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objectiveTo explore the specific molecular mechanism of neuronal apoptosis induced by ATM inactivation. MethodsCGNs matured 7 days in vitro were cultured 8 h with 25 K， 5 K or 25 K medium containing ATM-specific inhibitors （Ku55933， 10 µmol/L； Ku60019， 15 µmol/L） for Hoechst stain and apoptosis analysis， or cultured for different lengths of time （2， 4， 8 h） to detect the protein expression levels of ATM， caspase-3 and cleaved caspase-3 by Western blotting. ATM and GADD45α specific siRNA was transfected into C6 cells and CGNs， and its interference efficiency was verified by q-PCR and Western blotting. CGNs matured for 5 days in vitro were transfected with ATM specific siRNA and pCMV-EGFP by calcium phosphate for 48 h， Hoechst staining and apoptosis analysis were performed. CGNs matured for 7 days in vitro were treated with 25 K medium containing ATM specific inhibitors for 8 h， transcriptome sequencing， differential expression gene identification and pathway enrichment analysis were performed. CGNs matured for 5 days in vitro were co-transfected with GADD45α specific siRNA and pCMV-EGFP by calcium phosphate for 48 h， then treated with 5 K or 25 K medium containing 15 µmol/L Ku6 for 8 h. Hoechst staining and apoptosis analysis were performed. ResultsCompared with the 25 K， CGNs nuclear pyknosis rate， cleaved Caspase-3 and ATM protein expression level were increased in the 5 K and ATM-specific inhibitor groups. The mRNA and protein expression levels of ATM and GADD45α were effectively reduced after transfection of ATM and GADD45α specific siRNA in C6 cells and CGNs. Compared with control， CGNs transfected with ATM specific siRNA showed a higher nuclear pyknosis rate. Totally 835 genes were identified to be up-regulated and 848 genes to be down-regulated in the Ku55933 treatment group； 454 genes were identified to be up-regulated and 314 genes to be down-regulated in the Ku6 treatment group； 274 genes were co-up regulated in the Ku5 and Ku60019 treatment groups， while 179 genes were co-down-regulated in the Ku5 and Ku6 treatment groups and the expression of ATM downstream target GADD45α was upregulated. The enrichment results showed that TNF signaling pathway， NF-κB signaling pathway and Apoptosis signaling pathway were significantly enriched. Compared with control， mRNA and protein expression levels of GADD45α were increased in inhibitor treatment and 5 K， while knocking down GADD45α resulted in a decrease in nuclear pyknosis rate in the Ku60019 and 5 K treatment group. ConclusionLoss of ATM activity induces GADD45α-dependent cerebellar granular neuronal apoptosis.
ABSTRACT
As a member of growth arrest and DNA damage inducible gene family,GADD45αparticipats in the regulation of cell cycle,cell senescence,cell survival and apoptosis. GADD45αplays a critical role in the responses to cell injury induced by a variety of factors including cell stress and genotoxic chemicals. Different transcription factors and proteins are involved in transcriptional regulation of GADD45αgene. GADD45αprotein has been implicated in the regulation of genomic stability related cellular responses through interaction with other proteins. Genotoxicity test systems based on the char?acteristics of GADD45α in regulation of cell function,can be applied to the detection of potentially genotoxic compounds,which provides new ideas and methods about genotoxicity assessment. The molecular mechanism and research progress of GADD45α in genotoxicity test are summarized in this article.
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Objective To investigate the effect of trichostatin A on the expression of growth arrest and DNA damage-inducible protein 45 alpha (Gadd45α) in,proliferation of and apoptosis in a human epithelial carcinoma cell line A431.Methods Cultured A431 cells were treated with different concentrations (0.05,0.1,0.25,0.5,1 μmogL) of trichostatin A for various durations (6,12,24,48 hours).Subsequently,cell proliferation,cycle and apoptosis were detected by cell counting kit-8 (CCK8) and flow cytometry respectively.The expression of Gadd45eα mRNA and protein in cultured A431 cells was detected by reverse transcription-PCR and Western blot respectively.Results Trichostatin A inhibited the proliferation of A431 cells in a dose (0.05-1.0 μmol/L)-dependent manner at all the 4 time points (F =3554.71,P ＜ 0.05),as well as in a time (6-48 hours)-dependent manner at these tested concentrations (F =1685.18,P ＜ 0.05).A statistical increase was induced in the early apoptosis rate,late apoptosis rate and Gadd45α mRNA expression in A431 cells by the 24 hour-treatment with trichostatin A of 0.1 to 0.5μmol/L.Elevated percentage of cells at G1 phase (26.910％ ± 0.799％,30.406％ ±0.625％,32.896％ ± 0.599％ vs.21.633％ ± 1.144％,F =105.93,P ＜ 0.05) and expression of Gadd45α protein (0.6536 ± 0.2193,0.6990 ± 0.0110,0.9040 ± 0.1971 vs.0.3766 ± 0.0241,F =332.88,P ＜ 0.01) were observed in A431 cells treated with trichostatin A of 0.1,0.25 and 0.5 μmol/L for 24 hours compared with untreated A431 cells.Conclusions Trichostatin A can enhance the mRNA and protein expression of Gadd45α in A431 cells,which may be involved in the suppression of cell proliferation as well as acceleration of apoptosis of A431 cells by trichostatin A.
