Abstract
Hexavalent chromium [Cr(VI)] damages DNA and causes cancer, but it is unclear which DNA damage responses (DDRs) most critically protect cells from chromate toxicity. Here, genome-wide quantitative functional profiling, DDR measurements and genetic interaction assays in Schizosaccharomyces pombe reveal a chromate toxicogenomic profile that closely resembles the cancer chemotherapeutic drug camptothecin (CPT), which traps Topoisomerase 1 (Top1)-DNA covalent complex (Top1cc) at the 3’ end of single-stand breaks (SSBs), resulting in replication fork collapse. ATR/Rad3-dependent checkpoints that detect stalled and collapsed replication forks are crucial in Cr(VI)-treated cells, as is Mus81-dependent sister chromatid recombination (SCR) that repairs single-ended double-strand breaks (seDSBs) at broken replication forks. Surprisingly, chromate resistance does not require base excision repair (BER) or interstrand crosslink (ICL) repair, nor does co-elimination of XPA-dependent nucleotide excision repair (NER) and Rad18-mediated post-replication repair (PRR) confer chromate sensitivity in fission yeast. However, co-elimination of Tdp1 tyrosyl-DNA phosphodiesterase and Rad16-Swi10 (XPF-ERCC1) NER endonuclease synergistically enhances chromate toxicity in top1Δ cells. Pnk1 polynucleotide kinase phosphatase (PNKP), which restores 3’-hydroxyl ends to SSBs processed by Tdp1, is also critical for chromate resistance. Loss of Tdp1 ameliorates pnk1Δ chromate sensitivity while enhancing the requirement for Mus81. Thus, Tdp1 and PNKP, which prevent neurodegeneration in humans, repair an important class of Cr-induced SSBs that collapse replication forks.
Highlights
Chromium, with its unique combination of hardness, corrosion-resistance and lustrous appearance, is an exceptionally important industrial metal [1]
The resulting ‘toxicogenomic’ profile of chromate closely matches camptothecin, a natural product representing a class of chemotherapeutic drugs that cause replication fork collapse by poisoning Topoisomerase 1 (Top1), which relaxes supercoiled DNA by creating and resealing single-strand breaks (SSBs)
Parallel mutant phenotyping by barcode sequencing (Bar-seq) [26, 27] was used to identify haploid deletion mutants that are sensitive to 10 μM potassium dichromate (K2Cr2O7), which slightly inhibits the growth of wild type
Summary
With its unique combination of hardness, corrosion-resistance and lustrous appearance, is an exceptionally important industrial metal [1]. Occupational exposures have provided compelling evidence that Cr(VI) is a respiratory carcinogen [2], and mouse studies established that Cr(VI) in drinking water causes tumors in the alimentary canal [3] For these reasons, chronic exposure to Cr(VI) through groundwater contamination is a significant health concern [4]. Cr(VI) does not interact with DNA, but intracellular reduction traps protein and DNA-reactive chromate products [Cr (V), Cr(IV) and Cr(III)] inside cells. These chromates may cause DNA damage through CrDNA adduct formation, DNA interstrand crosslinking or DNA-protein crosslinks (DPCs) [6, 9,10,11]. The growth competition assay revealed that Chk is required for chromium resistance (Fig 2C), which is consistent with functional profiling data showing that crb2Δ cells are Cr-sensitive
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
