title: Requirement of BMP-2-induced phosphatidylinositol 3-kinase and Akt serine/threonine kinase in osteoblast differentiation and Smad-dependent BMP-2 gene transcription.
abstract: The mechanism by which bone morphogenetic protein-2 (BMP-2) induces osteoblast differentiation is not precisely known. We investigated the involvement of the phosphatidylinositol (PI) 3-kinase/Akt signal transduction pathway in modulation of this process. BMP-2 stimulated PI 3-kinase activity in osteogenic cells. Inhibition of PI 3-kinase activity with the specific inhibitor Ly-294002 prevented BMP-2-induced alkaline phosphatase, an early marker of osteoblast differentiation. Expression of dominant-negative PI 3-kinase also abolished osteoblastic induction of alkaline phosphatase in response to BMP-2, confirming the involvement of this lipid kinase in this process. BMP-2 stimulated Akt serine/threonine kinase activity in a PI 3-kinase-dependent manner in osteoblast precursor cells. Inhibition of Akt activity by a dominant-negative mutant of Akt blocked BMP-2-induced osteoblastic alkaline phosphatase activity. BMP-2 stimulates its own expression during osteoblast differentiation. Expression of dominant-negative PI 3-kinase or dominant-negative Akt inhibited BMP-2-induced BMP-2 transcription. Because all the known biological activities of BMP-2 are mediated by transcription via BMP-specific Smad proteins, we investigated the involvement of PI 3-kinase in Smad-dependent BMP-2 transcription. Smad5 stimulated BMP-2 transcription independent of addition of the ligand. Dominant-negative PI 3-kinase or dominant-negative Akt inhibited Smad5-dependent transcription of BMP-2. Furthermore dominant-negative Akt inhibited translocation of BMP-specific Smads into nucleus. Together these data provide the first evidence that activation of BMP receptor serine/threonine kinase stimulates the PI 3 kinase/Akt pathway and define a role for this signal transduction pathway in BMP-specific Smad function during osteoblast differentiation.
authors.affiliation: Department of Pathology, University of Texas Health Sciences Center, San Antonio, Texas 78229, USA. choudhury@uthscsa.edu
authors.forename: Nandini
authors.initials: N
authors.lastname: Ghosh-Choudhury
authors.forename: Sherry L
authors.initials: SL
authors.lastname: Abboud
authors.forename: Riko
authors.initials: R
authors.lastname: Nishimura
authors.forename: Anthony
authors.initials: A
authors.lastname: Celeste
authors.forename: Lenin
authors.initials: L
authors.lastname: Mahimainathan
authors.forename: Goutam Ghosh
authors.initials: GG
authors.lastname: Choudhury
mesh_terms: D030201:Activin Receptors, Type I / Q000378:metabolism; D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D055396:Bone Morphogenetic Protein 2; D052005:Bone Morphogenetic Protein Receptors, Type I; D019485:Bone Morphogenetic Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000502:physiology*; D002454:Cell Differentiation; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004789:Enzyme Activation; D005786:Gene Expression Regulation; D005799:Genes, Dominant; D015151:Immunoblotting; D008156:Luciferases / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D008856:Microscopy, Fluorescence; D009154:Mutation; D010006:Osteoblasts / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010750:Phosphoproteins / Q000378:metabolism; D011233:Precipitin Tests; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D017978:Receptors, Growth Factor; D011994:Recombinant Proteins / Q000378:metabolism; D015398:Signal Transduction; D051785:Smad Proteins; D051902:Smad5 Protein; D015534:Trans-Activators / Q000378:metabolism*; D014158:Transcription, Genetic; D014162:Transfection; D016212:Transforming Growth Factor beta
chemical_list: D030201:Activin Receptors, Type I; D000469:Alkaline Phosphatase; D055396:Bone Morphogenetic Protein 2; D052005:Bone Morphogenetic Protein Receptors, Type I; D019485:Bone Morphogenetic Proteins; D004268:DNA-Binding Proteins; D008156:Luciferases; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010750:Phosphoproteins; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D017978:Receptors, Growth Factor; D011994:Recombinant Proteins; D051785:Smad Proteins; D051902:Smad5 Protein; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; C525719:Bmp2 protein, mouse; C497798:Smad5 protein, mouse