We seek to understand the molecular responses that occur when skin is exposed to UV radiation in order to devise novel strategies to protect against damage and carcinogenesis. In this proposal we will examine two major risk factors for skin cancer: UV radiation and pigment (melanin) phenotype. Our studies focus on the melanocyte, and its cell surface receptor, the melanocortin-1 receptor (Mc1r), which regulates melanin synthesis. We hypothesize that Mc1r protects melanocytes against UV-mediated mutagenesis and transformation by modulating melanization and recovery from UV-mediated cellular injury. Loss-of-function polymorphisms in Mc1r correlate with fair skin and a high incidence of melanoma, while robust Mc1r function correlates with darker skin and UV resistance. We have developed a novel genetically-matched murine model of human skin as well as a protocol for growing primary melanocytes from these mice. These isogenic melanocytes span eumelanotic, pheomelanotic, and amelanotic melanin composition, will serve a unique and potent tool to delineate the role of Mc1r function in response to UV. Using our unique animal model and primary melanocytes derived thereof, we propose the following aims:
Aim 1. Characterize the mechanism of Mc1r-mediated enhancement of nucleotide excision repair (NER);
Aim 2. Determine whether Mc1r signaling protects against UV-mediated oxidative damage;
and Aim 3. Determine the ability of pharmacologic Mc1r rescue to protect against UV damage. With respect to Aim 1, we will examine the role of Mc1r in the repair of UV-induced photolesions by southwestern and flow cytometric analysis and determine the influence of Mc1r on cellular levels of nucleotide excision repair enzymes by qRT-PCR and Western analysis. We will investigate a molecular link between Mc1r signaling and enhanced repair enzyme levels by examining expression of the NER enzymes basally and in the setting of UV irradiation and by investigating the ability of cAMP-responsive transcription factors downstream of Mc1r signaling (namely Mitf and CREB) to bind to and induce transcription of NER enzyme promoters.
In Aim 2 we will study whether pheomelanin, which is produced as a result of low Mc1r function, promotes oxidative damage in melanocytes by complementary measures of oxidative load (DCF-mediated fluorescence flow cytometry, Southwestern blotting, hOGG1-adapted Comet assay, TBARS assay, and direct quantification of oxidative DNA adducts by GC/MS). Importantly, we will directly test whether pheomelanin functions as a pro-carcinogen by an HPRT-based forward mutagenesis approach in primary melanocytes. Finally, we will directly test the ability of forskolin, an activator of adenylyl cyclase, to bypass defective Mc1r function to enhance recovery from UV-mediated DNA damage and to rescue UV protection in melanocytes and in whole skin. Together, these studies will lay the foundation for future translational studies designed to develop novel small molecule-based approaches for UV and cancer protection to prevent many cases of melanoma.

Public Health Relevance

Though it has long been known that people with functional defects of the melanocortin 1 receptor (Mc1r) protein are at high risk of developing melanoma, the way(s) in which Mc1r protects against melanoma are not understood. Using pigment cells known as melanocytes, we will study how the Mc1r protein influences UV- mediated DNA and cellular damage in melanocytes, and contributes to melanoma resistance. Our goal is to develop the strategy of pharmacologic Mc1r rescue toward translational applicability so that many cases of melanoma can be prevented.

National Institute of Health (NIH)
National Cancer Institute (NCI)
Research Project (R01)
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Cancer Etiology Study Section (CE)
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Ogunbiyi, Peter
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University of Kentucky
Schools of Medicine
United States
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Jarrett, Stuart G; Carter, Katharine M; Bautista, Robert-Marlo et al. (2018) Sirtuin 1-mediated deacetylation of XPA DNA repair protein enhances its interaction with ATR protein and promotes cAMP-induced DNA repair of UV damage. J Biol Chem 293:19025-19037
Jarrett, Stuart Gordon; Carter, Katharine Marie; D'Orazio, John August (2017) Paracrine regulation of melanocyte genomic stability: a focus on nucleotide excision repair. Pigment Cell Melanoma Res 30:284-293
Jarrett, Stuart G; Carter, Katharine M; Shelton, Brent J et al. (2017) The melanocortin signaling cAMP axis accelerates repair and reduces mutagenesis of platinum-induced DNA damage. Sci Rep 7:11708
Jarrett, Stuart G; D'Orazio, John A (2017) Hormonal Regulation of the Repair of UV Photoproducts in Melanocytes by the Melanocortin Signaling Axis. Photochem Photobiol 93:245-258
Wolf Horrell, Erin M; Jarrett, Stuart G; Carter, Katharine M et al. (2017) Divergence of cAMP signalling pathways mediating augmented nucleotide excision repair and pigment induction in melanocytes. Exp Dermatol 26:577-584
Wolf Horrell, Erin M; Boulanger, Mary C; D'Orazio, John A (2016) Melanocortin 1 Receptor: Structure, Function, and Regulation. Front Genet 7:95
Jarrett, Stuart G; Wolf Horrell, Erin M; D'Orazio, John A (2016) AKAP12 mediates PKA-induced phosphorylation of ATR to enhance nucleotide excision repair. Nucleic Acids Res 44:10711-10726
Jarrett, Stuart G; Wolf Horrell, Erin M; Boulanger, Mary C et al. (2015) Defining the Contribution of MC1R Physiological Ligands to ATR Phosphorylation at Ser435, a Predictor of DNA Repair in Melanocytes. J Invest Dermatol 135:3086-3095
Jarrett, Stuart G; D'Orazio, John A (2014) Ctr1-ing BRAF signaling with copper. Pigment Cell Melanoma Res 27:689-91
Jarrett, Stuart G; Wolf Horrell, Erin M; Christian, Perry A et al. (2014) PKA-mediated phosphorylation of ATR promotes recruitment of XPA to UV-induced DNA damage. Mol Cell 54:999-1011

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