Objective  To investigate the effects of apurinic/apyrimidinic endonuclease 1 (APE1) on the inhibitory action of bortezomib on human osteosarcoma U2-OS cells and the underlying biological mechanisms.

  Methods  An shRNA plasmid that targets APE 1 was constructed and transfected into U2-OS cells. The mRNA and protein levels of APE 1 were detected via reverse transcription polymerase chain reaction and Western blot analysis. The inhibition of cell proliferation induced by PS-341 and APE 1-siRNA was examined with an 3-(4,5-dimethylthiazol-2-yl) 2, 5-diphenyl tetrazolium bromide assay. The change in nuclear NF-κB and APE1 expression induced by PS-341 and APE1 in osteosarcoma U2-OS cells was examined using Western blot analysis.

  Results  The APEI-shRNA expression plasmid was successfully constructed and transfected into U2-OS cells. The expression inhibition rate was about 47.6 % at the mRNA level, and was about 62.6 % at the protein level. Osteosarcoma cell proliferation was inhibited, as indicated by the MTT analysis. The median inhibitory concentration of PS-341 was 371.54 nmoL/L before APEI-shRNA transfection, which significantly decreased to 109.64 nmoL/L after APE 1-shRNA transfection (P < 0.01). The Western blot analysis indicated that both PS-341 and APE 1-siRNA downregulated nuclear NF-κB protein expression in the U2-OS ceils. The effect was more significant than that of combination of the above two.

  Conclusion  After APEI-shRNA plasrnid transfection into the osteosarcoma U2-OS cells, APE1 expression was inhibited at the protein and mRNA levels. The osteosarcoma cell proliferation rate was also decreased, and the PS-341 inhibitory effect on the osteosarcoma cells was promoted. The biological mechanisms may be related to the downregulation of nuclear NF-κB expression.