Regulation of insulin-like growth factor-I expression in mouse preadipocyte Ob1771 cells.
In mouse preadipocyte Ob1771 cells, transcription of the insulin-like growth factor-I (IGF-I) gene was stimulated by growth hormone (GH), and IGF-I protein combined with GH in medium was required for their differentiation to adipocytes. During induction of the differentiation, the intracellular expression of each class of IGF-I mRNA was analyzed by reverse transcriptase-polymerase chain reaction. When the cells were cultured in the presence of GH, the class 1del. IGF-I mRNA was a major molecular species among IGF-I mRNAs. In the presence of both GH and IGF-I, the splicing pattern of IGF-I mRNA changed from class 1del. to class 1. Moreover, as detected by Western blotting, the IGF-I protein was present in cells and in the medium only when the cells were cultured in the presence of both GH and IGF-I. We found that IGF-I secreted from Ob1771 cells could act in an autocrine/paracrine fashion and induce the differentiation of other Ob1771 cells. It was demonstrated that the translation efficiency of class 1 mRNA was higher than that of class 1del. mRNA in vitro. These results suggested that stimulation with exogenous IGF-I in the presence of GH was required for the production of class 1 IGF-I mRNA and that the production of the IGF-I protein was activated by increasing the translation efficiency through shifting the splicing pattern of IGF-I mRNA from class 1del. to class 1. Exogenous IGF-I triggered the differentiation by initiating the synthesis of endogenous IGF-I.
Kamai
Y
Y
Laboratory of Biochemistry, Department of Agricultural Chemistry, Faculty of Agriculture, Kyoto University, Kyoto 606-01, Japan.
Mikawa
S
S
Endo
K
K
Sakai
H
H
Komano
T
T
D017667:Adipocytes / Q000166:cytology / Q000502:physiology*; D017398:Alternative Splicing; D000818:Animals; D002454:Cell Differentiation; D002460:Cell Line; D017931:DNA Primers / Q000737:chemistry; D005786:Gene Expression Regulation; D013006:Growth Hormone / Q000502:physiology*; D007334:Insulin-Like Growth Factor I / Q000235:genetics*; D051379:Mice; D008969:Molecular Sequence Data; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000235:genetics; D014158:Transcription, Genetic
D017931:DNA Primers; D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone