Matrix metalloproteinase-7 induces homotypic tumor cell aggregation via proteolytic cleavage of the membrane-bound Kunitz-type inhibitor HAI-1 [Molecular Bases of Disease]

Matrix metalloproteinase-7 (MMP-7) plays important roles in tumor progression and metastasis. Our previous studies have demonstrated that MMP-7 binds to colon cancer cells via cell surface-bound cholesterol sulfate and induces significant cell aggregation by cleaving cell-surface protein(s). These aggregated cells exhibit a dramatically enhanced metastatic potential. However, the molecular mechanism inducing this cell-cell adhesion through the proteolytic action of MMP-7 remained to be clarified. Here, we explored MMP-7 substrates on cell surface; the proteins on cell surface were first biotinylated and a labeled protein fragment specifically released from the cells after MMP-7-treatment was analyzed using LC-MS/MS. We found that hepatocyte growth factor activator inhibitor type 1 (HAI-1), a membrane-bound Kunitz-type serine protease inhibitor, is an MMP-7 substrate. We also found that the cell-bound MMP-7 cleaves HAI-1 mainly between Gly-451 and Leu-452 and thereby releases the extracellular region as soluble HAI-1 (sHAI-1). We further demonstrated that this sHAI-1 can induce cancer cell aggregation and determined that the HAI-1 region corresponding to amino acids 141-249, which does not include the serine protease inhibitor domain, has the cell aggregation-inducing activity. Interestingly, cell surface cholesterol sulfate-independent proteolytic action of MMP-7 is critical for the sHAI-1-mediated induction of cell aggregation, whereas cholesterol sulfate is needed for the MMP-7-catalyzed generation of sHAI-1. Considering that MMP-7-induced cancer cell aggregation is an important mechanism in cancer metastasis, we propose that sHAI-1 is an essential component of MMP-7-induced stimulation of cancer metastasis and may therefore represent a suitable target for antimetastatic therapeutic strategies.

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