SLX4 Knockout Cell Line (HEK 293)

Fanconi anemia (FA) is a devastating hereditary disease characterized by bone marrow failure (BMF) and acute myeloid leukemia (AML). As FA-deficient cells are hypersensitive to DNA interstrand crosslinks (ICLs), ICLs are widely assumed to be the lesions responsible for FA symptoms. Here, we show that FA-mutated cells are hypersensitive to persistent replication stress and that FA proteins play a role in the break-induced-replication (BIR)-like pathway for fork restart. Both the BIR-like pathway and ICL repair share almost identical molecular mechanisms of 53BP1-BRCA1-controlled signaling response, SLX4- and FAN1-mediated fork cleavage and POLD3-dependent DNA synthesis, suggesting that the FA pathway is intrinsically one of the BIR-like pathways. Replication stress not only triggers BMF in FA-deficient mice, but also specifically induces monosomy 7, which is associated with progression to AML in patients with FA, in FA-deficient cells.

SLX4 and XPF are two proteins involved in DNA repair, but very little is known about their potential roles in other processes of cancer cell biology. We developed original cell models with CRISPR-Cas9-mediated knock-out of SLX4 and/or XPF using five different cell lines (A549, NCI-H1703, COLO-357, HT-29 and HEK-293 T), and performed characterization with cell biology experiments including migration assays, drug sensitivity testing, cell proliferation assessment and Western blots for relevant proteins. Results showed decreased migration of all models in HT-29 cells, of XPF-deficient COLO-357 cells and of SLX4-deficient HEK-293 T cells. Modified cell models had overall increased sensitivity to cisplatin and mitomycine C, and some models showed an increased frequency of double-stranded DNA damages. One NCI-H1703 cell model showed major karyotypic modifications, and epithelial to mesenchymal transition (EMT)-related proteins were modified in several models. Finally, knocking out one or both proteins in A549 cells had not the same impact on in vivo growth in mice. These original cell models allowed us to identify new and DNA repair-unrelated cellular roles of SLX4 and XPF in cancer cell biology. Our results should be considered within work on Nucleotide Excision Repair (NER) inhibition targeting SLX, XPF or other related proteins.