Autophosphorylation of ataxia-telangiectasia mutated is regulated by protein phosphatase 2A

Abstract

Ionizing radiation induces autophosphorylation of the ataxia-telangiectasia mutated (ATM) protein kinase on serine 1981; however, the precise mechanisms that regulate ATM activation are not fully understood. Here, we show that the protein phosphatase inhibitor okadaic acid (OA) induces autophosphorylation of ATM on serine 1981 in unirradiated cells at concentrations that inhibit protein phosphatase 2A-like activity in vitro. OA did not induce gamma-H2AX foci, suggesting that it induces ATM autophosphorylation by inactivation of a protein phosphatase rather than by inducing DNA double-strand breaks. In support of this, we show that ATM interacts with the scaffolding (A) subunit of protein phosphatase 2A (PP2A), that the scaffolding and catalytic (C) subunits of PP2A interact with ATM in undamaged cells and that immunoprecipitates of ATM from undamaged cells contain PP2A-like protein phosphatase activity. Moreover, we show that IR induces phosphorylation-dependent dissociation of PP2A from ATM and loss of the associated protein phosphatase activity. We propose that PP2A plays an important role in the regulation of ATM autophosphorylation and activity in vivo.

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

“…Guo et al (2002) showed that the B55a regulatory subunit dissociates from the A and C subunits after DNA damage in ATM-dependent manner. A later study also showed that ATM interacts directly with the A subunit, and that the A and C subunits coimmunoprecipitate with ATM in unirradiated human cells but dissociate after IR exposure (Goodarzi et al, 2004). They also showed that overexpression of a dominant-negative form of the C subunit-induced autophosphorylation of ATM on Ser-1981 in the absence of IR.…”

“…Recent articles show that two phosphatases, protein phosphatase 2A (PP2A) and protein phosphatase 5 (PP5), both affect ATM activity in vivo (Ali et al, 2004;Goodarzi et al, 2004). PP2A is a member of the protein serine/threonine phosphatase family and is composed of a catalytic (C) subunit, a scaffolding A subunit and a regulatory B subunit.…”

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

“…What is not clear yet is whether ATM pS367 and pS1893 coincide with pS1981 at the break site or whether they are associated with movement of ATM from the site to the flanking regions. 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.…”

Chk1–cyclin A/Cdk1 axis regulates origin firing programs in mammals

“…In response to DSBs, a conformational change in the ATM protein stimulates it to auto-phosphorylate Ser1981 in an intermolecular manner. In contrast, the auto-phosphorylation of ATM at Ser1981 is suppressed under unperturbed conditions by a constitutive interaction with PP2A that dephosphorylates Ser1981 (Goodarzi et al 2004). Acetylation of ATM by Tip60 is also reported to be important for its full activation (Sun et al 2005).…”