Whole genome methylation sequencing reveals epigenetic landscape and abnormal expression of FABP5 in extramammary Paget's disease

BACKGROUND: Extramammary Paget's disease (EMPD) is a rare cutaneous malignant tumor with a high recurrence rate after surgery. However, the genetic and epigenetic alterations underlying its pathogenesis remain unknown. DNA methylation is an important epigenetic modification involved in many biological processes. METHODS: In this study, enzymatic methyl‐sequencing (EM‐seq) technique was used to investigate the landscape of genome‐wide DNA methylation from three pairs of tumor tissues and adjacent tissues of patients with EMPD. Additionally, we conducted histopathological examinations to assess the expression of fatty acid‐binding protein 5 (FABP5) in another three paired samples from EMPD patients. RESULTS: The cluster analysis showed the good quality of the samples. A differential methylation region (DMR) heat map was used to quantitatively characterize genome‐wide methylation differences between tumors and controls. Global DNA methylation level is lower in EMPD tissue compared to matched controls, indicating that DNA methylation discriminates between tumor and normal skin. And the top hypomethylation gene on the promoter region in tumor tissues was FABP5 on chromosome 8 with 38.44% decreased median methylation. We next identified the expression of FABP5 in paired tumors and adjacent tissues in three additional patients with EMPD. Immunofluorescence results showed FABP5 highly expressed in tumor tissues and co‐located with CK7, CK20 and EMA. GO and KEGG enrichment analysis showed DMR genes on promoter are mainly enriched in the calcium ion transport, GTPase mediated signal transduction, Rap1 signaling pathway and GnRH signaling pathway. CONCLUSION: Taken together, our findings provide the first description of the whole genome methylation map of EMPD and identify FABP5 as a pathogenic target of EMPD.