Objective        To investigate the proteasome inhibitor

epoxomicin (EPO)

inducing the cell apoptosis and its relation with endoplasmic reticulum stress protein GADD153/CHOP.       Methods        After DU145 cells were treated with EPO at different doses and/or for different times

the cell proliferation was detected by using MTS assay. Cell apoptosis was examined by flow cytometry. The mRNA expression of endoplasmic reticulum stress-related genes

GADD153 and GRP78 was tested by real-time PCR

while the protein levels were detected by Western blotting. GADD153 siRNA was transfected to silence the gene

which was verified by real-time PCR and Western blotting. Cell proliferation and apoptosis were tested again after the transfection with MTS assay and flow cytometry.       Results       Cell proliferation was inhibited after EPO treatment in a time- and dose-dependent fashion. The apoptotic rate was also in a dose-dependent manner. With the elapse of time

the mRNA levels of GADD153 and GRP78 were increased obviously when DU145 cells were treated with EPO

and reached the highest in 72 h after treatment. The same tendency was observed in the protein levels of GADD153 and GRP78

and the highest levels were also seen in 72 h (P0.05). The mRNA and protein expression of GADD153 was decreased obviously after the transfection with GADD153 siRNA

with the dose of 50 nmol/L most significant. The inhibitory effects of EPO on the proliferation and apoptosis in DU145 cells were partly blocked by silencing the gene GADD153.       Conclusion       Proteasome inhibitor EPO inhibits the cell proliferation and apoptosis in DU145 cells

which might be due to activate the endoplasmic reticulum stress and up-regulate its associated molecule GADD153.