Ionizing radiation, but not ultraviolet radiation, induces mitotic catastrophe in mouse epidermal keratinocytes with aberrant cell cycle checkpoints.

Ultraviolet radiation (UVR) and ionizing radiation (IR) are common genotoxic stresses that damage human skin, although the specific damages to the genomic DNA are different. Here, we show that in the mouse glabrous skin, both UVR and IR induce DNA damage, cell cycle arrest, and condensed cell nuclei. However, only IR induces mitotic catastrophe (MC) in the epidermis. This is because UVR induces a complete blockage of pRB phosphorylation and cell cycle arrest in the G1 phase, whereas pRB phosphorylation remains positive in a significant portion of the epidermal keratinocytes following IR exposure. Furthermore, Cyclin B1 expression is significantly downregulated only by IR but not UVR. Finally, there are more MC cells in the epidermis of p53-/- mice after IR exposure as compared to wild-type mice. Our results suggest that although both IR and UVR are genotoxic, they show distinct impacts on the cell cycle machinery and thus damage the epidermal keratinocytes via different mechanisms.

E-Cadherin-Mediated Cell Contact Controls the Epidermal Damage Response in Radiation Dermatitis.

Radiotherapy is a primary oncological treatment modality that also damages normal tissue, including the skin, and causes radiation dermatitis (RD). Here, we explore the mechanism of acute epidermal damage in radiation dermatitis. Two distinctive phases in the damage response were identified: an early destructive phase, where a burst of reactive oxygen species induces loss of E-cadherin-mediated cell contact, followed by a regenerative phase, during which Wnt and Hippo signaling are activated. A blocking peptide, as well as a neutralizing antibody to E-cadherin, works synergistically with ionizing radiation to promote the epidermal damage. In addition, ROS disassembles adherens junctions in epithelial cells via posttranslational mechanisms, that is, activation of Src/Abl kinases and degradation of ß-catenin/E-cadherin. The key role of tyrosine kinases in this process is further substantiated by the rescue effect of the tyrosine kinase inhibitor genistein, and the more specific Src/Abl kinase inhibitor dasatinib: both reduced ROS-induced degradation of ß-catenin/E-cadherin in vitro and ameliorated skin damage in rodent models. Finally, we confirm that the same key molecular events are also seen in human radiation dermatitis. Therefore, we propose that loss of cell contact in epidermal keratinocytes through reactive oxygen species-mediated disassembly of adherens junctions is pivotal for the acute epidermal damage in radiation dermatitis.