No abstract

The translationally controlled tumor protein (TCTP) is essential for survival by mechanisms that as yet are incompletely defined. Here we describe an important role of TCTP in response to DNA damage. Upon exposure of normal human cells to low-dose γ rays, the TCTP protein level was greatly increased, with a significant enrichment in nuclei. TCTP up-regulation occurred in a manner dependent on ataxia-telangiectasia mutated (ATM) kinase and the DNA-dependent protein kinase and was associated with protective effects against DNA damage. In chromatin of irradiated cells, coimmunoprecipitation experiments showed that TCTP forms a complex with ATM and γH2A.X, in agreement with its distinct localization with the foci of the DNA damage-marker proteins γH2A.X, 53BP1, and P-ATM. In cells lacking TCTP, repair of chromosomal damage induced by γ rays was compromised significantly. TCTP also was shown to interact with p53 and the DNA-binding subunits, Ku70 and Ku80, of DNA-dependent protein kinase. TCTP knockdown led to decreased levels of Ku70 and Ku80 in nuclei of irradiated cells and attenuated their DNA-binding activity. It also attenuated the radiation-induced G 1 delay but prolonged the G 2 delay. TCTP therefore may play a critical role in maintaining genomic integrity in response to DNA-damaging agents.low dose ionizing radiation | adaptive responses | DNA repair | cell cycle checkpoints | genomic stability

Hypoxia-inducible factor 1 (HIF-1) has been associated with distant tumor metastasis; however, its function in multiple metastatic processes has not yet been fully elucidated. In the present study, we demonstrated that cancer cells transiently upregulated HIF-1 activity during their metastatic colonization after extravasation in the lungs in hypoxia-independent and reactive oxygen species (ROS)-dependent manners. Transient activation induced the expression of lactate dehydrogenase A and phosphorylation of the E1α subunit of pyruvate dehydrogenase, which indicated the reprogramming of glucose metabolic pathways from mitochondrial oxidative phosphorylation to anaerobic glycolysis and lactic acid fermentation. The administration of the HIF-1 inhibitor, YC-1, inhibited this reprogramming, increased intratumoral ROS levels, and eventually suppressed the formation of metastatic lung tumors. These results indicate that HIF-1-mediated metabolic reprogramming is responsible for the survival of metastatic cancers during their colonization in lungs by reducing cytotoxic ROS levels; therefore, its blockade by HIF-1-inhibitors is a rational strategy to prevent tumor metastasis.

Her-2/neu (ErbB2) oncogene, the second member of the epidermal growth factor receptor (EGFR) family, encodes a transmembrane tyrosine kinase receptor in Her-2-positive tumors. Accumulating evidences demonstrate that signaling networks activated by EGFR and transcription factor NFjB are associated with cell response to ionizing radiation (IR). The present study shows that overexpression of ErbB2 enhanced NF-jB activation induced by IR in human breast carcinoma MCF-7 cells transfected with ErbB2 genes (MCF-7/ErbB2). Stable transfection of dominantnegative mutant IjB (MCF-7/ErbB2/mIjB) or treatment with anti-ErbB2 antibody, Herceptin, inhibited NF-jB activation and radiosensitized MCF-7/ErbB2 cells. Consistent with NF-jB regulation, basal and IR-induced Akt, a kinase downstream of ErbB2, was activated in MCF-7/ ErbB2 cells and inhibited by Herceptin. To identify specific genes affected by ErbB2-mediated NF-jB activation, a group of IR-responsive elements Cyclin B1, Cyclin D1, Bcl-2, Bcl/XL, BAD and BAX were evaluated. Basal levels of prosurvival elements Cyclin B1, Cyclin D1, Bcl-2 and Bcl/XL but not apoptotic BAD and BAX were upregulated in MCF-7/ErbB2 cells with striking enhancements in Bcl-2 and Bcl/XL. IR further induced Cyclin B1 and Cyclin D1 expression that was reduced by Herceptin. Bcl-2 kept a high steady level after Herceptin þ IR treatment and, in contrast to control MCF-7/Vector cells, Bcl/XL was inhibited in MCF-7/ErbB2 cells by Herceptin þ IR treatment. However, all four prosurvival proteins were downregulated by inhibition of NF-jB in MCF-7/ErbB2/mIjB cells. These results thus provide evidence suggesting that overexpression of ErbB2 is able to enhance NF-jB response to IR, and that a specific prosurvival network downstream of NF-jB is triggered by treatments using anti-ErbB2 antibody combined with radiation.

