Loss of PTPN12 Stimulates Progression of ErbB2-Dependent Breast Cancer by Enhancing Cell Survival,Migration, and Epithelial-to-Mesenchymal Transition

PTPN12 is a cytoplasmic protein tyrosine phosphatase (PTP) reported to be a tumor suppressor in breast cancer, through its capacity to dephosphorylate oncogenic receptor protein tyrosine kinases (PTKs), such as ErbB2. However, the precise molecular and cellular impact of PTPN12 deficiency in breast cancer progression remains to be fully clarified. Here, we addressed this issue by examining the effect of PTPN12 deficiency on breast cancer progression in vivo, in a mouse model of ErbB2-dependent breast cancer using a conditional PTPN12-deficient mouse. Our studies showed that lack of PTPN12 in breast epithelial cells accelerated breast cancer development and lung metastases in vivo. PTPN12-deficient breast cancer cells displayed enhanced tyrosine phosphorylation of the adaptor Cas, the adaptor paxillin, and the kinase Pyk2. They exhibited no detectable increase in ErbB2 tyrosine phosphorylation. PTPN12-deficient cells were more resistant to anoikis and had augmented migratory and invasive properties. Enhanced migration was corrected by inhibiting Pyk2. PTPN12-deficient breast cancer cells also acquired partial features of epithelial-to-mesenchymal transition (EMT), a feature of more aggressive forms of breast cancer. Hence, loss of PTPN12 promoted tumor progression in a mouse model of breast cancer, supporting the notion that PTPN12 is a tumor suppressor in human breast cancer. This function was related to the ability of PTPN12 to suppress cell survival, migration, invasiveness, and EMT and to inhibit tyrosine phosphorylation of Cas, Pyk2, and paxillin. These findings enhance our understanding of the role and mechanism of action of PTPN12 in the control of breast cancer progression.