TI - FGF -dependent activation of ERK2 is essential for induction of DUSP6/MKP-3 mRNA and protein . AB - To dissect the signalling events responsible for FGF-inducible DUSP6/MKP-3 expression , we have employed chemical inhibitors at concentrations where specificity is optimal . First , cells were treated with SU5402 ( 50 muM ) , a specific FGFR inhibitor [29] , and then exposed to FGFs for 5 h ( Figure 2A ) . As expected , this drug blocked both the FGF -dependent phosphorylaTION of ERK and PHOSphorylation of the Akt protein kinase , a target of the PI3K pathway . SU5402 also blocked the induction of DUSP6/MKP-3 protein by FGF2 , FGF4 and FGF8 , clearly demonstrating a requirement for FGFR activation in this response . We next employed the specific MEK ( MAPK/ERK kinase ) inhibitor PD184352 ( 2 muM ) , which is a more specific and potent inhibitor of the MAPK pathway than PD98059 [30,31] . In contrast with SU5402 , this drug did not affect PHOSphorylation of Akt , but completely blocked the FGF -mediated activation of ERK1/2 and the induction of DUSP6/MKP-3 protein (Figure 2B) . LY294002 ( 10 muM ) had no effect on either FGF -induced ERK activation or DUSP6/MKP-3 expression , but , as expected , it caused a dramatic reduction in the levels of PHOSphorylated Akt (Figure 2C) . In addition to these inhibitors , we also determined that FGF -mediated induction of DUSP6/MKP-3 was unaffected by inhibition of either the TOR ( target of rapamycin ) pathway using rapamycin ( 100 nM ) or phospholipase C activity using U-73122 ( 4 muM ) ( results not shown ) . Finally , we used real-time PCR to measure relative levels of DUSP6/MKP-3 mRNA in FGF-treated NIH 3T3 cells in the absence and presence of either PD184352 or LY294002 . Clearly , inhibition of the ERK MAPK pathway blocks FGF-inducible DUSP6/MKP-3 mRNA expression (Figure 2D) .