5329

PLAUR

Hypoxia activates genetic programs that facilitate cell survival; however, in cancer, it may promote invasion and metastasis. In this study, we show that breast cancer cells cultured in 1.0% O(2) demonstrate changes consistent with epithelial-mesenchymal transition (EMT). Snail translocates to the nucleus, and E-cadherin is lost from plasma membranes. Vimentin expression, cell migration, Matrigel invasion, and collagen remodeling are increased. Hypoxia-induced EMT is accompanied by increased expression of the urokinase-type plasminogen activator receptor (uPAR) and activation of cell signaling factors downstream of uPAR, including Akt and Rac1. Glycogen synthase kinase-3beta is phosphorylated, and Snail expression is increased. Hypoxia-induced EMT is blocked by uPAR gene silencing and mimicked by uPAR overexpression in normoxia. Antagonizing Rac1 or phosphatidylinositol 3-kinase also inhibits development of cellular properties associated with EMT in hypoxia. Breast cancer cells implanted on chick chorioallantoic membranes and treated with CoCl(2), to model hypoxia, demonstrate increased dissemination. We conclude that in hypoxia, uPAR activates diverse cell signaling pathways that cooperatively induce EMT and may promote cancer metastasis.

Epidermal growth factor (EGF) signaling has been shown to induce epithelial to mesenchymal transition (EMT) in many types of cancer cells. However, the molecular mechanism of EGF-induced EMT in gastric cancer remains largely unknown. In the present study, we found that human gastric cancer cell lines SGC-7901 and BGC-823 underwent EMT phenotypic changes upon exposure to EGF. The induction of EMT was consistent with aggressive characteristics such as increased cell migration, invasion and clonogenic growth. Additionally, EGF stimulation also led to the upregulation of urokinase plasminogen activator receptor (uPAR) both at mRNA and protein levels. Knockdown of uPAR by siRNA significantly attenuated EMT induction by EGF in SGC-7901 and BGC-823 cells. Furthermore, EGF increased ERK1/2 activity and blocking ERK1/2 signaling with its inhibitor, U0126, markedly inhibited EGF-induced uPAR expression and consequently EMT. Collectively, the present study demonstrated that EGF induced aggressiveness of gastric cancer cells by activating EMT, which involved the activation of the ERK1/2 pathway and, subsequently, uPAR expression.