Identification of Itch Mediators and Its Novel Pathway: Implications for Understanding Radiation-Induced Skin Effects

Background: Radiation-induced skin reactions often lead to itching and pain. While many cytokines bind and activate nociceptors to initiate pain and the precedent itch upon radiation-induced skin desquamation, little is known that radiotherapy-induced itch can arise from the activation of Notch signaling. With regard to the enhanced transactivation activity of Notch after irradiation and the Notch-induced intense scratching of mice, we anticipated that a downstream effector of Notch mediates the itch sensation. Aim: The purpose of this study was to investigate the role of Notch receptor in mediating radiation-induced itch. Methods: Primary human keratinocytes, HEK293T/17, and A549 cells with or without NICD (Notch intracellular domain) overexpression were applied for analytical assays, including qRT-PCR, SDS-PAGE, immunoprecipitation, and luciferase assays, for delineating the relationship between Notch and Cathepsin S as well as the effect of Cathepsin S on the itch-inducing stimulus, thymic stromal lymphopoietin (TSLP). Results: Cathepsin S mRNA and protein were upregulated in response to the overexpression of Notch intracellular domains in primary human keratinocytes. A consensus binding site for Notch-regulated transcription factor CBF-1 (C-repeat/dehydration-responsive element binding factor 1) was identified in the promoter region of Cathepsin S. Along with the observation that Cathepsin S immunoprecipitated with PAR2 (protease-activated receptor 2), TSLP