E3 ubiquitin ligase Smurf1 mediates core-binding factor alpha1/Runx2 degradation and plays a specific role in osteoblast differentiation.
Osteoblast differentiation and bone formation is stimulated by bone morphogenetic protein (BMP)-2 and its downstream signaling molecules Smad1 and -5 and the osteoblast-specific transcription factor core-binding factor alpha1 (Cbfa1). Proteolytic degradation of Smad1 and Cbfa1 is proteasome-dependent, and intracellular concentrations of Smad1 and Cbfa1 are enhanced by inhibition of the 26 S proteasome. Smad1 degradation is mediated by the E3 ubiquitin ligase Smurf1 (Smad ubiquitin regulatory factor 1), but the specific E3 ligase responsible for Cbfa1 degradation has not been identified. Because Cbfa1 interacts with Smad1, whose degradation is mediated by Smurf1, we examined the effect of Smurf1 on Cbfa1 degradation in osteoblast precursor cells. Smurf1 interacts directly with Cbfa1 and mediates Cbfa1 degradation in a ubiquitin- and proteasome-dependent manner. Because Smurf1 controls the intracellular concentrations of several key molecules in the bone formation cascade, we examined the effect of a mutant form of Smurf1 in osteoblasts and found that expression of mutant Smurf1 markedly enhanced osteoblast differentiation. Smurf1 therefore appears to be an important regulatory factor in osteoblast differentiation and a potential molecular target for identification of bone anabolic agents.
Department of Cellular and Structural Biology, University of Texas Health Science Center, San Antonio, Texas 78229-3900, USA.
Ming
M
Zhao
Mei
M
Qiao
Babatunde O
BO
Oyajobi
Gregory R
GR
Mundy
Di
D
Chen
D000818:Animals; D001842:Bone and Bones / Q000502:physiology; D002454:Cell Differentiation; D002460:Cell Line; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D050659:Core Binding Factor Alpha 1 Subunit; D050660:Core Binding Factors; D018076:DNA, Complementary / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015151:Immunoblotting; D008025:Ligases / Q000378:metabolism / Q000502:physiology*; D008156:Luciferases / Q000378:metabolism; D051379:Mice; D009363:Neoplasm Proteins; D010006:Osteoblasts / Q000166:cytology* / Q000378:metabolism; D010447:Peptide Hydrolases / Q000378:metabolism; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D046988:Proteasome Endopeptidase Complex; D011485:Protein Binding; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D012886:Skull / Q000378:metabolism; D051785:Smad Proteins; D051898:Smad1 Protein; D015534:Trans-Activators / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism*; D014162:Transfection; D044767:Ubiquitin-Protein Ligases
D050659:Core Binding Factor Alpha 1 Subunit; D050660:Core Binding Factors; D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D009363:Neoplasm Proteins; D051785:Smad Proteins; D051898:Smad1 Protein; C497401:Smad1 protein, mouse; D015534:Trans-Activators; D014157:Transcription Factors; D005576:Colforsin; D008156:Luciferases; C492381:Smurf1 protein, mouse; D044767:Ubiquitin-Protein Ligases; D010447:Peptide Hydrolases; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease; D008025:Ligases