Carbon ion irradiation abrogates Lin28B-induced X-ray resistance in melanoma cells

The Lin28/let-7 axis plays an important role in tumor initiation and developmental processes. Lin28B is upregulated in a variety of cancers, and its overexpression enhances cancer cell proliferation and radioresistance through the suppression of let-7 micro RNA expression. In this study, we investigated the role of the Lin28/let7 axis as a target for radiosensitization of melanoma cancer cells. The overexpression of Lin28B reduced mature let-7 microRNA expression in melanoma cell lines, and enhanced the sphere-forming ability of melanoma cell lines, which is a characteristic of cancer stem cell (CSC) populations. Interestingly, Lin28B-overexpressed melanoma cells were more resistant to X-ray irradiation than control cells, and Lin28B-induced radioresistance was abolished after carbon ion irradiation. Consistent with these results, Lin28B overexpression reduced the numbers of γH2A.X foci after X-ray irradiation, whereas carbon ion irradiation had no such effect. Our results suggest that a carbon ion beam is more effective than an X-ray beam in terms of killing cancer cells, possibly due to elimination of CSC populations.