518 Chronic UV exposure decreases sun sensitivity by a tanning independent mechanism

Keratinocytes protect themselves from UV-induced damage and death by signalling to melanocytes produce transfer melanin their nuclei further UV damage. The keratinocyte-melanocyte communication axis defines the tanning response, which is integral epidermal homeostasis. We studied effects of occasional, moderate chronic UVA/UVB exposure on keratinocytes in vitro using immortalised human monoculture. show that led signature 7 mutations with predominant C>T nucleotide substitutions across genome. observed any treatment history were better able withstand exposure, showing decreased sensitivity, despite absence melanocytes. explored our findings vivo immunocompetent wild type mice, a striking decrease sunburn cells (apoptotic keratinocytes), TUNEL, p53 TT-dimers 24 hours after skin had prior significant This response independent protection, as mouse are intradermal do not keratinocytes. These data confers protection independently response. investigating transcriptional immune changes may infer mechanism.