Data from Endogenous γ-H2AX-ATM-Chk2 Checkpoint Activation in Bloom's Syndrome Helicase–Deficient Cells Is Related to DNA Replication Arrested Forks Article Swipe
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· 2023
· Open Access
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· DOI: https://doi.org/10.1158/1541-7786.c.6543121
· OA: W4392689893
<div>Abstract<p>The Bloom syndrome helicase (BLM) is critical for genomic stability. A defect in BLM activity results in the cancer-predisposing Bloom syndrome (BS). Here, we report that BLM-deficient cell lines and primary fibroblasts display an endogenously activated DNA double-strand break checkpoint response with prominent levels of phosphorylated histone H2AX (γ-H2AX), Chk2 (p<sup>T68</sup>Chk2), and ATM (p<sup>S1981</sup>ATM) colocalizing in nuclear foci. Interestingly, the mitotic fraction of γ-H2AX foci did not seem to be higher in BLM-deficient cells, indicating that these lesions form transiently during interphase. Pulse labeling with iododeoxyuridine and immunofluorescence microscopy showed the colocalization of γ-H2AX, ATM, and Chk2 together with replication foci. Those foci costained for Rad51, indicating homologous recombination at these replication sites. We therefore analyzed replication in BS cells using a single molecule approach on combed DNA fibers. In addition to a higher frequency of replication fork barriers, BS cells displayed a reduced average fork velocity and global reduction of interorigin distances indicative of an elevated frequency of origin firing. Because BS is one of the most penetrant cancer-predisposing hereditary diseases, it is likely that the lack of BLM engages the cells in a situation similar to precancerous tissues with replication stress. To our knowledge, this is the first report of high ATM-Chk2 kinase activation and its linkage to replication defects in a BS model. (Mol Cancer Res 2007;5(7):713–24)</p></div>
