title: Differentiation of C2C12 myoblasts is critically regulated by FAK signaling.
abstract: This study examined whether focal adhesion kinase (FAK) plays a role in the differentiation of C(2)C(12) myoblasts into myotubes. Differentiation of C(2)C(12) myoblasts induced by switch to differentiation culture medium was accompanied by a transient reduction of FAK phosphorylation at Tyr-397 (to approximately 50%, at 1 and 2 h), followed by an increase thereafter (to 240% up to 5 days), although FAK protein expression remained unchanged. FAK and phosphorylated FAK were found at the edge of lamellipodia in proliferating cells, whereas the later increase in FAK phosphorylation in differentiating cells was accompanied by its preferential location at the tip of well-organized actin stress fibers. Hyperexpression of FAK autophosphorylation site (Tyr-397) mutant (MT-FAK) reduced FAK phosphorylation at Tyr-397 in proliferating cells and was accompanied by reduction of cyclin D1 and increase of myogenin expression. These cells failed to progress to myotubes in differentiation medium. In contrast, hyperexpression of a wild-type FAK construction (WT-FAK) increased baseline and abolished the transient reduction of FAK phosphorylation at Tyr-397 in serum-starved C(2)C(12) cells. Cells transfected with WT-FAK failed to reduce cyclin D1 and to increase myogenin expression, as well as to progress to terminal differentiation in differentiation medium. These data indicate that FAK signaling plays a critical role in the control of cell cycle as well as in the progression of C(2)C(12) cells to terminal differentiation. Transient inhibition of FAK phosphorylation at Tyr-397 contributes to trigger the myogenic genetic program, but its later activation is also central to terminal differentiation into myotubes.
authors.affiliation: Departamento de Clínica Médica, Faculdade de Ciências Médicas, Universidade Estadual de Campinas, Cidade Universitária Zefferino Vaz, 13081-970 Campinas, SP, Brazil.
authors.forename: Carolina F M Z
authors.initials: CF
authors.lastname: Clemente
authors.forename: Marcus A F
authors.initials: MA
authors.lastname: Corat
authors.forename: Sara T O
authors.initials: ST
authors.lastname: Saad
authors.forename: Kleber G
authors.initials: KG
authors.lastname: Franchini
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002454:Cell Differentiation / Q000502:physiology*; D002460:Cell Line; D049109:Cell Proliferation; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; D051379:Mice; D024510:Muscle Development / Q000502:physiology; D009154:Mutation; D032446:Myoblasts / Q000166:cytology*; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D013347:Subcellular Fractions / Q000378:metabolism; D014018:Tissue Distribution
chemical_list: D011505:Protein-Tyrosine Kinases; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; C496051:Ptk2 protein, mouse