NR4A3 potentials M1-like macrophage polarization to facilitate anti-tumor immune responses in breast cancer.

Breast cancer (BC) is commonly labeled a "cold tumor" due to its dense population of immunosuppressive cells, particularly M2-like macrophages, which contribute to its resistance to therapy. Thus, there is a pressing need to shift the macrophage polarization towards M1 and revitalize the tumor immune microenvironment (TIME) to improve BC prognosis. In this study, we leveraged published RNA-sequencing data and performed multiplex immunohistochemistry on clinical specimens to identify NR4A3 as a promising biomarker for favorable outcomes in BC. High NR4A3 expression correlates with an inflamed TIME, characterized by heightened T-cell infiltration and activation. NR4A3 was preferentially expressed in macrophages and fostered M1-like macrophage polarization through direct binding to p65, thereby enhancing NF-κB transcriptional activity. Overexpression of Nr4a3 in tumor-infiltrating macrophages significantly inhibited the growth of E0771 tumors in a syngeneic mouse model, accompanied by increased T-cell infiltration and elevated production of functional cytokines. Conversely, suppression of Nr4a3 in macrophages compromised T-cell recruitment and diminished their anti-tumor capabilities. Consistent with these findings, co-culture experiments involving human T cells and NR4A3-overexpressing THP1 cells further demonstrated enhanced T-cell functionality. Collectively, our findings uncover a novel role for NR4A3 in macrophage polarization and TIME remodeling, offering a potential biomarker for favorable BC prognosis and a therapeutic target to enhance immunotherapy efficacy.