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Membrane type 4 matrix metalloproteinase (MT4-MMP, MMP-17) is a glycosylphosphatidylinositol-anchored proteinase
1Department of Cancer Cell Research, Institute of Medical Science, University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan.
Abstract:
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.
Insights
Matrix metalloproteinase 4 (MT4-MMP) is the first identified GPI-anchored proteinase in the MMP family. This unique anchoring mechanism suggests distinct biological functions for MT4-MMP.
Area of Science:
- Biochemistry
- Molecular Biology
- Cell Biology
Background:
- Matrix metalloproteinases (MMPs) are crucial enzymes involved in extracellular matrix remodeling.
- Most membrane-type MMPs (MT-MMPs) possess a cytoplasmic tail, but MT4-MMP has a unique C-terminal structure.
- This unique structure suggests a potential alternative membrane anchoring mechanism for MT4-MMP.
Purpose of the Study:
- To investigate whether MT4-MMP is anchored to the cell membrane via glycosylphosphatidylinositol (GPI).
- To characterize the anchoring mechanism of MT4-MMP.
Main Methods:
- Transfection of cells with MT4-MMP.
- Labeling with [(3)H]ethanolamine to detect GPI incorporation.
- Treatment with phosphatidylinositol-specific phospholipase C (PI-PLC) to assess release from the cell surface.
Main Results:
- [(3)H]ethanolamine specifically labeled the C-terminal end of MT4-MMP in a sequence-dependent manner.
- PI-PLC treatment released MT4-MMP from the surface of transfected cells.
- MT4-MMP was observed to be shed from the cell surface by endogenous metalloproteinases.
Conclusions:
- MT4-MMP is the first identified GPI-anchored proteinase within the MMP family.
- GPI anchoring confers unique biological properties and functions to MT4-MMP.
- The shedding of MT4-MMP suggests its involvement in extracellular matrix dynamics.