Background：Factor inhibiting HIF-1 （FIH-1） exists as a homodimer and binds to HIF-1alpha. Specifically, FIH-1 operates as an asparaginyl hydroxylase. It catalyzes the hydroxylation of the beta-carbon of Asparagine residue 803 within the carboxy terminal transactivation domain of HIF-1alpha. This hydroxylation event blocks the association of HIF-1alpha with co-activators. FIH-1 also binds to von Hippel-Lindau （VHL） tumor suppressor protein, which represses transcriptional ac-tivity of HIF-1alpha. In transiently transfected human osteosarcoma cells, FIH-1 localizes to the cytoplasm.
