title: Hypoxia-inducible factor-2alpha correlates to distant recurrence and poor outcome in invasive breast cancer.
abstract: Differential regulation as well as target gene specificity of the two hypoxia-inducible factor (HIF)-alpha subunits HIF-1alpha and HIF-2alpha in various tumors and cell lines have been suggested. In breast cancer, the prognostic significance of HIF-1alpha is not clear-cut and that of HIF-2alpha is largely unknown. Using IHC analyses of HIF-1alpha, HIF-2alpha, and vascular endothelial growth factor (VEGF) expression in a tissue microarray of invasive breast cancer specimens from 512 patients, we investigated the expression patterns of the 2 HIF-alpha subunits in relation to established clinicopathologic variables, VEGF expression, and survival. HIF-1alpha and HIF-2alpha protein levels and their effect on survival were additionally analyzed in a second cohort of 179 patients. To evaluate the individual role of each subunit in the hypoxic response and induction of VEGF, HIF-alpha protein and HIF-alpha and VEGF mRNA levels were further studied in cultured breast cancer cells after hypoxic induction and/or knockdown of HIF-alpha subunits by siRNA by Western blot and Quantitative Real-Time PCR techniques. We showed that although HIF-1alpha and HIF-2alpha protein levels in breast cancer specimens were not interrelated, high levels of both HIF-1alpha and HIF-2alpha associated to high VEGF expression. HIF-2alpha expression was an independent prognostic factor associated to reduced recurrence-free and breast cancer-specific survival, whereas HIF-1alpha did not exhibit these correlations. In cultured cells, acute hypoxia induced both HIF-proteins. At prolonged hypoxia, HIF-2alpha remained accumulated, whereas HIF-1alpha protein levels decreased, in agreement with the oxygen level and time-dependent induction of HIFs recently reported in neuroblastoma.
authors.affiliation: Center for Molecular Pathology, Department of Laboratory Medicine, University Hospital MAS, Malmö, Sweden.
authors.forename: Karolina
authors.initials: K
authors.lastname: Helczynska
authors.forename: Anna-Maria
authors.initials: AM
authors.lastname: Larsson
authors.forename: Linda
authors.initials: L
authors.lastname: Holmquist Mengelbier
authors.forename: Esther
authors.initials: E
authors.lastname: Bridges
authors.forename: Erik
authors.initials: E
authors.lastname: Fredlund
authors.forename: Signe
authors.initials: S
authors.lastname: Borgquist
authors.forename: Göran
authors.initials: G
authors.lastname: Landberg
authors.forename: Sven
authors.initials: S
authors.lastname: Påhlman
authors.forename: Karin
authors.initials: K
authors.lastname: Jirström
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D051792:Basic Helix-Loop-Helix Proteins / Q000032:analysis / Q000502:physiology*; D001943:Breast Neoplasms / Q000401:mortality / Q000473:pathology*; D045744:Cell Line, Tumor; D005260:Female; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000032:analysis; D008875:Middle Aged; D009362:Neoplasm Metastasis; D010100:Oxygen / Q000494:pharmacology; D042461:Vascular Endothelial Growth Factor A / Q000032:analysis; D000099162:Endothelial PAS Domain-Containing Protein 1
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D010100:Oxygen; D042461:Vascular Endothelial Growth Factor A; D000099162:Endothelial PAS Domain-Containing Protein 1; C497442:HIF1A protein, human