Abstract

HER2 and α V β 6 integrin are independent predictors of breast cancer survival and metastasis. We identify an α V β 6 /HER2 cross-talk mechanism driving invasion, which is dysregulated in drug-resistant HER2+ breast cancer cells. Proteomic analyses reveal ligand-bound α V β 6 recruits HER2 and a trafficking subnetwork, comprising guanosine triphosphatases RAB5 and RAB7A and the Rab regulator guanine nucleotide dissociation inhibitor 2 (GDI2). The RAB5/RAB7A/GDI2 functional module mediates direct cross-talk between α V β 6 and HER2, affecting receptor trafficking and signaling. Acute exposure to trastuzumab increases recruitment of the subnetwork to α V β 6 , but trastuzumab resistance decouples GDI2 recruitment. GDI2, RAB5, and RAB7A cooperate to regulate migration and transforming growth factor–β activation to promote invasion. However, these mechanisms are dysregulated in trastuzumab-resistant cells. In patients, RAB5A , RAB7A , and GDI2 expression correlates with patient survival and α V β 6 expression predicts relapse following trastuzumab treatment. Thus, the RAB5/RAB7A/GDI2 subnetwork regulates α V β 6 -HER2 cross-talk to drive breast cancer invasion but is subverted in trastuzumab-resistant cells to drive α V β 6 -independent and HER2-independent tumor progression.