EFA6R suppresses ovarian cancer cell migration and invasion

Exchange factor for ADP-ribosylation factor (Arf)6 (EFA6)R expression loss in ovarian cancer has shown to decrease patient survival. EFA6R contains the catalytic Sec7, pleckstrin homology (PH), and coiled-coil (CC) domains. To gain further insight into the role of EFA6R, this study further investigated EFA6R expression in OC and its putative role as a metastatic suppressor. EFA6R mRNA expression, assessed by RT-qPCR, was significantly downregulated in OC tissues and cell lines. OC tissue microarray staining with EFA6R antibody showed that loss of protein expression correlated with increased cancer grade. Furthermore, EFA6R protein levels, assessed by immunoblotting, were significantly reduced in OC tissues and cell lines. Treatment of SKOV-3 cells with 5-aza-2deoxycytidine, an epigenetic regulator, restored EFA6R expression and attenuated functional cell migration and invasion, which was reversed by siRNA-mediated knockdown of EFA6R expression. This study also revelated that exogenously expressed EFA6R localises to the plasma membrane, through its PH domain, and thereby inhibits cell migration and invasion in the CC domain-dependent and an Arf6-independent manner. EFA6R loss-of-function involves epigenetic mechanisms in which downregulation increases OC tumour cell migration and invasion. Summary statementEFA6R expression is epigenetically regulated in ovarian cancer cells and loss of expression correlates with increased tumour grade and enhanced tumour cell migration. EFA6R appears to mediate these effects independently of Arf6.