A new effector pathway links ATM kinase with the DNA damage response

Abstract

The related kinases ATM (ataxia-telangiectasia mutated) and ATR (ataxia-telangiectasia and Rad3-related) phosphorylate a limited number of downstream protein targets in response to DNA damage. Here we report a new pathway in which ATM kinase signals the DNA damage response by targeting the transcriptional cofactor Strap. ATM phosphorylates Strap at a serine residue, stabilizing nuclear Strap and facilitating formation of a stress-responsive co-activator complex. Strap activity enhances p53 acetylation, and augments the response to DNA damage. Strap remains localized in the cytoplasm in cells derived from ataxia telangiectasia individuals with defective ATM, as well as in cells expressing a Strap mutant that cannot be phosphorylated by ATM. Targeting Strap to the nucleus reinstates protein stabilization and activates the DNA damage response. These results indicate that the nuclear accumulation of Strap is a critical regulator in the damage response, and argue that this function can be assigned to ATM through the DNA damage-dependent phosphorylation of Strap.

Cofactor Strap regulates oxidative phosphorylation and mitochondrial p53 activity through ATP synthase

“…At the later stages of damage, both Strap and p53 take on a more nuclear localisation (Figure 4e) where Strap can function as a nuclear p53 co-factor. [9][10][11] Although our study supports a role of Strap in mitochondrial-dependent apoptosis, we cannot rule out the possibility that Strap, as a general stress-responsive p53 co-factor, may have a role in other p53 functions, such as p53-dependent necrosis. 36 It is also interesting to note that alterations in ATP levels would likely influence AMPK (AMP-activated protein kinase), which monitors cellular energy status.…”

“…10 Its nuclear localisation is dependent on DNA-damage-activated protein kinases, mediated by both ATM and Chk2 kinases. 10,11 The results described here reveal an unexpected level of Strap control, through its localisation to mitochondria, interaction with ATP synthase and its subsequent influence on ATP production. Our results thus define a dual role for Strap that integrates metabolic reprogramming mediated by the key enzyme ATP synthase with the p53 response.…”

“…L-Strap was prepared by fusing the Bcl2 mitochondrial targeting signal (DFSWLSLKTLLSLALV-GACITLGAYGHK) onto the C-terminal region of Strap in HA-WT Strap. 9,10 Antibodies. The following antibodies were used: Flag peptide M2 (Sigma), HA11 (Covance, Cambridge, UK), calnexin (Millipore, Nottingham, UK), cleaved PARP and cytochrome oxidase IV (Cell Signaling Technology, Leiden, The Netherlands), b-actin (Sigma), ATP synthase b-subunit (BD Pharmingen, Oxford, UK), PCNA, p53 and cytochrome c (Santa Cruz, Heidelberg, Germany) and Strap.…”

“…9 Upon DNA damage, for example, it is phosphorylated by the DNA damage signalling ATM and Chk2 kinases, resulting in Strap stabilisation, altered cellular location and enhanced p53 activity. 10,11 An analysis of the three-dimensional structure of Strap highlighted its unusual domain organisation, being composed of tandem TPR motifs together with an OB-fold, with both domains required for it to function in the p53 response. 12 The location of phosphorylated residues in Strap suggested a structural model whereby Strap unfolds to become more accessible during the DNA-damage response.…”

The Role of JMY in p53 Regulation.

“…Strap contains six tetratricopeptide (TPR) repeat motifs, having several of these protein binding regions one Strap protein can link to different substrates forming multiple complexes [8,19,20]. Following DNA damage, a protein kinase Atm phosphorylates Strap on Serine 203 ( Figure 2).…”