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

Abstract

Under normal O2 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 O2. The mechanisms by which HIF-2α is stabilized during hypoxia remain controversial. To address this, we are using an O2-sensitive immortalized rat adrenomedullary chromaffin (MAH) cell line. In MAH cells, HIF-2α induction occurs within 15 min exposure to hypoxia (2% O2) 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% O2, 1 hr). The inhibitory effects of rotenone appear to be dependent on O2 concentration. At higher O2 levels (5%), HIF-2α induction is inhibited by low concentrations of rotenone (10 nM), that are ineffective at lower O2 levels (2%). We propose that mitochondrial O2 consumption during hypoxia lowers or depletes cytoplasmic O2 concentration, permitting HIF-2α stabilization. Blocking mitochondrial respiration increases cytoplasmic O2 concentration and triggers HIF-2α degradation. Supported by the Heart and Stroke Foundation of Ontario and Canada