Long-term persistence of X-ray-induced genomic instability in quiescent normal human diploid cells.

Ionizing radiation can induce genomic instability in the progeny of irradiated cells, as was demonstrated in various experimental systems. Most in vitro studies have utilized replicating cells, but it is not clear whether radiation-induced genomic instability persists in quiescent cells. Here we show the induction of X-ray-induced genomic instability in normal human diploid cells irradiated and maintained in a quiescent state for up to 24 months while cells were subcultured approximately once every 2-3 months. Every 12 months, a fraction of the irradiated cell population was stimulated to divide by culturing at a low density, and we found that these cells showed increased frequencies of phosphorylated ATM foci, decreased colony-forming ability, and increased frequency of chromosomal aberrations. No significant increases in ROS levels were detected in long-term cultured cells. These results suggest that there are ROS-independent mechanism(s) induced by radiation, which can generate persistent delayed effects in quiescent cells, and could ultimately contribute to carcinogenesis

DNA double-strand break induction in Ku80-deficient CHO cells following Boron Neutron Capture Reaction

<p>Abstract</p> <p>Background</p> <p>Boron neutron capture reaction (BNCR) is based on irradiation of tumors after accumulation of boron compound. ¹⁰B captures neutrons and produces an alpha (⁴He) particle and a recoiled lithium nucleus (⁷Li). These particles have the characteristics of high linear energy transfer (LET) radiation and have marked biological effects. The purpose of this study is to verify that BNCR will increase cell killing and slow disappearance of repair protein-related foci to a greater extent in DNA repair-deficient cells than in wild-type cells.</p> <p>Methods</p> <p>Chinese hamster ovary (CHO-K1) cells and a DNA double-strand break (DSB) repair deficient mutant derivative, xrs-5 (Ku80 deficient CHO mutant cells), were irradiated by thermal neutrons. The quantity of DNA-DSBs following BNCR was evaluated by measuring the phosphorylation of histone protein H2AX (gamma-H2AX) and 53BP1 foci using immunofluorescence intensity.</p> <p>Results</p> <p>Two hours after neutron irradiation, the number of gamma-H2AX and 53BP1 foci in the CHO-K1 cells was decreased to 36.5-42.8% of the levels seen 30 min after irradiation. In contrast, two hours after irradiation, foci levels in the xrs-5 cells were 58.4-69.5% of those observed 30 min after irradiation. The number of gamma-H2AX foci in xrs-5 cells at 60-120 min after BNCT correlated with the cell killing effect of BNCR. However, in CHO-K1 cells, the RBE (relative biological effectiveness) estimated by the number of foci following BNCR was increased depending on the repair time and was not always correlated with the RBE of cytotoxicity.</p> <p>Conclusion</p> <p>Mutant xrs-5 cells show extreme sensitivity to ionizing radiation, because xrs-5 cells lack functional Ku-protein. Our results suggest that the DNA-DSBs induced by BNCR were not well repaired in the Ku80 deficient cells. The RBE following BNCR of radio-sensitive mutant cells was not increased but was lower than that of radio-resistant cells. These results suggest that gamma-ray resistant cells have an advantage over gamma-ray sensitive cells in BNCR.</p

Protective roles of ascorbic acid in oxidative stress induced by depletion of superoxide dismutase in vertebrate cells.

Superoxide dismutases (SODs) are antioxidant proteins that convert superoxide to hydrogen peroxide. In vertebrate cells, SOD1 is mainly present in the cytoplasm, with small levels also found in the nucleus and mitochondrial intermembrane space, and SOD2 is present in the mitochondrial matrix. Previously, the authors conditionally disrupted the SOD1 or SOD2 gene in DT40 cells and found that depletion of SOD1 caused lethality, while depletion of SOD2 led to growth retardation. The observations from previous work showed that the lethality observed in SOD1-depleted cells was completely rescued by ascorbic acid. Ascorbic acid is a water-soluble antioxidant present in biological fluids; however, the exact target for its antioxidant effects is not known. In this study, the authors demonstrated that ascorbic acid offset growth defects observed in SOD2-depleted cells and also lowered mitochondrial superoxide to physiological levels in both SOD1- or SOD2-depleted cells. Moreover, depletion of SOD1 or SOD2 resulted in the accumulation of intracellular oxidative stress, and this increased oxidative stress was reduced by ascorbic acid. Taken together, this study suggests that ascorbic acid can be applied as a nontoxic antioxidant that mimics the functions of cytoplasmic and mitochondrial SODs

