PARENT SESSION
9:00 AM to 11:00 AM
Wednesday, April 24, 2002
Symposium 21
Role of ATM and ATR
Room: Nevada 6-7
Chair: Jung, Mira²²Department of Radiation Medicine, Georgetown University School of Medicine, 3970 Reservoir Road, NW, Washington DC, DC, Co-Chair: Lavin, Maritn³³Queensland Institute of Medical REsearch, Bancroft Centre, GPO Royal Brisbane Hospital, Herston, Brisbane, Queensland, Australia
Speakers: Lavin, Martin⁴; Jung, Mira⁵; Cimprich, Karlene⁶⁴Queensland Institute of Medical Research, Bancroft Centre, GPO Royal Brisbane Hospital, Herston, Brisbane, Queensland, Australia⁵Department of Radiation Medicine, Georgetown University School of Medicine, 3970 Reservoir Road, NW, Washington DC, DC⁶Department of Molecular Pharmacology, Stanford University School of Medicine, Palo Alto, California

(S21-3) Analysis of ATR-mediated signaling in the DNA damage and replication checkpoints.

Barr, Sharon¹, Byun, Tony¹, Hekmat-Nejad, Mohammad¹, Lupardus, Patrick¹, Yee, Muh-ching¹, Cimprich, Karlene^*,1, ¹ Stanford University, Stanford, CA

ABSTRACT-
To maintain genomic stability, cells depend on the DNA damage and replication checkpoints. Proteins from the phosphatidylinositol kinase-related protein kinase family (PIKKs) are required for the response to DNA damage in every species studied, and genetic studies in yeast suggest these proteins are upstream components of the signal transduction cascade that is initiated by DNA damage. ATR (ATM and Rad3-related) is a human member of the PIKK family of proteins that has been suggested to be a critical component of the DNA damage checkpoint as well as the checkpoint that coordinates the completion of DNA synthesis with the initiation of mitosis. To test this hypothesis and to learn more about the functions of ATR, we have cloned the homolog of ATR in Xenopus laevis and studied the function of this protein in Xenopus egg extracts. Using a chromatin binding assay, we show that ATR is a replication-dependent, chromatin-binding protein that accumulates on chromatin after UV or aphidicolin treatment. The association of ATR with chromatin is inhibited by preventing the initiation of replication. Importantly, there is an early rise in the activity of Cdc2-cyclin B in egg extracts depleted of ATR in the presence and absence of the replication inhibitor aphidicolin. In addition, the premature mitosis observed upon depletion of ATR in aphidicolin-treated extracts is accompanied by the loss of Chk1 phosphorylation. Together these studies suggest that ATR may recognize some DNA replication intermediates or a protein that associates with DNA during replication that may be modified or more abundant when replication is stalled. Progress on the identification of ATR substrates as well as recent results which provide insight into the regulation of ATR activity will also be reported.

KEYWORDS: ATR, checkpoint