Siah Proteins, HIF Prolyl Hydroxylases, and the Physiological Response to Hypoxia

AbstractNew evidence suggests that at least two members of the family of hypoxia-inducible factor (HIF) prolyl hydroxylases that regulate HIF stability in response to oxygen (O2) availability are also targeted for proteosome-dependent degradation by the E3 ubiquitin ligases Siah1a and Siah2. This preview examines cellular responses to O2 deprivation (hypoxia) and the complexity of the regulation of the HIF O2 sensing pathway in mammals

Succinate links TCA cycle dysfunction to oncogenesis by inhibiting HIF- prolylhydroxylase

Several mitochondrial proteins are tumor suppressors. These include succinate dehydrogenase (SDH) and fumarate hydratase, both enzymes of the tricarboxylic acid (TCA) cycle. However, to date, the mechanisms by which defects in the TCA cycle contribute to tumor formation have not been elucidated. Here we describe a mitochondrion-to-cytosol signaling pathway that links mitochondrial dysfunction to oncogenic events: succinate, which accumulates as a result of SDH inhibition, inhibits HIF-α prolyl hydroxylases in the cytosol, leading to stabilization and activation of HIF-1α. These results suggest a mechanistic link between SDH mutations and HIF-1α induction, providing an explanation for the highly vascular tumors that develop in the absence of VHL mutations