Upregulation of Wnt signaling under hypoxia promotes lung cancer progression

The hypoxic tumor microenvironment induces epithelial-mesenchymal transition (EMT) in tumor cells and increases tumor cell malignancy. Previous studies indicated that malfunction of Wnt signaling is observed in some lung cancer patients. Athough crosstalk between hypoxia and Wnt signaling in tumor cells has recently been revealed, the detailed underlying mechanisms have not been well defined. In the present study, we demonstrated that hypoxia in lung adenocarcinoma cells can enhance Wnt signaling activity by stabilizing beta-catenin and altering its localization into the nucleus. Overexpression of HIF-2 alpha increased beta-catenin expression, promoted cell mobility, and induced morphological changes to a greater degree than HIF-1 alpha overexpression. Knockdown of HIF-2 alpha decreased beta-catenin expression and inhibited hypoxia-induced cell mobility. Moreover, we identified that phosphorylational activation of AKT1 by hypoxia and HIF-2 alpha was required for Wnt activation upon hypoxia treatment. Downregulation of HIF-2 alpha and beta-catenin reduced colony formation when cells were exposed to long-term hypoxia treatment. Taken together, our data support that hypoxia activates PI3K/AKT as well as Wnt signaling in a HIF-2 alpha-dependent manner, thus elevating the resistance of lung cancer cells to chronic hypoxia-induced stress.