title: Up-Regulation of ENO1 by HIF-1α in Retinal Pigment Epithelial Cells after Hypoxic Challenge Is Not Involved in the Regulation of VEGF Secretion.
abstract: OBJECTIVE
  Alpha-enolase (ENO1), a major glycolytic enzyme, is reported to be over-expressed in various cancer tissues. It has been demonstrated to be regulated by the Hypoxia-inducible factor 1-α (HIF-1α), a crucial transcriptional factor implicated in tumor progression and cancer angiogenesis. Choroidal neovascularization (CNV), which is a leading cause of severe vision loss caused by newly formed blood vessels in the choroid, is also engendered by hypoxic stress. In this report, we investigated the expression of ENO1 and the effects of its down-regulation upon cobalt (II) chloride-induced hypoxia in retinal pigment epithelial cells, identified as the primary source of ocular angiogenic factors.
  
  
  METHODS
  HIF-1α-diminished retinal pigment epithelial cells were generated by small interfering RNA (siRNA) technology in ARPE-19 cells, a human retinal pigment epithelial cell line. Both normal and HIF-1α-diminished ARPE-19 cells were then subjected to hypoxic challenge using cobalt (II) chloride (CoCl2) or anaerobic chamber. The relation between ENO1 expression and vascular endothelial growth factor (VEGF) secretion by retinal pigment epithelial cells were examined. Protein levels of HIF-1α and ENO1 were analyzed using Western Blot, while VEGF secretion was essayed by enzyme-linked immunosorbent assay (ELISA). Cytotoxicity after hypoxia was detected by Lactate Dehydrogenase (LDH) Assay.
  
  
  RESULTS
  Upon 24 hr of CoCl2-induced hypoxia, the expression levels of ENO1 and VEGF were increased along with HIF-1α in ARPE-19 cells, both of which can in turn be down-regulated by HIF-1α siRNA application. However, knockdown of ENO1 alone or together with HIF-1α did not help suppress VEGF secretion in hypoxic ARPE-19 cells.
  
  
  CONCLUSIONS
  ENO1 was demonstrated to be up-regulated by HIF-1α in retinal pigment epithelial cells in response to hypoxia, without influencing VEGF secretion.
authors.affiliation: Department of Ophthalmology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China.
authors.forename: Feihui
authors.initials: F
authors.lastname: Zheng
authors.affiliation: Department of Ophthalmology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China.
authors.forename: Wai-Chi
authors.initials: WC
authors.lastname: Jang
authors.affiliation: Department of Ophthalmology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China.
authors.forename: Frederic K C
authors.initials: FK
authors.lastname: Fung
authors.affiliation: Department of Ophthalmology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China.
authors.forename: Amy C Y
authors.initials: AC
authors.lastname: Lo
authors.affiliation: Department of Ophthalmology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, China.
authors.forename: Ian Y H
authors.initials: IY
authors.lastname: Wong
mesh_terms: D014408:Biomarkers, Tumor / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D015687:Cell Hypoxia; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D003035:Cobalt / Q000494:pharmacology*; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D004847:Epithelial Cells / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D005786:Gene Expression Regulation; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D010100:Oxygen / Q000494:pharmacology*; D010751:Phosphopyruvate Hydratase / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D055213:Retinal Pigment Epithelium / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D015398:Signal Transduction; D025521:Tumor Suppressor Proteins / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D042461:Vascular Endothelial Growth Factor A / Q000235:genetics* / Q000378:metabolism
chemical_list: D014408:Biomarkers, Tumor; D004268:DNA-Binding Proteins; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D034741:RNA, Small Interfering; D025521:Tumor Suppressor Proteins; C467484:VEGFA protein, human; D042461:Vascular Endothelial Growth Factor A; D003035:Cobalt; D007770:L-Lactate Dehydrogenase; C095157:ENO1 protein, human; D010751:Phosphopyruvate Hydratase; C018021:cobaltous chloride; D010100:Oxygen