AIM:To study the cell cycle alterations of human hepatomacell line HepG_2 in vitro after ~(60)Co γ-irradiation and furtherto examine the mechanisms underlying the enhancementof radiosensitivity to γ-irradiation in HepG_2 transientlytransfected with wild type p27~(kipl).METHODS:The proliferation of HepG_2 cells was evaluatedwith MTT assay,and the cell cycle profile and apoptosiswere assessed by cell morphology,DNA fragmentationanalysis and flow cytometry.HepG_2 cells were transfectedwith p27~(kip1) wild type by using Lipofectamine(LF2000),andthe expression and subcellular localization of p27~(kip1) in HepG_2were detected by immunocytochemistry.RESULTS:~(60)Co γ-irradiation inhibited the growth of HepG_2cells in a dose-dependent manner.Apoptosis of HepG_2 cellswas induced 48 h after γ ray exposure.Furthermore researchwas carried out to induce exogenous expression of p27~(kip1)in HepG_2.The expression of p27~(kip1) induced G_0/G_1 phasearrest in HepG_2 cells.The overexpression of p27~(kip1) enhanced~(60)Co γ-irradiation-induced radiosensitivity in HepG_2 cells.CONCLUSION:Overexpression of p27~(kip1) is a rational approachto improve conventional radiotherapy outcomes,which maybe a possible strategy for human hepatoma therapy.Guan XX,Chen LB,Ding GX,De W,Zhang AH.Transfection ofp27~(kip1) enhances radiosensitivity induced by ~(60)Co γ-irradiation inhepatocellular carcinoma HepG_2 cell line.World J Gastroenterol2004;10(21):3103-3106http://www.wjgnet.com/1007-9327/10/3103.asp AIM: To study the cell cycle alterations of human hepatoma cell line HepG_2 in vitro after ~ (60) Co γ-irradiation and furtherto examine the mechanisms underlying the enhancement of radiosensitivity to γ-irradiation in HepG_2 transiently transfected with wild type p27 ~ (kipl) .METHODS : The proliferation of HepG_2 cells was evaluated with MTT assay, and the cell cycle profile and apoptosiswere assessed by cell morphology, DNA fragmentationanalysisand flow cytometry.HepG_2 cells were transfectedwith p27 ~ (kip1) wild type by using Lipofectamine (LF2000), andtheexpressionand Results of subcellular localization of p27 ~ (kip1) in HepG_2were detected by immunocytochemistry .RESULTS: ~ (60) Coγ-irradiation inhibited the growth of HepG_2cells in a dose-dependent manner.Apoptosis of HepG_2cellswas induced 48 h after γ ray exposure.Furthermore researchwas carried out to induce exogenous expression of p27 ~ (kip1) in HepG_2.The expression of p27 ~ (kip1) induced G_0 / G_1 phasearrest in HepG_2 cells.The overexpression of p27 ~ (kip1) enhanced ~ (60) Co γ-irradiation-induced radiosensitivity in HepG_2 cells.CONCLUSION: Overexpression of p27 ~ (kip1) is a rational approach to improve conventional radiotherapy outcomes, which maybe a possible strategy for human hepatoma therapy. Guan XX, Chen LB, Ding GX, De W, Zhang AH. Transfection of p27 kip1 enhances radiosensitivity induced by ~ (60) Co γ-irradiation in hepatocellular carcinoma HepG_2 cell line. World J Gastroenterol 2004; 10 (21): 3103-3106 http: /www.wjgnet.com/1007-9327/10/3103.asp