Hypoxia Inducible Factor (HIF)-2 Alpha is Required for the Development of the Catecholaminergic Phenotype of Sympathoadrenal Cells

The basic helix-loop-helix transcription factor, hypoxia inducible factor (HIF)-2alpha has been implicated in the development of the catecholaminergic phenotype in cells of the sympathoadrenal (SA) lineage; however, the underlying mechanisms and HIF-2alpha targets remain unclear. Using an immortalized rat adrenomedullary chromaffin cell line (MAH cells) derived from a fetal SA progenitor, we examined the role of HIF-2alpha in catecholamine biosynthesis. Chronic hypoxia (2% O(2), 24 h) induced HIF-2alpha in MAH cells but expression of the rate-limiting enzyme, tyrosine hydroxylase (TH) and catecholamine levels were unaltered. Interestingly, HIF-2alpha depleted MAH cells showed dramatically lower (5-12 times) levels of dopamine and noradrenaline compared with wild-type and scrambled controls, even in normoxia (21% O(2)). This was correlated with a marked reduction in the expression of DOPA decarboxylase (DDC) and dopamine beta hydroxylase (DbetaH) but not TH. Chromatin immunoprecipitation assays revealed that HIF-2alpha was bound to the DDC gene promoter which contains two putative hypoxia response elements. These data suggest that a basal level of HIF-2alpha function is required for the normal developmental expression of DDC and DbetaH in SA progenitor cells, and that loss of this function leads to impaired catecholamine biosynthesis.