TSPYL5 Promotes Triple‐Negative Breast Cancer Metastasis by Antagonizing USP10‐Mediated PTEN Stabilization to Unleash a ZEB1‐Dependent EMT Program

ABSTRACT Hyperactivation of the PI3K/AKT pathway is a hallmark of metastatic triple‐negative breast cancer (TNBC), but its drivers in TNBC retaining wild‐type PTEN are poorly understood. Here, we identify Testis‐Specific Y‐Like Protein 5 (TSPYL5) ‐the top metastasis‐associated gene from an unbiased bioinformatics screen‐ as a master regulator that resolves this paradox. Clinically, TSPYL5 amplification and overexpression are robust predictors of metastatic progression and poor prognosis. High‐resolution single‐cell and spatial analyses reveal that TSPYL5 defines a malignant subpopulation with stem‐like, genomically unstable, and pro‐metastatic properties. Functionally, TSPYL5 is sufficient to drive spontaneous polymetastasis from orthotopic tumors and is indispensable for post‐intravasation colonization, culminating in overt liver metastases in 60% of animals—a phenotype absent in controls. Mechanistically, TSPYL5 sequesters the deubiquitinase USP10, thereby preventing it from stabilizing the tumor suppressor PTEN. This TSPYL5‐USP10 interaction triggers the proteasomal degradation of PTEN, circumventing its wild‐type status to hyperactivate PI3K/AKT signaling and unleash a ZEB1‐driven metastatic program. This study delineates a complete TSPYL5‐USP10‐PTEN axis, providing a new paradigm for the post‐translational tumor suppressor inactivation in TNBC. Our work validates TSPYL5 as a biomarker for PI3K pathway dependency and establishes the TSPYL5‐USP10 interface as a tractable therapeutic target to restore PTEN function and combat metastatic TNBC.