Adverse effect of mild temperature hyperthermia combined with hexamethylenetetramine compared to its effect combined with tirapazamine in the treatment of solid tumors

This study aimed to assess the effect on solid tumors of mild temperature hyperthermia (MTH) combined with hexamethylenetetramine (HMTA) or tirapazamine (TPZ). Squamous cell carcinoma (SCC VII) tumor-bearing mice were continuously administered 5-bromo-2′-deoxyuridine (BrdU) to label intratumor proliferating (P) cells. Mice received HMTA or TPZ through intraperitoneal single or subcutaneous continuous administration, with or without MTH (40°C, 60 min), followed or not by γ-ray irradiation or cisplatin treatment. After HMTA or TPZ administration without γ-ray irradiation or cisplatin treatment, immediately after γ-ray irradiation, or 1 h after cisplatin treatment, the response of quiescent (Q) cells was assessed in terms of micronucleus frequency using immunofluorescence staining for BrdU. The response of the total (P + Q) tumor cells was determined based on a comparison with non-BrdU-treated tumors. Without MTH, HMTA and TPZ had a nearly equal radiosensitizing and cisplatin sensitivity-enhancing effect on both total and Q cells. With MTH, radio- and cisplatin-sensitizing effects by HMTA were reduced, particularly in the Q cells. In contrast, the enhancing effects of TPZ were increased, particularly in the Q cells. Continuous administration of HMTA and TPZ resulted in higher radio- and cisplatin-sensitizing effects than intraperitoneal single administration. In terms of tumor cytotoxicity as a whole, including Q cells, the administration of γ-ray irradiation or cisplatin treatment combined with continuous HMTA administration is promising, taking into account the clinical use of HMTA. However, MTH should not be combined with HMTA administration

Usefulness of hexamethylenetetramine in combination with chemotherapy using free and pegylated liposomal doxorubicin in vivo, referring to the effect on quiescent cells

SCC VII tumor-bearing mice were continuously given 5-bromo-2'-deoxyuridine (BrdU) to label all intratumor proliferating (P) cells. They received hexamethylenetetramine (HMTA) either once intraperitoneally or continuously subcutaneously together with chemotherapy using intraperitoneally administered free doxorubicin (DXR) or intravenously injected pegylated liposomal doxorubicin (PLD). One hour after the free DXR loading or 24 h after the PLD loading, the response of intratumor quiescent (Q) cells was assessed in terms of the micronucleus frequency using immunofluorescence staining for BrdU. The response of the total (P + Q) tumor cell population was determined from the tumors not treated with BrdU. Encapsulation of DXR into pegylated liposomes significantly enhanced cytotoxicity, especially in Q cells. HMTA, especially when administered continuously, efficiently increased the sensitivity to DXR, particularly in Q cells. The increase in sensitivity on the continuous rather than single administration of HMTA was a little clearer in the total cell population than in Q cells. DXR's encapsulation into pegylated liposomes and combination with HMTA, particularly when administered continuously, apparently reduced the difference in sensitivity to free DXR between the total and Q cell populations. In terms of the tumor cell-killing effect as a whole, including Q cells, the encapsulation of DXR into pegylated liposomes and combination with HMTA, particularly through continuous administration, are very promising, taking into account that HMTA has been used clinically

