Environmental stress induces trinucleotide repeat mutagenesis in human cells

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 112; no. 12; pp. 3764 - 3769
• Main Authors: Chatterjee, Nimrat, Lin, Yunfu, Santillan, Beatriz A., Yotnda, Patricia, Wilson, John H.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 24.03.2015; National Acad Sciences
• Subjects: Biological Sciences; Cells; Cold Temperature; Deoxyribonucleic acid; DNA; DNA - chemistry; DNA - genetics; DNA Repair; DNA Replication; Gene Regulatory Networks; Genomic Instability; Genotype & phenotype; Green Fluorescent Proteins - chemistry; HEK293 Cells; Hot Temperature; Humans; Microsatellite Repeats; Mutagenesis; Mutation; Oxidative Stress; Phenotype; Stress response; Stress, Physiological; Trinucleotide Repeat Expansion; Trinucleotide Repeats; stress-induced mutagenesis; DNA rereplication; trinucleotide repeats; human cells; microsatellite repeats
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1421917112

The dynamic mutability of microsatellite repeats is implicated in the modification of gene function and disease phenotype. Studies of the enhanced instability of long trinucleotide repeats (TNRs)—the cause of multiple human diseases—have revealed a remarkable complexity of mutagenic mechanisms. Here, we show that cold, heat, hypoxic, and oxidative stresses induce mutagenesis of a long CAG repeat tract in human cells. We show that stress-response factors mediate the stress-induced mutagenesis (SIM) of CAG repeats. We show further that SIM of CAG repeats does not involve mismatch repair, nucleotide excision repair, or transcription, processes that are known to promote TNR mutagenesis in other pathways of instability. Instead, we find that these stresses stimulate DNA rereplication, increasing the proportion of cells with >4 C-value (C) DNA content. Knockdown of the replication origin-licensing factor CDT1 eliminates both stress-induced rereplication and CAG repeat mutagenesis. In addition, direct induction of rereplication in the absence of stress also increases the proportion of cells with >4C DNA content and promotes repeat mutagenesis. Thus, environmental stress triggers a unique pathway for TNR mutagenesis that likely is mediated by DNA rereplication. This pathway may impact normal cells as they encounter stresses in their environment or during development or abnormal cells as they evolve metastatic potential. Significance Environmental stress induces complex cellular responses that improve the odds of survival. One effect of the cellular stress response is to relax the fidelity of DNA repair, with the counterintuitive strategy of increasing mutagenesis to improve fitness. Because microsatellite repeats, which are intrinsically highly mutable, serve as tuning knobs for evolutionary change, we asked whether environmental stress increased their mutagenesis. We found that cold, heat, hypoxic, and oxidative stresses induce trinucleotide repeat (TNR) mutagenesis, in a way that depends on stress response factors and apparently involves DNA rereplication. Because TNRs are overrepresented in gene-regulatory proteins, stress-induced TNR mutagenesis may provide a path for the environment to subtly alter gene regulatory networks—with attendant changes in cell behavior—during development, disease, and evolution.