Hypoxia-inducible factor-1α modulates the down-regulation of the homeodomain protein CDX2 in colorectal cancer

Hypoxia-inducible factor-1α (HIF-1α) is the main active subunit of HIF-1, which promotes tumor cell survival and critical steps involved in tumor progression and aggressiveness. To clarify the possible involvement of the HIF-1α subunit and homeodomain protein CDX2 in the development and progression of colorectal cancer (CRC), we examined in vivo the immunohistochemical expression of HIF-1α and its topological correlation with CDX2 expression in colorectal adenocarcinoma. We then examined the in vitro effect of hypoxia mimicked by CoCl₂ on mRNA and protein expression of HIF-1α and CDX2 using two human colon cancer cell lines, SW480 and LS174T. In addition, hypoxia-induced changes in the mRNA expression of Snail were also analyzed. Of the 62 cases of CRC examined, 43 (69.4%) and 39 (62.9%) were positive for CDX2 and HIF-1α, respectively, such that their expression was correlated with differentiation grade, tumor stage and lymph node metastasis (χ² test, p<0.01). Furthermore, HIF-1α expression observed in 10 of the 16 (62.5%) poorly differentiated CRCs showed a topological correlation with loss of CDX2 expression. Realtime PCR and Western blotting demonstrated that CDX2 expression was decreased by CoCl₂ (100 μM) in both SW480 and LS174T cells. mRNA and protein expression of HIF-1α and mRNA expression of Snail was increased by hypoxia in both colon cancer cell lines. In conclusion, the present observations support that hypoxia-inducible factor-1α induces down-regulation of CDX2 in colon carcinoma cells and that Snail may be involved in this regulation process. These findings suggest that hypoxia plays an important role in the malignant progression of CRC.