Objective  To observe the effect of PD98059

an inhibitor of MAPK/ERK kinase(MEK)

on Fas ligand (FasL) expression in human cholangiocarcinoma cells (QBc-939) and to study its mechanism.   Methods  QBc-939 cells were pretreated with PD98059 (20 μmol/L) or DMSO (vehicle) for 4 h and incubated with RIMP1640 for 24 h. Then

expression of FasL

c-Myc and phosphorylated c-Myc was detected by Western blotting and RT-PCR

and compared with that of parent QBc-939 cells not treated with PD98059. GAPDH mRNA served as an internal control. In addition

QBc-939 cells were transfected with luciferase reporter constructs of the FasL promoter (FasL-P1288)

treated with PD98059 or DMSO for 4 h and incubated with RIMP1640 for 24 h. Dual-luciferase activity level was measured using the dual-luciferase reporter assay system. Finally

after treatment with PD98059

chromatin immunoprecipitation assay was performed. Chromatin-bound DNA selected by anti-p-c-Myc (Ser-62) was amplified with FasL-specific primers.   Results  PD98059

a specific MAPK-ERK cascade inhibitor

significantly attenuated the phosphorylation of c-Myc on Ser-62 and FasL up-regulation in QBc-939 cells. The luciferase reporter assay revealed that the FasL promoter activity level was significantly lower in cells treated with PD98059 than in those not treated with PD98059. Furthermore

chromatin immunoprecipitation assay showed that the phosphorylated c-Myc was bond to the human FasL promoter in vivo.   Conclusion  PD98059 inhibits FasL expression in human cholangiocarcinoma cells by inhibiting the MAPK-ERK kinase activity

decreasing the c-Myc phosphorylation level

and activating the FasL promoter.