Repressive role of stabilized hypoxia inducible factor 1α expression on transforming growth factor β-induced extracellular matrix production in lung cancer cells

Activation of transforming growth factor beta (TGF-beta) combined with persistent hypoxia often affects the tumor microenvironment. Disruption of cadherin/catenin complexes induced by these stimulations yields aberrant extracellular matrix (ECM) production, characteristics of epithelial-mesenchymal transition (EMT). Hypoxia-inducible factors (HIF), the hallmark of the response to hypoxia, play differential roles during development of diseases. Recent studies show that localization of cadherin/catenin complexes at the cell membrane might be tightly regulated by protein phosphatase activity. We aimed to investigate the role of stabilized HIF-1 alpha expression by protein phosphatase activity on dissociation of the E-cadherin/beta-catenin complex and aberrant ECM expression in lung cancer cells under stimulation by TGF-beta. By using lung cancer cells treated with HIF-1 alpha stabilizers or carrying doxycycline-dependent HIF-1 alpha deletion or point mutants, we investigated the role of stabilized HIF-1 alpha expression on TGF-beta-induced EMT in lung cancer cells. Furthermore, the underlying mechanisms were determined by inhibition of protein phosphatase activity. Persistent stimulation by TGF-beta and hypoxia induced EMT phenotypes in H358 cells in which stabilized HIF-1 alpha expression was inhibited. Stabilized HIF-1 alpha protein expression inhibited the TGF-beta-stimulated appearance of EMT phenotypes across cell types and species, independent of de novo vascular endothelial growth factor A (VEGFA) expression. Inhibition of protein phosphatase 2A activity abrogated the HIF-1 alpha-induced repression of the TGF-beta-stimulated appearance of EMT phenotypes. This is the first study to show a direct role of stabilized HIF-1 alpha expression on inhibition of TGF-beta-induced EMT phenotypes in lung cancer cells, in part, through protein phosphatase activity.