Abstract 6000: Distinct HOX gene family DNA methylation profiles in histologically normal skin dependent on dermoscopic pattern of adjacent nevi
Authors: Muse Meghan E. , Schaider Helmut , Oey Harald , Soyer H. Peter , Christensen Brock C. , Stark Mitchell S. 
Published: April 2023

Abstract
Melanoma may arise within a pre-existing nevus, but commonly forms in the skin adjacent to nevi. We have performed global DNA methylation profiling using the Illumina EPIC array (&gt;800K loci) of 32 dermoscopically ('globular' vs 'non-globular' pattern) and histopathologically classified nevi, together with matching adjacent perilesional skin, and discovered that methylation patterns can accurately decompose the proportion of cell types present in the tissue. In this study, we sought to assess whether there are differences in the DNA methylation profiles of histologically normal skin samples that surround nevi, independent of cellular composition. Among the 739,270 CpG loci included in the analysis, there were a total of 8,200 CpG loci identified as significantly differentially methylated (Q &lt; 0.05) in ‘globular skin’ vs ‘non-globular skin’ adjusted for age, sex, and the estimated relative proportions of epithelial cells, fibroblasts, and melanocytes in each sample. After imposing a more stringent threshold (M value of ≥0.5) a total 816 CpG loci were found to be DM, with 696 loci identified as significantly hypermethylated, and 120 loci significantly hypomethylated (Q &lt; 0.05 and ΔM &gt; 0.5) in ‘globular’ vs ‘non-globular’ skin. Mapping of the DM (Q &lt; 0.05 and |ΔM| &lt; 0.5) CpG loci to their respective genes revealed that eight of the top 20 DM genes, by proportion of differentially methylated loci, were positioned in proximity to suggest regulation of members of the HOX gene family. We next assessed the differential gene expression of the eight DM HOX genes in the perilesional skin as well as the matching adjacent nevus. After adjusting for age, sex, and sample cellular composition, none of the assessed HOX genes demonstrated statistically significant (P ≤ 0.05) differential expression in the nevi, however, ‘non-globular skin’ demonstrated a statistically significant (P &lt; 0.05) increase in the expression of five of the eight HOX genes relative to ‘globular skin’. Importantly, this increased gene expression corresponds to the methylation status of the DM loci. HOX genes are known to be involved in limb and axial development as well as the positioning of dermal fibroblasts. Moreover, melanocytes from different anatomic positions have distinct transcriptional profiles and the anatomical position of melanocytes plays a key role in determining whether genetic alterations will subsequently drive melanoma formation. This positioning of melanoma subtypes (cutaneous vs acral) was recently shown to be related to interaction of specific HOX genes with site-specific oncogenic alterations. The distinct HOX gene family members we have revealed, differ to those related to melanoma development and positioning, as such we propose that these may contribute to the positioning of acquired melanocytic nevi, and in combination with common somatic alterations in BRAF, may contribute to nevus formation.
Citation Format: Meghan E. Muse, Helmut Schaider, Harald Oey, H. Peter Soyer, Brock C. Christensen, Mitchell S. Stark. Distinct HOX gene family DNA methylation profiles in histologically normal skin dependent on dermoscopic pattern of adjacent nevi [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6000.