Aim:Thynidine phosphorylase(TP)acts as a proangiogenic growth factor which may regulate mammalian Target of Rapamycin(mTOR).We investigated whether the TP substrate thymidine and overexpression of TP affected mTOR sig...Aim:Thynidine phosphorylase(TP)acts as a proangiogenic growth factor which may regulate mammalian Target of Rapamycin(mTOR).We investigated whether the TP substrate thymidine and overexpression of TP affected mTOR signaling by comparing Colo320(TP deficient)cells and its TP-transfected variant(Colo320TP1).Methods:Drug resistance was assessed with the sulforhodamine B assay,protein expression with Western blotting,cell cycle distribution and cell death with Fluorescence-activated cell sorting analysis,and autophagy with immunofluorescence.Results:Colo320 and Colo320TP1 cells had comparable levels of sensitivity to the mTOR inhibitor rapamycin.Thymidine treatment led to 13-and 50-fold resistance to rapamycin in Colo320 and Colo320TP1 cells,respectively.In Colo320TP1 cells,the thymidine phosphorylase inhibitor(TPI)reversed the thymidine induced resistance to rapamycin,but not in Colo320 cells,indicating a role for TP in the protection.Thymidine increased p70/S6k-phosphorylation(downstream of mTOR)in Colo320TP1,but it was not affected in Colo320.As a mechanism behind resistance,we studied the levels of autophagy and found that,in Colo320TP1 cells,autophagy was highly induced by thymidine-rapamycin,which was decreased by TPI.In addition,the autophagy inhibitor 3-methyl-adenine completely inhibited autophagy and its protection.Conclusion:Rapamycin resistance in TP-expressing cancer cells may therefore be related to thymidine-mediated autophagy activation.展开更多
文摘Aim:Thynidine phosphorylase(TP)acts as a proangiogenic growth factor which may regulate mammalian Target of Rapamycin(mTOR).We investigated whether the TP substrate thymidine and overexpression of TP affected mTOR signaling by comparing Colo320(TP deficient)cells and its TP-transfected variant(Colo320TP1).Methods:Drug resistance was assessed with the sulforhodamine B assay,protein expression with Western blotting,cell cycle distribution and cell death with Fluorescence-activated cell sorting analysis,and autophagy with immunofluorescence.Results:Colo320 and Colo320TP1 cells had comparable levels of sensitivity to the mTOR inhibitor rapamycin.Thymidine treatment led to 13-and 50-fold resistance to rapamycin in Colo320 and Colo320TP1 cells,respectively.In Colo320TP1 cells,the thymidine phosphorylase inhibitor(TPI)reversed the thymidine induced resistance to rapamycin,but not in Colo320 cells,indicating a role for TP in the protection.Thymidine increased p70/S6k-phosphorylation(downstream of mTOR)in Colo320TP1,but it was not affected in Colo320.As a mechanism behind resistance,we studied the levels of autophagy and found that,in Colo320TP1 cells,autophagy was highly induced by thymidine-rapamycin,which was decreased by TPI.In addition,the autophagy inhibitor 3-methyl-adenine completely inhibited autophagy and its protection.Conclusion:Rapamycin resistance in TP-expressing cancer cells may therefore be related to thymidine-mediated autophagy activation.
