Aurora A Kinase Plays a Key Role in Mitosis Skip during Senescence Induced by Ionizing Radiation.

Objective: To investigate the fate and underlying mechanisms of G2 phase arrest in cancer cells elicited by ionizing radiation (IR). Methods: Human melanoma A375 and 92-1 cells were treated with X-rays radiation or Aurora A inhibitor MLN8237 (MLN) and/or p21 depletion by small interfering RNA (siRNA). Cell cycle distribution was determined using flow cytometry and a fluorescent ubiquitin-based cell cycle indicator (FUCCI) system combined with histone H3 phosphorylation at Ser10 (pS10 H3) detection. Senescence was assessed using senescence-associated-ß-galactosidase (SA-ß-Gal), Ki67, and γH2AX staining. Protein expression levels were determined using western blotting. Results: Tumor cells suffered severe DNA damage and underwent G2 arrest after IR treatment. The damaged cells did not successfully enter M phase nor were they stably blocked at G2 phase but underwent mitotic skipping and entered G1 phase as tetraploid cells, ultimately leading to senescence in G1. During this process, the p53/p21 pathway is hyperactivated. Accompanying p21 accumulation, Aurora A kinase levels declined sharply. MLN treatment confirmed that Aurora A kinase activity is essential for mitosis skipping and senescence induction. Conclusion: Persistent p21 activation during IR-induced G2 phase blockade drives Aurora A kinase degradation, leading to senescence via mitotic skipping.

Radiation-Induced Bystander Effect on the Genome of Bone Marrow Mesenchymal Stem Cells in Lung Cancer.

Aims: Radiation by-radiation effect (RIBE) can induce the genomic instability of bone marrow mesenchymal stem cells (BMSCs) adjacent to lung cancer, and this effect not only exists in the short-term, but also accompanies it in the long-term, but its specific mechanism is not clear. Our goal is to explore the similarities and differences in the mechanism of genomic damage in tumor-associated BMSCs induced by short-term and long-term RIBE, and to provide a theoretical basis for adjuvant drugs for protection against RIBE at different clinical time periods. Results: We found that both short- and long-term RIBE induced genomic instability. We could show a high expression of TGF-ß1, TNF-α, and HIF-1α in tumor-associated BMSCs after short-term RIBE whereas only TNF-α and HIF-1α expression was increased in long-term RIBE. We further confirmed that genomic instability is associated with the activation of the HIF-1α pathway and that this is mediated by TNF-α and TGF-ß1. In addition, we found differences in the mechanisms of genomic instability in the considered RIBE windows of analysis. In short-term RIBE, both TNF-α and TGF-ß1 play a role, whereas only TNF-α plays a decisive role in long-term RIBE. In addition, there were differences in BMSC recruitment and genomic instability of different tissues with a more pronounced expression in tumor and bone marrow than compared to lung. Innovation and Conclusion: We could show dynamic changes in the expression of the cytokines TGF-ß1 and TNF-α during short- and long-term RIBE. The differential expression of the two is the key to causing the genomic damage of tumor-associated BMSCs in the considered windows of analysis. Therefore, these results may serve as a guideline for the administration of radiation protection adjuvant drugs at different clinical stages. Antioxid. Redox Signal. 38, 747-767.

MiR-663a Inhibits Radiation-Induced Epithelium-to-Mesenchymal Transition by Targeting TGF-ß1.

Objective: miR-663a has been reported to be downregulated by X-ray irradiation and participates in radiation-induced bystander effect via TGF-ß1. The goal of this study was to explore the role of miR-663a during radiation-induced Epithelium-to-mesenchymal transition (EMT). Methods: TGF-ß1 or IR was used to induce EMT. After miR-663a transfection, cell migration and cell morphological changes were detected and the expression levels of miR-663a, TGF-ß1, and EMT-related factors were quantified. Results: Enhancement of cell migration and promotion of mesenchymal changes induced by either TGF-ß1 or radiation were suppressed by miR-663a. Furthermore, both X-ray and carbon ion irradiation resulted in the upregulation of TGF-ß1 and downregulation of miR-663a, while the silencing of TGF-ß1 by miR-663a reversed the EMT process after radiation. Conclusion: Our findings demonstrate an EMT-suppressing effect by miR-663a via TGF-ß1 in radiation-induced EMT.

Astragalus polysaccharide inhibits radiation-induced bystander effects by regulating apoptosis in Bone Mesenchymal Stem Cells (BMSCs).

The purpose of this study was to investigate the effects of astragalus polysaccharides (APS) on the proliferation and apoptosis of bone marrow mesenchymal stem cells (BMSCs) induced by X-ray radiation-induced A549 cells bystander effect (RIBE), and to explore their mechanisms. In this study, APS increased the reduced cell proliferation rate induced by RIBE and inhibiting the apoptosis of bystander cells. In terms of mechanism, APS up-regulates the proteins Bcl-2, Bcl-xl, and down-regulates the proteins Bax and Bak, which induces a decrease in mitochondrial membrane potential, which induces the release of Cyt-c and AIF, which leads to caspase-dependent and caspase-independent pathway to cause apoptosis. In addition, we believe that ROS may be the main cause of these protein changes. APS can inhibit the generation of ROS in bystander cells and thus inhibit the activation of the mitochondrial pathway, further preventing cellular damage caused by RIBE.

Bone Loss Induced by Simulated Microgravity, Ionizing Radiation and/or Ultradian Rhythms in the Hindlimbs of Rats.

OBJECTIVE: To better understand the pathological causes of bone loss in a space environment, including microgravity, ionizing radiation, and ultradian rhythms. METHODS: Sprague Dawley (SD) rats were randomly divided into a baseline group, a control group, a hindlimb suspension group, a radiation group, a ultradian rhythms group and a combined-three-factor group. After four weeks of hindlimb suspension followed by X-ray exposure and/or ultradian rhythms, biomechanical properties, bone mineral density, histological analysis, microstructure parameters, and bone turnover markers were detected to evaluate bone loss in hindlimbs of rats. RESULTS: Simulated microgravity or combined-three factors treatment led to a significant decrease in the biomechanical properties of bones, reduction in bone mineral density, and deterioration of trabecular parameters. Ionizing radiation exposure also showed adverse impact while ultradian rhythms had no significant effect on these outcomes. Decrease in the concentration of the turnover markers bone alkaline phosphatase (bALP), osteocalcin (OCN), and tartrate-resistant acid phosphatase-5b (TRAP-5b) in serum was in line with the changes in trabecular parameters. CONCLUSION: Simulated microgravity is the main contributor of bone loss. Radiation also results in deleterious effects but ultradian rhythms has no significant effect. Combined-three factors treatment do not exacerbate bone loss when compared to simulated microgravity treatment alone.