ABSTRACT
DNA interstrand cross-links (ICLs) represent a physical barrier to the progression of cellular machinery involved in DNA metabolism. Thus, this type of adduct represents a serious threat to genomic stability and as such, several DNA repair pathways have evolved in both higher and lower eukaryotes to identify this type of damage and restore the integrity of the genetic material. Human cells possess a specialized ICL-repair system, the Fanconi anemia (FA) pathway. Conversely yeasts rely on the concerted action of several DNA repair systems. Recent work in higher eukaryotes identified and characterized a novel conserved FA component, FAN1 (Fanconi anemia-associated nuclease 1, or FANCD2/FANCI-associated nuclease 1). In this study, we characterize Fan1 in the yeast Schizosaccharomyces pombe. Using standard genetics, we demonstrate that Fan1 is a key component of a previously unidentified ICL-resolution pathway. Using high-throughput synthetic genetic arrays, we also demonstrate the existence of a third pathway of ICL repair, dependent on the SUMO E3 ligase Pli1. Finally, using sequence-threaded homology models, we predict and validate key residues essential for Fan1 activity in ICL repair.
Subject(s)
DNA Repair , Esterases/metabolism , Schizosaccharomyces pombe Proteins/metabolism , Schizosaccharomyces/genetics , Ubiquitin-Protein Ligases/metabolism , DNA Damage , Endodeoxyribonucleases/metabolism , Esterases/chemistry , Esterases/genetics , Evolution, Molecular , High-Throughput Screening Assays , Ligases , Models, Molecular , Mutation Rate , Protein Structure, Tertiary , Recombination, Genetic , Schizosaccharomyces/metabolism , Schizosaccharomyces pombe Proteins/chemistry , Schizosaccharomyces pombe Proteins/genetics , Sequence Homology , Signal Transduction/genetics , Ubiquitin-Protein Ligases/geneticsABSTRACT
Excision repair cross-complementation group 1 (ERCC1) is a DNA repair enzyme that is frequently defective in non-small cell lung cancer (NSCLC). Although low ERCC1 expression correlates with platinum sensitivity, the clinical effectiveness of platinum therapy is limited, highlighting the need for alternative treatment strategies. To discover new mechanism-based therapeutic strategies for ERCC1-defective tumours, we performed high-throughput drug screens in an isogenic NSCLC model of ERCC1 deficiency and dissected the mechanism underlying ERCC1-selective effects by studying molecular biomarkers of tumour cell response. The high-throughput screens identified multiple clinical poly (ADP-ribose) polymerase 1 and 2 (PARP1/2) inhibitors, such as olaparib (AZD-2281), niraparib (MK-4827) and BMN 673, as being selective for ERCC1 deficiency. We observed that ERCC1-deficient cells displayed a significant delay in double-strand break repair associated with a profound and prolonged G2/M arrest following PARP1/2 inhibitor treatment. Importantly, we found that ERCC1 isoform 202, which has recently been shown to mediate platinum sensitivity, also modulated PARP1/2 sensitivity. A PARP1/2 inhibitor-synthetic lethal siRNA screen revealed that ERCC1 deficiency was epistatic with homologous recombination deficiency. However, ERCC1-deficient cells did not display a defect in RAD51 foci formation, suggesting that ERCC1 might be required to process PARP1/2 inhibitor-induced DNA lesions before DNA strand invasion. PARP1 silencing restored PARP1/2 inhibitor resistance in ERCC1-deficient cells but had no effect in ERCC1-proficient cells, supporting the hypothesis that PARP1 might be required for the ERCC1 selectivity of PARP1/2 inhibitors. This study suggests that PARP1/2 inhibitors as a monotherapy could represent a novel therapeutic strategy for NSCLC patients with ERCC1-deficient tumours.