Role of RalGPS2, a new possible oncogene, in trasformed and cancer cells

Ral GTPases have been implicated in tumorigenesis and metastasis in vitro and animal models; furthermore Ral pathway appears to play a prominent role in transformation of human cells (Smith et al. 2007 Clin. Cancer Res. 13, 3803-3813). RalGPS2 is a GEF for RalA belonging to RalGPS family that contains a well conserved Ras-GEF domain, a PxxP motif and a PH domain. Previous experiments demonstrated that RalGPS2 activates RalA in vivo, while its PH-PxxP domain acts as a dominant negative for RalA activation in NIH3T3 and PC12 cells. These data suggest that RalGPS2 PH-PxxP domain could inhibit RalA activation influencing cytoskeleton rearrangements. The aim of this project is to analyse the role of RalGPS2 and of its PH-PxxP domain in human bladder cancer cells (5637) and rodent transformed cells (NIH3T3-k-Ras). RalA and RalGPS2 were highly expressed in 5637 cells and the overexpression of PH-PxxP domain reduced the level of RalA-GTP. Besides the overexpression of PH and PH-PxxP domains in both cell lines induced a marked cytoskeleton re-organization: in particular the PH domain caused formation of thin vesiculating protrusion while the PH-PxxP domain caused formation of long inter-cellular structure probably involved in the exchange of signals and cellular components between cells.