Fig. 5

Decreased levels of the E3 ligase COP1 increase c-Jun in drug-resistant A549/CDDP, MCF7/ADR and HepG2/ADR cells. a Parental cancer cells and drug-resistant cancer cells were treated with 20 μg/ml cycloheximide (CHX) for the indicated times (0~32 h), and c-Jun expression was detected by western blotting. b Parental cancer cells and drug-resistant cancer cells were treated with 10 μM MG132 or solvent DMSO for 8 h, and cellular c-Jun expression was then detected by western blotting. c Cells were treated with 10 μM MG132 for 8 h; then, the cells were lysed and immunoprecipitated with c-Jun antibodies or IgG control. Next, the immunoprecipitates were subjected to immunoblot analysis to detect ubiquitin. Parental cancer cells and drug-resistant cancer cells were collected, and COP1 expression was detected by qRT-PCR (d) and western blotting (e). Drug-resistant cancer cells were transfected with COP1 expression plasmids for 48 h, and COP1 and c-Jun expression was detected by western blotting (f). All experiments were performed independently in triplicate. ^*P ≤ 0.05, ^**P ≤ 0.01, ^***P ≤ 0.001