[Expression and pathobiological implication of hypoxia-inducible factor-1alpha in human colorectal carcinoma]

To investigate the transcription level and protein expression of HIF-1alpha and VEGF in SW480 cell line and colorectal adenocarcinoma, and to determine whether HIF-1alpha plays a role in angiogenesis through its regulation of VEGF.

HIF-1alpha mRNA expression was analyzed by in situ hybridization. HIF-1alpha and VEGF protein expressions were determined by immunochemical streptavidin/peroxidase (SP) in SW480 cells and colorectal carcinoma tissue samples and Western blot, using proteins extracted from SW480 cells. Tumor tissue microvessel density (MVD) was determined by CD34 immunostaining of colorectal carcinomas.

The levels of HIF-1alpha mRNA changed significantly in response to different oxygen concentrations and an addition of genistein in SW480 cells. Immunocytochemistry revealed that the levels of HIF-1alpha, VEGF protein expression in SW480 cells were significantly higher under hypoxia than those in nomoxia (P < 0.01, P < 0.05 respectively). However, addition of genistein, an inhibitor of HIF-1alpha, suppressed such responses to hypoxia. Western blot analysis showed that SW480 cells exposed to hypoxia expressed a high level of HIF-1alpha protein, compared to a weak expression in nomoxia. The addition of genistein in hypoxia suppressed the over-expression of HIF-1alpha. The positive rates of HIF-1alpha mRNA by in situ hybridization in colorectal adenomas and adenocarcinomas were 38.9% (7/18) and 67.7% (42/62), respectively. The percentage of HIF-1alpha mRNA positive cells varied significantly from colorectal adenomas to adenocarcinomas at different Duke stages (P < 0.05), and HIF-1alpha mRNA was higher in adenocarcinomas than in adenomas (P < 0.01). The positive rates of HIF-1alpha and VEGF protein expression in adenocarcinomas were 43.5% (27/62) and 37.1% (23/62), respectively. The expression of VEGF elevated as the Duke tumor staging increased. The conformation rate of HIF-1alpha and VEGF was 74.2% (46/62). MVD was significantly higher in HIF-1alpha and/or VEGF positive tumors than those without (P < 0.01 and P < 0.05 respectively). Among the four groups, i.e. HIF-1alpha+/VEGF+, HIF-1alpha+/VEGF-, HIF-1alpha+/VEGF- and HIF-1alpha-/VEGF-, the difference of MVD was highly significant (P < 0.01). HIF-1alpha expression was correlated significantly with VEGF expression and microvessel density.

These findings suggest hypoxia induces the expression of HIF-1alpha and VEGF in colorectal adenocarcinoma. HIF-1alpha may play an important role in angiogenesis and tumor progression by regulating the expression of VEGF in human colorectal carcinoma.