CD44v5 enhances the IL-4/IL-4Rα/STAT6/SAM68 aix inducing M2 polarization and promoting triple-negative breast cancer progression.

[BACKGROUND] Triple-negative breast cancer (TNBC) is an aggressive subtype with a poor prognosis and limited treatment options. Tumor-associated macrophages (TAMs), the predominant and abundant immune cells in the tumor immune microenvironment (TIME), critically drive TNBC progression. Consequently, TAM reprogramming has emerged as a promising therapeutic approach. However, a major barrier remains the incomplete understanding of the molecular mechanisms governing TAM reprogramming.

[METHODS] The role of CD44v5 in TAM polarization was evaluated with a CD44v5 monoclonal antibody and CD44v5-knockdown cell lines. Subsequently, cell functional assays, including wound healing, invasion, and colony formation assays, were performed to assess changes in the MDA-MB-468 cell line. Cytokine secretion levels (IL-4 and IL-6) were measured by electrochemiluminescence immunoassay (ECLIA).

[RESULTS] We found that M2 macrophages and tumor-associated macrophages (TAMs) polarized through the IL4/IL4R signaling pathway and exerted similar protumorigenic functions, and that IL4 is the key protumorigenic factor secreted by M2 macrophages. Interestingly, CD44v5 blockade effectively inhibited M2 polarization and promoted the phenotypic shift to M1 macrophages, which was supported by increased CD86 expression and decreased IL-4 secretion. Furthermore, molecular docking analysis and colocalization microscopy confirmed that CD44v5 colocalized with IL-4Rα, preventing its internalization.

[CONCLUSION] CD44v5 promotes M2 macrophage polarization by stabilizing and enhancing the IL-4Rα/STAT6/IL-4 signaling pathway, thereby facilitating the progression of triple-negative breast cancer. CD44v5 serves as an important therapeutic target for the reprogramming of both TAMs and M2 macrophages, thereby providing a novel strategy for the treatment of TNBC.