SILAC proteomics based on 3D cell spheroids unveils the role of RAC2 in regulating the crosstalk between triple-negative breast cancer cells and tumor-associated macrophages.

Triple-negative breast cancer (TNBC) is the most aggressive subtype of breast cancer, and is characterized by a high infiltration of tumor-associated macrophages (TAMs). TAMs contribute significantly to tumor progression by intricately interacting with tumor cells. Deeply investigating the interaction between TNBC cells and TAMs is of great importance for finding potential biomarkers and developing novel therapeutic strategies to further improve the clinical outcomes of TNBC patients. In this study, we confirmed the interplay using both 3D and 2D co-culture models. The stable-isotype labeling by amino acids in cell culture (SILAC)-based quantitative proteomics was conducted on 3D cell spheroids containing TNBC cells and macrophages to identify the potential candidate in regulating the crosstalk between TNBC and TAMs. Ras-related C3 botulinum toxin substrate 2 (RAC2) was identified as a potential molecule for further exploration, given its high expression in TNBC and positive correlation with M2 macrophage infiltration. The suppression of RAC2 inhibited TNBC cell proliferation, migration, invasion, and epithelial-mesenchymal transition (EMT) in vitro. Meanwhile, knocking down RAC2 in TNBC cells impaired macrophage recruitment and M2 polarization. Mechanistically, RAC2 exerted its roles in TNBC cells and TAMs by regulating the activation of P65 NF-κB and P38 MAPK, while TAMs further elevated RAC2 expression and P65 NF-κB activation by secreting soluble mediators including IL-10. These findings highlight the significance of RAC2 as a crucial molecule in the crosstalk between TNBC and TAMs, suggesting it could be a promising therapeutic target in TNBC.