title: Flavonoids-induced accumulation of hypoxia-inducible factor (HIF)-1alpha/2alpha is mediated through chelation of iron.
abstract: Hypoxia-inducible factor-1 alpha (HIF-1alpha) is the regulatory subunit of the heterodimeric transcription factor HIF-1 that is the key regulator of cellular response to low oxygen tension. Under normoxic conditions, HIF-1alpha is continuously degraded by the ubiquitin-proteasome pathway through pVHL (von Hippel-Lindau tumor suppressor protein). Under hypoxic conditions, HIF-1alpha is stabilized and induces the transcription of HIF-1 target genes. Quercetin, a flavonoid with anti-oxidant, anti-inflammatory, and kinase modulating properties, has been found to induce HIF-1alpha accumulation and VEGF secretion in normoxia. In this study, the molecular mechanisms of quercetin-mediated HIF-1alpha accumulation were investigated. Previous studies have shown that, in addition to being induced by hypoxia, HIF-1alpha can be induced through the phosphatidylinositol 3-kinase (PI3K)/Akt and p53 signaling pathways. But our study revealed, through p53 mutant-type as well as p53 null cell lines, that neither the PI3K/Akt nor the p53 signaling pathway is required for quercetin-induced HIF-1alpha accumulation. And we observed that HIF-1alpha accumulated by quercetin is not ubiquitinated and the interaction of HIF-1alpha with pVHL is reduced, compared with HIF-1alpha accumulated by the proteasome inhibitor MG132. The use of quercetin's analogues showed that only quercetin and galangin induce HIF-1/2alpha accumulation and this effect is completely reversed by additional iron ions. This is because quercetin and galangin are able to chelate cellular iron ions that are cofactors of HIF-1/2alpha proline hydroxylase (PHD). These data suggest that quercetin inhibits the ubiquitination of HIF-1/2alpha in normoxia by hindering PHD through chelating iron ions.
authors.affiliation: Department of Surgery and Pharmacology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15213, USA.
authors.forename: Sung-Soo
authors.initials: SS
authors.lastname: Park
authors.forename: Insoo
authors.initials: I
authors.lastname: Bae
authors.forename: Yong J
authors.initials: YJ
authors.lastname: Lee
mesh_terms: D051792:Basic Helix-Loop-Helix Proteins / Q000378:metabolism*; D015687:Cell Hypoxia; D045744:Cell Line, Tumor; D044950:Flavanones / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism*; D007501:Iron / Q000378:metabolism*; D007976:Leupeptins / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D061988:Proteasome Inhibitors; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D011794:Quercetin / Q000494:pharmacology*; D015398:Signal Transduction / Q000187:drug effects; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D054875:Ubiquitination; D051794:Von Hippel-Lindau Tumor Suppressor Protein / Q000502:physiology; D000099162:Endothelial PAS Domain-Containing Protein 1
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D044950:Flavanones; D005419:Flavonoids; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D007501:Iron; D007976:Leupeptins; D019869:Phosphatidylinositol 3-Kinases; D046988:Proteasome Endopeptidase Complex; D061988:Proteasome Inhibitors; D051057:Proto-Oncogene Proteins c-akt; D011794:Quercetin; D016159:Tumor Suppressor Protein p53; D051794:Von Hippel-Lindau Tumor Suppressor Protein; D000099162:Endothelial PAS Domain-Containing Protein 1; C037032:galangin; C043561:chrysin; C085514:wogonin; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde