Background: Although FOXO transcription factors may have an anti-angiogenic role, little is known about their role in tumor angiogenesis. The present study was performed to investigate the correlation between the constitutive expression of phosphorylated FOXO1 (pFOXO1) and angiogenesis in gastric cancer.
Methods: Immunohistochemistry was performed on tissue array slides containing 272 gastric carcinoma specimens, and the correlations between the cytoplasmic pFOXO1 expression in gastric cancer cells and CD34-immunopositive microvessel area (MVA) or the expressions of angiogenesis-related molecules were analyzed. In vitro analyses with Western blotting and semiquantitative reverse transcription-polymerase chain reaction were performed using the stable SNU-638 gastric cancer cell line transfected with lentivirus-delivered FOXO1 short hairpin RNA.
Results: The cytoplasmic expression of pFOXO1 in tumor cells was observed in 85% of gastric carcinoma cases, and was found to be positively associated with higher MVA (P = 0.048). Moreover, pFOXO1 expression was positively correlated with the expressions of several angiogenesis-related proteins, including hypoxia inducible factor-1α (HIF-1α, P = 0.003), vessel endothelial growth factor (P = 0.004), phosphorylated protein kinase B (P < 0.001), and nuclear factor-κB (P = 0.040). In contrast, the expression of pFOXO1 was not correlated with that of phosphorylated signal transducer and activator of transcription 3 or β-catenin. In addition, cell culture experiments showed that FOXO1 suppression increased the mRNA and protein expressions of HIF-1α.
Conclusion: Our results suggest that pFOXO1 expression in cancer cells plays a role in gastric cancer angiogenesis via mechanisms involving various angiogenesis-related molecules. Animal experiments are needed to confirm the anti-angiogenic role of FOXO1 in human gastric cancer.