Figure 4

Effects of MALAT1 depletion on cell cycle and apoptosis reflected by flow cytometry and the possible mechanism for cell cycle arrest. (A) Representative images of cell cycle distribution, the bar chart represented the percentage of cells in G0/G1, S, or G2/M phases, as indicated. (B) Representative images of cell apoptosis determined by flow cytometry analysis, the bar chart represented the sum percentage of early and late apoptotic cells. (C) Western-blotting analysis of the ATM-CHK2 pathway in EC109 and EC9706 cells; The phosphorylated forms of ATM, CHK2, CDC25C, and CDK1 were up-regulated upon MALAT1 knockdown, while the total amounts of these proteins exhibited no detectable changes. (D) The putative mechanism of MALAT1 knockdown induced cell cycle arrest in G2/M on human esophageal cancer cells. ATM is activated by phosphorylation upon MALAT1 knockdown. This activation possibly increases the level of P-CHK2 by phosphorylation at Thr68 of CHK2, while the activated P-CHK2 further inactivates CDC25C by phosphorylation at Ser216 of CDC25C. As a result, the dephosphorylation capacity of P-CDC25C on P-CDK1 (Tyr15) is inhibited, so the inactivated form of CDK1 accumulates, which contributes to G2/M phase arrest. (+): activation, (−): inactivation. *P < 0.05, **P < 0.01.