Mouse SLX4 is a tumor suppressor that stimulates the activity of the nuclease XPF-ERCC1 in DNA crosslink repair.
Bottom Line: Slx4-deficient mice develop epithelial cancers and have a contracted hematopoietic stem cell pool.The N-terminal domain of SLX4 (mini-SLX4) that only binds to XPF-ERCC1 is sufficient to confer resistance to DNA crosslinking agents.Recombinant mini-SLX4 enhances XPF-ERCC1 nuclease activity up to 100-fold, directing specificity toward DNA forks.
Affiliation: MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge, CB2 0QH, UK.Show MeSH
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Mentions: We previously characterized homozygous mice carrying the Btbd12tm1a(EUCOMM)Wtsi allele (hereafter referred to as Slx4f3). These mice have been maintained for many generations in a pure C57BL/6NTac background. Homozygous Slx4f3/f3 mice were born at sub-Mendelian ratios, were sterile, prone to developmental defects, and hematological cytopenias—these features persist in our colony following transmission of the allele through several generations. Transformed murine embryonic fibroblasts (MEFs) made from these mice were hypersensitive to DNA crosslinks and accumulated broken chromosomes (Crossan et al., 2011). These features bear striking resemblance to FA. We have now followed a cohort of Slx4f3/f3 homozygous mice for up to 2 years: most of these animals succumbed to malignancies within this time frame. The pattern of tumors was atypical, with epithelial-type cancers predominating (rectal squamous cell carcinoma and hepatocellular carcinoma) (Figures 1A–1C). Though some human FA patients develop a range of cancers, most of them have hematopoietic stem cell defects, leading to bone marrow failure (Ceccaldi et al., 2012; Garaycoechea and Patel, 2014). Our previous work showed that the blood from a small proportion of homozygous Slx4f3/f3 mice displayed reduced white blood cell and platelet numbers, prompting us to determine the frequency of hematopoietic stem and progenitor cells (HSPC) residing in the bone marrow of 8- to 12-week old mice. Flow cytometry analysis of the bone marrow for the Lineage−c-kit+Sca1+ (LKS) population shows that this is contracted in Slx4f3/f3 compared to controls (Figure 1D). Furthermore, we carried out a spleen colony forming assay in lethally irradiated recipients, using wild-type or Slx4f3/f3 bone marrow (CFU-S10). These data confirm the reduction in the frequency of HSPCs observed by flow cytometry (Figure 1E). In summary, mouse Slx4 is a tumor suppressor that also functions to preserve hematopoiesis.
Affiliation: MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge, CB2 0QH, UK.