Activation of the mitogen-activated protein kinase pathway by bone sialoprotein regulates osteoblast differentiation.
Bone sialoprotein (BSP) is an abundant protein in the extracellular matrix of bone that has been suggested to have several different physiological functions, including the nucleation of hydroxyapatite (HA), promotion of cell attachment and binding of collagen. Studies in our lab have demonstrated that increased expression of BSP in osteoblast cells can increase expression of the osteoblast-related genes Runx2 and Osx as well as alkaline phosphatase and osteocalcin and increase matrix mineralization. To determine the molecular mechanisms responsible for the BSP-mediated increase in osteoblastic differentiation, several functional domain mutants of BSP were expressed in primary rat bone osteoblastic cells, including the contiguous glutamic acid sequences (polyGlu) and the arginine-glycine-aspartic acid (RGD) motif. Markers of osteoblast differentiation, including matrix mineralization and alkaline phosphatase staining, were increased in cells expressing BSP mutants of the polyGlu sequences but not in cells expressing RGD-mutated BSP. We also determined the dependence on integrin-associated pathways in promoting BSP-mediated differentiation responses in osteoblasts by demonstrating the activation of focal adhesion kinase, MAP kinase-associated proteins ERK1/2, ribosomal s6 kinase 2 and the AP-1 protein cFos. Thus, the mechanism regulating osteoblast differentiation by BSP was determined to be dependent on integrin-mediated intracellular signaling pathways.
Gordon
Jonathan A R
JA
Department of Biochemistry and Schulich Dentistry, CIHR Group in Skeletal Development and Remodeling, Schulich School of Medicine & Dentistry, University of Western Ontario, London, Ont., Canada.
Hunter
Graeme K
GK
Goldberg
Harvey A
HA
D000818:Animals; D001857:Bone Matrix / Q000201:enzymology; D002113:Calcification, Physiologic; D002454:Cell Differentiation; D002460:Cell Line; D004789:Enzyme Activation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D051416:Focal Adhesion Protein-Tyrosine Kinases / Q000378:metabolism; D006801:Humans; D058574:Integrin-Binding Sialoprotein; D020935:MAP Kinase Signaling System; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D010006:Osteoblasts / Q000166:cytology* / Q000201:enzymology*; D010012:Osteogenesis; D010766:Phosphorylation; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D051381:Rats; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000378:metabolism; D012795:Sialoglycoproteins / Q000378:metabolism*; D013379:Substrate Specificity
C546871:IBSP protein, human; C546872:Ibsp protein, mouse; C546873:Ibsp protein, rat; D058574:Integrin-Binding Sialoprotein; D016760:Proto-Oncogene Proteins c-fos; D012795:Sialoglycoproteins; D051416:Focal Adhesion Protein-Tyrosine Kinases; D038744:Ribosomal Protein S6 Kinases, 90-kDa; C069330:ribosomal protein S6 kinase, 90kDa, polypeptide 3; D048049:Extracellular Signal-Regulated MAP Kinases; D020928:Mitogen-Activated Protein Kinases