Hypothesis for HIF-2α deregulation through putative mutations present in its 5′ IRE and mutational sequence screening of the 5′ UTR of HIF2A. (A)Iron and oxygen regulation of HIF-2α (EPAS1) in oxygen homeostasis. Availability of iron influences the level of HIF-induced Epo gene transcription via binding to the 5′ IRE of HIF2A. In iron deficiency, the IRE is bound by iron regulatory proteins (IRPs), which prevent HIF-2α translation, but when iron is replete, the IRPs cannot bind the IRE and do not impede HIF-2α protein expression. In hypoxia, HIF-2α is free to escape proteasomal degradation and induce Epo gene expression. The loss of translational inhibition due to mutations in the HIF2A IRE may result in inappropriately high HIF-2α levels with deregulated Epo production, thus allowing for the development of erythrocytosis. (B) Sequence of the 5′ UTR region of HIF2A. The IRE region is indicated in yellow (nucleotides 81298 to 81330; RefSeq AC016696). Primer sets 1 and 2 are as indicated by black and blue arrows, respectively. All SNPs are indicated in blue. Described SNP rs17039192 is labeled Y and located at nucleotide 81261. The 3 uncharacterized SNPs are indicated by R, K, and R, and are located at nucleotides 81405, 81411, and 81424. TATA box and ATG sequences are underlined.