title: Human HIF-3alpha4 is a dominant-negative regulator of HIF-1 and is down-regulated in renal cell carcinoma.
abstract: A universal response to changes in cellular oxygen tension is governed by a family of heterodimeric transcription factors called hypoxia-inducible factor (HIF). Tumor hypoxia, as well as various cancer-causing mutations, has been shown to elevate the level of HIF-1alpha, signifying a critical role of the HIF pathway in cancer development. The recently identified third member of the human HIF-alpha family, HIF-3alpha, produces multiple splice variants that contain extra DNA binding elements and protein-protein interaction motifs not found in HIF-1alpha or HIF-2alpha. Here we report the molecular cloning of the alternatively spliced human HIF-3alpha variant HIF-3alpha4 and show that it attenuates the ability of HIF-1 to bind hypoxia-responsive elements located within the enhancer/promoter of HIF target genes. The overexpression of HIF-3alpha4 suppresses the transcriptional activity of HIF-1 and siRNA-mediated knockdown of the endogenous HIF-3alpha4 increases transcription by hypoxia-inducible genes. HIF-3alpha4 itself is oxygen-regulated, suggesting a novel feedback mechanism of controlling HIF-1 activity. Furthermore, the expression of HIF-3alpha4 is dramatically down-regulated in the majority of primary renal carcinomas. These results demonstrate an important dominant-negative regulation of HIF-1-mediated gene transcription by HIF-3alpha4 in vivo and underscore its potential significance in renal epithelial oncogenesis.
authors.affiliation: Department of Laboratory Medicine and Pathobiology, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Mindy A
authors.initials: MA
authors.lastname: Maynard
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Evans
authors.forename: Tomoko
authors.initials: T
authors.lastname: Hosomi
authors.forename: Shuntaro
authors.initials: S
authors.lastname: Hara
authors.forename: Michael A S
authors.initials: MA
authors.lastname: Jewett
authors.forename: Michael
authors.initials: M
authors.lastname: Ohh
mesh_terms: D000595:Amino Acid Sequence; D051017:Apoptosis Regulatory Proteins; D051784:Aryl Hydrocarbon Receptor Nuclear Translocator / Q000378:metabolism; D001483:Base Sequence; D051792:Basic Helix-Loop-Helix Proteins; D002292:Carcinoma, Renal Cell / Q000378:metabolism*; D045744:Cell Line, Tumor; D003001:Cloning, Molecular; D015536:Down-Regulation; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000037:antagonists & inhibitors* / Q000502:physiology; D007680:Kidney Neoplasms / Q000378:metabolism*; D008969:Molecular Sequence Data; D034741:RNA, Small Interfering / Q000494:pharmacology; D012097:Repressor Proteins; D020218:Response Elements; D014157:Transcription Factors / Q000235:genetics / Q000502:physiology*; D014158:Transcription, Genetic
chemical_list: D051017:Apoptosis Regulatory Proteins; D051784:Aryl Hydrocarbon Receptor Nuclear Translocator; D051792:Basic Helix-Loop-Helix Proteins; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D034741:RNA, Small Interfering; D012097:Repressor Proteins; D014157:Transcription Factors; C497396:ARNT protein, human; C497442:HIF1A protein, human; C116973:HIF3A protein, human