Smad-Runx interactions during chondrocyte maturation
UMass Chan Affiliations
Department of Cell BiologyDocument Type
Journal ArticlePublication Date
2001-03-27Keywords
AnimalsBone Morphogenetic Proteins
Cells, Cultured
Chick Embryo
Chondrocytes
Collagen
Core Binding Factor Alpha 1 Subunit
Core Binding Factor Alpha 2 Subunit
Core Binding Factor alpha Subunits
DNA-Binding ProteinsHypertrophyLuciferases*Neoplasm ProteinsPhosphoproteinsPromoter Regions, Genetic*Proto-Oncogene Proteins*Signal TransductionSmad ProteinsSmad5 ProteinTrans-ActivatorsTranscription FactorsTranscription, GeneticTransfectionCell Biology
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BACKGROUND: Intracellular signaling triggered by bone morphogenetic proteins (BMPs) results in activated Smad complexes that regulate transcription of BMP-responsive genes. However, the low specificity of Smad binding to regulatory sequences implies that additional tissue-specific transcription factors are also needed. Runx2 (Cbfal) is a transcription factor required for bone formation. We have examined the role of Smads and Runx2 in BMP induction of type X collagen, which is a marker of chondrocyte hypertrophy leading to endochondral bone formation. METHODS: Pre-hypertrophic chondrocytes from the cephalic portion of the chick embryo sternum were placed in culture in the presence or absence of rhBMP-2. Cultures were transiently transfected with DNA containing the BMP-responsive type X collagen promoter upstream of the luciferase gene. The cultures were also transfected with plasmids, causing over-expression of Smads or Runx2, or both. After 24-48 hours, cell extracts were examined for levels of luciferase expression. RESULTS: In the presence of BMP-2, chondrocytes over-expressing BMP-activated Smadl or Smad5 showed significant enhancement of luciferase production compared with that seen with BMP alone. This enhancement was not observed with over-expression of Smad2, a transforming growth factor beta (TGF-beta)-activated Smad. Overexpression of Runx2 in BMP-treated cultures increased transcriptional activity to levels similar to those seen with Smads 1 or 5. When chondrocytes were simultaneously transfected with both Runx2 and Smad 1 or 5, promoter activity was further increased, indicating that BMP-stimulated Smad activity can be augmented by increasing the levels of Runx2. CONCLUSIONS: These results implicate the skeletal tissue transcription factor Runx2 in regulation of chondrocyte hypertrophy and suggest that maximal transcription of the type X collagen gene in pre-hypertrophic chondrocytes involves interaction of BMP-stimulated Smads with Runx2. Clinical Relevance: Many skeletal abnormalities are associated with impaired regulation of chondrocyte hypertrophy in growth plates. These studies demonstrate that both BMP-activated Smads and Runx2 levels can modulate chondrocyte transition to hypertrophy.Source
J Bone Joint Surg Am. 2001;83-A Suppl 1(Pt 1):S15-22. Link to article on publisher's websitePermanent Link to this Item
http://hdl.handle.net/20.500.14038/49637PubMed ID
11263661Related Resources
Link to Article in PubMedCollections
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