Phosphorylation of GTP cyclohydrolase I and modulation of its activity in rodent mast cells. GTP cyclohydrolase I hyperphosphorylation is coupled to high affinity IgE receptor signaling and involves protein kinase C.
GTP cyclohydrolase I controls the de novo pathway for the synthesis of tetrahydrobiopterin, which is the essential cofactor for tryptophan 5-monooxygenase and thus, for serotonin production. In mouse bone marrow-derived mast cells, the kit ligand selectively up-regulates GTP cyclohydrolase I activity (Ziegler, I., Hültner, L. , Egger, D., Kempkes, B., Mailhammer, R., Gillis, S., and Rödl, W. (1993) J. Biol. Chem. 268, 12544-12551). Immunoblot analysis now confirms that this long term enhancement is caused by increased expression of the enzyme. Furthermore we show that GTP cyclohydrolase I is subject to modification at the post-translational level. In vivo labeling with [32P]orthophosphate demonstrates that in primary mast cells and in transfected RBL-2H3 cells overexpressing GTP cyclohydrolase I, the enzyme exists in a phosphorylated form. Antigen binding to the high affinity receptor for IgE triggers an additional and transient phosphorylation of GTP cyclohydrolase I with a concomitant rise in its activity, and in consequence, cellular tetrahydrobiopterin levels increase. These events culminate 8 min after stimulation and can be mimicked by phorbol ester. The hyperphosphorylation is greatly reduced by the protein kinase C inhibitor Ro-31-8220. In vitro phosphorylation studies indicate that GTP cyclohydrolase I is a substrate for both casein kinase II and protein kinase C.
GSF-Institut für Klinische Molekularbiologie und Tumorgenetik, D-81377 München, Germany. hesslinger@gsf.de
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Hesslinger
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Kremmer
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Hültner
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Ueffing
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Ziegler
D000818:Animals; D001708:Biopterins / Q000031:analogs & derivatives / Q000096:biosynthesis; D047390:Casein Kinase II; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006136:GTP Cyclohydrolase / Q000378:metabolism*; D007211:Indoles / Q000494:pharmacology; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000378:metabolism; D008407:Mast Cells / Q000201:enzymology*; D051379:Mice; D010766:Phosphorylation; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism; D051745:Protein Kinase C-delta; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D017455:Receptors, IgE / Q000378:metabolism*; D015398:Signal Transduction; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D004791:Enzyme Inhibitors; D007211:Indoles; D007527:Isoenzymes; D017455:Receptors, IgE; D001708:Biopterins; C497259:Prkcd protein, mouse; D047390:Casein Kinase II; D017346:Protein Serine-Threonine Kinases; D011493:Protein Kinase C; D051745:Protein Kinase C-delta; D006136:GTP Cyclohydrolase; C003402:sapropterin; D013755:Tetradecanoylphorbol Acetate; C064758:Ro 31-8220