Subjects: Biology >> Biophysics >> Biology submitted time 2016-05-12
Abstract: Rad9, Rad1 and Hus1 are essential genes conserved from yeast to humans. They form a heterotrimer complex (9-1-1 complex) that participates in the cell cycle checkpoint activation and DNA damage repair in eukaryotic cells. Rad9, Rad1 and Hus1 deficient cells are hypersensitive to ionizing radiation and mouse cells deleted for anyone of the three genes are highly sensitive to the killing by gamma rays. We propose that ionizing radiation-induced transcription of these genes is a mechanism by which cells respond to radiation-induced damage. In this study we used quantitative real-time RT-PCR(qPCR) to analyze the mRNA levels of Rad9, Rad1 and Hus1 in various tissues isolated from mice that were either mock irradiated or exposed to 10 Gy gamma radiation. Our results indicated that the mRNA levels of Rad9, Rad1 and Hus1 genes were very different among these tissues, and we found high natural levels of mRNA in the spleen, lung, ovary and testis of mice before exposure to radiation. The mRNA levels of the three genes were well correlated across these tissues, being high, medium or low in each of the tissues simultaneously. The mRNA levels of the three genes were analyzed at 2, 6, 12, 24 and 48 h after irradiation. In most tissues Rad9 was strongly induced at 2 and 12 h time points and Hus1 was strongly induced at 2, 12 and 48 h time points, but Rad1 was minimally induced in most of the tissues with the exception of slightly higher levels in the heart and lung tissues at the 48 h time point. These results suggest that the regulation mechanisms for the mRNA levels of the three genes in response to ionizing radiation are complex and not well orchestrated. We also detected the induction of Rad9 and Hus1 proteins in the heart and liver of the animals after irradiation, and found that Rad9 protein levels were highly induced in both the heart and liver, while the Hus1 protein levels were significantly induced only in the liver, suggesting that Rad9 and Hus1 protein levels are not regulated in a coordinated manner in response to irradiation. We then went on to measure the mRNA levels of the three genes and the Rad9 and Hus1 protein levels in the mouse liver cell line (NCTC 1469) in response to irradiation in vitro. All three genes in the cultured cells were minimally induced at mRNA level, obviously different from the highly dynamic induction in liver. Rad9 and Hus1 were significantly induced at the protein level, but the induced Rad9 protein levels were higher than the Hus1 levels. Taken together, the good correlation of the mRNA levels of Rad9, Hus1 and Rad1 genes across different tissues isolated from the animals that were mock irradiated and the lack of correlation in mRNA as well as protein levels after irradiation suggest that the 9-1-1 complex has evolved to play various physiological roles in tissues rather than dealing with high doses of gamma radiation or other genotoxic agents. (C) 2015 by Radiation Research Society
Peer Review Status:Awaiting Review
Subjects: Biology >> Biophysics >> Biology submitted time 2016-05-12
Abstract: Previously reported studies have demonstrated the involvement of p21(Waf1/CIP1) in radiation-induced bystander effects (RIBE). Mouse embryonic fibroblasts (MEFs) lacking Hus1 fail to proliferate in vitro, but inactivation of p21 allows for the continued growth of Hus1-deficient cells, indicating the close connection between p21 and Hus1 cells. In this study, wildtype MEFs, Hus1(+/+)p21(-/-) MEFs and p21(-/-)Hus1(-/-) MEFs were used in a series of radiation-induced bystander effect experiments, the roles of p21 and Hus1 in the induction and transmission of radiation-induced damage signals were investigated. Our results showed that after 5 cGy alpha particle irradiation, wild-type MEFs induced significant increases in gamma-H2AX foci and micronuclei formation in bystander cells, whereas the bystander effects were not detectable in p21(-/-)Hus1(+/+) MEFs and were restored again in p21(-/-)Hus1(-/-) MEFs. Media transfer experiments showed that p21(-/-)Hus1(+/+) MEFs were deficient in the production bystander signals, but could respond to bystander signals. We further investigated the mitogen-activated protein kinases (MAPKs) that might be involved in the bystander effects. It was found that although knocking out p21 did not affect the expression of connexin43 and its phosphorylation, it did result in inactivation of some MAPK signal pathway kinases, including JNK1/2, ERK1/2 and p38, as well as a decrease in reactive oxygen species (ROS) levels in irradiated cells. However, the activation of MAPK kinases and the ROS levels in irradiated cells were restored in the cell line by knocking out Hus1. These results suggest that p21(Waf1/CIP1) and Hus1 play crucial roles in the generation and transmission of bystander damage signals after low-dose a particle irradiation. (C) 2015 by Radiation Research
Peer Review Status:Awaiting Review
Subjects: Biology >> Biophysics submitted time 2016-05-11
Abstract: Microgravity is a major stress factor that astronauts have to face in space. In the past, the effects of microgravity on genomic DNA damage were studied, and it seems that the effect on genomic DNA depends on cell types and the length of exposure time to microgravity or simulated microgravity (SMG). In this study we used mouse embryonic stem (MES) and mouse embryonic fibroblast (MEF) cells to assess the effects of SMG on DNA lesions. To acquire the insight into potential mechanisms by which cells resist and/or adapt to SMG, we also included Rad9-deleted MES and Mdc1-deleted MEF cells in addition to wild type cells in this study. We observed significant SMG-induced DNA double strand breaks (DSBs) in Rad9(-/-) MES and Mdc1(-/-) MEF cells but not in their corresponding wild type cells. A similar pattern of DNA single strand break or modifications was also observed in Rad9(-/-) MES. As the exposure to SMG was prolonged, Rad9(-/-) MES cells adapted to the SMG disturbance by reducing the induced DNA lesions. The induced DNA lesions in Rad9(-/-) MES were due to SMG-induced reactive oxygen species (ROS). Interestingly, Mdc1(-/-) MEF cells were only partially adapted to the SMG disturbance. That is, the induced DNA lesions were reduced over time, but did not return to the control level while ROS returned to a control level. In addition, ROS was only partially responsible for the induced DNA lesions in Mdc1(-/-) MEF cells. Taken together, these data suggest that SMG is a weak genomic DNA stress and can aggravate genomic instability in cells with DNA damage response (DDR) defects.
Peer Review Status:Awaiting Review