Modulation of apoptosis by endogenous Bcl-x_L expression in MKN-45 human gastric cancer cells

Abstract

This study was designed to clarify the role of endogenous Bcl-x_L expression in modulating apoptosis of malignant cells. Administration of bcl-x-antisense oligonucleotides decreased Bcl-x_L protein levels in the MKN-45 human gastric cancer cell line. The decrease in Bcl-x_L protein content resulted in increased cell death induced by serum deprivation or Fas-antibody administration. Flow cytometric analysis revealed that the increased apoptotic cell death was more prominent in bcl-x-antisense-treated cells as compared to control cells, bcl-x-sense-treated cells, or bcl-x-nonsense-treated cells. To inhibit the effect of intrinsic Bcl-x_L protein, we overexpressed Bak, which binds Bcl-x_L and inhibits the anti-apoptotic effect of Bcl-x_L, by transfection into MKN-45 cells. Bak-overexpressing cells showed increased apoptotic cell death induced by Fas-antibody when compared to parent cells and MKN-neo-transfected cells. Bak-overexpressing cells also showed greater sensitization to 5-fluorouracil and cisplatin than parent cells and MKN-neo-transfected cells. In conclusion, we demonstrated that administration of bcl-x-antisense oligonucleotides or overexpression of Bak protein induces sensitization to apoptosis in MKN-45 gastric cancer cells, suggesting that endogenous Bcl-x_L expression in cancer cells is an important modulator of apoptosis.