Insulin-like growth factor binding protein-5 modulates muscle differentiation through an insulin-like growth factor-dependent mechanism.
The insulin-like growth factor binding proteins (IGFBPs) are a family of six secreted proteins which bind to and modulate the actions of insulin-like growth factors-I and -II (IGF-I and -II). IGFBP-5 is more conserved than other IGFBPs characterized to date, and is expressed in adult rodent muscle and in the developing myotome. We have shown previously that C2 myoblasts secrete IGFBP-5 as their sole IGFBP. Here we use these cells to study the function of IGFBP-5 during myogenesis, a process stimulated by IGFs. We stably transfected C2 cells with IGFBP-5 cDNAs under control of a constitutively active promoter. Compared with vector-transfected control cells, C2 myoblasts expressing the IGFBP-5 transgene in the sense orientation exhibit increased IGFBP-5 levels in the extracellular matrix during proliferation, and subsequently fail to differentiate normally, as assessed by both morphological and biochemical criteria. Compared to controls, IGFBP-5 sense myoblasts show enhanced survival in low serum medium, remaining viable for at least four weeks in culture. By contrast, myoblasts expressing the IGFBP-5 antisense transcript differentiate prematurely and more extensively than control cells. The inhibition of myogenic differentiation by high level expression of IGFBP-5 could be overcome by exogenous IGFs, with des (1-3) IGF-I, an analogue with decreased affinity for IGFBP-5 but normal affinity for the IGF-I receptor, showing the highest potency. These results are consistent with a model in which IGFBP-5 blocks IGF-stimulated myogenesis, and indicate that sequestration of IGFs in the extracellular matrix could be a possible mechanism of action. Our observations also suggest that IGFBP-5 normally inhibits muscle differentiation, and imply a role for IGFBP-5 in regulating IGF action during myogenic development in vivo.
James
P L
PL
Department of Biochemistry, Washington University, School of Medicine, St. Louis, Missouri 63110, USA.
Stewart
C E
CE
Rotwein
P
P
D000818:Animals; D016375:Antisense Elements (Genetics); D015153:Blotting, Western; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology; D002460:Cell Line / Q000502:physiology; D018076:DNA, Complementary / Q000494:pharmacology; D005109:Extracellular Matrix / Q000737:chemistry; D015870:Gene Expression / Q000502:physiology; D018975:Insulin-Like Growth Factor Binding Protein 5 / Q000032:analysis / Q000235:genetics*; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology / Q000502:physiology*; D051379:Mice; D018485:Muscle Fibers, Skeletal / Q000166:cytology / Q000502:physiology*; D018008:Myogenin / Q000235:genetics; D010641:Phenotype; D010957:Plasmids; D014158:Transcription, Genetic / Q000502:physiology; D014162:Transfection; D019076:Transgenes / Q000502:physiology
D016375:Antisense Elements (Genetics); D018076:DNA, Complementary; D018975:Insulin-Like Growth Factor Binding Protein 5; C503801:Myog protein, mouse; D018008:Myogenin; D007334:Insulin-Like Growth Factor I