Figure 1.

PPM1G regulates endogenous p27 phosphorylation at T198 during early G1 phase. A. Dynamic phosphorylation of p27 during G1 phase. HeLa cells were arrested at G0 phase and then released into the cell cycle. Cell lysates were collected at the indicated time points. Phosphorylation of p27 was analyzed by Western blot using specific antibodies. B. Phosphatase screening. 293T cells were transfected with YFP-p27 and Flag tagged phosphatase. Phosphorylation of p27 at T198 (p27pT198) was determined by Western blot. C. PPM1G knockdown increases p27pT198 levels at early G1 phase. Control and PPM1G-depleted HeLa cells stably expressing shRNA against human PPM1G or harboring empty vector were generated. Cells were treated as described in A, and collected at the indicated time points. Levels of PPM1G, p27, and p27pT198 were determined by Western blot.