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

膜型基质金属蛋白酶（MT 1-MMP）表达于肿瘤细胞表面，在肿瘤的侵袭和转移中起重要作用。然而，MT 1-MMP的功能仍然没有得到解决，并且不能通过经典的生物化学方法来研究。我们开发了一种新型表达克隆方法来筛选调节MT 1-MMP活性或作为其底物的分子，并鉴定了几种分子。例如，多配体蛋白聚糖-1（其表达已知与肿瘤的恶性程度具有反向相关性）被证明被切割以脱落胞外结构域。多配体蛋白聚糖-1的表达被证明抑制胶原蛋白上的细胞迁移，这被MT 1-MMP对多配体蛋白聚糖-1的切割所废除。此外，我们确定了转移抑制基因产物KiSS-1蛋白作为MMP的底物。由KiSS-1基因编码的Metastin肽也显示被MMP切割。已知Metastin通过与G蛋白偶联受体（GPCR）结合来抑制细胞迁移。由于转移蛋白被肿瘤细胞产生的MMP灭活，表达GPCR的肿瘤细胞的迁移可以通过用转移蛋白和MMP抑制剂共同处理来抑制。提示对MT 1-MMP功能的研究有助于开发以MT 1-MMP为靶点的新型治疗药物。

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.