Abstract 1271: UV irradiation and epigenetic change in melanocyte 5-hydroxymethylcytosine
Authors: Wang Kevin Y. , Zdravkovic Tanja , Lian Christine 
Published: September 2020

Background

Melanoma is the main cause of death from skin cancer. Excessive sun exposure with resultant UV irradiation, particularly during childhood, is established as its major environmental risk factor. Epigenetics are becoming increasingly recognized as potential reversible regulators of genomic anomalies responsible for cancerous growth. Loss of DNA hydroxymethylation marks 5-hydroxymethylcytosine (5-hmC) a functionally significant epigenetic event in melanomagenesis, but whether decreased 5-hmC is driven by UV irradiation remains unknown. The aim of this study is to characterize 5-hmC levels in potential melanoma precursor lesions and cultured samples by UV irradiation in vitro.

Methods

70 human skin excision cases of chronic UV exposed skin and matched controls were evaluated. In addition, discarded human foreskins were exposed to biologically relevant doses of UVB (302 nm) and UVA (365 nm) irradiation. Tissue samples were then incubated in DMEM medium and after 24 hours fixed in 10% formalin overnight and stored in 70% ethanol prior to sectioning and staining. A dual anti-5-hmC and anti-MART-1 immunohistochemical (IHC) staining protocol was performed, and resultant semiquantitative immunoreactivity scores were analyzed statistically by one-way ANOVA analysis and Bonferroni's Multiple comparisons test or unpaired T-test using GraphPad Prism version 7 (GraphPad Software, La Jolla, CA). All p-values were two-tailed, with a p&lt;0.05 considered statistically significant.

Results

When comparing sun-protected versus chronically sun-exposed sites of the excision specimens, lower levels of 5-hmC immunoreactivity were noted in melanocytes of sun-protected specimens than sun-exposed samples (p = 0.017). Moreover, a more significant difference (p = 0.0053) was detected between 5-hmC staining in normal skin melanocytes versus 5-hmC loss detected in so-called “atypical melanocytic hyperplasia of sun-damaged skin” that surrounds melanomas. Finally, we sought to determine whether we could induce in vitro a UV effect on 5-hmC similar to that seen with chronic sun-damage. Significant decreased immunoreactivity for 5-hmC was observed in foreskin melanocytes after UV irradiation- a finding that replicated what we observed in patient samples containing chronically UV-altered melanocytes.

Conclusions

Our results suggest that UVB irradiation's effect on the epigenome may play a crucial role in the development of melanoma. Implementation of the dual staining for anti-5-hmC and anti-MART-1 may be helpful in defining melanocytes altered in the direction of melanomagenesis, and thus may serve as a practical assay in determining potential melanoma precursor fields amenable to surveillance and prophylactic therapies.

Citation Format: Kevin Y. Wang, Tanja Zdravkovic, Christine Lian. UV irradiation and epigenetic change in melanocyte 5-hydroxymethylcytosine [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1271.