Hypoxia upregulates adhesion ability to peritoneum through a transforming growth factor-β-dependent mechanism in diffuse-type gastric cancer cells

Gastric cancer cells leaving the primary tumour are exposed to low oxygen levels in the peritoneal cavity; however, peritoneal metastatic phenotypes of hypoxic cancer cells remain unclear. We used 6 gastric cancer cell lines, including 3 diffuse-type gastric cancer (DGC) and 3 non-DGC cell lines. Using adhesion assay, we examined the effect of hypoxic conditions on their ability to adhere to peritoneal components. The expression level of transforming growth factor-β (TGF-β) and integrins mRNA of cancer cells was examined using reverse transcriptase-polymerase chain reaction. We further examined the effect of anti-integrin neutralising antibodies and a TGF-β receptor inhibitor on the adhesion ability of hypoxic cancer cells. The binding ability of DGC cells was higher than that of non-DGC cells; it was significantly increased by hypoxic (1% O2) conditions compared to normoxic (21% O2) conditions. In contrast, no remarkable change in adhesion ability was observed in the non-DGC cells under normoxic and hypoxic conditions. Integrins and TGF-β expression of hypoxic DGC cells was significantly higher than that of normoxic cells. TGF-β increased the adhesion ability and α2-, α3- and α5-integrin expression of hypoxic DGC cells, whereas the TGF-β receptor inhibitor decreased them. Neutralising antibodies against α2-, α3- and α5-integrin inhibited the adhesion ability of DGC cells. These findings suggested that hypoxic conditions promote the adhesion of DGC cells to the peritoneum. The upregulation of α2-, α3- and α5-integrin by TGF-β under hypoxic conditions may be one of the mechanisms responsible for the high metastatic potential of hypoxic DGC cells to the peritoneum.