1α,25(OH)2D3 Radiosensitizes Cancer Cells by Activating the NADPH/ROS Pathway.

The radioresistance of tumors affect the outcome of radiotherapy. Accumulating data suggest that 1α,25(OH)2D3 is a potential anti-oncogenic molecule in various cancers. In the present study, we investigated the radiosensitive effects and underlying mechanisms of 1α,25(OH)2D3 in vitro and in vivo. We found that 1α,25(OH)2D3 enhanced the radiosensitivity of lung cancer and ovarian cancer cells by promoting the NADPH oxidase-ROS-apoptosis axis. Compared to the group that only received radiation, the survival fraction and self-renewal capacity of cancer cells treated with a combination of 1α,25(OH)2D3 and radiation were decreased. Both apoptosis and ROS were significantly increased in the combination group compared with the radiation only group. Moreover, N-acetyl-L-cysteine, a scavenger of intracellular ROS, reversed the apoptosis and ROS induced by 1α,25(OH)2D3, indicating that 1α,25(OH)2D3 enhanced the radiosensitivity of cancer cells in vitro by promoting ROS-induced apoptosis. Moreover, our results demonstrated that 1α,25(OH)2D3 promoted the ROS level via activating NADPH oxidase complexes, NOX4, p22phox, and p47phox. In addition, knockdown of the vitamin D receptor (VDR) abolished the radiosensitization of 1α,25(OH)2D3, which confirmed that 1α,25(OH)2D3 radiosensitized tumor cells that depend on VDR. Similarly, our study also evidenced that vitamin D3 enhanced the radiosensitivity of cancer cells in vivo and extended the overall survival of mice with tumors. In summary, these results demonstrate that 1α,25(OH)2D3 enhances the radiosensitivity depending on VDR and activates the NADPH oxidase-ROS-apoptosis axis. Our findings suggest that 1α,25(OH)2D3 in combination with radiation enhances lung and ovarian cell radiosensitivity, potentially providing a novel combination therapeutic strategy.

B­cell translocation 1 gene inhibits cellular metastasis­associated behavior in breast cancer.

B-cell translocation gene 1 (BTG1) is a member of the BTG/transducer of ERBB2 family, which regulates cell cycle progression in a variety of cell types and may have a role in inhibiting proliferation, promoting apoptosis and stimulating cellular differentiation in numerous cell types. However, the role of BTG1 in cancer metastasis is yet to be elucidated. In the present study, analysis of clinical specimens revealed that BTG1 mRNA levels were lower in lymph node metastases than those in benign breast tumors and normal human breast tissue. The effect of BTG1 on the metastatic behavior of breast cancer cells following stable transfection with a BTG1 expression vector was also investigated. The overexpression of BTG1 was observed to inhibit cell adhesion, migration and invasion. Furthermore, the overexpression of BTG1 was found to be involved in the inhibition of the metastasis-related proteins matrix metalloproteinase-2 and -9, as well as the promotion of the cell-cell adhesion-associated protein E-cadherin. In syngeneic nude mice breast tumor models, hepatic metastasis and angiogenesis were observed in the mice injected with the control cells, but not in those injected with pcDNA3-BTG1 cells. Immunohistochemistry revealed that overexpression of BTG1 decreased vascular endothelial growth factor expression in tumors. To the best of our knowledge, this is the first study to show that BTG1 overexpression decreases migration and invasion of breast cancer cells and thereby inhibits distant metastasis in mice breast tumor models.

BTG1 inhibits breast cancer cell growth through induction of cell cycle arrest and apoptosis.

BTG1, which belongs to the BTG/Tob family, regulates cell cycle progression in a variety of cell types and appears to play roles in inhibiting proliferation, promoting apoptosis and stimulating cellular differentiation in multiple cell types. However, it remains unclear whether BTG1 is a breast cancer suppressor gene, and the role of BTG1 in breast cancer cell growth has not yet been determined. In the present study, we observed that BTG1 was weakly expressed in human breast tumors and in breast cancer cells (MCF-7 and MDA-MB-231). In addition, we investigated the potential effects of BTG1 on breast cancer cell proliferation, cell cycle distribution and apoptosis after stable transfection with the BTG1 expression vector. We found that overexpression of BTG1 inhibited cell proliferation, induced G0/G1 cell cycle arrest and promoted apoptosis. Further investigation indicated that overexpression of BTG1 was involved in the inhibition of the expression of cell cycle-related proteins, cyclin B1 and cyclin D1, and pro-apoptotic factors, Bax and caspase-3, and was also involved in the promotion of anti-apoptotic factor Bcl-2. In vivo, animal experiments showed that tumors overexpressing BTG1 displayed a slower growth rate than the control xenografts. TUNEL end staining assay revealed that BTG1 induced tumor necrosis and apoptosis. Taken together, our data revealed that, in breast cancer cells, BTG1 inhibits cell growth through induction of cell cycle arrest and apoptosis. These results indicate that BTG1 may be used as a novel therapeutic target for human breast cancer treatment.

