Developmental regulation of Mac25/insulin-like growth factor-binding protein-7 expression in skeletal myogenesis.
Mac25 is a newly discovered member of the insulin-like growth factor-binding protein (IGFBP) family, recently assigned the name IGFBP-7, Mac25/IGFBP-7 is hypothesized to have growth-suppressing activity, since mac25/IGFBP-7 mRNA is down-regulated in several tumor cell lines and is highly expressed in senescent mammary epithelial cells. In this study, mac25/ IGFBP-7 mRNA expression was characterized in the C2 skeletal myogenic cell line, which undergoes a transition from actively dividing, undifferentiated myoblasts to nondividing, differentiated myotubes. Mac25/ IGFBP-7 mRNA levels were 2.5-fold higher in dividing C2 myoblasts than in nondividing myotubes. The inverse correlation between mac25/IGFBP-7 expression and myogenic differentiation was further examined by treating myogenic cultures with transforming growth factor-beta (TGF-beta) or insulin-like growth factor-I (IGF-I). TGF-beta inhibited myogenic differentiation by 98% and stimulated mac25/IGFBP-7 mRNA expression 2-fold. IGF-I stimulated differentiation by 50% and inhibited mac25/IGFBP-7 expression 2- to 3-fold. These findings indicate that, in contrast to other cell systems examined so far, expression of this new member of the IGFBP family is not always correlated with a nonproliferative state.
Damon
S E
SE
Geriatric Research, Education, and Clinical Center, VA Puget Sound Health Care System, American Lake Division, Tacoma, Washington 98493, USA.
Haugk
K L
KL
Swisshelm
K
K
Quinn
L S
LS
D000818:Animals; D015415:Biomarkers; D001943:Breast Neoplasms; D002352:Carrier Proteins / Q000096:biosynthesis*; D002454:Cell Differentiation; D002455:Cell Division; D002460:Cell Line; D003402:Creatine Kinase / Q000096:biosynthesis; D005260:Female; D018507:Gene Expression Regulation, Developmental; D006133:Growth Substances / Q000494:pharmacology; D006801:Humans; D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D007527:Isoenzymes; D007700:Kinetics; D051379:Mice; D018482:Muscle, Skeletal / Q000166:cytology* / Q000378:metabolism*; D012333:RNA, Messenger / Q000096:biosynthesis; D013997:Time Factors; D014158:Transcription, Genetic / Q000187:drug effects; D016212:Transforming Growth Factor beta / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D015415:Biomarkers; D002352:Carrier Proteins; D006133:Growth Substances; D018969:Insulin-Like Growth Factor Binding Proteins; D007527:Isoenzymes; D012333:RNA, Messenger; D016212:Transforming Growth Factor beta; C102529:insulin-like growth factor binding protein-related protein 1; D007334:Insulin-Like Growth Factor I; D003402:Creatine Kinase