EGLN3, also named as HPH-1, HIF-PH3, HPH-3 and PHD3, is a cellular oxygen sensor that catalyzes, under normoxic conditions, the post-translational formation of 4-hydroxyproline in hypoxia-inducible factor(HIF) alpha proteins. It hydroxylates a specific proline found in each of the oxygen-dependent degradation(ODD) domains(N-terminal, NODD, and C-terminal, CODD) of HIF1A. It is a regulator of cardiomyocyte and neuronal apoptosis. EGLN3 can be a prognostic marker for gastric cancer.