Carcinogenesis Advance Access originally published online on November 4, 2007
Carcinogenesis 2008 29(1):44-51; doi:10.1093/carcin/bgm232
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A hypoxia-independent up-regulation of hypoxia-inducible factor-1 by AKT contributes to angiogenesis in human gastric cancer
1 Department of Anatomy
2 Cancer Research Institute
3 Department of Pathology
4 Department of Pharmacology, Seoul National University College of Medicine, Seoul 110-799, Korea
5 Korean Minjok Leadership Academy, Gangwon-do, Korea
6 Department of Microbiology, Hanyang University College of Medicine, Seoul 133-791, Korea
7 Radiation Health Research Institute, Korea Hydro and Nuclear Power Co., Ltd, Seoul 132-703, Korea
* To whom correspondence should be addressed. Tel: +82 2 3499 6663; Fax: +82 2 3499 6669; Email: seonynam{at}khnp.co.kr
Underlying mechanisms involved in the activation of hypoxia-inducible factor-1 (HIF-1) in cancer cells are diverse and cell type specific. Although both HIF-1
and AKT (protein kinase B) have been implicated in gastric tumor promotion and angiogenesis, it remains unclear whether HIF-1 mediates the role of AKT in terms of promoting vascular endothelial growth factor (VEGF) expression. The present study was performed to investigate the correlation between HIF-1 activation and AKT activation in gastric cancer using human gastric cancer specimens, in vitro cell experiments and in vivo animal experiments. Immunohistochemistry performed on tissue array slides containing 268 surgical specimens of gastric carcinomas showed immunoreactivity for HIF-1 in 29% of samples. Moreover, HIF-1 was positively associated with phosphorylated AKT (pAKT) (P = 0.002) or VEGF (P = 0.002), and the immunoreactivities of pAKT and VEGF were positively correlated (P < 0.001). Western blot analysis and reverse transcription–polymerase chain reaction in cell experiments revealed that the over-expression of constitutively active AKT (CA-AKT) promotes the expressions of HIF-1 protein and VEGF messenger ribonucleic acid in Seoul national university (SNU)-216 and SNU-668 gastric cancer cells under normoxic conditions, whereas kinase-dead mutant of AKT down-regulated these expressions under the same conditions. Xenografts in nude mice derived from stable gastric cancer cells over-expressing CA-AKT showed higher tumor incidence, larger tumor volumes, higher microvessel density and stronger HIF-1 immunoreactivity than those derived from vector control cells. Thus, we propose that the hypoxia-independent promotion of the AKT–HIF-1–VEGF pathway contributes, at least in part, to gastric cancer tumorigenesis and angiogenesis.
Abbreviations: CA-AKT, constitutively active AKT; HIF-1, hypoxia-inducible factor-1; KD-AKT, kinase-dead mutant of AKT; mRNA, messenger ribonucleic acid; MVD, microvessel density; pAKT, phosphorylated AKT; PI3K, phosphatidylinositol-3 kinase; VEGF, vascular endothelial growth factor; AKT, protein kinase B; SNU, Seoul national university; GSK, glycogen synthase kinase
These authors contributed equally to this work. Received April 12, 2007; revised September 19, 2007; accepted October 19, 2007.