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 Hif2α (MPC and MTT) or expressing both Hif1α and Hif2α (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 Hif1α- and Hif2α-driven effects we expressed Hif2α in MTT and MPC-mCherry cells (naturally lacking Hif2α). Presence of Hif2α 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 Hif1α in PC12 diminished these effects. Pseudohypoxic conditions, simulated by expression of Hif2α 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 (24-48 h) by HIF1α. Continuous activation of
hypoxia-related genes under pseudohypoxia leads to a HIF2α-mediated phosphorylation of TH (permanent status).