A trafficking regulatory subnetwork governs αVβ6 Integrin-HER2 crosstalk to control breast cancer invasion and drug resistance

Abstract HER2 and αVβ6 integrin are independent predictors of breast cancer survival and metastasis. We investigated αVβ6 signalling and identified an αVβ6/HER2 crosstalk mechanism, which drives invasion and is dysregulated in drug resistant HER2+ breast cancer cells. Proteomic approaches revealed ligand-bound αVβ6 recruits HER2 and a trafficking regulatory subnetwork comprising the small GTPases RAB5 and RAB7A, and the Rab regulator GDI2. We show that the RAB5/RAB7A/GDI2 functional module mediates direct crosstalk between αVβ6 and HER2, impacting receptor trafficking and signalling. Acute exposure to trastuzumab increases recruitment of the RAB5/RAB7A/GDI2 subnetwork to αVβ6, but trastuzumab resistance decouples GDI2 recruitment from this trafficking module. Consequently, GDI2, RAB5 and RAB7A cooperate to regulate migration and TGFβ activation to promote tumour cell invasion and dissemination. However, these mechanisms are dysregulated following acquired trastuzumab resistance. In patients, RAB5, RAB7A & GDI2 expression correlates with patient survival and αVβ6 expression predicts therapeutic response following breast cancer relapse. Thus, the RAB5/RAB7A/GDI2 subnetwork regulates αVβ6-HER2 crosstalk to drive breast cancer invasion, but is subverted in trastuzumab resistant cells to drive αVβ6- and HER2-independent tumour progression.