Critical Role of Transient Activity of MT1-MMP for ECM Degradation in Invadopodia

Focal degradation of extracellular matrix (ECM) is the first step in the invasion of cancer cells. MT1-MMP is a potent membrane proteinase employed by aggressive cancer cells. In our previous study, we reported that MT1-MMP was preferentially located at membrane protrusions called invadopodia, where MT1-MMP underwent quick turnover. Our computer simulation and experiments showed that this quick turnover was essential for the degradation of ECM at invadopodia (Hoshino, D., et al., (2012) PLoS Comp. Biol., 8: e1002479). Here we report on characterization and analysis of the ECM-degrading activity of MT1-MMP, aiming at elucidating a possible reason for its repetitive insertion in the ECM degradation. First, in our computational model, we found a very narrow transient peak in the activity of MT1-MMP followed by steady state activity. This transient activity was due to the inhibition by TIMP-2, and the steady state activity of MT1-MMP decreased dramatically at higher TIMP-2 concentrations. Second, we evaluated the role of the narrow transient activity in the ECM degradation. When the transient activity was forcibly suppressed in computer simulations, the ECM degradation was heavily suppressed, indicating the essential role of this transient peak in the ECM degradation. Third, we compared continuous and pulsatile turnover of MT1-MMP in the ECM degradation at invadopodia. The pulsatile insertion showed basically consistent results with the continuous insertion in the ECM degradation, and the ECM degrading efficacy depended heavily on the transient activity of MT1-MMP in both models. Unexpectedly, however, low-frequency/high-concentration insertion of MT1-MMP was more effective in ECM degradation than high-frequency/low-concentration pulsatile insertion even if the time-averaged amount of inserted MT1-MMP was the same. The present analysis and characterization of ECM degradation by MT1-MMP together with our previous report indicate a dynamic nature of MT1-MMP at invadopodia and the importance of its transient peak in the degradation of the ECM.Author Summary: Metastasis is the major cause of death in cancer patients. If metastasis is blocked, the survival rate will be greatly increased. Cancer cells are surrounded by ECM (extracellular matrix), which prevents their free movement. MT1-MMP is a potent membrane proteinase that degrades ECM, which is the first step of cancer cell invasion. Thus, the control of MT1-MMP activity is a key to the prevention of metastasis. Here we found a sharp transient peak in the ECM-degrading activity of MT1-MMP by computer simulations, and computational elimination of this peak greatly prolonged the ECM degradation. MT1-MMP is transported intracellularly to the surface of the membrane of cancer cells, and its insertion into the membrane is thought to occur in a pulsatile manner. Therefore, we asked whether the ECM-degrading efficacy was the same in low-frequency/high-concentration and high-frequency/low-concentration insertions of MT1-MMP. Unexpectedly, the low-frequency/high-concentration regimen resulted in much faster ECM degradation even if the time-averaged amount of MT1-MMP insertion was the same. Thus, reduction of the sharp transient activity and vesicular content of MT1-MMP are important therapeutic targets.