The Role Of Taurine On Apoptosis And Autophagy Of Human Colorectal Cancer Cells

Colorectal cancer(CRC)is one of the common human malignant tumor in gastrointestinal tract,and its incidence ranks third in malignant tumor of the world.Autophagy is a kind of programmed cell death and has essential roles in tumorigenesis and tumor development.Recently,many studies have shown that Taurine could inhibit proliferation and promote apoptosis and autophagy in cancer cells.PI3K/Akt/mTOR pathway is a central regulating mechanism which plays a role in the normal cell’s physiological function,cancer spread,tumorigenesis and metastasis.There’s been research finding that PI3K/Akt/mTOR pathway can activate the autophagy of prostate cancer cells.Mammalian sterile 20-like kinase 1(Mst1)is orthologous genes of drosophila Hippo genes in mammals,playing a role in controling cell cycle,promoting apoptosis and suppressing tumor growth.Studies have shown that Akt kinase can promote MST1’s phosphorylation and inhibit cell apoptosis.In addition,Akt inhibitor MK-2206 can induce autophagy and apoptosis in tumor cells.Cell apoptosis and autophagy are regulated by many common factors and can be mutually transformational in certain conditions.Therefore,this study focuses on the human colorectal cancer cells from the level of molecules,cells and animal to observe the role of Tau in inducing autophagy and apoptosis in colorectal cancer cells,and explored its possible mechanism.Objective:1.Observing the effect of Tau on proliferation and apoptosis in human colorectal cancer cells;2.Observing the effect of Tau on autophagy in human colorectal cancer cells;3.Observed the effect of Tau on nude mice xenograft,and preliminarily explored its possible mechanism.Methods:1.Different concentrations and time of taurine treating the SW480 and HT-29 cells,detect colorectal cancer cell proliferation inhibition rate by MTT assay,and detect BAX,Bcl-2,caspase-3,YAP and phospho-YAP(Ser127)proteins by western blot.2.Different concentrations of taurine treating the SW480 cells,detect the formation of autophagic vacuoles by MDC staining.Transfecting GFP-RFP-LC3 plasmid into HT-29 cells and then treating the HT-29 cells with different concentration of Tau,detect the forming of autophagic vacuoles by fluorescence microscope.Using western blot to detect the expression of MST1,AKT,phospho-AKT(Ser473),Beclin1 and LC3B-Ⅱproteins with different concentrations of Tau.3.Building the human colorectal cancer model of HT-29 cells in nude mice,observe the growth of xenografts to research the effects of tau therapy and tau combining with Akt inhibitor MK-2206 therapy and explore its possible mechanism.Then useing immunohistochemistry to detect the proteins expression of phospho-MST1(Thr183),phospho-YAP(Ser127),phospho-Akt(Ser473),cleaved caspase-3,Beclin1 and LC3 B.Results:1.Treating the HT-29 and SW480 cells with Tau,the cell growth inhibition rate increased significantly along with the Tau concentration and processing time.With Tau concentration increasing,the phosphorylation of YAP forming into Phospho-YAP(Ser127)was increased.Besides,the levels of pro-apoptotic related proteins BAX and caspase-3 were significantly increased,and the the level of anti-apoptotic related protein Bcl-2 was significantly decreased.2.Treating the HT-29 and SW480 cells with Tau,the level of MST1 protein was significantly increased with the increasing of the Tau concentration.3.Treating the HT-29 cells with Tau,the phosphorylation of Akt forming into phospho-Akt(Ser473)was significantly decreased with the increasing of the Tau concentration.4.Treating the HT-29 and SW480 cells with Tau,the number of autophagic vacuoles was significantly increased with the increasing of the Tau concentration.5.Treating the HT-29 and SW480 cells with Tau,with Tau concentration increasing,the levels of autophagy related proteins Beclin1 and LC3B-Ⅱwere significantly increased.6.Nude mice xenograft experimental results show that treating with Tau、MK-2206 and Tau combining with MK-2206,the volume of xenograft tumor are lower than the control group in 27 days,and the volume of xenograft tumor of the group Tau combining with MK-2206 is the lowest.Besides,the positive rates of phospho-MST1(Thr183),phospho-YAP(Ser127),cleaved caspase-3,Beclin1 and LC3 B proteins in the xenografts tissues were significantly increased and the positive rate of phospho-Akt(Ser473)was significantly decreased.Conclusion:1.Tau can inhibit proliferation in colorectal cancer cells,and its mechanism may be that Tau can regulate the expression of apoptosis related proteins.2.Tau can promote autophagy in colorectal cancer cells,and its mechanism may be connected with the MST1,Akt signaling pathway and the expression of autophagy related proteins Beclin1 and LC3 B.3.Tau can suppress the growth of HT-29 colorectal cancer cells nude mice xenograft,its possible mechanism may be that Tau can promote apoptosis and autophagy in colorectal cancer cells.