Ras and Notch signaling have recently been shown to cooperate in the maintenance of neoplatic transformation.To investigate the interaction between Notch and Ras/MAPK pathways and its potential mechanisms in human glioma cell line U251,we treated cells with DAPT (a γ-secretase inhibitor) to block Notch activity,TGF-α (a ERK agonist) to activate Ras signaling and PD98059 (a specific inhibitor of MEK1/2) to reduce phosphoration of ERK separately or simultaneously.It was showed that DAPT inhibited U251 cell profiferation whereas TGF-α stimulated cell proliferation in a time-and dose-dependent manner.The expression of Notch pathway signaling molecules Notch 1,RBP-Jκ and Hes 1 was down-regulated in the level of mRNA and protein after 24 h DAPT exposure.TGF-α transiently increased phosphoration level of ERK1/2 and up-regulated the mRNA and protein expression of Hes 1,which is a primary Notch target gene,but no change was observed on upstream components Notch1 and RBP-Jκ.PD98059 was added 2 h prior to treatment could inhibit ERK1/2 phosphoration activated by TGF-α,but it did not affect the Notch1,RBP-Jκ and Hes1.Taken together,these results suggest that DAPT effectively blocked Notch signaling transduction and inhibited proliferation of U251 cells.TGF-α transiently promoted ERK 1/2 phosphoration and stimulated U251 cells proliferation in a longer period.TGF-α induced the Notch target gene Hes 1 expression was independent on both Notch and ERK activation.