Radiotherapy has played a key role in the control of tumor growth in many cancer patients. It is usually difficult to determine what fraction of the tumor cell population is radioresistant after a course of radiotherapy. The response of tumor cells to radiation is believed to be accompanied by complex changes in the gene expression pattern. It may be possible to use these to sensitize radioresistant tumor cells and improve radiocurability. Based on the biological effects of ionizing radiation, in the present study, we developed one oligonucleotide microarray to analyze the expression of 143 genes in cells of two lung cancer cell lines with different radiosensitivities. Compared to NCI-H446 cells, expression of 18 genes significantly increased the basal levels in the radioresistant A549 cells, in which eight genes were up-regulated and 10 genes were down-regulated. In A549 cells irradiated with 5 Gy, 22 (19 up-regulated and three down-regulated) and 26 (eight up-regulated and 18 down-regulated) differentially expressed genes were found 6 and 24 h after irradiation, respectively. In NCI-H446 cells, the expression of 17 (nine up-regulated and eight down-regulated) and 18 (six up-regulated and 12 down-regulated) genes was altered 6 and 24 h after irradiation, respectively. RT-PCR was performed, and we found that MDM2, BCL2, PKCZ and PIM2 expression levels were increased in A549 cells and decreased in NCI-H446 cells after irradiation. Genes involved in DNA repair, such as XRCC5, ERCC5, ERCC1, RAD9A, ERCC4 and the gene encoding DNA-PK, were found to be increased to a higher level in A549 cells than in NCI-H446 cells. Antisense suppression of MDM2 resulted in increased radiosensitivity of A549 cells. Taken together, these results demonstrate the possibility that a group of genes involved in DNA repair, regulation of the cell cycle, cell proliferation and apoptosis is responsible for the different radioresistance of these two lung cancer cells. This list of genes may be useful in attempts to sensitize the radioresistant lung cancer cells.

Imogolite nanotubes (INTs) were synthesized from tetraethoxysilane, aluminum nitrate nonahydrate, and ammonia solution by the method of Arancibia-Miranda, and their dispersion was modified by 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF6) to obtain ionic liquid (IL)-functionalized INTs (INTs-PF6-ILs). Then, the flame retardant INTs-PF6-ILs was complexed with ammonium polyphosphate (APP) and applied to unsaturated polyester resin (UPR). The limiting oxygen index value and the UL-94 level of the UPR/APP/INTs-PF6-ILs composites reached 28 and V-0, respectively. The residual carbon of the composites in thermogravimetric analysis increased by 19.47%, compared with that of pure UPR. The cone calorimeter test result showed that the peak of heat release rate and total heat rate values of the UPR/APP/INTs-PF6-ILs composites were lowered by 41 and 34% than those of the pure UPR, respectively. The effect of heat combustion and the maximum mass loss rate of UPR/APP/INTs-PF6-ILs composites were also greatly decreased. There were no holes or folds observed on the surface of the UPR/APP/INTs-PF6-ILs composites’ residual carbon in scanning electron microscopy images. The intact residual carbon could have effectively insulated the heat and oxygen to improve the flame retardant performance.

Summary Graphene oxide (GO) was prepared from graphite powder by the classic Hummers method, and modified by 1‐N‐butyl‐3‐methylimidazolium hexafluorophosphate (IL) and 3‐aminopropyltriethoxysilane (KH550) to obtain ionic liquid functionalized graphene oxide (ILGO). ILGO, compounded with traditional flame retardants (ammonium polyphosphate and expandable graphite), was used in unsaturated polyester resin (UPR) to enhance the flame retardancy. The flame retardant property and thermal degradation of the UPR composites were analyzed by limiting oxygen index (LOI), UL‐94, cone calorimeter test (CCT), and thermogravimetric analysis (TGA). The results show that there is an obvious synergism between ILGO and the traditional flame retardants. The LOI value of UPR‐4 containing ILGO reaches 28.2% and passes V‐0 of UL‐94, and UPR‐4's the initial temperature (Ti), maximum degradation temperature (Tmax), and residual carbon greatly increase. The experimental data shows that ILGO can promote UPR to form more residual carbon during combustion, enhance thermal stability, and make the material not easy to decompose. The morphology of carbon layer measured after CCT was observed by scanning electron microscope (SEM). SEM images show that the surface of char layer of UPR‐4 containing ILGO becomes smoother, flatter and denser, compared with UPR containing only flame retardants. The cohesiveness and compact structure residual carbon can effectively prevent the oxygen, combustible gas, and heat transfer between the flame zone and the base material to reduce flammability.

MDM2 (murine double minute 2) is well-documented to play a key role in radiation response and tumor radiosensitivity, thus offering an attractive clinic drug target to enhance tumor sensitivity to anti-cancer radiotherapy. In this study, we designed and tested two siRNA fragments against human MDM2 in non-small cell human lung cancer A549 cells. Transfection of mammalian expression vector pUR/U6 containing either MDM2 siRNA1 or siRNA2 fragment was shown to reduce MDM2 mRNA levels by 72% and 31%, respectively. Western blotting detected a similar inhibition of MDM2 protein levels in cells transfected with MDM2 siRNA1. A549 cells transfected with the expression vector for siRNA1 significantly decreased cell proliferation and rendered cells more sensitive to radiation. The basal apoptotic and necrotic cells, 1% and 2%, respectively, detected among A549 cells were increased to 2.6% and 14.4% after γ-irradiation with 5 Gy. Transfection of MDM2 siRNA1 induced 30.1% apoptosis and 12.7% necrosis while combined treatment of siRNA1 and 5-Gy radiation increased apoptosis and necrosis to 45.9% and 15.2%, respectively. These data provide the first evidence that specific siRNA fragment (MDM2 siRNA1) targeting human MDM2 mRNA is able to enhance lung cancer radiosensitivity.