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p68 (Ddx5) interacts with Runx2 and regulates osteoblast differentiation
Eric D Jensen1, Lingling Niu, Giuseppina Caretti
1The Cancer Center and Department of Orthopaedic Surgery, University of Minnesota, Minneapolis, Minnesota 55455, USA.
Journal of Cellular Biochemistry
|October 26, 2007
Summary
The transcription factor Runx2 interacts with the RNA helicase p68 (Ddx5). While p68 co-activates Runx2, it inhibits osteoblast differentiation, revealing a complex regulatory role in bone development.
Area of Science:
- Molecular Biology
- Developmental Biology
- Cell Biology
Background:
- Runx2 is a critical transcription factor for osteoblast differentiation.
- Runx2 integrates cellular signaling pathways through interactions with other proteins.
- Understanding Runx2's interactome is key to deciphering osteogenesis regulation.
Purpose of the Study:
- To identify novel proteins interacting with Runx2.
- To characterize the functional role of the identified protein p68 (Ddx5) in Runx2-mediated gene expression and osteoblast differentiation.
Main Methods:
- Affinity purification and proteomic techniques to identify Runx2 interacting proteins.
- Co-localization studies within the nucleus.
- In vitro transcription assays.
- Cellular differentiation assays using C2C12 cells.
- Gene expression analysis in calvarial progenitor cells.
Main Results:
- The DEAD box RNA helicase p68 (Ddx5) was identified as a novel Runx2 interacting protein.
- p68 co-localized with Runx2 in nuclear foci and acted as a co-activator for Runx2.
- p68's helicase activity was not required for its co-activation function.
- Suppression of p68 accelerated osteoblast differentiation in C2C12 cells.
- Runx2 was found to suppress p68 expression in calvarial progenitor cells.
Conclusions:
- p68 is a novel co-activator of Runx2, but paradoxically inhibits osteogenic differentiation of progenitor cells.
- Runx2 actively regulates p68 expression in osteoblast precursors.
- The interplay between Runx2 and p68 is crucial for controlling osteoblast specification and maturation.
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