title: Hypoxia-inducible factor-1β (HIF-1β) is upregulated in a HIF-1α-dependent manner in 518A2 human melanoma cells under hypoxic conditions.
abstract: Solid tumors include hypoxic areas due to excessive cell proliferation. Adaptation to low oxygen levels is mediated by the hypoxia-inducible factor (HIF) pathway promoting invasion, metastasis, metabolic alterations, chemo-resistance and angiogenesis. The transcription factor HIF-1, the major player within this pathway consists of HIF-1α and HIF-1β. The alpha subunit is continuously degraded under normoxia and becomes stabilized under reduced oxygen supply. In contrast, HIF-1β is generally regarded as constitutively expressed and being present in excess within the cell. However, there is evidence that the expression of this subunit is more complex. The aim of this study was to investigate the role of HIF-1β in human melanoma cells. Among a panel of five different cell lines, in 518A2 cells exposed to the hypoxia-mimetic cobalt chloride HIF-1β was rapidly elevated on protein level. Knockdown experiments performed under cobalt chloride-exposure and hypoxia revealed that this effect was mediated by HIF-1α. The non-canonical relationship between these subunits was further confirmed by pharmacologic inhibition of HIF-1α and by expression of a dominant-negative HIF mutant. Overexpression of HIF-1α showed a time delay in HIF-1β induction, thus arguing for HIF-1β de novo synthesis rather than protein stabilization by heterodimerization. A Hen's egg test-chorioallantoic membrane model of angiogenesis and invasion indicated a local expression of HIF-1β and implies a biological relevance of these findings. In summary, this study demonstrates the HIF-1α-dependent regulation of HIF-1β under hypoxic conditions for the first time. The results indicate a novel cell specific mechanism which might prevent HIF-1β to become a limiting factor.
authors.affiliation: Department of Biomedical Research, Medical University of Vienna, Waehringer Guertel 18-20, 1090 Vienna, Austria. mmandl@mail.austria.com
authors.forename: Markus
authors.initials: M
authors.lastname: Mandl
authors.forename: Barbara
authors.initials: B
authors.lastname: Kapeller
authors.forename: Roman
authors.initials: R
authors.lastname: Lieber
authors.forename: Karin
authors.initials: K
authors.lastname: Macfelda
mesh_terms: D000818:Animals; D051784:Aryl Hydrocarbon Receptor Nuclear Translocator / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000235:genetics; D015687:Cell Hypoxia / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D045744:Cell Line, Tumor; D002642:Chick Embryo; D003035:Cobalt / Q000494:pharmacology; D055785:Gene Knockdown Techniques; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D008545:Melanoma / Q000378:metabolism* / Q000473:pathology* / Q000503:physiopathology; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology*
chemical_list: C497396:ARNT protein, human; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D051784:Aryl Hydrocarbon Receptor Nuclear Translocator; D003035:Cobalt; C018021:cobaltous chloride