Impacts of RNA interference targeting the polo-like kinase-1 gene on the invasion of and anoikis in human malignant melanoma cells

Objective To investigate the effects of down-regulation of polo-like kinase-1 (PLK1) gene by RNA interference (RNAi) on the invasion of a human malignant melanoma cell line A375 and their possible mechanisms.Methods Cultured A375 cells were classified into several groups:blank control group receiving no treatment,liposome group transfected with lipofectamine only,and three siRNA groups transfected with three concentrations of a small interference RNA (siRNA) targeting PLK1 respectively.After additional culture,real time quantitative PCR and Western blot analysis were performed to quantify the expressions of PLK1 mRNA and protein in A375 cells respectively,Transwell invasion assay to evaluate the invasive capacity of A375 cells,agarose gel electrophoresis and terminal deoxynucleotidyl-transferase-mediated dUTP-biotin nick end labelling (TUNEL) to detect anoikis in A375 cells.The colony-forming capacity was also evaluated for A375 cells.Statistical analysis was carried out by one-factor analysis of variance.Results There was a significant decrease in PLK1 mRNA and protein expressions as well as in colony-forming units in the siRNA groups compared with the blank control group (all P ＜ 0.05).The invasive capacity of A375 cells was significantly inhibited in the siRNA groups with the number of migrating cells in Transwell assay being 39 ± 5,19 ± 5 and 9 ± 3 in A375 cells transfected with 3.125,6.250 and 12.500 nmol/L siRNAs respectively,compared to 56 ± 5 in the blank control group (all P ＜ 0.05).A characteristic DNA ladder was observed on agarose gel electrophoresis in the siRNA (6.250 nmol/L) group.Compared with the blank control group and liposome group,the three siRNA groups showed increased apoptotic index (3.86％ ± 0.35％ (3.125 nmol/L siRNA),7.35％ ± 0.36％ (6.250 nmol/L siRNA) and 17.56％ ± 0.38％ (12.500 nmol/L siRNA) vs.1.15％ ± 0.25％ (blank control group) and 1.18％ ± 0.22％ (liposome group),all P ＜ 0.05).Conclusions PLK1 siRNA can inhibit the invasion of malignant melanoma cells,likely by inducing anoikis in these cells. Key words: Melanoma;  RNA interference;  Genes, PLK1;  Neoplasm invasiveness