Mechanism of inhibiting proliferation of human ovarian cancer cells of the line HO-8910 by dexamethasone: the role of RhoB signaling pathway

Abstract

To observe the effect of dexamethasone (Dex) on the proliferation of human ovarian cancer cells of the line HO-8910, and explore the role of RhoB signaling pathway in this process. Human ovarian cancer cells of the line HO-8910he were cultured in culture fluids with or without different concentrations of Dex. The cell growth levels in anchor-dependent and anchor-independent manner were detected by MTT and soft agar assay. Another HO-8910 cells were inoculated in gel with different concentrations of Dex. HO-8910 was transfected with the eukaryotic expression plasmid RhoB-wt, blank plasmids pcDNA3 and RhoB-RNAi, and then the mRNA expression of RhoB, a small GTPase gene, was examined by semi-quantitative RT-PCR. and the protein expressions of RhoB, p-Akt, and p21(cip1/waf1) and p27, both cyclin kinase inhibitors (CDIs), were detected by Western blotting. HO-8910 cells were co-transfected with the reporter gene p21-luc containing p21 promoter and marker reporter gene pRL-tk-luc, then treated with Dex for 24 h. Western blotting was used to detect the transcription of p21(cip1/waf1) gene. The RhoB mRNA expression was significantly increased 2 hours after the treatment of 100 nM Dex, and peaked 4 hours later as high as 2.5 times that of the control group. Western blotting showed that the RhoB protein expression increased along the increase of the Des concentration. The protein expression of RhoB in the HO-8910 cells transfected with RhoB-wt was 2.02 times that in the HO-8910 cells transfected with blank plasmid, and the protein expression of RhoB in the HO-8910 cells transfected with RhoB-RNAi was 36% of that of the blank plasmid group (P < 0.01). The HO-8910 cell proliferation of the RhoB-RNA1 group was not significantly different from that of the control group, however, the proliferation of the HO-8910 cell treated by 100 nM Dex for 6 days was significantly inhibited with an inhibition rate of 13% (P < 0.01). Western blotting showed that Dex down-regulated the p-Akt protein expression. Dex time and dose-dependently up-regulated the protein expression of p21(cip1/waf1) and p27. The HO-8910 cells co-transfected with p21-luc and pRL-tk-luc and then treated with Dex for 24 h showed an higher p21-luc activity, 1.72 times that of the control group (P < 0.05). The mechanism of inhibiting the proliferation by Dex in ovarian cancer cells may involve the depression of PI3K/p-Akt, and then up-regulation of RhoB and its downstream signal molecules p21(cip1/waf1) and p27 proteins.