title: Identification of a homeodomain binding element in the bone sialoprotein gene promoter that is required for its osteoblast-selective expression.
abstract: Bone sialoprotein is a 70-kDa extracellular matrix component that is intimately associated with biomineralization, yet the cis-acting elements of the Bsp gene that restrict its expression to mineralizing cells remain uncharacterized. To identify such elements, we analyzed a 2472-base pair fragment of the murine promoter that directs osteoblast-selective expression of a luciferase reporter gene and found that the region between -338 and -178 relative to the transcriptional start is crucial for its osteoblast-selective activity. We identified an element within this region that binds a protein complex in the nuclear extracts of osteoblastic cells and is required for its transcriptional activity. Introduction of a mutation that disrupts a homeodomain binding site within this sequence eliminates both its in vitro binding and nearly all of the osteoblastic-selective activity of the 2472-base pair promoter. We further found that the Dlx5 homeoprotein, which is able to regulate the osteoblast-specific osteocalcin promoter, can bind this element and stimulate its enhancer activity when overexpressed in COS7 cells. These data represent the first description of an osteoblast-specific element within the bone sialoprotein promoter and demonstrate its regulation by a member of a family of factors known to be involved in skeletogenesis.
authors.affiliation: Department of Biological Chemistry, School of Medicine, University of Michigan, Ann Arbor, Michigan 48109-1078, USA.
authors.forename: M D
authors.initials: MD
authors.lastname: Benson
authors.forename: J L
authors.initials: JL
authors.lastname: Bargeon
authors.forename: G
authors.initials: G
authors.lastname: Xiao
authors.forename: P E
authors.initials: PE
authors.lastname: Thomas
authors.forename: A
authors.initials: A
authors.lastname: Kim
authors.forename: Y
authors.initials: Y
authors.lastname: Cui
authors.forename: R T
authors.initials: RT
authors.lastname: Franceschi
mesh_terms: D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D005786:Gene Expression Regulation; D018398:Homeodomain Proteins / Q000235:genetics*; D058574:Integrin-Binding Sialoprotein; D051379:Mice; D008969:Molecular Sequence Data; D009928:Organ Specificity; D010006:Osteoblasts / Q000502:physiology*; D011401:Promoter Regions, Genetic / Q000235:genetics*; D012795:Sialoglycoproteins / Q000235:genetics
chemical_list: D018398:Homeodomain Proteins; C546872:Ibsp protein, mouse; D058574:Integrin-Binding Sialoprotein; D012795:Sialoglycoproteins