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.