Prolyl hydroxylase that mediates hydroxylation of proline residues in target proteins, such as PKM, TELO2, ATF4 and HIF1A (By similarity). Target proteins are preferentially recognized via a LXXLAP motif (By similarity). Cellular oxygen sensor that catalyzes, under normoxic conditions, the post-translational formation of 4-hydroxyproline in hypoxia-inducible factor (HIF) alpha proteins (PubMed:11595184). Hydroxylates a specific proline found in each of the oxygen-dependent degradation (ODD) domains (N-terminal, NODD, and C-terminal, CODD) of HIF1A (By similarity). Also hydroxylates HIF2A (By similarity). Has a preference for the CODD site for both HIF1A and HIF2A (By similarity). Hydroxylation on the NODD site by EGLN3 appears to require prior hydroxylation on the CODD site (By similarity). Hydroxylated HIFs are then targeted for proteasomal degradation via the von Hippel-Lindau ubiquitination complex (By similarity). Under hypoxic conditions, the hydroxylation reaction is attenuated allowing HIFs to escape degradation resulting in their translocation to the nucleus, heterodimerization with HIF1B, and increased expression of hypoxy-inducible genes (By similarity). ELGN3 is the most important isozyme in limiting physiological activation of HIFs (particularly HIF2A) in hypoxia (By similarity). Also hydroxylates PKM in hypoxia, limiting glycolysis (By similarity). Under normoxia, hydroxylates and regulates the stability of ADRB2 (By similarity). Regulator of cardiomyocyte and neuronal apoptosis (By similarity). In cardiomyocytes, inhibits the anti-apoptotic effect of BCL2 by disrupting the BAX-BCL2 complex (PubMed:20849813). In neurons, has a NGF-induced proapoptotic effect, probably through regulating CASP3 activity (PubMed:10386996, PubMed:11060309). Also essential for hypoxic regulation of neutrophilic inflammation (By similarity). Plays a crucial role in DNA damage response (DDR) by hydroxylating TELO2, promoting its interaction with ATR which is required for activation of the ATR/CHK1/p53 pathway (By similarity). Also mediates hydroxylation of ATF4, leading to decreased protein stability of ATF4 (By similarity). 2-oxoglutarate + L-prolyl-[protein] + O2 = CO2 + succinate + trans-4-hydroxy-L-prolyl-[protein] 2-oxoglutarate + L-prolyl-[hypoxia-inducible factor alpha subunit] + O2 = CO2 + succinate + trans-4-hydroxy-L-prolyl-[hypoxia-inducible factor alpha subunit] Binds 1 Fe(2+) ion per subunit. Interacts with ADRB2; the interaction hydroxylates ADRB2 facilitating its ubiquitination by the VHL-E3 ligase complex (By similarity). Interacts with PAX2; the interaction targets PAX2 for destruction (By similarity). Interacts with PKM; the interaction hydroxylates PKM in hypoxia (By similarity). Interacts with WDR83; the interaction leads to almost complete elimination of HIF-mediated reporter activity (PubMed:16407229). Interacts with BCL2 (via its BH4 domain); the interaction disrupts the BAX-BCL4 complex inhibiting the anti-apoptotic activity of BCL2 (By similarity). Colocalizes with WDR83 in the cytoplasm. Highly expressed in vascular smooth muscle. Moderately expressed in esophagus, stomach, small bowel and aorta. Low levels in tail and kidney. Expression also in pheochromocytoma cell line PC-12. By PDGF and angiotensin II in aortic smooth muscle cells. By deprivation of NGF in neuronal cell cultures. Induced during coronary heart ligation. The Beta(2)beta(3) 'finger-like' loop domain is important for substrate (HIFs' CODD/NODD) selectivity. Ubiquitinated by SIAH1 and/or SIAH2 in response to the unfolded protein response (UPR), leading to its degradation. Extended N-terminus.