BACKGROUNDExpression of polo-like kinase 1 (Plk1) is elevated in lung cancer and has been proposed as having prognostic value and related to resistance to chemotherapy and radiation. In addition, Plk1 has several functions in mitotic progression. In this study, the authors investigated the effect of Plk1 depletion on cell cycle progression and proliferation in A549 cells, a lung cancer cell line.

METHODSA recombinant plasmid containing antisense RNA targeting Plk1 (pcDNA3-Plk1) was transfected into A549 cells. Reverse transcription-polymerase chain reaction and Western blot were used to examine Plk1 gene expression. Cell proliferation was evaluated by direct cell counting and bromodeoxyuridine (BrdU) labelling. Cell cycle and apoptosis were examined by flow cytometry. Expression of alpha-tubulin was detected by immunofluorescence, and the inhibition rate (IR) by chemotherapeutic agents was determined by 3-(4,5-dimethylthiazol-2-yl) 2,5-diphenyl-tetrazolium bromide assay.

RESULTSAfter transfection into A549 cells, pcDNA3-Plk1 reduced Plk1 mRNA by 46.75% for 24 hours and by 61.84% for 48 hours. Plk1 protein was significantly decreased simultaneously (P < 0.05). Abnormal morphological changes of cells and growth inhibition were observed in pcDNA3-Plk1 transfected groups. The BrdU labelling index was 25.59% 48 hours after transfection, which was significantly lower than that of the control groups (P < 0.05). Forty-eight hours after transfection, there showed absence of microtubule polymerization and spindle abnormalities in staining for alpha-tubulin. A549 cells showed a strong G2/M arrest and apoptosis 72 hours post transfection. IR of vinorelbine in pcDNA3-Plk1 transfected groups was significantly higher than that of the other groups (P < 0.05, respectively).

CONCLUSIONSPlk1 depletion interferes with spindle formation, induces cell cycle arrest and apoptosis, and consequently inhibits cell proliferation in A549 cells. Moreover, it sensitizes lung cancer cells to chemotherapy.