ATM ASSOCIATES WITH AND PHOSPHORYLATES P53 - MAPPING THE REGION OF INTERACTION

The human genetic disorder ataxia-telangiectasia (AT) is characterized by immunodeficiency. progressive cerebellar ataxia. radiosensitivity, cell cycle checkpoint defects and cancer predisposition(1). The gene mutated in this syndrome, ATM (for AT mutated), encodes a protein cont aining a phosphatidyl-inositol 3-kinase (PI-3 kinase)-like domain(2,3) . ATM also contains a proline-rich region(4) and a leucine zipper(2,5) , both of which implicate this protein in signal transduction. The pro line-rich region has been shown to bind to the SH3 domain of c-Abl, wh ich facilitates its phosphorylation and activation by ATM (refs 4,6). Previous results have demonstrated that AT cells are defective in the G1/S checkpoint activated after radiation damage and that this defect is attributable to a defective p53 signal transduction pathway(7,8). W e report here direct interaction between ATM and p53 involving two reg ions in ATM. one at the amino terminus and the other at the carboxy te rminus, corresponding to the PI-3 kinase domain. Recombinant ATM prote in phosphorylates p53 on serine 15 near the N terminus. Furthermore, e ctopic expression of ATM in AT cells restores normal ionizing radiatio n (IR)-induced phosphorylation of p53, whereas expression of ATM antis ense RNA in control cells abrogates the rapid IR-induced phosphorylati on of p53 on serine 15. These results demonstrate that ATM can bind p5 3 directly and is responsible for its serine 15 phosphorylation. there by contributing to the activation and stabilization of p53 during the IR-induced DNA damage response.