Overexpression of hypoxia-inducible factor 1α induces migration and invasion through Notch signaling

Choriocarcinoma (CC) is the highest malignant gestational trophoblastic tumor which causes high mortality without timely treatment. HIF-1α is a very important molecule promoting neoplasm aggressiveness, metastasis through the induction of the epithelial to mesenchymal transition (EMT). Several researches have shown that Notch signaling is necessary for coupling hypoxia to the EMT. However, the pathway in choriocarcinoma remains undetermined. In this study, overexpression of HIF-1α inhibited epithelial index E-cadherin, cytokeratin 18 (CK18) and cytokeratin 19 (CK19) in two choriocarcinoma cell lines (JAR and JEG-3, respectively). The reciprocal changes associated with the EMT phenotypic transformation. The migration and invasive capability was significantly enhanced. HIF-1α overexpression was positively correlated with Notch1 and Hes1 (P<0.01; respectively). Using DAPT (Notch1 inhibitor) to knock down Notch1 expression, morphological and molecular typical changes of the EMT were detected in vitro. Knockdown of Notch1 prominently reduced MMP2 and MMP9 activities, and increased E-cadherin, CK18 and CK19 expression in JAR and JEG-3 cells (P<0.01). In vivo, serum-free suspension containing 5x106 JAR cells (lv-HIF-1α and lv-NC, respecticely) were implanted subcutaneously or injected intravenously into female NOD SCID mice, which were injected with DAPT or DMSO six times at 3-day intervals. Mice with subcutaneous nodules were injected i.v. fluorine-18 fluorodeoxyglucose (18F-FDG) and then scanned in small animal PET/CT (SA-PET/CT), and mice with lung metastasis were monitored by using the in vivo imaging system (IVIS). The in vivo data showed that inhibition of Notch signaling by DAPT treatment effectively suppressed metastatic tumor growth, metabolic activity and invasion. In summary, overexpression of HIF-1α promotes choriocarcinoma cell aggressiveness and metastasis through the regulation of the EMT dependenting on Notch signaling pathway.