title: HIF-1-mediated up-regulation of cardiotrophin-1 is involved in the survival response of cardiomyocytes to hypoxia.
abstract: OBJECTIVE
  Cardiotrophin-1 (CT-1) is a cytokine of the interleukin-6 superfamily which is up-regulated in cardiac diseases, in part via hypoxia-dependent mechanisms. However, no evidence for a direct regulation of CT-1 gene (CTF1) promoter by hypoxia inducible factor-1 (HIF-1) has been provided.
  
  
  RESULTS
  Hypoxia increased CT-1 mRNA levels in the murine adult cardiomyocyte cell line HL-1 in a time-dependent manner. Interestingly, in a murine model (C57BL/6), we show that systemic hypoxia also significantly up-regulated CT-1 in myocardial tissue. The effect of hypoxia on CT-1 expression was mediated through a transcriptional mechanism, since hypoxia increased luciferase activity of constructs containing CTF1 promoter sequences. The increase in CT-1 levels was significantly reduced by drugs that prevent calcium mobilization, such as lercanidipine, or that inhibit the activation of the PI3K/Akt pathway (wortmannin) or mammalian target of rapamycin (rapamycin). The CT-1 elevation was similarly induced by HIF-1α over-expression in co-transfection experiments and prevented by HIF-1α silencing. The direct interaction of HIF-1α with the CTF1 promoter was confirmed through site-directed mutagenesis of hypoxia response elements, electrophoreric mobility shift, and ChIP assays. Hypoxia induced HL-1 apoptosis (measured as annexin-V binding or caspase 3/7 activity) which was increased when CT-1 was silenced in knocked-down cells by lentiviral vectors.
  
  
  CONCLUSIONS
  Hypoxia increased CT-1 levels in cardiac cells (in vitro and in vivo) through a direct regulation of CTF1 promoter by HIF-1α. This CT-1 activation by hypoxia may protect cells from apoptosis, thus supporting a protective role for CT-1 as a survival factor for cardiomyocytes.
authors.affiliation: Division of Cardiovascular Sciences,  Center for Applied Medical Research, University of Navarra, Avda. Pío XII 55, 31008 Pamplona,  Spain.
authors.forename: Pablo A
authors.initials: PA
authors.lastname: Robador
authors.forename: Gorka
authors.initials: G
authors.lastname: San José
authors.forename: Cristina
authors.initials: C
authors.lastname: Rodríguez
authors.forename: Anna
authors.initials: A
authors.lastname: Guadall
authors.forename: María U
authors.initials: MU
authors.lastname: Moreno
authors.forename: Javier
authors.initials: J
authors.lastname: Beaumont
authors.forename: Ana
authors.initials: A
authors.lastname: Fortuño
authors.forename: Javier
authors.initials: J
authors.lastname: Díez
authors.forename: José
authors.initials: J
authors.lastname: Martínez-González
authors.forename: Guillermo
authors.initials: G
authors.lastname: Zalba
mesh_terms: D000818:Animals; D017209:Apoptosis; D016207:Cytokines / Q000235:genetics / Q000378:metabolism*; D004195:Disease Models, Animal; D017930:Genes, Reporter; D057809:HEK293 Cells; D006801:Humans; D000860:Hypoxia / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D032383:Myocytes, Cardiac / Q000378:metabolism* / Q000473:pathology; D011401:Promoter Regions, Genetic; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D015398:Signal Transduction; D013997:Time Factors; D014162:Transfection; D015854:Up-Regulation
chemical_list: D016207:Cytokines; C497443:Hif1a protein, mouse; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D012333:RNA, Messenger; C092073:cardiotrophin 1