Assessment of ATM phosphorylation on <i>Ser</i>‐1981 induced by DNA topoisomerase I and II inhibitors in relation to <i>Ser</i>‐139‐histone H2AX phosphorylation, cell cycle phase, and apoptosis

Abstract

The data are consistent with the role of ATM as a mediator of H2AX phosphorylation in response to DNA damage by topo1 (Tpt) or topo 2 (Mtx) inhibitor. The observed cell-cycle-phase related differences in response to Tpt vs Mtx suggest that while the collisions of DNA replication forks with the "cleavable complexes" stabilized by topo1 inhibitor are the primary cause of DSBs induced by Tpt, the collisions of RNA polymerase molecules with the complexes stabilized by the topo2 inhibitor play a major role for induction of DSBs by Mtx. The present report is the first that (i) describes cytometric analysis of ATM activation and (ii) demonstrates activation of the enzyme (kinase) and its consequence (substrate phoshorylation), both in relation to cell-cycle phase and onset of apoptosis within the same cells.