Impact of Extrinsic and Intrinsic Hypoxia on Catecholamine Biosynthesis in Absence or Presence of Hif2α in Pheochromocytoma Cells

Pheochromocytomas and paragangliomas (PPGLs) with activated pseudohypoxic pathways are associated with an immature catecholamine phenotype and carry a higher risk for metastasis. For improved understanding of the underlying mechanisms we investigated the impact of hypoxia and pseudohypoxia on catecholamine biosynthesis in pheochromocytoma cells naturally lacking Hif2&alpha
(MPC and MTT) or expressing both Hif1&alpha
and Hif2&alpha
(PC12). Cultivation under extrinsic hypoxia or in spheroid culture (intrinsic hypoxia) increased cellular dopamine and norepinephrine contents in all cell lines. To distinguish further between Hif1&alpha
driven effects we expressed Hif2&alpha
in MTT and MPC-mCherry cells (naturally lacking Hif2&alpha
). Presence of Hif2&alpha
resulted in similarly increased cellular dopamine and norepinephrine under hypoxia as in the control cells. Furthermore, hypoxia resulted in enhanced phosphorylation of tyrosine hydroxylase (TH). A specific knockdown of Hif1&alpha
in PC12 diminished these effects. Pseudohypoxic conditions, simulated by expression of Hif2&alpha
under normoxia resulted in increased TH phosphorylation, further stimulated by extrinsic hypoxia. Correlations with PPGL tissue data led us to conclude that catecholamine biosynthesis under hypoxia is mainly mediated through increased phosphorylation of TH, regulated as a short-term response (24&ndash
48 h) by HIF1&alpha
Continuous activation of hypoxia-related genes under pseudohypoxia leads to a HIF2&alpha
mediated phosphorylation of TH (permanent status).