Synthesis of insulin-like growth factor binding proteins and of the acid-labile subunit of the insulin-like growth factor ternary binding protein complex in primary cultures of human hepatocytes.
OBJECTIVE
The liver is the main source of circulating insulin-like growth factor binding proteins. In man, the cellular origin of insulin-like growth factor binding proteins has remained obscure.


METHODS
Human hepatocytes isolated from surgical specimens were purified and cultured using a collagen gel immobilization technique. Gene expression of individual insulin-like growth factor binding proteins and of the acid-labile subunit of the insulin-like growth factor binding proteins by Western ligand blotting and immunoblot analysis. Neutral size chromatography of medium samples was used to detect insulin-like growth factors binding protein complexes.


RESULTS
In cultured hepatocytes transcripts for insulin-like growth factor binding protein-1, -2, -3, -4 and for acid labile subunit could be demonstrated. Ligand blotting revealed the secretion of insulin-like growth factor binding proteins of molecular weights of 24 kD, 30 kD, 34 kD, 43 kD and 46 kD, respectively. Using polyclonal antisera, these proteins were identified as insulin-like growth factor binding protein-1, -2 and the insulin-like growth factor binding protein-3 doublet. Neural size chromatography of culture supernatants showed the presence of an insulin-like growth factor binding protein complex of approximately 40 kD, but absence of the high molecular weight ternary complex of 150 kD.


CONCLUSIONS
It is concluded that in man parenchymal liver cells have to be regarded as a source of acid-labile subunit and of circulating insulin-like growth factor binding proteins including insulin-like growth factor binding protein-3.
Scharf
J G
JG
Department of Medicine, Georg-August-Universität, Göttingen, Germany.
Schmidt-Sandte
W
W
Pahernik
S A
SA
Koebe
H G
HG
Hartmann
H
H
D015152:Blotting, Northern; D002352:Carrier Proteins / Q000096:biosynthesis* / Q000235:genetics; D002478:Cells, Cultured; D002845:Chromatography; D006023:Glycoproteins / Q000096:biosynthesis* / Q000235:genetics; D006801:Humans; D015151:Immunoblotting; D018969:Insulin-Like Growth Factor Binding Proteins / Q000096:biosynthesis* / Q000235:genetics; D008099:Liver / Q000166:cytology / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000378:metabolism
D002352:Carrier Proteins; D006023:Glycoproteins; D018969:Insulin-Like Growth Factor Binding Proteins; D012333:RNA, Messenger; C075944:insulin-like growth factor binding protein, acid labile subunit