Activation of DNA damage checkpoints in CHO cells requires a certain level of DNA damage

Integration of Physiological, Transcriptomic and Metabolomic Reveals Molecular Mechanism of Paraisaria dubia Response to Zn2+ Stress

Utilizing mycoremediation is an important direction for managing heavy metal pollution. Zn²⁺ pollution has gradually become apparent, but there are few reports about its pollution remediation. Here, the Zn²⁺ remediation potential of Paraisaria dubia, an anamorph of the entomopathogenic fungus Ophiocordyceps gracilis, was explored. There was 60% Zn²⁺ removed by Paraisaria dubia mycelia from a Zn²⁺-contaminated medium. To reveal the Zn²⁺ tolerance mechanism of Paraisaria dubia, transcriptomic and metabolomic were executed. Results showed that Zn²⁺ caused a series of stress responses, such as energy metabolism inhibition, oxidative stress, antioxidant defense system disruption, autophagy obstruction, and DNA damage. Moreover, metabolomic analyses showed that the biosynthesis of some metabolites was affected against Zn²⁺ stress. In order to improve the tolerance to Zn²⁺ stress, the metabolic mechanism of metal ion transport, extracellular polysaccharides (EPS) synthesis, and microcycle conidiation were activated in P. dubia. Remarkably, the formation of microcycle conidiation may be triggered by reactive oxygen species (ROS) and mitogen-activated protein kinase (MAPK) signaling pathways. This study supplemented the gap of the Zn²⁺ resistance mechanism of Paraisaria dubia and provided a reference for the application of Paraisaria dubia in the bioremediation of heavy metals pollution.

Early Passage Mesenchymal Stem Cells Display Decreased Radiosensitivity and Increased DNA Repair Activity

Cell therapies using human mesenchymal stem cells (MSCs) have received much attention in the past decade. In pursuit of the therapeutic potential of MSCs, cell expansion is required to generate a great number of cells with desired phenotype and functionality. Long‐term expansion in vitro, however, can lead to altered functions. To explore the changes in DNA damage responses (DDR) in MSCs expanded, DDR pathways following irradiation were characterized in early‐ and late‐passage bone marrow MSCs. Seventy‐two hours after irradiation, the percentage of sub‐G1 cells in early‐passage MSCs did not change significantly. Reduced TUNEL staining was observed in early‐passage MSCs compared to late‐passage MSCs 4 h after irradiation. Comet assay also revealed that early‐passage MSCs were more resistant to irradiation or DNA damages induced by genotoxic agents than late‐passage MSCs. ATM phosphorylation and γ‐H2AX and phospho‐p53 increased in early‐passage MSCs while decreased in late‐passage MSCs. Through inhibition by KU55933, DDR pathway in early‐passage MSCs was shown to be ATM‐dependent. Higher levels of poly (ADP‐ribose) polymerase‐1 (PARP‐1) and PAR synthesis were observed in early‐passage MSCs than in late‐passage MSCs. Knockdown of PARP‐1 in early‐passage MSCs resulted in sensitization to irradiation‐induced apoptosis. Overexpression of PARP‐1 in late passage MSCs could render irradiation resistance. Lower activity of DDR in late‐passage MSCs was associated with rapid proteasomal degradation of PARP‐1. In conclusion, early‐passage MSCs are more irradiation‐resistant and have increased DDR activity involving PARP‐1, ATM and their downstream signals. Stem Cells Translational Medicine2017;6:1504–1514

c-Myc degradation induced by DNA damage results in apoptosis of CHO cells

Although tripchlorolide (TC), a compound purified from a Chinese herb Tripterygium Wilfordii Hook, has been demonstrated to be a potent antitumor agent, its mechanisms of action are unknown. The present study shows that TC induces apoptosis of Chinese Hamster Ovary (CHO) cells. Most strikingly, TC was particularly potent in inducing apoptosis of the UV41 mutant CHO cells, which are deficient in the ERCC4 gene encoding a nucleotide excision repair protein. TC caused a higher level of DNA damage in UV41 cells than those in the wild-type CHO cells or EM9 cells, which are deficient in single-strand break repair. These results provided a critical link between apoptotic hypersensitivity and DNA damage in defective nucleotide excision repair pathway of UV41 cells by TC treatment. Further analysis showed that degradation of the c-Myc protein in TC-treated UV41 cells was much stronger than those in the wild-type CHOAA8 and the EM9. A proteasome inhibitor, MG132, reduced both the degradation of c-Myc and apoptosis in TC-treated UV41 cells. Expression of exogenous c-Myc also inhibited apoptosis of TC-treated UV41 cells. These results indicate that c-Myc degradation induced by DNA damage in the presence of TC contributes to induction of apoptosis of UV41 cells.