Study on novel functions of membrane-type matrix metalloproteinase in tumor metastasis

膜型基质金属蛋白酶（MT1-MMP）表达于肿瘤细胞表面，被认为在肿瘤侵袭转移过程中起重要作用。然而，MT1-MMP的功能仍未得到解决，无法通过经典的生化方法进行研究。我们开发了一种新的表达克隆方法来筛选调节MT1-MMP活性或作为其底物的分子，并鉴定了几个分子。例如，syndecan-1的表达被证明与肿瘤的恶性程度具有反向相关关系，它被证明可以切割以脱落外显子结构域。syndecan-1的表达抑制了细胞在胶原上的迁移，而MT1-MMP对syndecan-1的切割作用则消除了这种作用。此外，我们发现转移抑制基因产物KiSS-1蛋白是MMP的底物。KiSS-1基因编码的转移蛋白肽也被MMP剪切。已知Metastin通过与g蛋白偶联受体（GPCR）结合来抑制细胞迁移。由于转移汀被肿瘤细胞产生的MMPs灭活，因此与转移汀和MMP抑制剂共同作用可以抑制表达GPCR的肿瘤细胞的迁移。这些结果表明，对MT1-MMP功能的研究可能有助于开发针对MT1-MMP的新疗法。

Membrane-type matrix metalloproteinase(MT1-MMP) is expressed on the surface of tumor cells, and thought to play an important role in tumor invasion and metastasis. However, the functions of MT1-MMP still remain unsolved, and would not be investigated by classical biochemical approach. We have developed a novel expression cloning method to screen molecules, which either regulate MT1-MMP activity or serve as substrates for it, and identified several molecules. For example, syndecan-1, expression of which is known to have reverse co-relation with the malignancy of tumors, was demonstrated to be cleaved to shed the ecto-domain. Expression of syndecan-1 was shown to suppress cell migration on collagen, which was abrogated by the cleavage of syndecan-1 by MT1-MMP. Furthermore, we identified metastasis suppressor gene product KiSS-1 protein as a substrate for MMP. Metastin peptide encoded by KiSS-1 gene was also shown to be cleaved by MMP. Metastin is known to repress cell migration by binding to the G-protein-coupled receptor(GPCR). Since metastin is inactivated by MMPs produced by tumor cells, migration of tumor cells expressing GPCR could be suppressed by co-treatment with metastin and MMP inhibitor. These results suggest that study on functions of MT1-MMP may contribute to the development of novel therapy targeting MT1-MMP.