Figure 4. Effect of metformin on the level of constitutive expression of ATM-S1981P. Exponentially growing TK6 cells were untreated (Ctrl) or were grown in the presence of 0.1, 1.0, 5.0 and 10 mM metformin (MF) for 48 h. The expression of ATM-S1981P was detected with phospho-specific Ab. As in Fig. 3, the cells were gated in G1, S and G2M phases of the cell cycle and the mean values of ATM-S1981P for cells in each of these cell cycle phases were estimated. The figures show the percent reduction in mean values of ATM-S1981P IF of the metformintreated cells with respect to the mean values of the untreated cells (Ctrl) in the respective phases of the cell cycle.