To explain the basis of ODC as a tumor promoter in ESCC progression, we examined apoptosis and cell cycle in shODC-infected ESCC cells. Our results showed that knocking down ODC expression with shODC significantly increased total apoptosis of both KYSE450 and KYSE510 cell lines (Fig. 3a). In addition, compared to shMock, shODC expression also induced G2/M phase arrest and decreased the percentage of cells in S phase in both cell lines (Fig. 3b). We also compared apoptosis- (Fig. 3a) and cell cycle-related (Fig. 3b) markers by Western blot in shMock and shODC-expressing KYSE450 and KYSE510 cells. Our results showed that shODC was generally associated with increases in the expression levels of cleaved caspase 3, cleaved PARP, Bax, p53, p27, p21, E-cadherin, and phosphorylated CDK1 (Tyr15). In contrast, the expression levels of phosphorylated ERK1/2, Bcl-2, PCNA and cyclin B1 were mostly decreased.Fig. 3Silencing of ODC expression by shRNA induces apoptosis and G2/M arrest in ESCC cells. The effects of ODC on a apoptosis and b cell cycle were analyzed by flow cytometry (upper panels). The expression of markers associated with cell cycle and apoptosis were analyzed by Western blot (lower panels). All data are shown as means ± S.D. of triplicate values from 3 independent experiments