Hypoxia induces CXCR4 expression and biological activity in gastric cancer cells through activation of hypoxia-inducible factor-1α

Given the important role of CXCR4 in cancer metastasis, microenvironmental factors that modulate CXCR4 may have an impact on the process of tumor expansion. Hypoxia is a common feature of solid tumors and a significant microenvironmental factor that drives aggressive behavior. CXCR4 is upregulated in several cancer cells under hypoxic conditions, suggesting a relationship between tumor hypoxia and CXCR4. However, the role of hypoxia in regulating CXCR4 in gastric cancer remains poorly understood. KATO III gastric cancer cells were exposed to hypoxia or normoxia. CXCR4 expression in cells transfected with shRNA specific for HIF-1 alpha was investigated by western blotting and flow cytometry. Wound healing, migration and invasion assays were used to assess cell motility and the chemotactic response to CXCL12, a major CXCR4 ligand. CXCR4 expression at the protein level and in the cell membrane was significantly increased in KATO III cells following exposure to hypoxia. This upregulation of CXCR4 was implicated in increased cell motility and enhanced chemotactic responses (migration and invasion) to CXCL12 treatment in vitro. The increases in CXCR4 expression and metastatic potential in gastric cancer cells exposed to hypoxia were blocked by HIF-1 alpha-specific shRNA. Our results indicate that hypoxia upregulates CXCR4 in gastric cancer cells in a HIF-1 alpha-dependent manner, and that upregulation of CXCR4 plays a role in cancer cell migration and invasion. Thus, disrupting the hypoxia-HIF-1 alpha-CXCR4 axis could be an attractive therapeutic strategy for the treatment of gastric cancer.