Radon-induced reduced apoptosis in human bronchial epithelial cells with knockdown of mitochondria DNA.

Radon and radon progeny inhalation exposure are recognized to induce lung cancer. To explore the role of mitochondria in radon-induced carcinogenesis in humans, an in vitro partially depleted mitochondrial DNA (mtDNA) cell line (ρ-) was generated by treatment of human bronchial epithelial (HBE) cells (ρ+) with ethidium bromide (EB). The characterization of ρ- cells indicated the presence of dysfunctional mitochondria and might thus serve a reliable model to investigate the role of mitochondria. In a gas inhalation chamber, ρ- and ρ+ cells were exposed to radon gas produced by a radium source. Results showed that apoptosis was significantly increased both in ρ- and ρ+ cells irradiated by radon. Moreover, apoptosis in ρ- cells showed a lower level than in ρ+ cells. Radon was further found to depress mitochondrial membrane potential (MMP) of HBE cells with knockdown mtDNA. Production of reactive oxygen species (ROS) was markedly elevated both in ρ- and ρ+ cells exposed to radon. The distribution of phases of cell cycle was different in ρ- compared to ρ+ cells. Radon irradiation induced a rise in G2/M and decrease in S phase in ρ+ cells. In ρ- cells, G1, G2/M, and S populations remained similar to cells exposed to radon. In conclusion, radon-induced changes in ROS generation, MMP and cell cycle are all attributed to reduction of apoptosis, which may trigger and promote cell transformation, leading to carcinogenesis. Our study indicates that the use of the ρ- knockdown mtDNA HBE cells may serve as a reliable model to study the role played by mitochondria in carcinogenic diseases.

[Molecular mechanism of radiosensitizing effect of paclitaxel].

BACKGROUND & OBJECTIVE: Paclitaxel is a radiosensitizer which may stabilize microtubules, block the G2/M phase of the cell cycle and thus modulate the radioresponsiveness of tumor cells. However, its potential molecular mechanisms of radiosensitization have not been well understood yet. This study was to investigate the radiosensitizing effect of paclitaxel on human oral epithelium carcinoma (KB) cell line and to explore the molecular mechanism of radiosensitization. METHODS: The survival of KB cells following the treatment with paclitaxel and/or radiation was determined by colony-forming assay. The radiosensitizing effect was evaluated by calculating the sensitizing enhancement ratio (SER) with multi-target single hit model. The cell cycle distribution was analyzed by flow cytometry. Differentially expressed genes related to paclitaxel radiosensitization were screened using human Oligo microarray. Expressions of protein regulating cytokinesis 1 (PRC1) and cyclin B2 genes were confirmed by real-time quantitative PCR. RESULTS: The proliferation of KB cells was significantly inhibited by paclitaxel combined with ionizing radiation. The SERD0 and SERDq were (2.40 +/- 1.87) and (12.23 +/- 2.81) respectively, when the concentration of paclitaxel was 20 nmol/l. After the treatment with paclitaxel in combination with irradiation, the percentage of G1 phase cells decreased from (48.32 +/- 2.40)% to (15.73 +/- 7.00)% (P<0.01), and the percentage of G2/M phase cells increased from (13.66 +/- 2.16)% to (52.51 +/- 5.02)% (P<0.01). In total 176 differentially expressed genes were identified to be related to paclitaxel radiosensitization. Ten genes were found to regulate cell division, two of which were up-regulated and eight were down-regulated after the treatment. Moreover, the expression of PRC1 and cyclin B2 was decreased. CONCLUSION: The radiosensitizing effect of paclitaxel on KB cells may be due to the down-regulated expression of PRC1 and cyclin B2, resulting in inhibition of mitotic spindle formation and cell necrosis.