Nrf2 overexpression increases risk of high tumor mutation burden in acute myeloid leukemia by inhibiting MSH2

Nuclear factor erythroid 2-related factor 2 (Nrf2, also called NFE2L2) plays an important role in cancer chemoresistance. However, little is known about the role of Nrf2 in tumor mutation burden and the effect of Nrf2 in modulating DNA mismatch repair (MMR) gene in acute myeloid leukemia (AML). Here we show that Nrf2 expression is associated with tumor mutation burden in AML. Patients with Nrf2 overexpression had a higher frequency of gene mutation and drug resistance. Nrf2 overexpression protected the AML cells from apoptosis induced by cytarabine in vitro and increased the risk of drug resistance associated with a gene mutation in vivo. Furthermore, Nrf2 overexpression inhibited MutS Homolog 2 (MSH2) protein expression, which caused DNA MMR deficiency. Mechanistically, the inhibition of MSH2 by Nrf2 was in a ROS-independent manner. Further studies showed that an increased activation of JNK/c-Jun signaling in Nrf2 overexpression cells inhibited the expression of the MSH2 protein. Our findings provide evidence that high Nrf2 expression can induce gene instability-dependent drug resistance in AML. This study demonstrates the reason why the high Nrf2 expression leads to the increase of gene mutation frequency in AML, and provides a new strategy for clinical practice.

Nrf2 overexpression increases risk of high tumor mutation burden in acute myeloid leukemia through inhibiting MSH2

Background: Nuclear factor erythroid 2-related factor 2 (Nrf2, also called NFE2L2) has been shown to play a pivotal role in preventing cancer cells from being affected by chemotherapy. Gene mutation is a crucial reason of chemotherapy-resistance in acute myeloid leukemia (AML). However, the relationship between Nrf2 and tumor mutation burden and its mechanism in regulating chemotherapy-resistance remains unclear. Methods: The whole-exome sequencing analysis were used to measure tumor mutation. RNA sequencing, Oncomine, qRT-PCR, Western blotting and immunocytochemistry were employed to detect differences in genes and proteins. The KEGG pathway enrichment analysis and GeneMANIN were performed pathway analysis. Functional assays, such as annexin V/PI, Hoechst33342 staining and DCFH were performed to examine the apoptosis and reactive oxygen species (ROS) of AML cells in vitro. Subcutaneous xenograft model was established to investigate in vivo growth. Results: Nrf2 expression was associated with tumor mutation burden in AML. Patients with Nrf2 overexpression had higher frequency of gene mutation and drug resistance. Nrf2 overexpression protected the AML cells from apoptosis induced by cytarabine in vitro and increased the risk of gene mutant drug resistance in vivo. Furthermore, Nrf2 overexpression inhibited MSH2 protein expression, which caused DNA mismatch repair (MMR) deficiency. Mechanistically, the inhibition of MSH2 by Nrf2 was in a ROS-independent manner. Further studies showed that an increased activation of JNK/c-Jun signaling in Nrf2 overexpression cells, which inhibited the expression of MSH2 protein. Conclusions: Our findings provided evidence that high Nrf2 expression inhibited MSH2 expression, caused MMR deficiency and increased the tumor mutation burden, which can induce gene instability-dependent drug resistance in AML. This study demonstrates the reason why the high Nrf2 expression leads to the increase of gene mutation frequency in AML, and provides a new strategy for clinical practice.

Low MSH2 protein levels identify muscle-invasive bladder cancer resistant to cisplatin

