Disease relevance of EGLN3

• The inhibitor of transcription, actinomycin D, prevents the increase of EGLN3 mRNA induced by hypoxia, indicating that it is due to enhanced gene expression [1].
• In the human osteosarcoma cell line, U2OS, selective suppression of HIF-1alpha expression by RNA interference resulted in a complete loss of hypoxic induction of PHD2 and PHD3 [2].
• In a model of myocardial infarction, in situ hybridization showed periischemic enhancement for PHD2 mRNA and PHD3 mRNA, but not PHD1 mRNA [3].
• Except from a small increase of hypoxia-induced PHD3 mRNA levels in HeLa cells, there was also no significant effect of acidosis on PHD expression [4].
• Initial analysis, with age as a covariate, showed a possible association between PHD3 (marker D14S1049) and severe polycythemia (p=0.05) [5].

High impact information on EGLN3

• Siah2 null fibroblasts exhibit prolonged PHD3 half-life, resulting in lower levels of HIF1alpha expression during hypoxia [6].
• Significantly, hypoxia-induced HIF1alpha expression was completely inhibited in Siah1a/2 null cells, yet could be rescued upon inhibition of PHD3 by RNAi [6].
• In these domain-swapping experiments, prolyl hydroxylase domain 1 (PHD1) and PHD2 preferentially hydroxylated the proline located in the site of the original 564 ODD, while PHD3 preferred the proline 564 sequence, regardless of its location [7].
• Paradoxically, the expression of two family members (PHD2 and PHD3) is induced in hypoxic cell culture despite the reduced availability of the oxygen co-substrate, and it has been suggested that they become functionally relevant following re-oxygenation to rapidly terminate the HIF response [8].
• The RING finger ubiquitin ligase Siah2 controls the stability of various substrates involved in stress and hypoxia responses, including the PHD3, which controls the stability of HIF-1alpha [9].

Biological context of EGLN3

• EGLN1, EGLN2, and EGLN3 were also temporally expressed in an oxygen-dependent fashion, with greatest mRNA expression at 10-12 wk of gestation [10].
• Initially, we isolated a number of HRE consensus sequences in a region of 40 kb around the human EGLN3 gene and studied their evolutionary conservation [11].
• One of the HREs, located within a conserved region of the first intron of the EGLN3 gene 12 kb downstream of the transcription initiation site, bound HIF in vivo [11].
• In the present study, we have identified an HRE (hypoxia response element) in the region of the EGLN3 gene using a combination of bioinformatics and biological approaches [11].
• Three enzymes, prolyl hydroxylase domain-containing proteins 1, 2, and 3 (PHD1, -2, and -3; also known as HIF prolyl hydroxylase 3, 2, and 1, respectively), have recently been identified that catalyze proline hydroxylation of HIF alpha subunits [12].

Anatomical context of EGLN3

• In agreement with this possibility, pVHL-deficient cell lines, which present high HIF activity under normoxia, also showed dramatically increased normoxic levels of EGLN3 [1].
• Immunoreactivity for PHD1, PHD3, and seven in absentia homolog (SIAH)1 was noted in the pulmonary epithelium [13].
• In the present study, we report that human PHD2 and PHD3 are induced by hypoxia in primary and transformed cell lines [2].
• PHD2 mRNA was induced by hypoxia in the liver and PHD3 mRNA in liver, testis and heart [3].
• We also demonstrate that prolyl-hydroxylases 2 and 3 (PHD2, PHD3), one of the major factors coordinating HIF degradation under normoxic but not hypoxic conditions, are induced in osteoblasts under hypoxic conditions [14].

Associations of EGLN3 with chemical compounds

• These different genetic lesions may all act by decreasing the activity of a 2-oxoglutarate-dependent oxygenase, SM-20/EglN3/PHD3, resulting in reduced apoptosis of neural crest cells during development [15].
• In contrast, HIF-targets Pgf (placental growth factor) and Egln3 were strongly affected by the CH1 mutation, while Stc1 (stanniocalcin-1) and Slc2a1 (glucose-transporter-1) were moderately affected [16].

Regulatory relationships of EGLN3

• Interestingly, EGLN1 and EGLN3 mRNAs were also triggered by EGLN inhibitors, suggesting the involvement of HIFalpha in the control of its transcription [1].
• We further tested the regulation of these genes by HIF-1 and HIF-2 and found that siRNA targeted degradation of HIF-1alpha and HIF-2alpha results in decreased hypoxia-induced PHD3 expression [17].

Other interactions of EGLN3

• Phylogenetic analysis and domain organization show that EGLN1 represents the ancestral form of the gene family and that EGLN3 is the human orthologue of rat Sm-20 [18].
• Ectopic overexpression of HIF-2alpha in two different cell lines provided a much better induction of PHD3 gene than HIF-1alpha [17].
• In the present study we determined the role of Siah2 phosphorylation in the regulation of its activity toward PHD3 [9].
• Phospho-mutant forms of Siah2 (S29A or T24A/S29A) exhibit impaired degradation of PHD3, particularly after hypoxia [9].

References