title: Down-regulation of ubiquitin ligase Cbl induced by twist haploinsufficiency in Saethre-Chotzen syndrome results in increased PI3K/Akt signaling and osteoblast proliferation.
abstract: Genetic mutations of Twist, a basic helix-loop-helix transcription factor, induce premature fusion of cranial sutures in Saethre-Chotzen syndrome (SCS). We report here a previously undescribed mechanism involved in the altered osteoblastogenesis in SCS. Cranial osteoblasts from an SCS patient with a Twist mutation causing basic helix-loop-helix deletion exhibited decreased expression of E3 ubiquitin ligase Cbl compared with wild-type osteoblasts. This was associated with decreased ubiquitin-mediated degradation of phosphatidyl inositol 3 kinase (PI3K) and increased PI3K expression and PI3K/Akt signaling. Increased PI3K immunoreactivity was also found in osteoblasts in histological sections of affected cranial sutures from SCS patients. Transfection with Twist or Cbl abolished the increased PI3K/Akt signaling in Twist mutant osteoblasts. Forced overexpression of Cbl did not correct the altered expression of osteoblast differentiation markers in Twist mutant cells. In contrast, pharmacological inhibition of PI3K/Akt, but not ERK signaling, corrected the increased cell growth in Twist mutant osteoblasts. The results show that Twist haploinsufficiency results in decreased Cbl-mediated PI3K degradation in osteoblasts, causing PI3K accumulation and activation of PI3K/Akt-dependent osteoblast growth. This provides genetic and biochemical evidence for a role for Cbl-mediated PI3K signaling in the altered osteoblast phenotype induced by Twist haploinsufficiency in SCS.
authors.affiliation: Laboratory of Osteoblast Biology and Pathology, INSERM U 606, Lariboisière Hospital, 2 rue Ambroise Paré, 75475 Paris Cedex 10, France.
authors.forename: Hind
authors.initials: H
authors.lastname: Guenou
authors.forename: Karim
authors.initials: K
authors.lastname: Kaabeche
authors.forename: Cécilie
authors.initials: C
authors.lastname: Dufour
authors.forename: Hichem
authors.initials: H
authors.lastname: Miraoui
authors.forename: Pierre J
authors.initials: PJ
authors.lastname: Marie
mesh_terms: D000168:Acrocephalosyndactylia / Q000201:enzymology* / Q000235:genetics; D049109:Cell Proliferation; D003393:Cranial Sutures / Q000201:enzymology; D015536:Down-Regulation; D006801:Humans; D009687:Nuclear Proteins / Q000172:deficiency* / Q000235:genetics; D010006:Osteoblasts / Q000166:cytology* / Q000201:enzymology; D019869:Phosphatidylinositol 3-Kinases / Q000032:analysis / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000032:analysis / Q000378:metabolism; D050721:Proto-Oncogene Proteins c-cbl / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D014162:Transfection; D051879:Twist-Related Protein 1 / Q000172:deficiency* / Q000235:genetics; D025801:Ubiquitin / Q000378:metabolism
chemical_list: D009687:Nuclear Proteins; C103173:TWIST1 protein, human; D051879:Twist-Related Protein 1; D025801:Ubiquitin; D050721:Proto-Oncogene Proteins c-cbl; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt