Membrane‐type 6 matrix metalloproteinase (MT6‐MMP, MMP‐25) is the second glycosyl‐phosphatidyl inositol (GPI)‐anchored MMP

A recently identified membrane‐type 6 matrix metalloproteinase (MT6‐MMP) has a hydrophobic stretch of 24 amino acids at the C‐terminus. This hydrophobicity pattern is similar to glycosyl‐phosphatidyl inositol (GPI)‐anchored MMP, MT4‐MMP, and other GPI‐anchored proteins. Thus, we tested the possibility that MT6‐MMP was also a GPI‐anchored proteinase. Our results showed that MT6‐MMP as well as MT4‐MMP were labeled with [3H]ethanolamine indicating the presence of a GPI unit with incorporated label. In addition, phosphatidyl inositol‐specific phospholipase C treatment released MT6‐MMP from the surface of transfected cells. These results strongly indicate that MT6‐MMP is a GPI‐anchored protein. Since two members of MT‐MMPs are now assigned as GPI‐anchored proteinase, MT‐MMPs can be subgrouped into GPI type and transmembrane type.