The Impact Of PI3K Signaling Pathway On TRAIL-induced Apoptosis In Hep-2 Cells

Objective Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) could specifically induce apoptosis in various tumor cells by integrated with its special receptors,but it was nontoxic to normal cells. It had demonstrated that there were different susceptibilities in different tumor cells to TRAIL-induced apoptosis,and Hep-2 cells were not susceptible to TRAIL.The activation of phosphatidylinositol-3-kinases (PI3K) signaling pathway could restrain the apoptosis of cells, accelerate the cycle of cells and facilitate the metastasis of tumor cells, etc.Due to their mechanisms,there was a hypothesis that PI3K signaling pathway might impact on TRAIL-induced apoptosis in Hep-2 cells.The purpose of this study was to discuss how PI3K signaling pathway impacted on TRAIL-induced apoptosis in Hep-2 cells and why by inhibiting PI3K pathway with LY294002.Methods(1) Hep-2 cells were exposed to 20μmol/L LY294002,500ng/ml TRAIL,200ng/ml TRAIL,20μmol/L LY294002+500ng/ml TRAIL or 20μmol/L LY294002+200ng/ml TRAIL for 24h.Then their morphological changes were observed by phase contrast microscopy,and the apoptosis was measured by flow cytometry.(2) Hep-2 cells were exposed to 20μmol/L LY294002, 200ng/ml TRAIL or 20μmol/L LY294002+200ng/ml TRAIL for 12h or 48h. Then the apoptosis was measured by flow cytometry.(3) After Hep-2 cells were exposed to 20μmol/L LY294002 for 24h,the expression levels of TRAIL receptors(DR4,DRS,DcR1 and DcR2) were determined by flow cytometry.Results(1) The apoptosis of Hep-2 cells induced by LY294002 and TRAIL was significantly higher than that were induced only by TRAIL;(2) There were higher expression levels of TRAIL-decoy receptors(DcR1,DcR2) than those of TRAIL-death receptors(DR4,DRS) in Hep-2 cells,and after PI3K signaling pathway was inhibited by LY294002,the expression levels of TRAIL-death receptors increased while those of TRAIL-decoy receptors decreased.Conclusion(1) Hep-2 cells were not susceptible to TRAIL,but after PI3K pathway was inhibited,Hep-2 cells became more susceptible to TRAIL;(2) There were higher expression levels of TRAIL-decoy receptors(DcR1,DcR2) than those of TRAIL-death receptors(DR4,DR5) in Hep-2 cells,which was supposed as the reason why Hep-2 cells were resistant to TRAIL.(3) PI3K inhibitor could enhance the expression levels of TRAIL- death receptors and decrease the expression levels of TRAIL-decoy receptors.It might be why Hep-2 cells became more susceptible to TRAIL.