DNA polymerase delta Exo domain stabilizes mononucleotide microsatellites in human cells.

In prokaryotes and yeasts, DNA polymerase proofreading (PPR) and DNA mismatch repair (MMR) cooperatively counteracts replication errors leading to repeat sequence destabilization (i.e. insertions/deletions of repeat units). However, PPR has not thus far been regarded as a mechanism stabilizing repeat sequences in higher eukaryotic cells. In a human cancer cell line, DLD-1, which carries mutations in both MSH6 and the Exo domain of POLD1, we previously observed that mononucleotide microsatellites were markedly destabilized whereas being stable in the simple MMR-defective backgrounds. In this study, we introduced the Exo domain mutation found in DLD-1 cells into MSH2-null HeLa cell clones, using CRISPR/Cas9 system. In the established Exo-/MMR-mutated HeLa clones, mononucleotide repeat sequences were remarkably destabilized as in DLD-1 cells. In contrast, dinucleotide microsatellites were readily destabilized in the parental MMR-deficient backgrounds, and the instability was not notably increased in the genome-edited HeLa clones. Here, we show an involvement of the Exo domain functions of DNA polymerase delta in mononucleotide repeat stabilization in human cells, which also suggests a possible role division between DNA polymerase and MMR in repeat maintenance in the human genome.

Ablation of Selenbp1 Alters Lipid Metabolism via the Pparα Pathway in Mouse Kidney.

Selenium-binding protein 1 (Selenbp1) is a 2,3,7,8-tetrechlorodibenzo-p-dioxin inducible protein whose function is yet to be comprehensively elucidated. As the highly homologous isoform, Selenbp2, is expressed at low levels in the kidney, it is worthwhile comparing wild-type C57BL mice and Selenbp1-deficient mice under dioxin-free conditions. Accordingly, we conducted a mouse metabolomics analysis under non-dioxin-treated conditions. DNA microarray analysis was performed based on observed changes in lipid metabolism-related factors. The results showed fluctuations in the expression of numerous genes. Real-time RT-PCR confirmed the decreased expression levels of the cytochrome P450 4a (Cyp4a) subfamily, known to be involved in fatty acid ω- and ω-1 hydroxylation. Furthermore, peroxisome proliferator-activated receptor-α (Pparα) and retinoid-X-receptor-α (Rxrα), which form a heterodimer with Pparα to promote gene expression, were simultaneously reduced. This indicated that reduced Cyp4a expression was mediated via decreased Pparα and Rxrα. In line with this finding, increased levels of leukotrienes and prostaglandins were detected. Conversely, decreased hydrogen peroxide levels and reduced superoxide dismutase (SOD) activity supported the suppression of the renal expression of Sod1 and Sod2 in Selenbp1-deficient mice. Therefore, we infer that ablation of Selenbp1 elicits oxidative stress caused by increased levels of superoxide anions, which alters lipid metabolism via the Pparα pathway.

Elevation of endocannabinoids in the brain by synthetic cannabinoid JWH-018: mechanism and effect on learning and memory.

The impairment of learning and memory is a well-documented effect of both natural and synthetic cannabinoids. In the present study, we aimed to investigate the effect of acute administration of JWH-018, a synthetic cannabinoid, on the hippocampal metabolome to assess biochemical changes in vivo. JWH-018 elevated levels of the endocannabinoids, anandamide (AEA) and 2-arachidonoylglycerol (2-AG). The increase of endocannabinoid levels in response to JWH-018 could be inhibited by co-administration of AM251, a CB1 receptor antagonist. Biochemical analyses revealed that this was the result of suppression of two hydrolases involved in endocannabinoid degradation (fatty acid amide hydrolase [FAAH] and monoacylglycerol lipase [MAGL]). Additionally, we showed that JWH-018 causes a reduction in the levels of brain-derived neurotrophic factor (BDNF), which is known to modulate synaptic plasticity and adaptive processes underlying learning and memory. The decrease of BDNF following JWH-018 treatment was also rescued by co-administration of AM251. As both endocannabinoids and BDNF have been shown to modulate learning and memory in the hippocampus, the alteration of their levels in response to JWH-018 may explain the contribution of synthetic cannabinoids to impairment of memory.