PROJECT SUMMARY/ABSTRACT The incidence of most cancers has declined, but that of melanoma continues to rise. About 200,000 new cases of melanoma will be diagnosed in 2020. Although one major risk ultraviolet (UV) exposure, not all forms of melanoma are related to sun factor linked to melanoma incidence is exposure or occur in sun-exposed areas. A better understanding of UV-unrelated risk factors will help in developing more effective preventative strategies for melanoma. Recent studies, including ours, have shown that alcohol consumption is positively linked to an increased risk of melanoma. However, no studies have tested this connection and elucidated the mechanisms in vitro and in vivo. Alcohol is first metabolized to acetaldehyde (AcAH) by alcohol dehydrogenase (ADH), and then oxidized to acetic acid by mitochondrial aldehyde dehydrogenase 2 (ALDH2). Alongside these two major enzymes, another enzyme, cytochrome p450 2E1 (CYP2E1), is involved in the conversion of alcohol to AcAH and then to acetic acid. To understand the relation between alcohol-metabolizing enzymes and melanoma, we used The Cancer Genome Atlas (TCGA) database and analyzed ADH (1A, 1B and 1C), ALDH2 and CYP2E1. We found a strong correlation between low expression of ALDH2 mRNAs and worse prognosis of melanoma patients. ALDH2 could be inactivated by many environmental factors. To understand the role for ethanol and inactivated ALDH2 in skin biology, we used ten-week-old Aldh2 KO mice. Because carcinogenesis is a chronic process, we used a mouse model of chronic alcohol consumption, where 3-5% and 10% (v/v) ethanol was provided as sole drinking fluid. Our preliminary experiments revealed a unique DNA damage pattern and melanocyte proliferation by ethanol in Aldh2 KO mice. In this grant application, we hypothesize that ethanol and/or AcAH induce cellular stress responses leading to melanocyte activation and dark CPD formation, and propose to define transcriptomes associated with ethanol-induced skin changes in mice (Aim 1) and the mechanisms of dark CPD formation by ethanol/AcAH in melanocytes (Aim 2). The effect of ethanol and/or acetaldehyde on skin changes has yet to be studied. Given the unique DNA damage induced by UV, our findings that ethanol induces melanocyte proliferation and UV-induced DNA damage without UV exposure warrant further phenotypic, functional and mechanistic studies, which will be further explored in future R01 applications.