Response to low-dose X-irradiation is p53-dependent in a papillary thyroid carcinoma model system.

The link between high doses of radiation and thyroid cancer has been well established in various studies, as opposed to the effects of low doses. In this study, we investi-gated the effects of low-dose X-ray irradiation in a papillary thyroid carcinoma model with wild-type and mutated p53. A low dose of 62.5 mGy was enough to cause an upregulation of p16 and a decrease in the number of TPC-1 cells in the S phase, but not in the number of BCPAP p53-mutant cells. At a dose of 0.5 Gy, visible signs of senescence appeared only in the TPC-1 cells. We conclude that low doses of X-rays are enough to cause a change in cell cycle distribution, possibly p53-dependent p16 activation, but no significant apoptosis. Senescence requires higher doses of X-irradiation via a mechanism involving both p16 and p21.