Melanoma is a deadly type of skin cancer that is particularly difficult to treat owing to its resistance to radiation therapy. Here, we attempted to determine the key proteins responsible for melanoma radioresistance, with the aim of improving disease response to radiation therapy. Two melanoma cell lines, SK‐Mel5 and SK‐Mel28, with different radiosensitivities were analysed via RNA‐Seq (Quant‐Seq) and target proteins with higher abundance in the more radioresistant cell line, SK‐Mel28, identified. Among these proteins, integrin αvβ3, a well‐known molecule in cell adhesion, was selected for analysis. Treatment of SK‐Mel28 cells with cilengitide, an integrin αvβ3 inhibitor, as well as γ‐irradiation resulted in more significant cell death than γ‐irradiation alone. In addition, Akt, a downstream signal transducer of integrin αvβ3, showed high basic activation in SK‐Mel28 and was significantly decreased upon co‐treatment with cilengitide and γ‐irradiation. MK‐2206, an Akt inhibitor, exerted similar effects on the SK‐Mel28 cell line following γ‐irradiation. Our results collectively demonstrate that the integrin αvβ3‐Akt signalling pathway contributes to radioresistance in SK‐Mel28 cells, which may be manipulated to improve therapeutic options for melanoma.

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Melanoma is a notoriously radioresistant type of skin cancer. Elucidation of the specific mechanisms underlying radioresistance is necessary to improve the clinical efficacy of radiation therapy. To identify the key factors contributing to radioresistance, five melanoma cell lines were selected for study and genes that were upregulated in relatively radioresistant melanomas compared with radiosensitive melanoma cells determined via RNA sequencing technology. In particular, we focused on cyclin D1 (CCND1), a well known cell cycle regulatory molecule. In radiosensitive melanoma, overexpression of cyclin D1 reduced apoptosis. In radioresistant melanoma cell lines, suppression of cyclin D1 with a specific inhibitor or siRNA increased apoptosis and decreased cell proliferation in 2D and 3D spheroid cultures. In addition, we observed increased expression of γ‐H2AX, a molecular marker of DNA damage, even at a later time after γ‐irradiation, under conditions of inhibition of cyclin D1, with a response pattern similar to that of radiosensitive SK‐Mel5. In the same context, expression and nuclear foci formation of RAD51, a key enzyme for homologous recombination (HR), were reduced upon inhibition of cyclin D1. Downregulation of RAD51 also reduced cell survival to irradiation. Overall, suppression of cyclin D1 expression or function led to reduced radiation‐induced DNA damage response (DDR) and triggered cell death. Our collective findings indicate that the presence of increased cyclin D1 potentially contributes to the development of radioresistance through effects on RAD51 in melanoma and could therefore serve as a therapeutic target for improving the efficacy of radiation therapy.