Overexpression of insulin-like growth factor-II induces accelerated myoblast differentiation.
Previous studies have shown that exogenous insulin-like growth factors (IGFs) can stimulate the terminal differentiation of skeletal myoblasts in culture and have established a correlation between the rate and the extent of IGF-II secretion by muscle cell lines and the rate of biochemical and morphological differentiation. To investigate the hypothesis that autocrine secretion of IGF-II plays a critical role in stimulating spontaneous myogenic differentiation in vitro, we have established C2 muscle cell lines that stably express a mouse IGF-II cDNA under control of the strong, constitutively active Moloney sarcoma virus promoter, enabling us to study directly the effects of IGF-II overproduction. Similar to observations with other muscle cell lines, IGF-II overexpressing myoblasts proliferated normally in growth medium containing 20% fetal serum, but they underwent enhanced differentiation compared with controls when incubated in low-serum differentiation medium. Accelerated differentiation of IGF-II overexpressing C2 cells was preceded by the rapid induction of myogenin mRNA and protein expression (within 1 h, compared with 24-48 h in controls) and was accompanied by an enhanced proportion of the retinoblastoma protein in an underphosphrylated and potentially active form, by a marked increase in activity of the muscle-specific enzyme, creatine phosphokinase, by extensive myotube formation by 48 h, and by elevated secretion of IGF binding protein-5 when compared with controls. These results confirm a role for IGF-II as an autocrine/paracrine differentiation factor for skeletal myoblasts, and they define a model cell system that will be useful in determining the biochemical mechanisms of IGF action in cellular differentiation.
Stewart
C E
CE
Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
James
P L
PL
Fant
M E
ME
Rotwein
P
P
D000818:Animals; D002454:Cell Differentiation; D002460:Cell Line; D018076:DNA, Complementary; D007335:Insulin-Like Growth Factor II / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D009132:Muscles / Q000166:cytology* / Q000378:metabolism*; D018008:Myogenin / Q000235:genetics; D010766:Phosphorylation; D016160:Retinoblastoma Protein / Q000378:metabolism; D013997:Time Factors; D014162:Transfection
D018076:DNA, Complementary; C503801:Myog protein, mouse; D018008:Myogenin; D016160:Retinoblastoma Protein; D007335:Insulin-Like Growth Factor II