Extracellular Matrix Regulations of Membrane Type 1-Matrix Metalloproteinase (MT1-MMP) and Matrix Metalloproteinase-2 (MMP-2) in Human Breast Fibroblasts.

摘要

The tissue inhibitors of metalloproteinases (TIMPs) are specific inhibitors of MMP activity. However, TIMP-2 acts as a positive regulator by promoting pro-MMP-2 activation by MT1-MMP. We showed that binding of either TIMP-2 or TIMP-4 to active MTl-MMP inhibits the autocatalytic turnover of MTl- MMP on the cell surface. In spite of TIMP-4's ability to bind pro-MMP-2 we demonstrated that TIMP-4, unlike TIMP-2, does not promote pro-MMP-2 activation by MTl-MMP. When co-expressed with TIMP-2, TIMP-4 competitively reduced pro-MMP- 2 activation by MTl-MMP. Recent evidence indicates that MT1-MMP undergoes ectodomain shedding. We analyzed the released MT1-MMP forms and found a complex pattern of shedding involving two major fragments of 50 and 18 kDa. Inhibition studies using TIMP-2 and TIMP-4 demonstrated both autocatalytic (18kDa) and non- catalytic (50kDa) shedding mechanisms. Our studies suggest that autocatalytic shedding evolved as a specific mechanism to terminate MTl-MMP activity on the cell surface by disrupting enzyme integrity at a vital structural site. In contrast, functional data suggest that the non-autocatalytic shedding generates soluble active MTl-MMP species capable of binding TIMP-2. In addition to a balance between TIMP-2 and TIMP-4, a balance between shedded MTl-MMP species may be critical factors in determining the pericellular and extracellular activity of this enzyme.