Hypoxia Stimulates the EMT of Gastric Cancer Cells through Autocrine TGFβ Signaling

Epithelial mesenchymal transition (EMT) is considered to be correlated with malignancy of cancer cells and responsible for cancer invasion and metastasis. We previously reported that distant metastasis was associated with hypoxia in gastric cancer. We therefore investigated the effect of hypoxic condition on EMT of gastric cancer cells. Gastric cancer cells were cultured in normoxia (21% O-2) or hypoxia (1% O-2) for 24 h. EMT was evaluated as the percentage of spindle-shaped cells in total cells. Effect of transforming growth factor beta 1 (TGF beta 1) or tyrosine kinase inhibitors on the EMT was evaluated. The expression level of TGF beta 1 and TGF beta R was evaluated by real time RT-PCR. The TGF beta 1 production from cancer cells was measured by ELISA. Hypoxia stimulated EMT of OCUM-2MD3 and OCUM-12 cells, but not that of OCUM-2M cells. The expression level of TGF beta 1 mRNA under hypoxia was significantly higher than that under normoxia in all of three cell lines. The expression level of TGF beta R mRNA was significantly increased by hypoxia in OCUM-2MD3 cells, but not in OCUM-2M cells. TGF beta R inhibitor, SB431542 or Ki26894, significantly suppressed EMT of OCUM-2MD3 and OCUM-12. TGF beta 1 production from OCUM-2MD3 and OCUM-12 cells was significantly increased under hypoxia in comparison with that under normoxia. These findings might suggest that hypoxia stimulates the EMT of gastric cancer cells via autocrine TGF beta/TGF beta R signaling.