title: Human TopBP1 ensures genome integrity during normal S phase.
abstract: Cell cycle checkpoints are essential for maintaining genomic integrity. Human topoisomerase II binding protein 1 (TopBP1) shares sequence similarity with budding yeast Dpb11, fission yeast Rad4/Cut5, and Xenopus Cut5, all of which are required for DNA replication and cell cycle checkpoints. Indeed, we have shown that human TopBP1 participates in the activation of replication checkpoint and DNA damage checkpoints, following hydroxyurea treatment and ionizing radiation. In this study, we address the physiological function of TopBP1 in S phase by using small interfering RNA. In the absence of exogenous DNA damage, TopBP1 is recruited to replicating chromatin. However, TopBP1 does not appear to be essential for DNA replication. TopBP1-deficient cells have increased H2AX phosphorylation and ATM-Chk 2 activation, suggesting the accumulation of DNA double-strand breaks in the absence of TopBP1. This leads to formation of gaps and breaks at fragile sites, 4N accumulation, and aberrant cell division. We propose that the cellular function of TopBP1 is to monitor ongoing DNA replication. By ensuring proper DNA replication, TopBP1 plays a critical role in the maintenance of genomic stability during normal S phase as well as following genotoxic stress.
authors.affiliation: Department of Oncology, Mayo Clinic College of Medicine, Rochester, MN 55905, USA.
authors.forename: Ja-Eun
authors.initials: JE
authors.lastname: Kim
authors.forename: Sarah A
authors.initials: SA
authors.lastname: McAvoy
authors.forename: David I
authors.initials: DI
authors.lastname: Smith
authors.forename: Junjie
authors.initials: J
authors.lastname: Chen
mesh_terms: D064007:Ataxia Telangiectasia Mutated Proteins; D002352:Carrier Proteins / Q000235:genetics / Q000502:physiology*; D018797:Cell Cycle Proteins / Q000378:metabolism; D064447:Checkpoint Kinase 2; D002843:Chromatin / Q000378:metabolism; D004249:DNA Damage / Q000235:genetics; D004261:DNA Replication / Q000235:genetics; D004268:DNA-Binding Proteins / Q000378:metabolism; D042822:Genomic Instability / Q000235:genetics; D006657:Histones / Q000378:metabolism; D006801:Humans; D009687:Nuclear Proteins; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics / Q000494:pharmacology; D016196:S Phase / Q000235:genetics; D025521:Tumor Suppressor Proteins / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D002843:Chromatin; D004268:DNA-Binding Proteins; C468783:H2AX protein, human; D006657:Histones; D009687:Nuclear Proteins; D034741:RNA, Small Interfering; C110513:TOPBP1 protein, human; D025521:Tumor Suppressor Proteins; D064447:Checkpoint Kinase 2; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; C578634:CHEK2 protein, human; D017346:Protein Serine-Threonine Kinases