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Screening chelating inhibitors of HIF-prolyl hydroxylase domain 2 (PHD2) and factor inhibiting HIF (FIH).

ABSTRACT: Two primary O(2)-sensors for humans are the HIF-hydroxylases, enzymes that hydroxylate specific residues of the hypoxia inducible factor-? (HIF). These enzymes are factor inhibiting HIF (FIH) and prolyl hydroxylase-2 (PHD2), each an ?-ketoglutarate (?KG) dependent, non-heme Fe(II) dioxygenase. Although the two enzymes have similar active sites, FIH hydroxylates Asn(803) of HIF-1? while PHD2 hydroxylates Pro(402) and/or Pro(564) of HIF-1?. The similar structures but unique functions of FIH and PHD2 make them prime targets for selective inhibition leading to regulatory control of diseases such as cancer and stroke. Three classes of iron chelators were tested as inhibitors for FIH and PHD2: pyridines, hydroxypyrones/hydroxypyridinones and catechols. An initial screen of the ten small molecule inhibitors at varied [?KG] revealed a non-overlapping set of inhibitors for PHD2 and FIH. Dose response curves at moderate [?KG] ([?KG]~K(M)) showed that the hydroxypyrones/hydroxypyridinones were selective inhibitors, with IC(50) in the ?M range, and that the catechols were generally strong inhibitors of both FIH and PHD2, with IC(50) in the low ?M range. As support for binding at the active site of each enzyme as the mode of inhibition, electron paramagnetic resonance (EPR) spectroscopy were used to demonstrate inhibitor binding to the metal center of each enzyme. This work shows some selective inhibition between FIH and PHD2, primarily through the use of simple aromatic or pseudo-aromatic chelators, and suggests that hydroxypyrones and hydroxypyridones may be promising chelates for FIH or PHD2 inhibition.

SUBMITTER: Flagg SC

PROVIDER: S-EPMC3525482 | biostudies-literature | 2012 Aug

REPOSITORIES: biostudies-literature

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Screening chelating inhibitors of HIF-prolyl hydroxylase domain 2 (PHD2) and factor inhibiting HIF (FIH).

Flagg Shannon C SC Martin Cristina B CB Taabazuing Cornelius Y CY Holmes Breanne E BE Knapp Michael J MJ

Journal of inorganic biochemistry 20120317

Two primary O(2)-sensors for humans are the HIF-hydroxylases, enzymes that hydroxylate specific residues of the hypoxia inducible factor-α (HIF). These enzymes are factor inhibiting HIF (FIH) and prolyl hydroxylase-2 (PHD2), each an α-ketoglutarate (αKG) dependent, non-heme Fe(II) dioxygenase. Although the two enzymes have similar active sites, FIH hydroxylates Asn(803) of HIF-1α while PHD2 hydroxylates Pro(402) and/or Pro(564) of HIF-1α. The similar structures but unique functions of FIH and PH ...[more]

PMID: 22687491

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Project description:BackgroundColorectal cancer (CRC) is one of the most common and comprehensively studied malignancies. Hypoxic conditions during formation of CRC may support the development of more aggressive cancers. Hypoxia inducible factor (HIF), a major player in cancerous tissue adaptation to hypoxia, is negatively regulated by the family of prolyl hydroxylase enzymes (PHD1, PHD2, PHD3) and asparaginyl hydroxylase, called factor inhibiting HIF (FIH).MethodsPHD1, PHD2, PHD3 and FIH gene expression was evaluated using quantitative RT-PCR and western blotting in primary colonic adenocarcinoma and adjacent histopathologically unchanged colonic mucosa from patients who underwent radical surgical resection of the colon (n=90), and the same methods were used for assessment of PHD3 gene expression in HCT116 and DLD-1 CRC cell lines. DNA methylation levels of the CpG island in the promoter regulatory region of PHD1, PHD2, PHD3 and FIH were assessed using bisulfite DNA sequencing and high resolution melting analysis (HRM) for patients and HRM analysis for CRC cell lines.ResultsWe found significantly lower levels of PHD1, PHD2 and PHD3 transcripts (p=0.00026; p<0.00001; p<0.00001) and proteins (p=0.004164; p=0.0071; p<0.00001) in primary cancerous than in histopathologically unchanged tissues. Despite this, we did not observe statistically significant differences in FIH transcript levels between cancerous and histopathologically unchanged colorectal tissue, but we found a significantly increased level of FIH protein in CRC (p=0.0169). The reduced PHD3 expression was correlated with significantly increased DNA methylation in the CpG island of the PHD3 promoter regulatory region (p<0.0001). We did not observe DNA methylation in the CpG island of the PHD1, PHD2 or FIH promoter in cancerous and histopathologically unchanged colorectal tissue. We also showed that 5-Aza-2'-deoxycytidine induced DNA demethylation leading to increased PHD3 transcript and protein level in HCT116 cells.ConclusionWe demonstrated that reduced PHD3 expression in cancerous tissue was accompanied by methylation of the CpG rich region located within the first exon and intron of the PHD3 gene. The diminished expression of PHD1 and PHD2 and elevated level of FIH protein in cancerous tissue compared to histopathologically unchanged colonic mucosa was not associated with DNA methylation within the CpG islands of the PHD1, PHD2 and FIH genes.

Dataset Information

Screening chelating inhibitors of HIF-prolyl hydroxylase domain 2 (PHD2) and factor inhibiting HIF (FIH).

Publications

Screening chelating inhibitors of HIF-prolyl hydroxylase domain 2 (PHD2) and factor inhibiting HIF (FIH).

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