Radiosensitizing Effect Of Cathepsin L On Glioma Stem Cells

Aim : To investigate the changes of Cathepsin L activity after X ray irradiation on glioma stem cells(GSCs) ,and the relevance of Cathepsin L to Apoptosis and cell cycle , and the mechanism of Cathepsin L effect the radiosensitizing on GSCs.Methods : GSCs have been established in vitro culture system, and pretreated with appropriate dose of Cathepsin L inhibitor Z-FY-DMK before different doses of radiation treatment.The proliferative inhibition were assessed with clonogenic assay. The activation of proapoptotic effect were characterized by hoechst staining and acridine orange flourescentstaining.The recovery of GSCs in response to DNA damage were characterized by alkaline comet assay .Cell cycle were characterized by flow cytometry . Western blot analysis used to study the expression level of Cathepsin L,cell cycle related proteins and Apoptosis-related proteins. Immunohistochemistry methods used to study the expression of Cathepsin L and CUTL1 in Human glioma tissues and Normal human brain tissues.Results : Comparing to IR treatment / Z-FY-DMK treatment group,clonogenic assay indicated that The combined(Z-FY-DMK+IR) treatment group generated a decreased number of colonies ; hoechst staining and acridine orange flourescentstaining show that apoptosis level was significantly increased in the combined treatment group; alkaline comet assay indicated that less efficient repair in response to DNA damage in the combined treatment group. Flow cytometry analysis and Western blotting analysis indicated that G2-phase arrest was increased in the IR treatment group, and was decreased in the combined treatment group. Immunohistochemistry show that Cathepsin L and CUTL1 highly expressed in Human glioma tissues , weakly expressed or almost did not express in Normal human brain tissues.Conclusion: Together, these findings indicated that X-rays induced the proliferation inhibition, cell cycle arrest and apoptosis in GSCs. The apoptosis level was increased and the cell cycle arrest was decreased with the combined(Z-FY-DMK+IR) treatment. We have identified that Cathepsin L increases radiation sensitivity of GSCs by regulating the cell cycle and inducing apoptosis.