Differential regulation of insulin-like growth factor I (IGF-I) and IGF binding protein-1 messenger ribonucleic acids by amino acid availability and growth hormone in rat hepatocyte primary culture.
To determine the mechanisms involved in the nutritional regulation of insulin-like growth factor I (IGF-I) production and action, we studied the regulation of IGF-I and IGF-Binding Protein 1 (IGFBP-1) gene expression by GH and amino acid availability in rat hepatocyte primary culture. Hepatocytes were isolated by in situ collagenase perfusion and cultured on Matrigel in serum-free medium containing insulin and hydrocortisone. Rat GH (500 ng/ml) increased IGF-I messenger RNA (mRNA) abundance 6.9-fold at 24 h, as measured by Northern Blot using an IGF-I-specific riboprobe. In contrast, IGFBP-1 mRNA levels were decreased by 41% after 24 h of rat GH treatment. Hepatocytes were incubated for 24 h in three media differing in their amino acid concentrations: 0.2X, 1X, and 5X the normal rat plasma concentration. Amino acid deprivation (0.2X) decreased the abundance of IGF-I mRNAs (-56% after 24 h), whereas amino acid excess (5X) increased it (+70%) in comparison to the 1X medium. In contrast, amino acid deprivation increased IGFBP-1 mRNA abundance (+69%), whereas excess decreased it (-75%). Studies of the interaction between GH and amino acids, accomplished by the simultaneous manipulation of the two, suggest that each factor modulates the IGF-I mRNA and the IGFBP-1 mRNA and protein response to the other. We conclude that the IGF-I and IGFBP-1 genes are regulated in opposite ways by GH and amino acid availability. Our observations suggest that amino acids and GH regulate the production of IGF-I directly and exert indirect effects on IGF-I action by regulating the production of IGFBP-1.
Thissen
J P
JP
Department of Pediatrics, School of Medicine, University of North Carolina at Chapel Hill 27599.
Pucilowska
J B
JB
Underwood
L E
LE
D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D002352:Carrier Proteins / Q000235:genetics*; D002478:Cells, Cultured; D005260:Female; D005786:Gene Expression Regulation / Q000187:drug effects; D013006:Growth Hormone / Q000494:pharmacology; D018970:Insulin-Like Growth Factor Binding Protein 1; D007334:Insulin-Like Growth Factor I / Q000235:genetics*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D012333:RNA, Messenger / Q000032:analysis*; D051381:Rats; D017207:Rats, Sprague-Dawley
D000596:Amino Acids; D002352:Carrier Proteins; D018970:Insulin-Like Growth Factor Binding Protein 1; D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone