Carcinogenesis Advance Access published online on November 4, 2007
Carcinogenesis, doi:10.1093/carcin/bgm232
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
A hypoxia-independent upregulation of hypoxia-inducible factor-1 by AKT contributes to angiogenesis in human gastric cancer
1 Department of Anatomy, Seoul National University College of Medicine, Seoul 110-799, Korea
2 Cancer Research Institute, Seoul National University College of Medicine, Seoul 110-799, Korea
3 Department of Pathology, Seoul National University College of Medicine, Seoul 110-799, Korea
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 & Nuclear Power Co., LTD, Seoul 132-703, Korea
* To whom correspondence should be addressed: Seon Young Nam, Radiation Health Research Institute, Korea Hydro & Nuclear Power Co., LTD, Seoul 132-703, Korea. 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 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 RT-PCR in cell experiments revealed that the overexpression of constitutively active AKT (CA-AKT) promotes the expressions of HIF-1 protein and VEGF mRNA in SNU-216 and SNU-668 gastric cancer cells under normoxic conditions, whereas kinase-dead mutant of AKT (KD-AKT) downregulated these expressions under the same conditions. Xenografts in nude mice derived from stable gastric cancer cells overexpressing CA-AKT showed higher tumor incidence, larger tumor volumes, higher microvessel density (MVD), 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.
Note: B. L. Lee and W. H. Kim contributed equally.
Received April 12, 2007; revised September 19, 2007; accepted October 19, 2007.