Fig. 7

Gambogic acid (GA) reduces the expression of ribonucleotide reductase subunit-M2 (RRM2) by inhibiting the ERK/E2F1 signaling pathway. a PANC-1 and BxPC-3 cells were treated with 1, 2, and 4 μM GA for 24 h, respectively. Protein levels of RRM2 and E2F1 were detected using western blot analysis. b, c PANC-1 and BxPC-3 cells were treated with si-E2F1 for 48 h, and protein levels of RRM2 and E2F1 were detected using western blot analysis (b); the mRNA levels of RRM2 and E2F1 were detected by q-PCR (C). (D, E) PANC-1 and BxPC-3 cells were treated with 1 μM GA or 5 μM gemcitabine alone, or in combination (GA with gemcitabine) for 24 h. Expression of the p-ERK, ERK, E2F1 and RRM2 proteins were detected using western blot analysis and q-PCR (d). The mRNA expression of E2F1 and RRM2 was detected by q-PCR(e). f PANC-1 and BxPC-3 cells were pretreated with 2 μM of the proteasome inhibitor, MG-132 for 4 h, and then treated with 2 μM GA for 24 h. Protein expression of RRM2 was detected using western blot analysis. g PANC-1 and BxPC-3 cells were pretreated with 20 μM of the pan-caspase inhibitor, Z-VAD-FMK for 4 h, and then treated with 2 μM GA for 24 h. Protein expression of RRM2 was detected using western blot analysis. Data are presented as mean ± SD (n = 3); *** indicates P < 0.001