Gene expression profiling of lung cancer cells irradiated by carbon ion and X-rays
Background Lung cancer is the leading cause of cancer-related death in men and the third in women in Germany. Radiation therapy plays an important role in the multimodal treatment of lung cancer. Due to the excellent dose distribution and the higher relative biological effectiveness (RBE) in tumor,...
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Lung cancer is the leading cause of cancer-related death in men and the third in women in Germany. Radiation therapy plays an important role in the multimodal treatment of lung cancer. Due to the excellent dose distribution and the higher relative biological effectiveness (RBE) in tumor, heavy ion therapy with carbon shows promising clinical results in different types of cancer. However, the genetic differences of radiation induced reactions in cancer between heavy ion beams and conventional photon beams are not fully understood. In the present study, we compared the gene expression profiles of A549 cells after heavy ion radiation or X-ray radiation using a DNA microarray chip containing 11,800 human genes and identified differentially expressed genes. A set of selected differentially expressed genes was validated with quantitative real-time polymerase chain reaction (qRT-PCR).
The lung carcinoma cell line A549 was irradiated with carbon ion beams (9,8 MeV/nucleon) and X-ray (250 kV) using different doses. The biologically equivalent doses for each radiation quality were determined by clonogenic survival assay. The transcriptional profiling was determined with a high density cDNA microarray containing 11.800 genes, and genetic network and gene ontology analysis was performed. The expression changes of selected genes were validated by qRT-PCR.
Microarray analysis revealed a significant alteration in the expression of 49 genes (at least 2-fold) after carbon ion irradiation and not altered by X-rays, as compared with unirradiated control cells. Of these 49 differentially expressed genes identified, 29 and 20 genes were up- and down-regulated, respectively.
Moreover, the results of microarray analysis showed that the expression levels of 326 genes were altered significantly by carbon ion irradiation with biological equivalent dose to X-rays. Among these genes identified, 169 and 157 genes were more up-and down-regulated in carbon ion irradiation, as compared to X-rays.
The genetic network and functional classification of the 49 differentially expressed genes between carbon ions irradiation and control unirradiated cells revealed four merged networks which were associated with the regulation of cell cycle, cancer and cell death signaling and cell signaling.
The functional analysis of the up-regulated genes between carbon ion and X-ray determined three important functional networks involved in cellular growth and proliferation, cell cycle regulation, and oxidation reduction. Among the down-regulated genes, the functional analysis identified three important molecular functional networks associated with cellular function and maintenance of cancer, regulation of cell cycle in the DNA repair, and post translation modification. A set of 8 selected differentially expressed genes involved in cell cycle, DNA damage and transcription was analysed by qRT-PCR and confirmed the microarray data.
These results showed that these two types of radiations, although in the same biological relative doses, could induce significant gene expression in different levels in A549 cells. The functional classification of these differentially expressed genes revealed that carbon ions and X-ray irradiations have different effects on different signaling pathways through gene expression. The identification of differentially expressed gene in this study might add to the understanding of the complicated molecular responses to carbon ion irradiation and provided valuable resource for both experimental and clinical application of heavy ion beam for treatment of lung cancer.|