title: Distinct regulatory mechanisms of the human ferritin gene by hypoxia and hypoxia mimetic cobalt chloride at the transcriptional and post-transcriptional levels.
abstract: Cobalt chloride has been used as a hypoxia mimetic because it stabilizes hypoxia inducible factor-1α (HIF1-α) and activates gene transcription through a hypoxia responsive element (HRE). However, differences between hypoxia and hypoxia mimetic cobalt chloride in gene regulation remain elusive. Expression of ferritin, the major iron storage protein, is regulated at the transcriptional and posttranscriptional levels through DNA and RNA regulatory elements. Here we demonstrate that hypoxia and cobalt chloride regulate ferritin heavy chain (ferritin H) expression by two distinct mechanisms. Both hypoxia and cobalt chloride increased HIF1-α but a putative HRE in the human ferritin H gene was not activated. Instead, cobalt chloride but not hypoxia activated ferritin H transcription through an antioxidant responsive element (ARE), to which Nrf2 was recruited. Intriguingly, cobalt chloride downregulated ferritin H protein expression while it upregulated other ARE-regulated antioxidant genes in K562 cells. Further characterization demonstrated that cobalt chloride increased interaction between iron regulatory proteins (IRP1 and IRP2) and iron responsive element (IRE) in the 5'UTR of ferritin H mRNA, resulting in translational block of the accumulated ferritin H mRNA. In contrast, hypoxia had marginal effect on ferritin H transcription but increased its translation through decreased IRP1-IRE interaction. These results suggest that hypoxia and hypoxia mimetic cobalt chloride employ distinct regulatory mechanisms through the interplay between DNA and mRNA elements at the transcriptional and post-transcriptional levels.
authors.affiliation: Department of Biological Sciences, North Carolina State University, Campus Box 7633, Raleigh, NC 27695, United States.
authors.forename: Bo-Wen
authors.initials: BW
authors.lastname: Huang
authors.affiliation: Department of Biological Sciences, North Carolina State University, Campus Box 7633, Raleigh, NC 27695, United States.
authors.forename: Masaki
authors.initials: M
authors.lastname: Miyazawa
authors.affiliation: Department of Biological Sciences, North Carolina State University, Campus Box 7633, Raleigh, NC 27695, United States. Electronic address: ytsuji@ncsu.edu.
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Tsuji
mesh_terms: D001052:Apoferritins / Q000235:genetics; D045744:Cell Line, Tumor; D003035:Cobalt / Q000494:pharmacology*; D005293:Ferritins / Q000235:genetics*; D005786:Gene Expression Regulation / Q000235:genetics; D006801:Humans; D000860:Hypoxia / Q000235:genetics*; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics; D035925:Iron-Regulatory Proteins / Q000235:genetics; D011499:Protein Processing, Post-Translational / Q000187:drug effects / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics; D014158:Transcription, Genetic / Q000187:drug effects / Q000235:genetics*; D015533:Transcriptional Activation / Q000187:drug effects / Q000235:genetics
chemical_list: D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D035925:Iron-Regulatory Proteins; D012333:RNA, Messenger; D003035:Cobalt; D005293:Ferritins; D001052:Apoferritins; C018021:cobaltous chloride
keywords: Cobalt chloride; Ferritin; Hypoxia; Hypoxia inducible factor (HIF); Iron regulatory protein (IRP); Nrf2