Production of insulin-like growth factor binding-proteins by bovine adrenomedullary cells: differential regulation by IGF-I and dexamethasone.
In the present study we examined the production of insulin-like growth factor binding proteins (IGFBPs), in chromaffin cells, a model system for sympathetic neurons. Four IGFBPs of approximately 27, approximately 31, approximately 36 and a doublet of approximately 45-50 kDa, detected in Western ligand blots of conditioned medium, were identified in Western immunoblots as IGFBP-4, IGFBP-5, IGFBP-2 and IGFBP-3, respectively. In ligand blots IGFBP-3 and IGFBP-4 appeared as the most prominent species. IGF-I (1 nM) enhanced release of IGFBP-3 while dexamethasone (1 nM) diminished release of IGFBP-4. No significant proteolytic degradation of the IGFBPs was demonstrated. Cycloheximide completely attenuated release of the IGFBPs, indicating dependency on new synthesis of the proteins. These findings are consistent with autocrine modulation of the IGF system in bovine adrenomedullary chromaffin cells by IGFBPs. Furthermore, the specific stimulatory and inhibitory effects of IGF-I and dexamethasone, respectively, on release of the predominant species of IGFBP-3 and IGFBP-4, suggested that IGFBP production may be selectively modulated in a positive and negative manner.
Grønning
Mona
M
Department of Physiology, PKI, University of Bergen, Arstadveien 19, 5009 Bergen, Norway.
Serck-Hanssen
Guldborg
G
D000313:Adrenal Medulla / Q000378:metabolism*; D000818:Animals; D015153:Blotting, Western; D002417:Cattle; D002478:Cells, Cultured; D003907:Dexamethasone / Q000378:metabolism*; D018969:Insulin-Like Growth Factor Binding Proteins / Q000096:biosynthesis*; D007334:Insulin-Like Growth Factor I / Q000502:physiology*
D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I; D003907:Dexamethasone