MYO1G promoterhypomethylation correlateswith its mRNA expression,lymphocyte infiltration,and immunotherapyresponse in melanoma

Objectives: Myosin IG (MYO1G) plays a vital role in triggering an immune response via regulating T cell migration to detect antigen-presenting cells. However, the biological and clinical significance of MYO1G DNA methylation and gene expression in melanoma and its immune microenvironment remains unknown.

Materials and methods: We investigated and corroborated the correlations of MYO1G DNA methylation with gene expression, and clinicopathologic parameters in 461 melanomas from The Cancer Genome Atlas (TCGA). Subsequently, we associated MYO1G gene expression with overall survival in two independent cohorts including 94 immunotherapy-treated melanoma patients and 54 stage IV melanoma patients, respectively. Finally, the quantitative methylation-specific PCR (qMSP) assays were developed to measure the methylation levels of the cg22111043 and cg10673833 CpG sites located on MYO1G promoter region, and targeted bisulfite sequencing assay was used to validate accuracy of qMSP. We linked the methylation levels of the two CpG sites with MYO1G expression and progression-free survival in our cohort of 104 melanoma patients treated with immunotherapy. we used the AI-based cell segmentation and classification software Hover-Net to perform cell count and statistical analysis on the whole-slide images of pathology from 104 melanoma patients.

Results: We observed that MYO1G gene expression exhibited a significantly inverse correlation with its promoter methylation. Moreover, hypomethylation in MYO1G promoter (corresponding to high gene expression level) was significantly associated with enhanced infiltration levels of immune cells (CD8+ T cell, M1 macrophage, activated natural killer cells estimated by gene expression), increased cytolytic activity, augmented expression level of immune checkpoint molecules (PDCD1, LAG3, CTLA4, CD274, BTLA, TIGIT and HAVCR2) and favorable prognosis in melanoma. In the independent melanoma cohorts receiving immune checkpoint blockade treatment, high MYO1G expression was significantly linked to improved clinical outcome. In our cohort, patients with MYO1G promoter hypomethylation showed significantly elevated tumor-infiltrating lymphocytes level and prolonged progression-free survival after immunotherapy.

Conclusion: Our study highlights MYO1G promoter methylation as a key regulator of gene expression and a potential prognostic and predictive biomarker for immunotherapy response in melanoma. These findings offer new insights into the role of MYO1G in enhancing immune response in tumors