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Objective To detect the expression of DNA damage response genes induced by radiation in human peripheral blood lymphocyte,and to explore the new biomarkers of radiation.Methods The human peripheral blood cells were irradiated to X-rays at different doses of 0,1,2,3,4,and 5 Gy.The quantitative real.time qPCR wag used to detect the expressions of cyclin-dependent kinase inhibitor l a gene(Cdknl a)and growth arrest and DNA damage inducible gene(Gadd45a)in lymphoeytes at 4 and 24 h post-irradiation,respectively.The method of CB mieronucleus was used to determine the change of micronucleus ratio.Results The expression of Cdknl a in peripheral blood lymphocytes wag increased significantly at 4 and 24 h post-irradiation to 0-5 Gy.reached the peak at 4 Gy and began to decrease at 5 Gy,which showed a dose-dependent manner(r=0.946,0.975,P<0.05).Similarly,the expression of Gadd45α in human peripheral blood lymphocytes was also increased significantly at 4 and 24 h post-irradiation to 0-5 Gy in a dose-dependent manner,while the expression of Gadd45a at 4 h wag higher than that at 24 h(r=0.936,0.797,P<0.05).The ratio of micronuclei wag increased significantly at 4 and 24 h post-irradiation to 0-5 Gy(r=0.990,0.984,P<0.05).Conciusions Cdknl a and Gadd45α expression could be increaged significandy at 4 and 24 h post-irradiation to 0-5 Gy,showing a good linear relationship.which might be candidate for radiation biological dosimeter.
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Objective To investigate the effects of NB-UVB on the expression of Gadd45α as well as cell apoptosis and cycle of human HaCaT keratinocytes.Methods Cultured HaCaT cells were exposed to various doses (100,200,400 mJ/cm2)of NB-UVB followed by an additional culture of 6,12 and 24 hours,respectively.Reverse transcription PCR and Western blot were performed to detect the mRNA and protein expression of Gadd45α respectively in HaCaT cells,cell counting kit 8 (CCK8)to measure the proliferation of cells,and flow cytometry to determine the cell cycle distribution of HaCaT cells before and after the exposure to NB-UVB.Results Gadd45α was expressed in HaCaT cells.After exposure to NB-UVB of the three doses,the mRNA and protein levels of Gadd45α increased at 6 hours and 12 hours,but declined at 24 hours,and significant changes were observed in HaCaT cells at the three time points after exposure to NB-UVB of the three doses (all P<0.05).The Gadd45α/β-actin mRNA ratio was 1.4360±0.6551.1.8633±0.0979,1.9266±0.1724 in HaCaT cells 12 hours after irradiation to NB-UVB of 100,200 and 400 mJ/cm2,respectively,significantly higher than that in unirradiated cells(0.6000±0.1276,all P<0.05).Also,increased Gadd45α/β-actin protein ratio was noted in HaCaT cells 12 hours after irradiation to NB-UVB of 100,200 and 400 mJ/cm2 compared with unirradiated cells (0.0773±0.0005,0.1936±0.0015,0.2373±0.0015 vs.0.0290±0.0010,all P<0.05).NB-UVB inhibited the proliferation of HaCaT cells in a time-and dose-dependent manner.Flow cytometry showed that irradiated HaCaT cells were blocked in G2 phase of the cell cycle.and the percentage of HaCaT cells in G2 phase was 13.53%±1.03%,17.77%±2.25%,30.03%±4.29%afler exposure to NB-UVB of 100,200 and 400 mJ/cm2,respectively,compared to 9.24%±0.97%in unirradiated cells (all P<0.05).Conclusions The expression of Gadd45α is increased in HaCaT cells after exposure to NB-UVB,and Gadd45α may be involved in the NB-UVB-induced suprression of cell proliferation of and cell cycle arrest in HaCaT cells.