PPM1D and neoplasm: Moreover, constitutive activation of p38 by MKK3E reversed the stimulatory effect of WIP1 on tumor initiation (Fig. 6a, Supplementary Data Fig. S5, Supplementary Table S1), and inactivation of p38 by MKK6A reversed the inhibitory effect of GSK on tumor initiation (Fig. 6e, Supplementary Data Fig. S6, Supplementary Table S1).