Itoh Y, Kajita M, Kinoh H, Mori H, Okada A, Seiki M
Department of Cancer Cell Research, Institute of Medical Science, University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan.
J Biol Chem. 1999 Nov 26;274(48):34260-6. doi: 10.1074/jbc.274.48.34260.
Among the five membrane-type matrix metalloproteinases (MT-MMPs), MT1-, MT2-, MT3-, and MT5-MMPs have about a 20-amino acid cytoplasmic tail following the transmembrane domain. In contrast, a putative transmembrane domain of MT4-MMP locates at the very C-terminal end, and the expected cytoplasmic tail is very short or nonexistent. Such sequences often act as a glycosylphosphatidylinositol (GPI) anchoring signal rather than as a transmembrane domain. We thus examined the possibility that MT4-MMP is a GPI-anchored proteinase. Our results showed that [(3)H]ethanolamine, which can be incorporated into the GPI unit, specifically labeled the MT4-MMP C-terminal end in a sequence-dependent manner. In addition, phosphatidylinositol-specific phospholipase C treatment released the MT4-MMP from the surface of transfected cells. These results indicate that MT4-MMP is the first GPI-anchored proteinase in the MMP family. During cultivation of the transfected cells, MT4-MMP appeared to be shed from the cell surface by the action of an endogenous metalloproteinase. GPI anchoring of MT4-MMP on the cell surface indicates a unique biological function and character for this proteinase.
在五种膜型基质金属蛋白酶（MT-MMPs）中，MT1-MMP、MT2-MMP、MT3-MMP和MT5-MMP在跨膜结构域之后有一段约20个氨基酸的胞质尾。相比之下，MT4-MMP的假定跨膜结构域位于最末端的C端，预期的胞质尾非常短或不存在。这样的序列通常作为糖基磷脂酰肌醇（GPI）锚定信号而非跨膜结构域。因此，我们研究了MT4-MMP是一种GPI锚定蛋白酶的可能性。我们的结果表明，可掺入GPI单元的[³H]乙醇胺以序列依赖的方式特异性标记MT4-MMP的C端。此外，磷脂酰肌醇特异性磷脂酶C处理可将MT4-MMP从转染细胞表面释放。这些结果表明MT4-MMP是MMP家族中首个GPI锚定蛋白酶。在转染细胞培养过程中，MT4-MMP似乎通过内源性金属蛋白酶的作用从细胞表面脱落。MT4-MMP在细胞表面的GPI锚定表明该蛋白酶具有独特的生物学功能和特性。
