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Identification of the membrane-type matrix metalloproteinase MT1-MMP in osteoclasts
T Sato1, M del Carmen Ovejero, P Hou
1Department of Basic Research, Center for Clinical & Basic Research, Ballerup, Denmark.
Abstract:
The osteoclasts are the cells responsible for bone resorption. Matrix metalloproteinases (MMPs) appear crucial for this process. To identify possible MMP expression in osteoclasts, we amplified osteoclast cDNA fragments having homology with MMP genes, and used them as a probe to screen a rabbit osteoclast cDNA library. We obtained a cDNA of 1,972 bp encoding a polypeptide of 582 amino acids that showed more than 92% identity to human, mouse, and rat membrane-type 1 MMP (MT1-MMP), a cell surface proteinase believed to trigger cancer cell invasion. By northern blotting, MT1-MMP was found to be highly expressed in purified osteoclasts when compared with alveolar macrophages and bone stromal cells, as well as with various tissues. In situ hybridization on bone sections showed that MT1-MMP is expressed also in osteoclasts in vivo. Antibodies recognizing MT1-MMP reacted with specific plasma membrane areas corresponding to lamellipodia and podosomes involved, respectively, in migratory and attachment activities of the osteoclasts. These observations highlight how cells might bring MT1-MMP into contact with focal points of the extracellular matrix, and are compatible with a role of MT1-MMP in migratory and attachment activities of the osteoclast.
Insights
Osteoclasts utilize membrane-type 1 MMP (MT1-MMP) for bone resorption. This study confirms MT1-MMP expression in osteoclasts, suggesting its role in cell migration and matrix attachment.
Area of Science:
- Cell Biology
- Biochemistry
- Molecular Biology
Background:
- Osteoclasts are key cells in bone resorption.
- Matrix metalloproteinases (MMPs) are implicated in bone resorption.
- The specific MMPs involved in osteoclast function require further elucidation.
Purpose of the Study:
- To identify and characterize MMP expression in osteoclasts.
- To investigate the role of identified MMPs in osteoclast activity.
Main Methods:
- Screening of a rabbit osteoclast cDNA library using MMP homology probes.
- Northern blotting to assess MT1-MMP expression levels.
- In situ hybridization to localize MT1-MMP expression in bone tissue.
- Immunohistochemistry using anti-MT1-MMP antibodies.
Main Results:
- A cDNA encoding a protein highly homologous to human, mouse, and rat membrane-type 1 MMP (MT1-MMP) was identified.
- MT1-MMP showed high expression in purified osteoclasts compared to other cell types and tissues.
- In situ hybridization confirmed MT1-MMP expression in osteoclasts in vivo.
- Antibodies localized MT1-MMP to osteoclast lamellipodia and podosomes, sites of migration and attachment.
Conclusions:
- Osteoclasts express MT1-MMP, a proteinase previously linked to cancer cell invasion.
- MT1-MMP localization suggests a role in osteoclast migration and extracellular matrix interaction.
- These findings provide novel insights into the molecular mechanisms of bone resorption.