Identification of Key Genes Regulated by Lactylation Modification and Associated with Tumor Immune Microenvironment in Breast Cancer

Breast cancer (BRCA) is the most common cancer worldwide, with an incidence exceeding that of lung cancer. Protein lactylation, a newly identified post-translational modification involving the binding of lactic acid to lysine residues, plays an important role in BRCA. However, its role in BRCA progression remains largely unexplored. This study aims to identify and characterize the lactylation-related genes involved in BRCA biology. Transcriptomic and clinical data of BRCA and normal breast tissues were obtained from TCGA and GEO. Lactylation-related genes were curated from literature and intersected with BRCA datasets to identify candidates. A prognostic risk model was constructed using LASSO and Cox regression. Functional enrichment was performed using KEGG, GSVA, and GSEA. Immune correlations were evaluated by ESTIMATE, CIBERSORT. Single-cell RNA-seq data were integrated to assess gene expression heterogeneity across tumor and immune compartments. In vitro, MDA-MB-231 cells were treated with sodium L-lactate and lactylation-inducing agents, and gene expression was validated by Western blot and RT-qPCR, while EdU and wound healing assays evaluated proliferation and migration. We identified six hub genes associated with the immune microenvironment. Notably, S100A4 is significantly underexpressed, suggesting their potential regulatory roles in BRCA. Further analysis demonstrated that lactylation-related genes are closely linked to immune regulation in BRCA, indicating a possible crosstalk between metabolic modification and tumor immunity. Additionally, we found that lactylation significantly influences gene expression patterns and immune infiltration in BRCA. Importantly, lactic acid ions were shown to upregulate lactylation levels in BRCA cells, underscoring the functional impact of metabolic signals on post-translational modifications in tumorigenesis. Our findings indicate a potential mechanism wherein lactylation affects BRCA progression via lactic acid-driven regulation of the immune microenvironment; they also highlight the possible involvement of S100A4 in this process and offer new insights that could contribute to the diagnosis and treatment of BRCA.