Effects of radon on miR-34a-induced apoptosis in human bronchial epithelial BEAS-2B cells

Study on MicroRNAs as Potential Biomarkers of Radon-induced Radiation Damage

ABSTRACT

High concentrations of radon may cause radiation damage to the human body. Finding the biomarkers of radon-induced radiation damage is particularly important for the research and treatment of radon-induced lung cancer. In this study, the expression of γH2AX protein in peripheral blood lymphocytes of miners exposed to high concentrations of radon was detected by flow cytometry. To investigate the possible damage in peripheral blood lymphocytes of miners under a high radon environment, a microRNA (miRNA) microarray technique was used to screen the differentially expressed miRNAs in the peripheral plasma of miners exposed to different concentrations of radon. Prediction of the target genes and the possible biological functions of differentially expressed miRNAs in the peripheral plasma of miners was performed. The results indicated that the relative expression level of γH2AX protein in peripheral blood lymphocytes of miners was significantly higher than that of the control group (P < 0.05). Bioinformatics methods were used to predict the differential expression miRNA chip to screen the target genes of differentially expressed miRNAs and the signaling pathways that may be involved in screening differentially expressed miRNA target genes and to investigate the relationship between some different miRNA target genes and cellular pathways. The analysis of the cellular pathways predicted by differentially expressed miRNAs, including the process of cell cycle, provides new information for the study of miRNAs as potential biomarkers of radon-induced radiation damage in peripheral blood.

Proteomic and miRNA profiling of radon-induced skin damage in mice: FASN regulated by miRNAs

Radon is a naturally occurring radioactive gas and considered as a serious carcinogen to humans. Continuous radioactive decay of this gas emits high-energy alpha particles. Long-term radon exposure induces oxidative stress and inflammatory response, which results in chronic lung diseases. However, biological effects after radon exposure in other organs have been rarely reported. As the outermost organ of the human body, the skin suffers from environmental damage to agents such as air pollution. Epidemiological studies indicated that areas with high level of radon had a high incidence of skin cancer. However, whether radon exposure induces skin damage has not been reported yet. In this study, we established a radon-exposed mouse model and found that radon exposure affected the structure of skin tissues, which was manifested by inflammatory cell infiltration and skin atrophy. Using proteomic approach, we found 45 preferentially expressed proteins in 60 Working Level Months (WLM) group and 314 preferentially expressed proteins in 120 WLM group from radon-exposed skin tissues. Through microRNA (miRNA) sequencing profiling analysis, 57 dysregulated miRNAs were screened between the control and radon-treated mouse skin. By integrating the dysregulated proteins and miRNAs, radon-induced fatty acid synthase (FASN) was investigated in greater detail. Results showed that FASN was regulated by miR-206-3p and miR-378a-3p and involved in the pathogenesis of radon-induced skin damage. Overexpression of FASN inhibited the proliferation, and induced in WS1 cells. Our present findings illustrate the molecular change during radon-induced skin damage and the potential role of FASN during this process.

The level of free-circulating mtDNA in patients with radon-induced lung cancer

OBJECTIVE

According to the World Health Organization, radon is the second leading cause of lung cancer after smoking. Cell free circulating mitochondrial DNA (cf mtDNA) have been used not only as a biomarker of carcinogenesis but also as a biomarker of exposure to radiation, but nothing is known about changes in the level of cf mtDNA following radon exposure. Therefore, the purpose of this study was to estimate the cf mtDNA copy number as a biomarker of the response to radon exposure in lung cancer pathogenesis.

METHODS

207 subjects were examined including 41 radon-exposed lung cancer patients, 40 lung cancer patients without radon exposure and 126 healthy controls exposed/not exposed to high level of radon. Total cell free circulating DNA from blood samples was extracted and used to detect cell free circulating mitochondrial DNA copy number by quantitative real-time polymerase chain reaction (qRT-PCR).

RESULTS

Our data indicate that the level of cf mtDNA in the radon-induced lung cancer patients was significantly higher than that of the other study participants. There was a significant difference in the level of cf mtDNA in the blood plasma of healthy volunteers exposed and not exposed to high doses of radon. Moreover, in healthy volunteers living in areas with high radon levels, the mtDNA copy number was higher than that in patients with lung cancer who were not exposed to high doses of radon.

CONCLUSION

Our study provides evidence for a possible role of cf mtDNA as a promising biomarker of lung cancer induced by exposure to high dose of radon.

The Role of Mitochondrial miRNAs in the Development of Radon-Induced Lung Cancer

MicroRNAs are short, non-coding RNA molecules regulating gene expression by inhibiting the translation of messenger RNA (mRNA) or leading to degradation. The miRNAs are encoded in the nuclear genome and exported to the cytosol. However, miRNAs have been found in mitochondria and are probably derived from mitochondrial DNA. These miRNAs are able to directly regulate mitochondrial genes and mitochondrial activity. Mitochondrial dysfunction is the cause of many diseases, including cancer. In this review, we consider the role of mitochondrial miRNAs in the pathogenesis of lung cancer with particular reference to radon exposure.

