The involvement of the Ras superfamily of GTPases in the pathogenesis of 
rhabdomysarcoma (RMS) is not well understood. While mutant H-Ras leads to 
embryonal RMS (ERMS) formation in experimental animals and in Costello syndrome 
patients, no data exists on the potential role of Ras GTPases in the 
pathogenesis of alveolar RMS (ARMS). To address this issue better, we focused on 
the role of the GTP exchange factor RasGRF1 in this process. We observed that, 
in comparison to normal skeletal muscle cells, RasGRF1 mRNA is upregulated in 
the majority of human ARMS cell lines and subsequently confirmed its high 
expression in patient samples. By employing confocal microscopy analysis, we 
observed RasGRF1 accumulation in cell filopodia, which suggests its involvement 
in ARMS cell migration. Furthermore, we observed that RasGRF1 becomes 
phosphorylated in ARMS after stimulation by several pro-metastatic factors, such 
as SDF-1 and HGF/SF, as well as after exposure to growth-promoting Igf-2 and 
insulin. More importantly, activation of RasGRF1 expression correlated with 
activation of p42/44 MAPK and AKT. When the expression of RasGRF1 was 
down-regulated in ARMS cells by an shRNA strategy, these RasGRF1-kd RMS cells 
did not respond to stimulation by SDF-1, HGF/SF, Igf-2 or insulin by 
phosphorylation of p42/44 MAPK and AKT and lost their chemotactic 
responsiveness; however, their adhesion was not affected. We also observed that 
RasGRF1-kd ARMS cells proliferated at a very low rate in vitro, and, more 
importantly, after inoculation into immunodeficient SCID/beige inbred mice they 
formed significantly smaller tumors. We conclude that RasGRF1 plays an important 
role in ARMS pathogenesis and is a new potential therapeutic target to inhibit 
ARMS growth.