Osteogenic protein-1 downregulates endothelin A receptors in primary rat osteoblasts.
Osteogenesis is a complex process whereby growth factors and mediators from both local and systemic sources modulate the bone-forming activities of osteoblasts. In the present study we utilized primary cultures of fetal rat calvarial cells to characterize osteoblast responsiveness to the vascular mediator endothelin-1 (ET-1) and to investigate whether ET-1 responses are regulated by osteogenic protein-1 (OP-1). We found that a 1- to 2-day exposure to OP-1 diminished ET-1 receptor ligand binding and signal transduction by downregulating ET-1 receptor mRNA expression. ET-1-mediated calcium signaling and ligand binding were completely abolished by the ETA receptor antagonist BQ-123, suggesting that ET-1 effects are mediated by this receptor. Northern analysis of total RNA revealed that ETA mRNA expression was inhibited approximately 50% by OP-1 treatment, whereas ETB receptor mRNA was not detected by this method of analysis. In OP-1-treated cultures, the magnitude and duration of ET-1 calcium signals varied among individual cells. This finding may be related to a heterogeneous OP-1 response, indicated by alkaline phosphatase induction in only a subpopulation of cells. These results suggest that modulation of osteoblast function by ET-1 occurs during distinct periods of phenotypic development and imply that downregulation of ET-1 responsiveness may be necessary for optimal bone formation in vivo.
Kitten
A M
AM
Department of Biochemistry, University of Texas Health Science Center, San Antonio 78284-7760, USA.
Harvey
S A
SA
Criscimagna
N
N
Asher
M
M
Lee
J C
JC
Olson
M S
MS
D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D055419:Bone Morphogenetic Protein 7; D019485:Bone Morphogenetic Proteins / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism; D015536:Down-Regulation / Q000187:drug effects*; D065128:Endothelin Receptor Antagonists; D019332:Endothelin-1 / Q000378:metabolism / Q000494:pharmacology*; D005333:Fetus; D006801:Humans; D007700:Kinetics; D010006:Osteoblasts / Q000187:drug effects / Q000378:metabolism*; D010456:Peptides, Cyclic / Q000494:pharmacology; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D051381:Rats; D017207:Rats, Sprague-Dawley; D044022:Receptor, Endothelin A; D017466:Receptors, Endothelin / Q000096:biosynthesis*; D011994:Recombinant Proteins / Q000494:pharmacology; D012886:Skull; D016212:Transforming Growth Factor beta; D010738:Type C Phospholipases / Q000378:metabolism
C525819:BMP7 protein, human; C525821:Bmp7 protein, rat; D055419:Bone Morphogenetic Protein 7; D019485:Bone Morphogenetic Proteins; D065128:Endothelin Receptor Antagonists; D019332:Endothelin-1; D010456:Peptides, Cyclic; D044022:Receptor, Endothelin A; D017466:Receptors, Endothelin; D011994:Recombinant Proteins; D016212:Transforming Growth Factor beta; D000469:Alkaline Phosphatase; D010738:Type C Phospholipases; D043265:Phosphatidylinositol Diacylglycerol-Lyase; C072247:cyclo(Trp-Asp-Pro-Val-Leu); D002118:Calcium