Oxygen Sensing: Recent Insights from Idiopathic Erythrocytosis

Abstract
Idiopathic erythrocytosis (IE) is a rare condition in which there is an increase inred cell mass and hematocrit. As it is typically driven by elevated or inappropriatelynormal erythropoietin (Epo) levels, it has the potential to reveal the identities of proteinsinvolved in the oxygen sensing pathway that regulates the transcription factor, HypoxiaInducible Factor (HIF), and hence Epo production in humans. One example of this isprovided by Chuvash polycythemia, a form of erythrocytosis due to a mutation in the vonHippel Lindau tumor suppressor protein (VHL), a component of an E3 ubiquitin ligasecomplex that targets hydroxylated HIF for degradation. A recent report of familialerythrocytosis now implicates a different protein, Prolyl Hydroxylase Domain protein 2(PHD2), which is an enzyme that hydroxylates HIF.