1. Specific Residues of RUNX2 Are Obligatory for Formation of BMP2-Induced RUNX2-SMAD Complex to Promote Osteoblast Differentiation
- Author
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Soraya E. Gutierrez, Faiza Afzal, Amjad Javed, Jong-Sup Bae, Jitesh Pratap, Gary S. Stein, Jane B. Lian, Janet L. Stein, Andre J. van Wijnen, and Kaleem Zaidi
- Subjects
Bone sialoprotein ,musculoskeletal diseases ,Paper ,Histology ,Cellular differentiation ,Molecular Sequence Data ,Nuclear Localization Signals ,Bone Morphogenetic Protein 2 ,Core Binding Factor Alpha 1 Subunit ,Smad Proteins ,SMAD ,Biology ,Bone morphogenetic protein 2 ,Mice ,Structure-Activity Relationship ,stomatognathic system ,Transforming Growth Factor beta ,medicine ,Animals ,Humans ,Amino Acid Sequence ,Amino Acids ,Osteoblasts ,musculoskeletal, neural, and ocular physiology ,Osteoblast ,Cell Differentiation ,Transforming growth factor beta ,musculoskeletal system ,Molecular biology ,RUNX2 ,medicine.anatomical_structure ,embryonic structures ,biology.protein ,Mutant Proteins ,Anatomy ,Signal transduction ,HeLa Cells ,Signal Transduction - Abstract
BMP2 signaling and RUNX2 regulatory pathways converge for transcriptional control of bone formation in vivo. SMAD proteins are recruited to RUNX2 regulatory complexes via an overlapping nuclear matrix targeting signal/Smad interacting domain sequence (391–432) in Runx2. To establish the contribution of RUNX2-SMAD interaction to osteoblastogenesis, we characterized a number of point mutants. Only a triple mutation of amino acids 426–428 (HTY-AAA) results in loss of RUNX2 interactions with either BMP2- or TGF-β- responsive SMADs and fails to integrate the BMP2/TGF-β signal on target gene promoters. In a Runx2 null cell reconstitution assay, the HTY mutant did not activate the program of osteoblast differentiation (alkaline phosphatase, collagen type 1, osteopontin, bone sialoprotein and osteocalcin) in response to BMP2 signaling. Thus, subnuclear targeting function and formation of a RUNX2-SMAD osteogenic complex are functionally inseparable. Taken together, these studies provide direct evidence that RUNX2 is essential for execution and completion of BMP2 signaling for osteoblast differentiation.
- Published
- 2008