title: Regulation of insulin-like growth factor (IGF) I receptor expression during muscle cell differentiation. Potential autocrine role of IGF-II.
abstract: Muscle is an important target tissue for insulin-like growth factor (IGF) action. The presence of specific, high affinity IGF receptors, as well as the expression of IGF peptides and binding proteins by muscle suggest that a significant component of IGF action in this tissue is mediated through autocrine and/or paracrine mechanisms. To explore autocrine/paracrine action of IGFs in muscle, we studied the regulation of the IGF-I receptor and the expression of IGF peptides during differentiation of the mouse BC3H-1 muscle cell line. Differentiation from myoblasts to myocytes was associated with a 60% decrease in IGF-I receptor sites determined by Scatchard analysis. Analysis of mRNA abundance and protein labeling studies indicated that the decrease in IGF-I receptor sites was associated with similar reductions in IGF-I receptor gene expression and receptor biosynthesis. IGF-II peptide gene expression was detected in myoblasts and increased 15-fold with differentiation; the increase in IGF-II gene expression preceded the decrease in IGF-I receptor gene expression. In contrast, IGF-I peptide gene expression was low in myoblasts and decreased slightly with differentiation. To explore the potential role of endogenous IGF-II in the differentiation-associated decrease in IGF-I receptor expression, we investigated the effects of IGF-II treatment in myoblasts. The addition of IGF-II to undifferentiated myoblasts resulted in downregulation of the IGF-I receptor which was associated with decreased IGF-I receptor biosynthesis and decreased IGF-I receptor mRNA abundance. These studies suggest, therefore, that IGF-I receptor expression during muscle cell differentiation may be regulated, at least in part, through autocrine production of IGF-II.
authors.affiliation: Department of Pediatrics, University of California, San Francisco 94143.
authors.forename: S M
authors.initials: SM
authors.lastname: Rosenthal
authors.forename: A
authors.initials: A
authors.lastname: Brunetti
authors.forename: E J
authors.initials: EJ
authors.lastname: Brown
authors.forename: P W
authors.initials: PW
authors.lastname: Mamula
authors.forename: I D
authors.initials: ID
authors.lastname: Goldfine
mesh_terms: D000818:Animals; D015152:Blotting, Northern; D002454:Cell Differentiation; D002478:Cells, Cultured; D015536:Down-Regulation; D015870:Gene Expression; D006801:Humans; D066298:In Vitro Techniques; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D007335:Insulin-Like Growth Factor II / Q000502:physiology*; D051379:Mice; D009132:Muscles / Q000166:cytology / Q000502:physiology*; D012333:RNA, Messenger / Q000235:genetics; D011956:Receptors, Cell Surface / Q000235:genetics* / Q000378:metabolism; D017451:Receptors, Somatomedin
chemical_list: D012333:RNA, Messenger; D011956:Receptors, Cell Surface; D017451:Receptors, Somatomedin; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II