A role for the Tip60 histone acetyltransferase in the acetylation and activation of ATM

Abstract

FATC domain ͉ TRRAP ͉ NuA4 ͉ chromatin remodeling T he product of the ataxia telangiectasia (AT) gene, the AT mutant (ATM) protein kinase, is a key component of the signal-transduction pathway activated by DNA damage (1). In response to DNA strand breaks, ATM's kinase activity is upregulated, and ATM becomes autophosphorylated on Ser 1981 (2). ATM autophosphorylation initiates the conversion of the inactive ATM dimer to an active, monomeric ATM. ATM then phosphorylates multiple proteins involved in the DNA damage response, including nbs1, p53, chk2, and SMC1 (1, 3). These phosphorylated proteins, in turn, regulate the two key responses to DNA damage: the activation of cell-cycle checkpoints and the initiation of DNA repair.Although the downstream signaling pathways activated by ATM are well characterized, the mechanism by which DNA strand breaks are detected and how this leads to activation of ATM's kinase activity are less clear. The Mre11͞Rad50͞Nbs1 (MRN) complex, a DNA-binding complex involved in the detection and repair of DNA damage, may play a role in regulating ATM activity. MRN functions as an adaptor protein that links activated ATM with its target proteins [including chk2 (4) and SMC1 (3)] to allow productive phosphorylation (5, 6). Biochemical studies have shown that the DNA-dependent activation of ATM's kinase activity requires the functional MRN complex (7,8). However, although several studies have demonstrated that activation of ATM's kinase activity in cells lacking functional MRN complex is reduced (6, 9), other studies have shown that ATM activation is relatively normal in MRN-defective cells (5, 10). Furthermore, other proteins, including the p18 tumorsuppressor protein (11), have been shown to participate in ATM activation. Thus, although the MRN complex may regulate ATM activation under certain conditions, additional protein factors may also be required for ATM activation in vivo.Recent studies have shown that the repair of DNA doublestrand breaks requires the remodeling of chromatin structure (12-14). Furthermore, ATM can be activated by changes in chromatin structure that occur independently of DNA damage (2), leading to the proposal that ATM activation is mediated by alterations in chromatin structure at sites of DNA damage rather than through direct activation of ATM by strand breaks (1, 2). Chromatin remodeling is linked to the posttranslational modification of histones through phosphorylation, methylation, and acetylation (15). Histone acetyltransferases (HATs) can acetylate both histones and several nonhistone proteins (13,15). Here, we examined whether Tip60, a HAT previously implicated in the DNA-damage response, provides the link between DNA strand breaks in chromatin and the activation of ATM. The results indicate that DNA damage induces rapid acetylation of ATM by a mechanism that depends on the Tip60 HAT. Suppression of Tip60 blocks activation of ATM's kinase activity and sensitizes cells to ionizing radiation (IR). Furthermore, the FATC domain of ATM mediates the interaction bet...

Functional characterization of TIP60 sumoylation in UV-irradiated DNA damage response

“…Sumoylation promotes TIP60 HAT activity in response to UV irradiation Since TIP60 is sumoylated in response to UV irradiation ( Figure 2) and its HAT activity is activated by DNA damage (Sun et al, 2005), we tested whether the sumoylation modulates its HAT activity using histone-2A acetylation as a reporter (Yamamoto and Horikoshi, 1997). As shown in Figure 6a, the level of histone-2A acetylation is increased in cells expressing GFP-TIP60 with the highest level observed in cells expressing SUMO-TIP60dm.…”

“…Like p53, TIP60 accumulates in response to DNA damage (for example, Legube et al, 2004). Suppression of TIP60 blocks ATM activation and ATM-dependent phosphorylation of p53, suggesting that TIP60 is an upstream molecule in ATMdependent DNA damage response (Sun et al, 2005).…”

ATM and the Mre11 complex combine to recognize and signal DNA double-strand breaks

“…Not surprisingly, protein phosphatases have also been shown to play a role in ATM activation (Ali et al, 2004;Goodarzi et al, 2004). DNA-damaged-induced acetylation of ATM has been reported by Sun et al (2005) and this was shown to run in parallel with pS1981 after radiation exposure. They identified the Tip60 histone acetyltransferase as the enzyme responsible and revealed that a dominant negative form of Tip60 reduced both acetylation and autophosphorylation of ATM.…”

Activation and regulation of ATM kinase activity in response to DNA double-strand breaks

“…Price and co-workers showed that ATM is acetylated by the Tip60 complex after DNA damage and that disruption of Tip60 by siRNA causes defects in ATM autophosphorylation, suggesting that the activity of Tip60 is required for ATM autophosphorylation (Sun et al, 2005(Sun et al, , 2006. They also showed that Tip60 is required for ATM-dependent phosphorylation of p53 and Chk2 in bleomycin-treated cells and interacts with the C-terminal FATC domain on ATM.…”