upon activation, HRI phosphorylates the alpha subunit of eIF2, leading to a global reduction in protein synthesis and the selective translation of transcription factors like ATF4 that mediate stress adaptation or apoptosis. In therapeutic contexts, HRI is being investigated as a target for blood disorders such as beta-thalassemia and iron-deficiency anemia, where its modulation can balance globin production [PubMed: 32814885]. Additionally, HRI is a target in oncology, where small molecule activators like nelfinavir or BTd748 are explored to induce ISR-mediated cell death in proteosensitive cancers like multiple myeloma [PubMed: 33597248]. Pharmacological inhibitors are also being developed to treat anemia of inflammation and certain neurodegenerative conditions where the ISR is chronically overactive.

Other names

Heme-regulated inhibitorHeme-controlled repressorHCRHeme-regulated eIF2-alpha kinaseEIF2AK1

Phosphorylation of the alpha subunit of eukaryotic initiation factor 2 (eIF2α) at Ser-51, which inhibits the guanine nucleotide exchange factor eIF2B, leading to a global reduction in protein synthesis while selectively increasing the translation of stress-responsive mRNAs like ATF4 [PubMed: 31064770, UniProt: Q9BQI3].