Background: Hypoxia-inducible factor 1 (HIF-1), a transcription factor, is overexpressed in common human cancers and their metastases. This study aimed at determining the expression levels of HIF-1alpha and vascular endothelial growth factor (VEGF) in SW480 cells and in colorectal adenocarcinoma tissue and ascertaining whether HIF-1alpha and VEGF play important roles in tumor angiogenesis.
Methods: HIF-1alpha mRNA expression was analyzed using in situ hybridization and RT-PCR. HIF-1alpha and VEGF protein were detected in SW480 cells and colorectal adenomas and adenocarcinomas by immunohistochemistry using streptavidin/peroxidase (SP). Western blot was used to detect HIF-1alpha protein extracted from SW480 cells. Microvessel density (MVD) in colorectal carcinomas was determined by anti-CD34 immunostaining in colorectal carcinomas.
Results: Optical density values representing HIF-1alpha mRNA expression levels were found to be significantly higher in SW480 cells in hypoxic conditions than in cells under normoxic conditions (P < 0.05) or in hypoxic conditions but treated with genistein (P < 0.05). The levels of HIF-1alpha and VEGF protein expression in SW480 cells were significantly higher in the hypoxia group than in the normoxia group (P < 0.01, P < 0.05, respectively) and hypoxia/genistein group (P < 0.01, P < 0.05, respectively). The positive expression rates of HIF-1alpha mRNA changed dramatically when comparing colorectal adenomas with adenocarcinomas of different Dukes' stages (P < 0.05). HIF-1alpha mRNA was also expressed at higher levels in adenocarcinomas than that in adenomas (P < 0.01). HIF-1alpha protein expression correlated significantly with VEGF protein expression and MVD.
Conclusions: Hypoxia induces the expression of HIF-1alpha and VEGF in colorectal adenocarcinomas. HIF-1alpha may play an important role in angiogenesis and tumor progression by regulating the expression of VEGF in human colorectal carcinomas.