CDCA7 and HELLS mutations undermine nonhomologous end joining in centromeric instability syndrome
Motoko Unoki, … , Claire Francastel, Hiroyuki Sasaki
Motoko Unoki, … , Claire Francastel, Hiroyuki Sasaki
Published October 11, 2018
Citation Information: J Clin Invest. 2019;129(1):78-92. https://doi.org/10.1172/JCI99751.
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Research Article Cell biology Genetics

CDCA7 and HELLS mutations undermine nonhomologous end joining in centromeric instability syndrome

Abstract

Mutations in CDCA7 and HELLS that respectively encode a CXXC-type zinc finger protein and an SNF2 family chromatin remodeler cause immunodeficiency, centromeric instability, and facial anomalies (ICF) syndrome types 3 and 4. Here, we demonstrate that the classical nonhomologous end joining (C-NHEJ) proteins Ku80 and Ku70, as well as HELLS, coimmunoprecipitated with CDCA7. The coimmunoprecipitation of the repair proteins was sensitive to nuclease treatment and an ICF3 mutation in CDCA7 that impairs its chromatin binding. The functional importance of these interactions was strongly suggested by the compromised C-NHEJ activity and significant delay in Ku80 accumulation at DNA damage sites in CDCA7- and HELLS-deficient HEK293 cells. Consistent with the repair defect, these cells displayed increased apoptosis, abnormal chromosome segregation, aneuploidy, centrosome amplification, and significant accumulation of γH2AX signals. Although less prominent, cells with mutations in the other ICF genes DNMT3B and ZBTB24 (responsible for ICF types 1 and 2, respectively) showed similar defects. Importantly, lymphoblastoid cells from ICF patients shared the same changes detected in the mutant HEK293 cells to varying degrees. Although the C-NHEJ defect alone did not cause CG hypomethylation, CDCA7 and HELLS are involved in maintaining CG methylation at centromeric and pericentromeric repeats. The defect in C-NHEJ may account for some common features of ICF cells, including centromeric instability, abnormal chromosome segregation, and apoptosis.

Authors

Motoko Unoki, Hironori Funabiki, Guillaume Velasco, Claire Francastel, Hiroyuki Sasaki

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Figure 8

The C-NHEJ defect alone does not cause CG hypomethylation at satellite repeats.

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The C-NHEJ defect alone does not cause CG hypomethylation at satellite r...
(A and B) CG methylation (percent) at centromeric α-satellite (A) and pericentromeric satellite-2 repeats (B) in mutant cells. The methylation levels were measured by bisulfite sequencing (PCR products were cloned into TA vector and at least 10 clones were sequenced for each condition) at 2 and ≥4 months after the introduction of the mutation. Because the doubling time of the mutant cells was 25–30 hours (Figure 3A), 2 and ≥4 months roughly corresponded to 48–58 and ≥96–116 cell divisions, respectively. Restoration of the methylation levels in the “rescue” clones was evaluated at 6 weeks after the introduction of WT genes. Data are mean ± SEM. Statistical analysis was performed separately for the data obtained at 2 and ≥4 months and the data obtained after 6 weeks of WT restoration. For the former data sets, **P < 0.0007 (Mann-Whitney U test) was considered statistically significant at the 1% level after Bonferroni correction. For the latter data set, **P < 0.0004 (Mann-Whitney U test) was considered statistically significant at the 1% level after Bonferroni correction. The exact P values, which were significant (P < 0.05) before the correction, are shown for reference. See also Supplemental Figure 9.