Abstract
Signals from bone morphogenetic protein receptors (BMPRs) and cell adhesion to type I collagen are both important for osteoblastic differentiation and functions. BMP signals are mediated mostly by Smad and collagen signals are transduced by integrins to activate focal adhesion kinase (FAK) and its downstream molecules. This study was undertaken to clarify how extracellular matrix collagen signals converge with BMP actions. We show that integrin activation by collagen was involved in BMP signals because disruption of either collagen synthesis or collagen-alpha2beta1-integrin binding inhibited the stimulatory effect of BMP-2 on osteoblastic MC3T3-E1 cells. Downstream signals of collagen-integrin might be FAK-Ras-extracellular signal-regulated kinase (ERK) in osteoblastic cells. We further show that Ras-ERK signals enhanced the transcriptional activity of Smad1 in response to BMP in these cells transiently transfected with expression plasmids for a constitutively active mutant RasV12, a dominant negative mutant RasN17, and an ERK phosphatase CL100. Ras-ERK signals did not augment the transcriptional activity of Smad3 in response to transforming growth factor beta (TGF-beta) receptor activation but that of Smad1 in response to BMPR activation as examined in COS-1 cells. These observations suggest that the Ras-ERK pathway downstream of integrin-FAK is involved in Smad1 signals activated by BMP and provide a possible mechanism for cooperation between intracellular signals activated by integrin and BMPRs in osteoblastic cells.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Activin Receptors, Type I / genetics
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Activin Receptors, Type I / metabolism
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Animals
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Bone Morphogenetic Protein 2
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Bone Morphogenetic Proteins / metabolism*
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Bone Morphogenetic Proteins / pharmacology
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Cell Differentiation
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Cells, Cultured
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Collagen / metabolism*
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DNA-Binding Proteins / genetics
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DNA-Binding Proteins / metabolism*
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Enzyme Inhibitors / pharmacology
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Epidermal Growth Factor / pharmacology
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Flavonoids / pharmacology
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Focal Adhesion Kinase 1
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Focal Adhesion Protein-Tyrosine Kinases
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Humans
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Integrins / metabolism
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Mice
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Mitogen-Activated Protein Kinases / antagonists & inhibitors
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Mitogen-Activated Protein Kinases / drug effects
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Mitogen-Activated Protein Kinases / metabolism*
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Osteoblasts / cytology
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Osteoblasts / drug effects
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Osteoblasts / metabolism*
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Protein Serine-Threonine Kinases
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Protein-Tyrosine Kinases / genetics
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Protein-Tyrosine Kinases / metabolism
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Receptor, Transforming Growth Factor-beta Type I
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Receptors, Collagen
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Receptors, Transforming Growth Factor beta / genetics
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Receptors, Transforming Growth Factor beta / metabolism
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Signal Transduction
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Smad Proteins
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Smad1 Protein
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Trans-Activators / genetics
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Trans-Activators / metabolism*
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Transcription, Genetic
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Transforming Growth Factor beta*
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ras Proteins / metabolism*
Substances
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BMP2 protein, human
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Bmp2 protein, mouse
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Bone Morphogenetic Protein 2
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Bone Morphogenetic Proteins
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DNA-Binding Proteins
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Enzyme Inhibitors
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Flavonoids
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Integrins
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Receptors, Collagen
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Receptors, Transforming Growth Factor beta
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SMAD1 protein, human
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Smad Proteins
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Smad1 Protein
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Smad1 protein, mouse
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Trans-Activators
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Transforming Growth Factor beta
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Epidermal Growth Factor
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Collagen
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Protein-Tyrosine Kinases
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Focal Adhesion Kinase 1
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Focal Adhesion Protein-Tyrosine Kinases
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PTK2 protein, human
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Ptk2 protein, mouse
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Protein Serine-Threonine Kinases
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Mitogen-Activated Protein Kinases
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Activin Receptors, Type I
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Receptor, Transforming Growth Factor-beta Type I
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ras Proteins
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2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one