Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 98, Issue 23, Pages 13102-13107Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.231364598
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- NCI NIH HHS [P01CA81020, P01 CA081020] Funding Source: Medline
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ATR [ataxia-telangiectasia-mutated (ATM)- and Rad3-related] is a protein kinase required for both DNA damage-induced cell cycle checkpoint responses and the DNA replication checkpoint that prevents mitosis before the completion of DNA synthesis. Although ATM and ATR kinases share many substrates, the different phenotypes of ATM- and ATR-deficient mice indicate that these kinases are not functionally redundant. Here we demonstrate that ATR but not ATM phosphorylates the human Rad17 (hRad17) checkpoint protein on Ser(635) and Ser(545) in vitro. In undamaged synchronized human cells, these two sites were phosphorylated in late G(1), S, and G(2)/M, but not in early-mid G1. Treatment of cells with genotoxic stress induced phosphorylation of hRad17 in cells in early-mid G1. Expression of kinase-inactive ATR resulted in reduced phosphorylation of these residues, but these same serine residues were phosphorylated in ionizing radiation (IR)-treated ATM-deficient human cell lines. IR-induced phosphorylation of hRad17 was also observed in ATM-deficient tissues, but induction of Ser(645) was not optimal. Expression of a hRad17 mutant, with both serine residues changed to alanine, abolished IR-induced activation of the G(1)/S checkpoint in MCF-7 cells. These results suggest ATR and hRad17 are essential components of a DNA damage response pathway in mammalian cells.
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