Functional receptors for transforming growth factor-beta are retained by biochemically differentiated C2 myocytes in growth factor-deficient medium containing EGTA but down-regulated during terminal differentiation.
Transforming growth factor-beta (TGF-beta) has been shown to block the morphological and molecular events associated with myoblast differentiation. During fusion of C2 myoblasts, TGF-beta receptors are down-regulated, and muscle-specific genes become refractory to the inhibitory effects of TGF-beta. To define further the mechanisms that modulate TGF-beta receptor expression during myogenesis, we have developed culture conditions that support the differentiation of C2 cells in the absence of fusion and have examined the expression of functional TGF-beta receptors in biochemically differentiated mononucleated myocytes. Exposure of C2 myoblasts to growth factor-deficient medium containing 1.4 mM [ethylenebis(oxyethylenenitrilo)]tetraacetic acid (EGTA) leads to withdrawal from the cell cycle and high level expression of muscle-specific mRNAs and proteins. Under these conditions, TGF-beta receptors fail to be down-regulated, and the differentiation program remains sensitive to repression by TGF-beta. These studies demonstrate that EGTA uncouples muscle-specific gene expression from fusion in C2 cells and that in the absence of fusion, C2 myocytes retain a functional TGF-beta signaling system.
Hu
J S
JS
Department of Biochemistry and Molecular Biology, University of Texas M. D. Anderson Cancer Center, Houston 77030.
Olson
E N
EN
D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects; D002460:Cell Line; D003402:Creatine Kinase / Q000235:genetics; D003432:Cross-Linking Reagents; D015536:Down-Regulation; D004533:Egtazic Acid / Q000494:pharmacology*; D015870:Gene Expression / Q000187:drug effects*; D051379:Mice; D008970:Molecular Weight; D009132:Muscles / Q000166:cytology / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D011956:Receptors, Cell Surface / Q000235:genetics* / Q000378:metabolism; D011950:Receptors, Cholinergic / Q000235:genetics; D018125:Receptors, Transforming Growth Factor beta; D013388:Succinimides; D015291:Transforming Growth Factors / Q000494:pharmacology*; D014336:Troponin / Q000235:genetics; D020107:Troponin T
D003432:Cross-Linking Reagents; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; D011950:Receptors, Cholinergic; D018125:Receptors, Transforming Growth Factor beta; D013388:Succinimides; D014336:Troponin; D020107:Troponin T; D004533:Egtazic Acid; D015291:Transforming Growth Factors; D003402:Creatine Kinase; C019358:disuccinimidyl suberate