MDM2 and cancer: Out of these 273 phosphorylation sites, in proteins that are involved in cancer development, 55 phosphosites in 34 proteins were differentially phosphorylated by p38α and p38β (Figure 3 and Supplementary Table S4), including the tumor suppressor p53 and APC, Raf1, Mdm2, MAX, and AKT1 (Figure 3B).