Abnormal DNA synthesis activity induced by X-rays in nevoid basal cell carcinoma syndrome cells

DNA synthesis activity was examined in fibroblasts and isolated nuclei derived from patients with nevoid basal cell carcinoma syndrome (NBCCS) upon exposure to X-ray and ultraviolet (UV). The DNA synthesis activity in NBCCS fibroblasts increased after X-ray irradiation, i.e., to twice that on mock-irradiation, while it decreased in healthy donor-derived fibroblasts. The DNA synthesis activity in isolated nuclei of X-ray irradiated NBCCS fibroblasts also increased, i.e., more than twice that on mock-irradiated. In the experiments using synchronized cells, DNA synthesis activity showed the most marked increase when the fibroblasts at S phase were irradiated with X-rays. In contrast, UV-irradiated NBCCS fibroblasts showed no such increase in DNA synthesis. These results revealed that DNA synthesis is abnormally induced in X-ray irradiated NBCCS cells and that this abnormality might be related with the tendency of tumorigenesis in NBCCS patients after exposure to X-ray.