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  • Title: Developmental regulation of Mac25/insulin-like growth factor-binding protein-7 expression in skeletal myogenesis.
    Author: Damon SE, Haugk KL, Swisshelm K, Quinn LS.
    Journal: Exp Cell Res; 1997 Nov 25; 237(1):192-5. PubMed ID: 9417882.
    Abstract:
    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.
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