Although radiotherapy is routinely administered to high-risk endometrial carcinoma and offer a significant disease-free survival advantage, the therapeutic effect is sometimes limited by the occurrence of radioresistance. To determine the patterns of gene expression responsible for the radioresistance and to search for potential target genes for radiotherapy, we selected two cell lines with distinct radiosensitivities using colony-formation assay from four endometrial cancer cell lines. The cell cycle distribution showed higher fractions of G2/M phase cells in the radiosensitive cell line KLE after radiation compared with the radioresistant cell line ISK. Apoptosis assessment also showed significant elevation in the percentage of early apoptosis cells in KLE cells. Subsequently, gene expression changes after X-ray exposure were analyzed by using oligonucleotide microarrays. We identified, respectively, in ISK and KLE, 227 and 354 genes that exhibited ≥2-fold difference. However, only 53 genes showing differences more than double the median expression value between the two groups were defined as radiosensitivity (or radioresistance)-related genes. Among these, genes associated with DNA-repair, apoptosis, growth factor, signal transduction, cell cycle and cell adhesion were predominant. The validity of the expression level of 10 randomly selected genes was confirmed by real-time PCR and/or Western blotting. In conclusion, the differential gene expression changes that occur after radiation in the two cell lines will provide insight into molecular mechanisms of radioresistance in endometrial carcinoma, and also the means to find potential targets to achieve further gains in therapeutic benefit.

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