Mechanisms of Hydroxyurea-Mediated DNA Damage Potentiation in Fanconi Anemia Cells

Fanconi anemia (FA) is a rare disease with a deficient homologous recombination DNA repair pathway and high sensitivity to mitomycin C (MMC). In FA cells, hydroxyurea (HU), when applied in the G2 phase of the cell cycle, exacerbates the chromosomal aberrations (CAs) induced by MMC. Here, we study how exposure to HU in the G2 phase results in an increased CAs frequency in FA cells with or without prior treatment with MMC. We performed chromosome aberration analysis, flow cytometry, and mRNA and protein expression in lymphoblastoid cell lines. We found that HU alone induces post-replicative DNA damage in the form of DNA double-strand breaks (DSBs) in both wild-type and FA cells and a similar increase in the activation of DSBs marker ɣH2AX. HU potentiates the amount of CAs only in MMC-treated FA cells by multiple mechanisms, including (1) hindering the ɣH2AX signal, (2) impairing the translocation of ribonucleotide reductase (RNR) into the cell nucleus, and (3) promoting the activity of WIP1 phosphatase. Concomitantly, increased levels of cell death were observed in FA cell cultures. HU induces DNA damage and potentiates pre-existent damage in FA cells by preventing the translocation of the RNR component p53R2 into the nucleus and activating checkpoint recovery, thus allowing the survival of a proportion of FA cells that have adapted to DNA damage.