The ability of cancer cells to invade into surrounding tissues requires degradation of the extracellular matrix (ECM). Invasive structures, such as invadopodia, form on the plasma membrane of cancer cells and secrete ECM-degrading proteases that play crucial roles in cancer cell invasion. We have previously shown that protein tyrosine phosphatase alpha (PTPα) regulates focal adhesion formation and migration of normal cells. Here we report a novel role for PTPα in promoting triple-negative breast cancer cell invasion in vitro and in vivo. We show that PTPα knockdown reduces ECM degradation and cellular invasion of MDA-MB-231 cells through Matrigel. PTPα is not a component of TKS5-positive structures resembling invadopodia; rather, PTPα localizes with endosomal structures positive for MMP14, caveolin-1, and early endosome antigen 1. Furthermore, PTPα regulates MMP14 localization to plasma membrane protrusions, suggesting a role for PTPα in intracellular trafficking of MMP14. Importantly, we show that orthotopic MDA-MB-231 tumours depleted of PTPα exhibit reduced invasion into the surrounding mammary fat pad. These findings suggest a novel role for PTPα in regulating the invasion of triple-negative breast cancer cells.
Expression of receptor protein tyrosine phosphatase ζ is a risk factor for triple negative breast cancer relapse