BackgroundThe response to first-line, platinum-based treatment of muscle-invasive bladder cancer has not improved in three decades.ObjectiveThe objective of this study is to identify genes that predict cisplatin resistance in bladder cancer.DesignWe performed a whole-genome, CRISPR-based screen in a bladder cancer cell line treated with cisplatin to identify genes that mediate response to cisplatin. Targeted validation was performed in vitro across two bladder cancer cell lines. The top gene candidate was validated in a publicly available bladder cancer dataset containing 340 bladder cancer patients with treatment, protein, and survival information.Results and limitationsThe cisplatin resistance screen suggested the mismatch repair pathway through the loss of MSH2 and MLH1 contribute to cisplatin resistance. Bladder cancer cells depleted of MSH2 are resistant to cisplatin in vitro, in part due to a reduction in apoptosis. These cells maintain sensitivity to the cisplatin-analog, oxaliplatin. Bladder tumors with low protein levels of MSH2 have poorer overall survival when treated with cisplatin- or carboplatin-based therapy.ConclusionsWe generated in vitro and clinical support that bladder cancer cell lines and tumors with low levels of MSH2 are more resistant to cisplatin-based therapy. Further studies are warranted to determine the ability of MSH2 protein levels to serve as a prospective biomarker of chemotherapy response in bladder cancer.Patient summaryWe report the first evidence that the protein level of MSH2 may contribute to chemotherapy resistance observed in bladder cancer. MSH2 levels has the potential to serve as a biomarker of treatment response.

MutS-Homolog2silencing generates tetraploid meiocytes in tomato (Solanum lycopersicum)

SUMMARYMSH2 is the core protein of MutS-homolog family involved in recognition and repair of the errors in the DNA. While other members of MutS-homolog family reportedly regulate mitochondrial stability, meiosis, and fertility, MSH2 is believed to participate mainly in mismatch repair. The search for polymorphism inMSH2sequence in tomato accessions revealed both synonymous and nonsynonymous SNPs; however, SIFT algorithm predicted that none of the SNPs influenced MSH2 protein function. The silencing ofMSH2gene expression by RNAi led to phenotypic abnormalities in highly-silenced lines, particularly in the stamens with highly reduced pollen formation.MSH2silencing exacerbated formation of UV-B induced thymine dimers and blocked light-induced repair of the dimers. TheMSH2silencing also affected the progression of male meiosis to a varying degree with either halt of meiosis at zygotene stage or formation of diploid tetrads. The immunostaining of male meiocytes with centromere localized CENPC (Centromere protein C) protein antibody showed the presence of 48 univalent along with 24 bivalent chromosomes suggesting abnormal tetraploid meiosis. The mitotic cells of root tips of silenced lines showed diploid nuclei but lacked intervening cell plates leading to cells with syncytial nuclei. Thus we speculate that tetraploid pollen mother cells may have arisen due to the fusion of syncytial nuclei before the onset of meiosis. It is likely that in addition to Mismatch repair (MMR), MSH2 may have an additional role in regulating ploidy stability.

MISMATCH REPAIR AND REPAIR OF INSERTION/DELETION LOOPS IN EUKARYOTIC DNA

The mismatch repair (MMR) system detects non-Watson – Crick base pairs as well as the defects, appearing in course of DNA replication, and helps to eliminate them by catalyzing the excision of the defect-containing region of daughter DNA and its error-free resynthesis. Thus, MMR remarkably improves the fidelity of replication. After separation, both strands contain non-repairable damages and the mismatches may generate DNA mutation in 50 % of cell progeny after next replication. MMR dysfunction causes surge of mutation rate, abnormal recombination, and cancer in humans and animals. Therefore, the main MMR efficiency parameter is mismatch correction before the next replication cycle. Mismatch detection is made by the MSH2 protein, which forms a heterodimer with either MSH6 or MSH3 (Mut S), depending on the damage (MSH6 is needed for the amendment of single base mispairs, whereas both MSH3 and MSH6 can correct IDLs). A heterodimer of MLH1 and PMS2 (Mut L) controls the interaction between the mismatch-detecting complex of proteins and other proteins essential for MMR, including exonuclease 1, helicase, nuclear antigen of proliferating cells, single-stranded DNA-binding protein and DNA polymerases δ and ε. MLH1 can form a heterodimer with two additional proteins – MLH3 and PMS1. PMS2 is required for the correction of single based mismatches, and PMS2 and MLH3 contribute to the correction of IDLs. The Nobel Prize in Chemistry 2015 was awarded for the studies of DNA repair, i.a. MMR.