Secretion of insulin-like growth factor-I and binding proteins by rat liver fat-storing cells: regulatory role of platelet-derived growth factor.
Insulin-like growth factor (IGF-I) is synthesized in multiple organs, including the liver, and may play a role in tissue growth and repair. We report that liver fat-storing cells (FSC) secrete IGF-I immunoreactivity in the culture medium. Secretion of IGF-I immunoreactivity was blocked in the presence of cycloheximide, suggesting de novo synthesis. Culture medium conditioned by FSC was concentrated and applied to a Sephadex G100 column equilibrated in a denaturing buffer. Two major species with apparent mol wts of 7.5 and greater than 25 k were identified by IGF-I RIA. Reverse phase HPLC of the 7.5 kilodalton species (the size of IGF-I) showed that it eluted in a single peak. To determine whether the higher mol wt species possessed IGF-I binding activity, appropriate fractions were desalted, incubated with [125I]IGF-I for 2 h at 30 C and applied to a Sephadex G100 column equilibrated in a nondissociating buffer. The major peak of radioactivity was confined to a high mol wt region. Western blot ligand analysis revealed the presence of two insulin-like growth factor binding proteins of approximately 28 and 31 kilodaltons. Platelet-derived growth factor, a potent mitogen for FSC, resulted in a 230% increase in release of IGF-I immunoreactivity that could be accounted for by an increase in IGF-I binding activity. In addition IGF-I increased DNA synthesis in FSC and this effect was additive to that of platelet-derived growth factor. IGF-I treatment also resulted in an increase in cell number. IGF-I and insulin-like growth factor binding proteins secreted by FSC may play a role in the hepatic tissue response to injury via autocrine and/or paracrine mechanisms.
Department of Medicine, V.A. Medical Center, Cleveland, Ohio.
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M
Pinzani
H E
HE
Abboud
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DC
Aron
D000818:Animals; D015153:Blotting, Western; D002352:Carrier Proteins / Q000378:metabolism*; D002850:Chromatography, Gel; D002851:Chromatography, High Pressure Liquid; D004247:DNA / Q000096:biosynthesis; D007158:Immunologic Techniques; D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D050356:Lipid Metabolism; D008099:Liver / Q000166:cytology / Q000378:metabolism*; D008297:Male; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D013002:Somatomedins / Q000378:metabolism; D013936:Thymidine / Q000378:metabolism
D002352:Carrier Proteins; D018969:Insulin-Like Growth Factor Binding Proteins; D010982:Platelet-Derived Growth Factor; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I; D004247:DNA; D013936:Thymidine