title: Thrombospondin is an osteoblast-derived component of mineralized extracellular matrix.
abstract: Thrombospondin, the most abundant protein of platelet alpha granules, is a biosynthetic product of a variety of connective tissue cells and a component of many extracellular matrices. In this study, thrombospondin distribution in bone was investigated using a monoclonal antibody specific for the human protein. Thrombospondin was localized in osteoid of undemineralized, frozen sections of fetal subperiosteal bone, and identified as a component of mineralized bone matrix of neonatal and/or young (growing) bone of many animal species by Western blot analysis. Adult human bone cells were demonstrated to contain mRNA for thrombospondin by hybridization of a cDNA thrombospondin probe to a 6.1 kb mRNA. Pulse-chase experiments indicated that the protein was synthesized and the majority was secreted from osteoblastic cells. Treatment of the cells with TGF-beta (0.01-10 ng/ml) slightly decreased total thrombospondin synthesis, but caused an increase in the retention on newly synthesized thrombospondin in the cell layer/matrix fraction. In cell attachment assays, thrombospondin mediated adhesion, but not spreading of adult human bone cells.
authors.affiliation: Bone Research Branch, National Institute of Dental Research, Bethesda, Maryland 20892.
authors.forename: P G
authors.initials: PG
authors.lastname: Robey
authors.forename: M F
authors.initials: MF
authors.lastname: Young
authors.forename: L W
authors.initials: LW
authors.lastname: Fisher
authors.forename: T D
authors.initials: TD
authors.lastname: McClain
mesh_terms: D000818:Animals; D015153:Blotting, Western; D001846:Bone Development; D001857:Bone Matrix / Q000032:analysis*; D001842:Bone and Bones / Q000032:analysis* / Q000196:embryology; D002417:Cattle; D002448:Cell Adhesion; D002645:Chickens; D015342:DNA Probes; D004285:Dogs; D006023:Glycoproteins / Q000032:analysis* / Q000096:biosynthesis / Q000235:genetics; D000882:Haplorhini; D006801:Humans; D051379:Mice; D008903:Minerals / Q000378:metabolism*; D009693:Nucleic Acid Hybridization; D010006:Osteoblasts / Q000378:metabolism*; D011784:Quail; D012333:RNA, Messenger / Q000032:analysis; D011817:Rabbits; D051381:Rats; D012756:Sheep; D013552:Swine; D019699:Thrombospondins; D015291:Transforming Growth Factors / Q000494:pharmacology
chemical_list: D015342:DNA Probes; D006023:Glycoproteins; D008903:Minerals; D012333:RNA, Messenger; D019699:Thrombospondins; D015291:Transforming Growth Factors