Overexpression of CD2/CD27 could inhibit the activation of nitrogen metabolism pathways and suppress M2 polarization of macrophages, thereby preventing brain metastasis of breast cancer

OBJECTIVE: Our study aimed to reveal the possible molecular mechanisms of CD2 and CD27 in influencing the tumor microenvironment of breast cancer (BC) brain metastasis based on the TCGA (The Cancer Genome Atlas) and SRA (Sequence Read Archive) databases. METHODS: We calculated the proportions of tumor-infiltrating immune cells and the immune and stromal cell scores in 1222 BC samples from the TCGA-BRCA dataset, followed by identification of candidate DEGs. We further screened for BC brain metastasis-related DEGs in the BC brain metastasis dataset SUB12911144 from the SRA database. Finally, we established a mouse breast cancer brain metastasis model for in vivo validation. RESULTS: We further screened two immune-regulatory DEGs (CD2 and CD27). GSEA analysis showed that the downregulation of CD2 and CD27 expression was closely related to the activation of nitrogen metabolism pathways. CIBERSORT algorithm analysis showed a correlation between the expression of 16 types of tumor-infiltrating immune cells and CD2 and 19 types of tumor-infiltrating immune cells and CD27. In addition, CD2 and CD27 expression were negatively associated with the proportion of M2 macrophages. In vivo experimental results demonstrated that overexpression of CD2/CD27 could suppress the M2 polarization of macrophages and inhibit breast cancer brain metastasis. CONCLUSION: In the tumor microenvironment, overexpression of CD2/CD27 inhibited the activation of nitrogen metabolism pathways and suppressed M2 polarization of macrophages, thereby preventing brain metastasis of breast cancer.