DNA ligase I deficiency leads to replication-dependent DNA damage and impacts cell morphology without blocking cell cycle progression

Samuela Soza, Valentina Leva, Riccardo Vago, Giovanni Ferrari, Giuliano Mazzini, Giuseppe Biamonti, Alessandra Montecucco

Research output: Contribution to journalArticle


46BR.1G1 cells derive from a patient with a genetic syndrome characterized by drastically reduced repllcatlve DNA ligase I (LigI) activity and delayed joining of Okazaki fragments. Here we show that the replication defect in 46BR.1G1 cells results in the accumulation of both single-stranded and double-stranded DNA breaks. This is accompanied by phosphorylation of the H2AX historic variant and the formation of γH2AX foci that mark damaged DNA. Single-cell analysis demonstrates that the number of γH2AX foci in LigI-defective cells fluctuates during the cell cycle: they form in S phase, persist in mitosis, and eventually diminish in G 1 phase. Notably, replication-dependent DNA damage in 46BR.1G1 cells only moderately delays cell cycle progression and does not activate the S-phase-specific ATR/Chk1 checkpoint pathway that also monitors the execution of mitosis. In contrast, the ATM/Chk2 pathway is activated. The phenotype of 46BR.1G1 cells is efficiently corrected by the wild-type LigI but is worsened by a LigI mutant that mimics the hyperphosphorylated enzyme in M phase. Notably, the expression of the phosphomimetic mutant drastically affects cell morphology and the organization of the cytoskeleton, unveiling an unexpected link between endogenous DNA damage and the structural organization of the cell.

Original languageEnglish
Pages (from-to)2032-2041
Number of pages10
JournalMolecular and Cellular Biology
Issue number8
Publication statusPublished - Apr 2009


ASJC Scopus subject areas

  • Molecular Biology
  • Cell Biology

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