MDM2 and viral infectious disease: Phosphorylation of both p53 and MDM2 can be regulated by the same kinase, Casein Kinase 1 (CK1) isoforms - α, δ, and ε - which has been shown to phosphorylate p53 after transforming growth factor beta [33], some DNA damage signals [34] or virus infection [6], which frees p53 from MDM2 [35].