PLK1 is highly expressed in gastric cancer cells. A. PLK1 protein expression in gastric cancer lines (BGC-823, SGC-7901, MKN-45, MKN-28, and MGC-803) and gastric mucosal epithelial cell line (GES-1) was detected by western blotting analysis. GAPDH was used as an internal standard. B. Total RNAs were extracted from gastric cancer cells. PLK1 mRNA level was determined by means of quantitative real-time PCR and normalized to the level of GAPDH mRNA. The fold changes of mRNA expression of PLK1 gene were compared as a ratio to the GES-1 cells. The data are shown as mean ± SD of triplicates experiments. *P < 0.05, **P < 0.01 compared with the GES-1 cells.