Conversion of epithelial-to-mesenchymal transition to mesenchymal-to-epithelial transition is mediated by oxygen concentration in pancreatic cancer cells

Tumor metastasis is accompanied by a two-stage process of epithelial-to-mesenchymal transition (EMT) and mesenchymal-to-epithelial transition (MET). Currently, the exact mechanisms underlying EMT-MET conversion are unclear. In the present study, the mechanisms by which primary sites (hypoxic) and homing sites (normoxic or hyperoxic) participate in EMT-MET conversion were evaluated. Pancreatic cancer cells were grown under different oxygenation conditions. Cell morphology and epithelial (E)-cadherin and vimentin expression were examined. Transwell chambers were used to examine tumor invasiveness, and scratch assays were performed to examine cell migration. Reverse transcription-polymerase chain reaction and western blot analysis were used to quantitate the mRNA and protein expression of E-cadherin, vimentin, Snail and hypoxia-inducible factor (HIF)-1α. BxPc-3 and Panc-1 cells grown under hypoxic conditions demonstrated increased partial EMT, reduced E-cadherin expression, and increased vimentin expression, compared with cells grown under normoxic or hyperoxic conditions. Cells grown under hypoxic conditions also indicated increased migration and invasiveness. HIF-1α mRNA and protein expression was increased in cells grown under hypoxic conditions. These changes were reversed when a specific inhibitor of the HIF-1α receptor was used to block HIF-1α signaling. Differences in oxygen concentration at primary sites and homing sites are important in the EMT-MET process, and the underlying mechanism may involve HIF-1α-Snail signaling.