Abstract A34: MC1R signaling reduces UV mutagenesis by ATR-mediated recruitment of XPA to photolesions

The melanocortin 1 receptor (MC1R), which signals through cAMP, is a melanocytic Gs-coupled transmembrane receptor activated by binding to its high-affinity ligand, α-melanocyte stimulating hormone (MSH). Besides influencing pigment phenotype and mediating adaptive tanning, MC1R signaling is intricately linked with genome maintenance and DNA repair. Individuals harboring loss-of-function MC1R polymorphisms are UV sensitive and melanoma-prone. We have determined that MC1R-mediated cAMP signaling promotes nucleotide excision repair (NER) in a cAMP-dependent protein kinase A (PKA)-dependent manner. PKA directly phosphorylates ataxia telangiectasia and Rad3-related protein (ATR) at Ser435 which actively recruits the key NER protein xeroderma pigmentosum complementation group A (XPA) to sites of nuclear UV photodamage, accelerating clearance of UV-induced photolesions and reducing UV mutagenesis. Loss of Ser435 within ATR prevents PKA-mediated ATR phosphorylation, disrupts ATR-XPA binding, delays recruitment of XPA to UV-damaged DNA and elevates UV-induced mutagenesis. PKA-mediated ATR phosphorylation on Ser435 appears to induce a DNA repair-specific function of ATR independent of Chk1 phosphorylation and cell cycle arrest. Importantly, MC1R signaling defects and sub-optimal DNA repair are overcome by forskolin-mediated cAMP induction in melanocytes and in whole skin. Our findings mechanistically link cAMP-PKA signaling to NER and illustrate the potential benefits of cAMP pharmacological rescue to reduce UV mutagenesis in MC1R-defective, melanoma-susceptible individuals. Citation Format: Stuart Gordon Jarrett, Erin M. Wolf Horrell, Perry A. Christian, Jillian C. Vanover, Mary C. Boulanger, Yue Zou, John August D'Orazio. MC1R signaling reduces UV mutagenesis by ATR-mediated recruitment of XPA to photolesions. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Melanoma: From Biology to Therapy; Sep 20-23, 2014; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(14 Suppl):Abstract nr A34.