A Common Polymorphism in the Oxygen-dependent Degradation (ODD) Domain of Hypoxia Inducible Factor-1alpha (HIF-1alpha) Does Not Impair Pro-564 Hydroxylation

Background: The hypoxia-inducible factor (HIF) transcription complex, which is activated by low oxygen tension, controls a diverse range of cellular processes including angiogenesis and erythropoiesis. Under normoxic conditions, the alpha subunit of HIF is rapidly degraded in a manner dependent on hydroxylation of two conserved proline residues at positions 402 and 564 in HIF-1alpha in the oxygen-dependent degradation (ODD) domain. This allows subsequent recognition by the von Hippel-Lindau (VHL) tumor suppressor protein, which targets HIF for degradation by the ubiquitin-proteasome pathway. Under hypoxic conditions, prolyl hydroxylation of HIF is inhibited, allowing it to escape VHL-mediated degradation. The transcriptional regulation of the erythropoietin gene by HIF raises the possibility that HIF may play a role in disorders of erythropoiesis, such as idiopathic erythrocytosis (IE).

Results: Patients with IE were screened for changes in the HIF-1alpha coding sequence, and a change in the ODD domain that converts Pro-582 to Ser was identified in several patients. This same change, however, was also detected at a significant frequency, 0.073, in unaffected controls compared to 0.109 in the IE patient group. In vitro hydroxylation assays examining this amino acid change failed to reveal a discernible effect on HIF hydroxylation at Pro-564.

Conclusion: The Pro582Ser change represents a common polymorphism of HIF-1alpha that does not impair HIF-1alpha prolyl hydroxylation. Although the Pro582Ser polymorphism is located in the ODD domain of HIF-1alpha it does not diminish the association of HIF-1alpha with VHL. Thus, it is unlikely that this polymorphism accounts for the erythrocytosis in the group of IE patients studied.