Induction of hypoxia inducible factor 2α (HIF‐2α) may be dependent on mitochondrial O2 consumption in an immortalized adrenomedullary chromaffin cell line

Under normal O 2 levels, hypoxia inducible factor (HIF) ‐2α is hydroxylated via a set of oxygen‐dependent prolyl hydroxylases and degraded. During hypoxia, HIF‐2α is stabilized and translocates to the nucleus where it regulates genes critical for survival in low O 2 . The mechanisms by which HIF‐2α is stabilized during hypoxia remain controversial. To address this, we are using an O 2 ‐sensitive immortalized rat adrenomedullary chromaffin (MAH) cell line. In MAH cells, HIF‐2α induction occurs within 15 min exposure to hypoxia (2% O 2 ) and remains elevated for at least 24 hrs. This induction is blocked in the presence of rotenone (1 μM), myxothiazol (1 μM) and NaCN (1 mM), which inhibit mitochondrial complexes I, III, and IV, respectively. In addition, mitochondria‐deficient (ρ0) MAH cells fail to induce HIF‐2α during hypoxia (2% O 2 , 1 hr). The inhibitory effects of rotenone appear to be dependent on O 2 concentration. At higher O 2 levels (5%), HIF‐2α induction is inhibited by low concentrations of rotenone (10 nM), that are ineffective at lower O 2 levels (2%). We propose that mitochondrial O 2 consumption during hypoxia lowers or depletes cytoplasmic O 2 concentration, permitting HIF‐2α stabilization. Blocking mitochondrial respiration increases cytoplasmic O 2 concentration and triggers HIF‐2α degradation. Supported by the Heart and Stroke Foundation of Ontario and Canada