OTUD4-ZMYND8-DDX3X Axis Drives Immunosuppressive Microenvironment in Spinal Metastases of Triple-Negative Breast Cancer.

Triple-negative breast cancer (TNBC) exhibits a high propensity for spinal metastasis, leading to severe morbidity and limited therapeutic responses. However, the molecular mechanisms driving spinal colonization remain poorly defined. Here, we identify the epigenetic reader ZMYND8 as a key mediator of TNBC spinal metastasis. ZMYND8 is significantly upregulated in spinal metastatic lesions and correlates with adverse patient outcomes. Transcriptomic profiling reveals that spinal metastases display profoundly immunosuppressive microenvironments, with elevated M2 macrophage infiltration positively associated with ZMYND8 expression. Mechanistically, ZMYND8 functions as a scaffold protein that promotes assembly of the DDX3X-CK1ε complex, thereby activating WNT/β-catenin signaling and promoting spinal metastasis. Furthermore, we identify OTUD4 as a bona fide deubiquitinase that directly interacts with and stabilizes ZMYND8, thereby enhancing TNBC cell migration, invasion, and spinal colonization. The resulting OTUD4-ZMYND8-DDX3X signaling axis drives canonical WNT/β-catenin signaling, upregulates CSF1 expression and promotes M2 polarization of macrophages, collectively fostering invasive behavior and establishing an immunosuppressive niche conducive to spinal metastasis. Collectively, these findings establish the OTUD4-ZMYND8-DDX3X axis as a pivotal regulator of spinal metastasis in TNBC and highlight its potential as a therapeutic target for inhibiting metastatic progression.