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AP-1 and Cbfa/runt physically interact and regulate parathyroid hormone-dependent MMP13 expression in osteoblasts
1Deutsches Krebsforschungszentrum Heidelberg, Division of Signal Transduction and Growth Control (B0800), Im Neuenheimer Feld 280, D-69120 Heidelberg, Germany.
The Journal of Biological Chemistry
|March 29, 2001
Summary
Parathyroid hormone (PTH) increases matrix metalloproteinase-13 (MMP13) expression by enabling transcription factors AP-1 and Cbfa/Runt to interact. This interaction, along with a specific promoter element, is crucial for MMP13 gene activation in bone cells.
Area of Science:
- Molecular Biology
- Biochemistry
- Genetics
Background:
- Matrix metalloproteinase-13 (MMP13), or collagenase-3, is implicated in bone remodeling and osteosarcoma.
- Parathyroid hormone (PTH) regulates calcium homeostasis and influences MMP13 expression in bone cells.
- Previous studies identified AP-1 and Cbfa/Runt transcription factor binding sites in the MMP13 promoter, crucial for PTH-induced expression.
Purpose of the Study:
- To investigate the molecular mechanisms underlying PTH-induced MMP13 expression.
- To determine if AP-1 and Cbfa/Runt transcription factors directly interact.
- To identify the specific domains involved in the interaction and their role in MMP13 promoter activity.
Main Methods:
- Demonstrated protein-protein interactions between c-Jun/c-Fos (AP-1 components) and Cbfa/Runt proteins using co-immunoprecipitation or similar assays.
- Mapped the interaction domains, focusing on the leucine zipper of AP-1 factors and the Runt domain of Cbfa/Runt proteins.
- Utilized reporter gene assays (transient transfection) in fibroblasts and osteosarcoma cells to assess the functional significance of identified promoter elements and protein interactions.
Main Results:
- Confirmed direct physical interaction between AP-1 (c-Jun, c-Fos) and Cbfa/Runt transcription factors.
- Showed that the leucine zipper domain of c-Jun/c-Fos and the Runt domain of Cbfa/Runt are essential for this interaction.
- Identified a novel proximal osteoblast-specific element 2 (OSE2) site overlapping with a TRE motif, in addition to a distal OSE2 site, both critical for enhanced MMP13 promoter activity.
Conclusions:
- The cooperative function of AP-1 and Cbfa/Runt transcription factors, mediated by direct interaction, is essential for PTH-induced MMP13 expression.
- The identified proximal OSE2 site and the interaction between AP-1 and Cbfa/Runt proteins are key regulatory elements for MMP13 gene transcription.
- These findings elucidate a critical molecular mechanism controlling MMP13 expression in bone cells, relevant to bone metabolism and pathology.