Differential expression of DNA nonhomologous end-joining proteins Ku70 and Ku80 in melanoma progression

Ku70 and Ku80 heterodimers function as regulatory subunits of the DNA-dependent protein kinase and play a very important role in the repairing of DNA double-strand breaks. Although Ku70 is proposed as a candidate for a tumor suppressor gene, not many data are available on Ku70 and Ku80 expression in human tumors. The main aim of this study was to investigate the expression of Ku70 and Ku80 in the ultravioletinduced lesions-nevus cell nevi, lentigos maligna, and malignant melanomas. Nineteen nevus cell nevi, 23 lentigos maligna, 76 primary melanomas, and 31 melanoma metastases were stained immunohistochemically for the presence of Ku70 and Ku80 proteins. Ku70 and Ku80 expression was preserved in about 80% of nevi, 26% of lentigo maligna, 45% of primary melanomas, and 67% of melanoma metastases. Highly significant differences in Ku70 and Ku80 expression were found between nevi, lentigo maligna, and melanomas. In Cox regression, Ku70 and Ku80 were shown to be highly significant influences on patients' prognosis. Significant correlations between Ku70 and Ku80 expressions were found in nevi, lentigo maligna, and primary melanomas. These correlations were not more present in melanoma metastases. To summarize, earlier phases of melanoma progression seem to be connected with the loss of expression of Ku proteins. Metastatic spread is related to dysregulation of the Ku70 and Ku80 axis.