ATR阻害は非相同末端結合および相同組換え修復と非依存的に5-FUを増感する

The anticancer agent 5-fluorouracil (5-FU) is cytotoxic and often used to treat various cancers. 5-FU is thought to inhibit the enzyme thymidylate synthase, which plays a role in nucleotide synthesis and has been found to induce single- and double-strand DNA breaks. ATR Ser/Thr kinase (ATR) is a principal kinase in the DNA damage response and is activated in response to UV- and chemotherapeutic drug-induced DNA replication stress, but its role in cellular responses to 5-FU is unclear. In this study, we examined the effect of ATR inhibition on 5-FU sensitivity of mammalian cells. Using immunoblotting, we found that 5-FU treatment dose-dependently induced the phosphorylation of ATR at the autophosphorylation site Thr-1989 and thereby activated its kinase. Administration of 5-FU with a specific ATR inhibitor remarkably decreased cell survival, compared with 5-FU treatment combined with other major DNA repair kinase inhibitors. Of note, the ATR inhibition enhanced induction of DNA double-strand breaks and apoptosis in 5-FU-treated cells. Using gene expression analysis, we found that 5-FU induced the activation of the intra-S cell-cycle checkpoint. Cells lacking BRCA2 were sensitive to 5-FU in the presence of ATR inhibitor. Moreover, ATR inhibition enhanced the efficacy of the 5-FU treatment, independently of the nonhomologous end-joining and homologous recombination repair pathways. These findings suggest that ATR could be a potential therapeutic target in 5-FU-based chemotherapy.博士（医学）・甲第791号・令和3年3月15日© 2020 Ito et al. Published under exclusive license by The American Society for Biochemistry and Molecular Biology, Inc.This is an Open Access article under the CC BY license(https://creativecommons.org/licenses/by/4.0/)

27ヒドロキシコレステロールはエストロゲン受容体を介してヒトSLC22A12の発現を制御する

The excretion and reabsorption of uric acid both to and from urine are tightly regulated by uric acid transporters. Metabolic syndrome conditions, such as obesity, hypercholesterolemia, and insulin resistance, are believed to regulate the expression of uric acid transporters and decrease the excretion of uric acid. However, the mechanisms driving cholesterol impacts on uric acid transporters have been unknown. Here, we show that cholesterol metabolite 27-hydroxycholesterol (27HC) upregulates the uric acid reabsorption transporter URAT1 encoded by SLC22A12 via estrogen receptors (ER). Transcriptional motif analysis showed that the SLC22A12 gene promoter has more estrogen response elements (EREs) than other uric acid reabsorption transporters such as SLC22A11 and SLC22A13, and 27HC-activated SLC22A12 gene promoter via ER through EREs. Furthermore, 27HC increased SLC22A12 gene expression in human kidney organoids. Our results suggest that in hypercholesterolemic conditions, elevated levels of 27HC derived from cholesterol induce URAT1/SLC22A12 expression to increase uric acid reabsorption, and thereby, could increase serum uric acid levels.博士（医学）・甲第772号・令和3年3月15日© 2020 The Authors. The FASEB Journal published by Wiley Periodicals LLC on behalf of Federation of American Societies for Experimental Biology. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License(https://creativecommons.org/licenses/by-nc/4.0/), which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes

Dysregulation of Gene Expression in the Artificial Human Trisomy Cells of Chromosome 8 Associated with Transformed Cell Phenotypes

A change in chromosome number, known as aneuploidy, is a common characteristic of cancer. Aneuploidy disrupts gene expression in human cancer cells and immortalized human epithelial cells, but not in normal human cells. However, the relationship between aneuploidy and cancer remains unclear. To study the effects of aneuploidy in normal human cells, we generated artificial cells of human primary fibroblast having three chromosome 8 (trisomy 8 cells) by using microcell-mediated chromosome transfer technique. In addition to decreased proliferation, the trisomy 8 cells lost contact inhibition and reproliferated after exhibiting senescence-like characteristics that are typical of transformed cells. Furthermore, the trisomy 8 cells exhibited chromosome instability, and the overall gene expression profile based on microarray analyses was significantly different from that of diploid human primary fibroblasts. Our data suggest that aneuploidy, even a single chromosome gain, can be introduced into normal human cells and causes, in some cases, a partial cancer phenotype due to a disruption in overall gene expression