title: TopBP1 deficiency causes an early embryonic lethality and induces cellular senescence in primary cells.
abstract: TopBP1 plays important roles in chromosome replication, DNA damage response, and other cellular regulatory functions in vertebrates. Although the roles of TopBP1 have been studied mostly in cancer cell lines, its physiological function remains unclear in mice and untransformed cells. We generated conditional knock-out mice in which exons 5 and 6 of the TopBP1 gene are flanked by loxP sequences. Although TopBP1-deficient embryos developed to the blastocyst stage, no homozygous mutant embryos were recovered at E8.5 or beyond, and completely resorbed embryos were frequent at E7.5, indicating that mutant embryos tend to die at the peri-implantation stage. This finding indicated that TopBP1 is essential for cell proliferation during early embryogenesis. Ablation of TopBP1 in TopBP1(flox/flox) mouse embryonic fibroblasts and 3T3 cells using Cre recombinase-expressing retrovirus arrests cell cycle progression at the G(1), S, and G(2)/M phases. The TopBP1-ablated mouse cells exhibit phosphorylation of H2AX and Chk2, indicating that the cells contain DNA breaks. The TopBP1-ablated mouse cells enter cellular senescence. Although RNA interference-mediated knockdown of TopBP1 induced cellular senescence in human primary cells, it induced apoptosis in cancer cells. Therefore, TopBP1 deficiency in untransformed mouse and human primary cells induces cellular senescence rather than apoptosis. These results indicate that TopBP1 is essential for cell proliferation and maintenance of chromosomal integrity.
authors.affiliation: Cancer Experimental Resources Branch, National Cancer Center, Ilsandong-gu, Goyang-si, Gyeonggi-do 410-769, Korea.
authors.forename: Yoon
authors.initials: Y
authors.lastname: Jeon
authors.forename: Eun
authors.initials: E
authors.lastname: Ko
authors.forename: Kyung Yong
authors.initials: KY
authors.lastname: Lee
authors.forename: Min Ji
authors.initials: MJ
authors.lastname: Ko
authors.forename: Seo Young
authors.initials: SY
authors.lastname: Park
authors.forename: Jeeheon
authors.initials: J
authors.lastname: Kang
authors.forename: Chang Hwan
authors.initials: CH
authors.lastname: Jeon
authors.forename: Ho
authors.initials: H
authors.lastname: Lee
authors.forename: Deog Su
authors.initials: DS
authors.lastname: Hwang
mesh_terms: D016475:3T3 Cells; D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D001755:Blastocyst / Q000166:cytology / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002453:Cell Cycle / Q000502:physiology*; D045744:Cell Line, Tumor; D016922:Cellular Senescence / Q000502:physiology; D064447:Checkpoint Kinase 2; D043171:Chromosomal Instability / Q000502:physiology; D053960:DNA Breaks; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D020964:Embryo Loss / Q000235:genetics / Q000378:metabolism; D047108:Embryonic Development / Q000502:physiology*; D055785:Gene Knockdown Techniques; D006657:Histones / Q000235:genetics / Q000378:metabolism; D006801:Humans; D051379:Mice; D008822:Mice, Transgenic; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation / Q000502:physiology; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D064447:Checkpoint Kinase 2; D004268:DNA-Binding Proteins; D006657:Histones; D009687:Nuclear Proteins; D017346:Protein Serine-Threonine Kinases; C468783:H2AX protein, human; C110513:TOPBP1 protein, human; C492846:Topbp1 protein, mouse; C578634:CHEK2 protein, human; C578633:Chek2 protein, mouse; C475961:gamma-H2AX protein, mouse