PTPN1 and breast carcinoma: Activated calpain cleaves and activates PTP1B, which can then dephosphorylate Cav-1 tyrosine 14, as shown in Figure 3E. PTP1B was previously shown to bind and dephosphorylate Cav-1 and thereby decrease phospho-Cav-1-mediated breast cancer cell migration [16,47].