Polo-like kinase 1,a new therapeutic target in hepatocellular carcinoma

AIM:To investigate the role of polo-like kinase 1 (PLK1) as a therapeutic target for hepatocellular carcinoma (HCC).METHODS:PLK1 gene expression was evaluated in HCC tissue and HCC cell lines.Gene knockdown with short-interfering RNA (siRNA) was used to study PLK1 gene and protein expression using real-time reverse transcription polymerase chain reaction (RT-PCR) and Western blotting,and cell proliferation using 3-(4,5-dim ethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2(4-sulf ophenyl)-2H-tetrazolium (MTS) and bromodeoxyuridine (BrdU) assays.Apoptosis was evaluated using the terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay,and caspase-inhibition assay.Huh-7 cells were transplanted into nude mice and co-cultured with PLK1 siRNA or control siRNA,and tumor progression was compared with controls.RESULTS:RT-PCR showed that PLK1 was overexpressed 12-fold in tumor samples compared with controls,and also was overexpressed in Huh-7 cells.siRNA against PLK1 showed a reduction in PLK1 gene and protein expression of up to 96% in Huh-7 cells,and a reduction in cell proliferation by 68% and 92% in MTS and BrdU cell proliferation assays,respectively.There was a 3-fold increase in apoptosis events,and TUNEL staining and caspase-3 assays suggested that this was caspase-independent.The pan-caspase inhibitor Z-VAD-FMK was unable to rescue the apoptotic cells.Immnofluorescence co-localized endonuclease-G to fragmented chromosomes,implicating it in apoptosis.Huh-7 cells transplanted subcutaneously into nude mice showed tumor regression in siPLK1-treated mice,but not in controls.CONCLUSION:Knockdown of PLK1 overexpression in HCC was shown to be a potential therapeutic target,leading to apoptosis through the endonuclease-G pathway.