PTEN Loss Promotes PI3Kβ Phosphorylation and EPHA2/SRC/p-PI3KβY962 Complex Assembly to Drive Tumorigenesis

Loss of tumor suppressor PTEN drives cancer progression and therapeutic resistance, yet no targeted therapies exist for PTEN-deficient tumors. Here, we identify a critical druggable mechanism where PTEN-loss induces PI3Kβ phosphorylation for tumorigenesis. Using BioID interactome, we uncovered phosphorylation-dependent PI3Kβ-EPHA2 interaction in PTEN-null cells, driven by p-PI3KβY962. PTEN functions as a tyrosine phosphatase that normally dephosphorylates p-PI3KβY962. In PTEN-deficient contexts, enhanced p-PI3KβY962 forms a complex with EPHA2 and SRC, where both kinases contribute to PI3Kβ phosphorylation, activating oncogenic pERK/c-MYC and pAKT pathways. We developed a selective p-PI3KβY962 antibody detecting p-PI3KβY962 in PTEN-deficient tumors across preclinical models and clinical tumor specimens. Disrupting p-PI3KβY962 suppressed tumor growth in multiple PTEN-null models. Dasatinib, an FDA-approved SRC/EPHA2 inhibitor, effectively reduced p-PI3KβY962 and inhibited tumor progression in PTEN-null but not PTEN-WT tumors. These findings establish p-PI3KβY962 as a druggable target and biomarker for developing targeted therapy in PTEN-deficient cancers beyond conventional PI3K kinase inhibition.