Rare Variants in the DNA Repair Pathway and the Risk of Colorectal Cancer

High-throughput screening of the Saccharomyces cerevisiae genome for 2-amino-3-methylimidazo [4,5-f] quinoline resistance identifies colon cancer-associated genes

Heterocyclic aromatic amines (HAAs) are potent carcinogenic agents found in charred meats and cigarette smoke. However, few eukaryotic resistance genes have been identified. We used Saccharomyces cerevisiae (budding yeast) to identify genes that confer resistance to 2-amino-3-methylimidazo[4,5-f] quinoline (IQ). CYP1A2 and NAT2 activate IQ to become a mutagenic nitrenium compound. Deletion libraries expressing human CYP1A2 and NAT2 or no human genes were exposed to either 400 or 800 µM IQ for 5 or 10 generations. DNA barcodes were sequenced using the Illumina HiSeq 2500 platform and statistical significance was determined for exactly matched barcodes. We identified 424 ORFs, including 337 genes of known function, in duplicate screens of the "humanized" collection for IQ resistance; resistance was further validated for a select group of 51 genes by growth curves, competitive growth, or trypan blue assays. Screens of the library not expressing human genes identified 143 ORFs conferring resistance to IQ per se. Ribosomal protein and protein modification genes were identified as IQ resistance genes in both the original and "humanized" libraries, while nitrogen metabolism, DNA repair, and growth control genes were also prominent in the "humanized" library. Protein complexes identified included the casein kinase 2 (CK2) and histone chaperone (HIR) complex. Among DNA Repair and checkpoint genes, we identified those that function in postreplication repair (RAD18, UBC13, REV7), base excision repair (NTG1), and checkpoint signaling (CHK1, PSY2). These studies underscore the role of ribosomal protein genes in conferring IQ resistance, and illuminate DNA repair pathways for conferring resistance to activated IQ.

Identification of ERCC8 as a novel cisplatin-resistant gene in esophageal cancer based on genome-scale CRISPR/Cas9 screening

Esophageal cancer (ESCA) is one of the most common malignant tumors of the digestive system worldwide. As a first-line drug for chemotherapy, cisplatin resistance is the major obstacle in the successful treatment of esophageal cancer. Previous studies largely failed to identify the key genes associated with cisplatin resistance. Hence, the aim of this study was to screen the cisplatin resistance-related genes of esophageal cancer using CRISPR/Cas9 gene-editing technology and Brunello iBar library. Of note, we identified ERCC8 as a novel cisplatin-resistant gene by high-throughput sequencing and cisplatin resistance assays. Based on KEGG and GO analysis, we hypothesized that the mechanism of ERCC8 involvement in cisplatin resistance is through binding to damaged DNA to perform nucleotide excision repair, contributing to the restoration of basic DNA functions and cellular life activities in ESCA. In addition, Cell proliferation and wound healing assay confirmed that ERCC8 had little effect on the proliferation and migration of esophageal cancer cells in vitro. Survival analysis showed that ERCC8 expression was not associated with OS, DSS, or FPI in patients with ESCA. Immuno-infiltration analysis indicated that increased ERCC8 expression is associated with NK cells, macrophages, T helper cells, Th1 cells, and Th2 cells. Collectively, ERCC8 may serve as a new biomarker for predicting cisplatin resistance and have the prospect of becoming an effective target for the clinical treatment of cisplatin resistance in ESCA.