MLK4 orchestrates macrophage-induced triple-negative breast cancer invasion and ECM remodeling via enhanced paracrine signaling and NF-κB-MMP axis activation.

Tumor-associated macrophages (TAMs) are important mediators of triple-negative breast cancer (TNBC) progression, yet the molecular mechanisms driving this process remain incompletely defined. In this study, we identified MLK4, a member of the MAP3K family, as a regulator of TAM-driven oncogenic processes in TNBC. Using a co-culture of TNBC cells with macrophages, we demonstrated that high MLK4 expression in TNBC is essential for macrophage-induced cancer cell proliferation, extracellular matrix (ECM) remodeling, migration, and invasion. Mechanistically, we showed that the cross-talk between TAMs and TNBC cells drives tumor aggressiveness via an MLK4-dependent mechanism by enhancing NF-κB activation and downstream matrix metalloproteinases (MMPs) expression. We also identified the most prominently upregulated factors, including CXCL1 and IL-8, during the co-culture of macrophages and TNBC cells. We further showed that MLK4 expression correlates with increased macrophage infiltration in TNBC patient samples, indicating its potential role in shaping the immunosuppressive tumor microenvironment. Summarizing, our findings uncover a paracrine signaling involving CXCL1 and MLK4-NF-κB-MMPs axis, which mediates the interactions between TAMs and TNBC cells, enhancing proliferation, mesenchymal transition, ECM remodeling and cancer invasion. This work elucidates a new mechanism of macrophage-induced tumor progression and highlights MLK4 as a promising therapeutic target for disrupting cancer cells-macrophage reciprocal communication in TNBC.