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First published online 12 July 2005
doi: 10.1242/jcs.02427

Journal of Cell Science 118, 3247-3261 (2005)
Published by The Company of Biologists 2005
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Research Article

Decreased origin usage and initiation of DNA replication in haploinsufficient HCT116 Ku80+/- cells

Sahar Sibani1,2, Gerald B. Price1,* and Maria Zannis-Hadjopoulos1,2,{ddagger}

1 McGill Cancer Center, McGill University, Montreal, Quebec H3G 1Y6, Canada
2 Department of Biochemistry, McGill University, Montreal, Quebec H3G 1Y6, Canada

{ddagger} Author for correspondence (e-mail: maria.zannis{at}mcgill.ca)

Accepted 14 March 2005

One of the functions of the abundant heterodimeric nuclear protein, Ku (Ku70/Ku80), is its involvement in the initiation of DNA replication through its ability to bind to chromosomal replication origins in a sequence-specific and cell cycle dependent manner. Here, using HCT116 Ku80+/- cells, the effect of Ku80 deficiency on cell cycle progression and origin activation was examined. Western blot analyses revealed a 75% and 36% decrease in the nuclear expression of Ku80 and Ku70, respectively. This was concomitant with a 33% and 40% decrease in chromatin binding of both proteins, respectively. Cell cycle analysis of asynchronous and late G1 synchronized Ku80+/- cells revealed a prolonged G1 phase. Furthermore, these Ku-deficient cells had a 4.5-, 3.4- and 4.3-fold decrease in nascent strand DNA abundance at the lamin B2, ß-globin and c-myc replication origins, respectively. Chromatin immunoprecipitation (ChIP) assays showed that the association of Ku80 with the lamin B2, ß-globin and c-myc origins was decreased by 1.5-, 2.3- and 2.5-fold, respectively, whereas that of Ku70 was similarly decreased (by 2.1-, 1.5- and 1.7-fold, respectively) in Ku80+/- cells. The results indicate that a deficiency of Ku80 resulted in a prolonged G1 phase, as well as decreased Ku binding to and activation of origins of DNA replication.

Key words: Chromatin immunoprecipitation, Human, Replication origins, Nascent DNA abundance, Ku protein, Haploinsufficient




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