Pulmonary oxidative stress and apoptosis in mice chronically exposed to hydrothermal volcanic emissions

Recent studies have shown that exposure to hydrothermal emissions has a negative impact on the respiratory system. Still, volcanogenic air pollution studies are still outnumbered when compared to anthropogenic studies which can result in an unknown risk to the human populations living near volcanically active areas. This study was carried out in São Miguel Island, with noneruptive volcanically active environments, such as the Furnas volcano caldera. Its noneruptive volcanism presents itself as hydrothermal emissions, mainly by the release of nearly 1000 T d^-1 of CO₂ along with H₂S, and the radioactive gas radon; metals [e.g., mercury (Hg), cadmium (Cd), copper (Cu), and zinc (Zn)] and particulate matter are also released in a daily basis. We test the hypothesis whether chronic exposure to hydrothermal emissions causes pulmonary oxidative stress, using Mus musculus as a surrogate species. Mus musculus was live-captured in two villages with hydrothermal emissions and one village without any type of volcanic activity. The level of pulmonary oxidative stress was immunohistochemically assessed by using an OxyIHC^TM Oxidative stress detection kit, and the detection of terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end-labeling (TUNEL) was used to evaluate apoptosis in lung tissues. Mice chronically exposed to hydrothermal emissions presented increased levels of oxidative stress and amount of apoptotic cells. We demonstrate, for the first time, the high oxidative stress potential in the lungs of mice chronically exposed to hydrothermal emissions. This study highlights the usefulness of M. musculus as a bioindicator species and enforces the necessity of regularly biomonitor the inhabitants of hydrothermal areas to prevent respiratory pathologies.

MicroRNA-499 serves as a sensitizer for lung cancer cells to radiotherapy by inhibition of CK2α-mediated phosphorylation of p65

The present study aimed to define the tumor-suppressive role of microRNA-499 (miR-499) in lung cancer cells and its underlying mechanism. First, qRT-PCR analysis revealed poor expression of miR-499 in clinical samples and cell lines of lung cancer. Next, we performed loss- and gain-of-function experiments for the expression of miR-499 in lung cancer cells exposed to irradiation (IR) to determine the effect of miR-499 expression on cell viability and apoptosis as well as tumor growth. Results showed that overexpression of miR-499 inhibited cell viability, enhanced the radiosensitivity of lung cancer cells, and promoted cell apoptosis under IR. Furthermore, CK2α was verified to be a target of miR-499, and miR-499 was identified to repress p65 phosphorylation by downregulating CK2α expression, which ultimately diminished the survival rate of lung cancer cells under IR. Collectively, the key findings of the study illustrate the tumor-inhibiting function of miR-499 and confirmed that miR-499-mediated CK2α inhibition and altered p65 phosphorylation enhances the sensitivity of lung cancer cells to IR.

Radon Biomonitoring and microRNA in Lung Cancer

Radon is the number one cause of lung cancer in non-smokers. microRNA expression in human bronchial epithelium cells is altered by radon, with particular reference to upregulation of miR-16, miR-15, miR-23, miR-19, miR-125, and downregulation of let-7, miR-194, miR-373, miR-124, miR-146, miR-369, and miR-652. These alterations alter cell cycle, oxidative stress, inflammation, oncogene suppression, and malignant transformation. Also DNA methylation is altered as a consequence of miR-29 modification induced by radon. Indeed miR-29 targets DNA methyltransferases causing inhibition of CpG sites methylation. Massive microRNA dysregulation occurs in the lung due to radon expose and is functionally related with the resulting lung damage. However, in humans this massive lung microRNA alterations only barely reflect onto blood microRNAs. Indeed, blood miR-19 was not found altered in radon-exposed subjects. Thus, microRNAs are massively dysregulated in experimental models of radon lung carcinogenesis. In humans these events are initially adaptive being aimed at inhibiting neoplastic transformation. Only in case of long-term exposure to radon, microRNA alterations lead towards cancer development. Accordingly, it is difficult in human to establish a microRNA signature reflecting radon exposure. Additional studies are required to understand the role of microRNAs in pathogenesis of radon-induced lung cancer.

Role of miR-182-5p overexpression in trichloroethylene-induced abnormal cell cycle functions in human HepG2 cells

Trichloroethylene (TCE), a widely used industrial solvent, occurs frequently in the global environment. TCE was found to induce hepatocarcinogenesis in mice and one of the underlying mechanisms was reported to involve miR-182-5p overexpression. Subsequently, miR-182-5p overexpression was shown to contribute to chemical-induced enhanced cell proliferation in mouse liver cells by targeting the gene Cited2. The aim of this study was to compare our findings in mice with those in a human hepatoma cell line HepG2. Data demonstrated that TCE at 0.1mM exerted no marked effect on human hepatoma cell line HepG2 cell migration, cell cycle, apoptosis, and DNA damage, but significantly stimulated cell proliferation rate and increased mRNA expression levels of proliferating cell nuclear antigen (PCNA), a cell proliferation biomarker. In addition, TCE enhanced miR-182-5p expression levels but lowered Cited2 mRNA expression. In summary, data showed that similar to mouse liver cells, TCE exposure also upregulated cells miR-182-5p expression and inhibited Cited2 expression in human hepatoma cell line HepG2. Our results suggest that the TCE-mediated alterations in the observed cellular functions involve interaction with miR-182-5p. It is of interest that utilization of liver cancer tissues from the Cancer Genome Atlas (TCGA) database also demonstrated that upregulated miR-182-5p expression and reduced Cited2 mRNA expression was detected suggesting that TCE-induced hepatocarcinogenesis involved processes similar to those in humans.