GEP100 regulates epidermal growth factor-induced MDA-MB-231 breast cancer cell invasion through the activation of Arf6/ERK/uPAR signaling pathway

GEP100, a guanine nucleotide exchanging factor (GEF) for Arf6, plays a pivotal role in promoting breast cancer cell invasion both in vitro and in vivo. However, the precise mechanism for GEP100-mediated cell invasion is still poorly understood. In this study, we found that down-regulation of endogenous GEP100 in MDA-MB-231 cells significantly inhibited EGF-induced cell invasion, which was rescued by over-expression of ectopic GEP100. EGF increased Arf6 activity, ERK phosphorylation, and uPAR expression in a time dependent manner. Additionally, blocking Arf6 with Arf6 siRNA largely abolished EGF-induced cell invasion. GEP100 siRNA or Arf6 siRNA suppressed EGF-induced ERK activity and uPAR expression. Furthermore, blocking ERK signaling with U0126, a specific inhibitor for MEK, markedly inhibited EGF-induced uPAR expression and consequently cell invasion. Inhibition of uPAR expression by uPAR siRNA also significantly abolished EGF-induced cell invasion. Taken together, this study illustrates that GEP100 regulates an Arf6/ERK/uPAR signaling cascade in EGF-induced breast cancer cell invasion. These findings could provide a rationale for designing new therapies based on inhibition of breast cancer metastasis.