Insulin-like growth factor-I enhances tyrosine hydroxylase activation in bovine chromaffin cells.
Previous studies have shown that insulin-like growth factor-I (IGF-I) enhances secretagogue-stimulated Ca2+ uptake and catecholamine release in bovine chromaffin cells. This report describes the effect of IGF-I on the activity of tyrosine hydroxylase (tyrosine 3-monooxygenase, EC 1.14.16.2), the major regulatory enzyme in the pathway of catecholamine biosynthesis. Tyrosine hydroxylase activity was assayed by measuring 3,4-dihydroxyphenylalanine (Dopa) accumulation in the presence of brocresine, an inhibitor of Dopa decarboxylase. Chromaffin cells cultured in serum-free medium produced approximately 40% less Dopa when stimulated by 55 mM K+ than did cells that had been cultured in the presence of serum. Incubation of cells for 3 days in serum-free medium containing 10 nM IGF-I restored high K(+)-stimulated Dopa accumulation to a level comparable to that seen in cells cultured continuously in serum-containing medium. In eight experiments, IGF-I increased high K(+)-stimulated Dopa accumulation (expressed as picomoles per minute per milligram of protein) by 96 +/- 13%. IGF-I increased the protein content of chromaffin cells by approximately 30%; consequently, its effect on tyrosine hydroxylase activity was even greater when Dopa synthesis was expressed as picomoles per minute per 10(7) cells. IGF-I also enhanced the rate of Dopa accumulation in cells stimulated by dimethylphenylpiperazinium, 8-bromo-cyclic AMP, phorbol 12,13-dibutyrate, or Ba2+. The effect of IGF-I on high K(+)-stimulated tyrosine hydroxylase activity was measurable when enzyme activity was assayed in vitro, suggesting that this effect was due to a stable modification of the enzyme.(ABSTRACT TRUNCATED AT 250 WORDS)
Dahmer
M K
MK
Department of Pediatrics, University of Chicago, IL 60637.
Hart
P M
PM
Perlman
R L
RL
D000818:Animals; D001958:Brocresine / Q000494:pharmacology; D002417:Cattle; D002478:Cells, Cultured; D002838:Chromaffin System / Q000166:cytology / Q000201:enzymology* / Q000378:metabolism; D004295:Dihydroxyphenylalanine / Q000378:metabolism; D004789:Enzyme Activation; D015151:Immunoblotting; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism*
D001958:Brocresine; D004295:Dihydroxyphenylalanine; D007334:Insulin-Like Growth Factor I; D014446:Tyrosine 3-Monooxygenase