Posttranslational modifications of TIP60 and PRAK mediate oncogenic RAS-induced senescence.
Major finding: Posttranslational modifications of TIP60 and PRAK mediate oncogenic RAS-induced senescence.
Mechanism: TIP60 phosphorylation by p38 promotes TIP60-driven PRAK acetylation and kinase activation.
Impact: Senescence induction via the p38–TIP60–PRAK pathway functions as a tumor-suppressive mechanism.
Expression of oncogenes such as RAS triggers a stable growth arrest that protects cells against tumorigenesis. Activation of the mitogen-activated protein kinase (MAPK) p38 (also known as MAPK14) and its downstream target mitogen-activated protein kinase–activated protein kinase 5 (MAPKAPK5, also known as PRAK) is essential for this oncogene-induced senescence (OIS), but the signaling mechanisms that regulate the tumor suppressive-function of PRAK are unknown. Zheng and colleagues identified K(lysine) acetyltransferase 5 (KAT5, also known as TIP60), a member of the MYST family of histone acetyltransferases (HAT) that promotes p53-driven apoptosis, as a binding partner of PRAK in a yeast 2-hybrid assay and in senescent fibroblasts. This interaction required the HAT domain of TIP60 and TIP60 depletion blocked RAS-induced senescence, suggesting that TIP60-mediated acetylation of PRAK promotes OIS. Activation of oncogenic RAS stimulated phosphorylation of TIP60 at threonine 158 by p38α and p38δ in senescent cells; this modification enhanced the HAT activity of TIP60 and was necessary for TIP60-mediated acetylation of PRAK at lysine 364 (K364) and induction of senescence in response to oncogenic RAS. Moreover, PRAK acetylation by TIP60 during OIS was dependent on p38-mediated phosphorylation of both TIP60 and PRAK and resulted in increased PRAK kinase activity. Depletion of TIP60 or inhibition of PRAK acetylation via K364 mutation impaired PRAK enzymatic activity, decreased activation of the PRAK target p53 and expression of cyclin-dependent kinase inhibitor 1A (p21), and suppressed the prosenescent function of PRAK. Furthermore, expression of an acetylation-mimic PRAK mutant was sufficient to rescue senescence in TIP60-depleted cells, suggesting that TIP60 mediates senescence largely through activation of PRAK. These results provide insight into the regulation of TIP60 and PRAK function by posttranslational modifications and characterize the p38–TIP60–PRAK pathway as a critical regulator of oncogenic RAS-induced senescence.