EWS-Fli1, a fusion gene resulting from a chromosomal translocation t(11;22, 
q24;q12) and found in Ewing sarcoma and primitive neuroectodermal tumors, 
encodes a transcriptional activator and promotes cellular transformation. 
However, the precise biological functions of its products remain unknown. To 
investigate the role of EWS-Fli1 in cell growth signaling, we transfected Ewing 
sarcoma TC-135 cells with short interfering RNAs for EWS-Fli1. EWS-Fli1 
knockdown reduced cell growth and platelet-derived growth factor 
(PDGF)-BB-induced activation of the growth signaling enzymes. Interestingly, 
phospholipase D2 (but not the PDGF-BB receptor) showed marked down-regulation in 
the EWS-Fli1-knocked down TC-135 cells compared with the control cells. In Ewing 
sarcoma TC-135 cells, the PDGF-BB-induced phosphorylation of growth signaling 
involving extracellular signal-regulated kinase, Akt, p70S6K, and the expression 
of cyclin D3 were markedly inhibited by transfection with short interfering RNA 
phospholipase (PL)-D2. The PDGF-BB-induced activation of growth signaling was 
also suppressed by 1-butanol, which prevents the production of phosphatidic acid 
by phospholipase D (but not by t-butyl alcohol), thereby implicating PLD2 in 
PDGF-BB-mediated signaling in TC-135 cells. These results suggest that EWS-Fli1 
may play a role in the regulation of tumor proliferation-signaling enzymes via 
PLD2 expression in Ewing sarcoma cells.