Motor neuron and pancreas homeobox 1 (MNX1) suppresses Triple Negative Breast Cancer (TNBC) cell phagocytosis by macrophage through CD24 signaling.

Triple-negative breast cancer (TNBC) represents an aggressive subtype of breast cancer with limited therapeutic options. Motor neuron and pancreas homeobox 1 (MNX1) has been implicated in tumor progression, yet its roles in TNBC immune evasion remain unexplored. In the present study, we analyzed TCGA datasets and performed immunohistochemistry to evaluate MNX1 expression in TNBC tissues. DNA Affinity Purification and sequencing (DAP-seq) were used to identify MNX1 binding motifs. The regulatory relationship between MNX1 and CD24 was validated through dual luciferase reporter assays and expression manipulation in TNBC cell lines. Macrophage-mediated phagocytosis was assessed using in vitro co-culture systems and a humanized macrophage immune reconstruction mouse xenograft model. We found MNX1 expression was significantly elevated in TNBC tissues and correlated with poor patient prognosis. MNX1-knockdown significantly inhibited MDA-MB-468 cell proliferation in vitro and xenograft growth in vivo. In MDA-MB-231 cell, MNX1-overexpression promoted cell proliferation in vitro. We identified "TAATTA" as the MNX1 binding motif and demonstrated that MNX1 directly activates CD24 transcription. MNX1 knockdown in MDA-MB-468 cells enhanced macrophage phagocytosis, while its overexpression in MDA-MB-231 cells reduced phagocytosis. In the humanized mouse model, MNX1 downregulation increased macrophage infiltration and suppressed tumor growth. In summary, our findings reveal that MNX1 promotes TNBC immune evasion through transcriptional regulation of CD24. SIGNIFICANCE: We showed that CD24 is a novel target of transcription factor MNX1. MNX1-driven CD24-overexpression enables TNBC cells to evade from phagocytosis in both co-culturing TNBC cells with macrophage and in humanized macrophage immune reconstruction mouse xenograft model.