title: Ubiquitin-proteasome-mediated degradation and synthesis of MyoD is modulated by alphaB-crystallin, a small heat shock protein, during muscle differentiation.
abstract: alphaB-crystallin, a small heat shock protein, plays an important role in muscle homeostasis. It gets up-regulated during muscle differentiation and mice lacking alphaB-crystallin die prematurely with extensive muscle wastage. We have examined the role of alphaB-crystallin in muscle development using C2C12 myoblasts as a model system. Over-expression of alphaB-crystallin delays the muscle differentiation program significantly. C2C12 myoblasts over-expressing alphaB-crystallin (CRYAB-C2C12) display defect in cell-cycle exit upon induction of differentiation. During differentiation, CRYAB-C2C12 cells exhibit sustained level of cyclin D1 and delay in p21 and myogenin expression as compared to C2C12 cells. We find less accumulation of MyoD in CRYAB-C2C12 cells than in C2C12 cells. In vivo protein stability studies reveal faster ubiquitin-proteasome-mediated MyoD degradation in CRYAB-C2C12 cells (t(1/2)=1.42 h) than in C2C12 cells (t(1/2)=2.37 h). Immuno-precipitation experiments showed that MyoD gets ubiquitinated at earlier time points in CRYAB-C2C12 cells than in C2C12 cells. Our data reveal alterations in the synthesis and degradation of MyoD in CRYAB-C2C12 cells. The level of alphaB-crystallin as well as its Ser-59 phosphorylated form increases with increasing time of differentiation. Our studies show, inter alia, that alphaB-crystallin modulates myogenesis by altering MyoD level and provide an interesting insight in its role in myogenesis.
authors.affiliation: Centre for Cellular and Molecular Biology, Hyderabad 500 007, India.
authors.forename: Bhairab N
authors.initials: BN
authors.lastname: Singh
authors.forename: K Sridhar
authors.initials: KS
authors.lastname: Rao
authors.forename: Ch Mohan
authors.initials: ChM
authors.lastname: Rao
mesh_terms: D000818:Animals; D053148:Caspase 3 / Q000378:metabolism; D002454:Cell Differentiation / Q000502:physiology*; D002460:Cell Line; D049109:Cell Proliferation; D004789:Enzyme Activation; D050888:Heat-Shock Proteins, Small / Q000378:metabolism; D051379:Mice; D024510:Muscle Development / Q000502:physiology; D018482:Muscle, Skeletal / Q000166:cytology / Q000502:physiology*; D017570:MyoD Protein / Q000235:genetics / Q000378:metabolism*; D032446:Myoblasts / Q000166:cytology / Q000502:physiology; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism*; D038203:alpha-Crystallin B Chain / Q000235:genetics / Q000378:metabolism*
chemical_list: D050888:Heat-Shock Proteins, Small; D017570:MyoD Protein; D025801:Ubiquitin; D038203:alpha-Crystallin B Chain; D053148:Caspase 3; D046988:Proteasome Endopeptidase Complex