Characterization of bone morphogenetic protein-6 signaling pathways in osteoblast differentiation.
Bone morphogenetic protein (BMP)-6 is a member of the transforming growth factor (TGF)-(&bgr;) superfamily, and is most similar to BMP-5, osteogenic protein (OP)-1/BMP-7, and OP-2/BMP-8. In the present study, we characterized the endogenous BMP-6 signaling pathway during osteoblast differentiation. BMP-6 strongly induced alkaline phosphatase (ALP) activity in cells of osteoblast lineage, including C2C12 cells, MC3T3-E1 cells, and ROB-C26 cells. The profile of binding of BMP-6 to type I and type II receptors was similar to that of OP-1/BMP-7 in C2C12 cells and MC3T3-E1 cells; BMP-6 strongly bound to activin receptor-like kinase (ALK)-2 (also termed ActR-I), together with type II receptors, i.e. BMP type II receptor (BMPR-II) and activin type II receptor (ActR-II). In addition, BMP-6 weakly bound to BMPR-IA (ALK-3), to which BMP-2 also bound. In contrast, binding of BMP-6 to BMPR-IB (ALK-6), and less efficiently to ALK-2 and BMPR-IA, together with BMPR-II was detected in ROB-C26 cells. Intracellular signalling was further studied using C2C12 and MC3T3-E1 cells. Among the receptor-regulated Smads activated by BMP receptors, BMP-6 strongly induced phosphorylation and nuclear accumulation of Smad5, and less efficiently those of Smad1. However, Smad8 was constitutively phosphorylated, and no further phosphorylation or nuclear accumulation of Smad8 by BMP-6 was observed. These findings indicate that in the process of differentiation to osteoblasts, BMP-6 binds to ALK-2 as well as other type I receptors, and transduces signals mainly through Smad5 and possibly through Smad1.
Ebisawa
T
T
Department of Biochemistry, The Cancer Institute of JFCR, and Research for the Future Program, Japan Society for the Promotion of Science, Toshima-ku, Tokyo 170-8455, Japan.
Tada
K
K
Kitajima
I
I
Tojo
K
K
Sampath
T K
TK
Kawabata
M
M
Miyazono
K
K
Imamura
T
T
D016475:3T3 Cells; D030201:Activin Receptors, Type I; D030301:Activin Receptors, Type II; D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D055418:Bone Morphogenetic Protein 6; D052005:Bone Morphogenetic Protein Receptors, Type I; D052006:Bone Morphogenetic Protein Receptors, Type II; D019485:Bone Morphogenetic Proteins / Q000494:pharmacology / Q000502:physiology*; D002454:Cell Differentiation; D002455:Cell Division; D002460:Cell Line; D007700:Kinetics; D051379:Mice; D010006:Osteoblasts / Q000166:cytology*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism / Q000502:physiology; D017978:Receptors, Growth Factor / Q000502:physiology; D011994:Recombinant Proteins / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D014162:Transfection
C525817:Bmp6 protein, mouse; D055418:Bone Morphogenetic Protein 6; D019485:Bone Morphogenetic Proteins; D017978:Receptors, Growth Factor; D011994:Recombinant Proteins; D017346:Protein Serine-Threonine Kinases; D030201:Activin Receptors, Type I; D030301:Activin Receptors, Type II; C498211:BMPR1A protein, human; C498214:BMPR1B protein, human; C498219:Bmpr2 protein, mouse; D052005:Bone Morphogenetic Protein Receptors, Type I; D052006:Bone Morphogenetic Protein Receptors, Type II; D000469:Alkaline Phosphatase