The continuous increase in incidence rates of melanoma suggests novel prevention strategies may be needed in addition to current UVR-avoidance methods. Our long-term goal is to develop such prevention strategies based on a comprehensive understanding of the sex differentiated DNA damage repair in normal human melanocytes. The objective of this R21 proposal is to determine the sex hormonal regulation of UVR- induced DNA damage repair in human melanocytes in vitro and in vivo. Our preliminary epidemiology data showed that salivary testosterone (T) level and T/E2 (estradiol) levels is inversely correlated with melanoma risk; while our cell biology data showed that addition of testosterone in culture media enhanced DNA repair in normal human melanocytes. Our central hypothesis is that higher testosterone levels, or higher T/E2 ratios, protect NHMs from UV-induced DNA damage involving PARP1. We also hypothesize that NHMs from males and females require a different balanced T/E2, as the T/E2 levels apparently dramatically differ in the two sexes. Two specific aims are proposed: Specific Aim 1: To determine the T and T/E2 effects in DNA damage responses in NHMs in men and women (in vivo study). Human subjects will be recruited, and skin will be treated with solar simulated UV radiation in the absence and presence of topical application of testosterone (to alter T or T/E2 ratios). DNA damage markers, hormone receptors (AR and GPER1) and PARP1 levels will be monitored following a time course and percentage of marker positive cells will be compared in different conditions in melanocytes and other skin cells. The keratinocytes-melanocytes interaction impacted by sex hormones will be examined by TNFα and TNFR1. Specific Aim 2: To test T/E2 effect in cultured melanocytes derived from male or female origins and to determine sex hormone-modulated DNA repair pathway in vitro. Hormonal effect will be detected by inclusion of the hormones at various ratios before UVR treatment. Gene knockdown of AR and GPER1, or AR-specific inhibitors or agonists will be used to manipulate T/AR and E2/GPER1, and DNA damage responses and signal pathways will be examined. The innovation: to the best of our knowledge, this study is the first to hypothesize a balanced T and E2 is critical for skin melanoma prevention with T/AR system acting as a tumor suppressor through enhancing DNA repair capacity. The proposed study is significant because it is expected to make a paradigm change in melanoma prevention by adding new parameters such as sex hormone test for risk assessment, or adjusting hormone levels through diet or supplement for prevention. If successful, it is expected to lead to a paradigm change of the prevention from current “avoiding UVR” to future “avoiding UVR plus hormone balance”.

Melanoma incidence rates continue to increase with undefined etiological reasons, with women at reproductive age especially susceptible to melanoma as compared to men of the same younger age. In this application we investigate a sex hormone-regulated DNA repair mechanism for explanation of the age-dependent sex difference in melanoma incidence. Completion of this study will provide a paradigm change to melanoma prevention in the future.