Estrogen Inhibits ATR Signaling to Cell Cycle Checkpoints and DNA Repair

Abstract

DNA damage activates the ataxia telangiectasia–mutated and Rad3-related (ATR) kinase signal cascade. How this system is restrained is not understood. We find that in estrogen receptor (ER)-positive breast cancer cells, UV or ionizing radiation and hydroxyurea rapidly activate ATR-dependent phosphorylation of endogenous p53 and Chk1. 17-β-estradiol (E₂) substantially blocks ATR activity via plasma membrane-localized ERα. E₂/ER reduces the enhanced association of ATR andTopBP1 proteins that follows DNA damage and strongly correlates to ATR activity. E₂ inhibits ATR activation through rapid PI3K/AKT signaling: AKT phosphorylates TopBP1 at Serine 1159, thereby preventing the enhanced association of ATR with TopBP1 after DNA damage. E₂ also inhibits Claspin:Chk1 protein association via AKT phosphorylation of Chk1, preventing Chk1 signaling to the G2/M checkpoint. ATR-phosphorylation of p53 induces p21 transcription, prevented by E₂/ER. E₂ delays the assembly and prolongs the resolution of γH2AX and Rad51 nuclear foci and delays DNA repair. E₂/ER also increases the chromosomal damage seen from cell exposure to IR. Therefore, the restraint of ATR cascade activation may be a novel estrogen action relevant to breast cancer.