B-50 phosphorylation and polyphosphoinositide metabolism in nerve growth cone membranes.
The neuron-specific phosphoprotein B-50 (Mr 48 kDa, isoelectric point, IEP, 4.5), which is identical to GAP43, is a member of a family of growth-associated proteins. Protein B-50 is a major phosphoprotein in nerve growth cones isolated from fetal rat brain. In a growth cone particulate fraction (GCp), endogenous B-50 phosphorylation is Ca2+-dependent and is unaffected by cAMP. Addition of purified protein kinase C (PKC) to GCP enhances B-50 phosphorylation. In heat-inactivated GCp, B-50 is one of the major substrates of purified PKC. Endogenous B-50 phosphorylation in GCP is stimulated in a dose-dependent manner by 4 beta-phorbol diesters, known to activate PKC, but not by the inactive 4 alpha-phorbol derivatives. In synaptic plasma membranes (SPM) isolated from adult rat brain, the degree of B-50 phosphorylation has been implicated in the modulation of receptor-mediated polyphosphoinositide (PPI) hydrolysis. In addition to B-50 and its kinase, PKC, the GCp fraction was also shown to contain all other components of such a modulatory system: the phosphatidylinositol 4-phosphate (PIP)-kinase, as shown on Western blots with affinity-purified IgGs against PIP-kinase, and the polyphosphoinosides, PIP and phosphatidylinositol 4,5-bisphosphate (PIP2), since the addition of gamma-32P-ATP to the GCp fraction not only results in B-50 phosphorylation but also in the labeling of phosphatidic acid (PA), PIP, and PIP2. ACTH1-24, which inhibits B-50 phosphorylation in the GCp fraction in a dose-dependent manner (IC50 = 5 x 10(-6) M), stimulates PIP2 labeling dose-dependently in the same preparation.(ABSTRACT TRUNCATED AT 250 WORDS)
Van Hooff
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Division of Molecular Neurobiology, Rudolf Magnus Institute for Pharmacology, University of Utrecht, The Netherlands.
De Graan
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Oestreicher
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D000324:Adrenocorticotropic Hormone / Q000494:pharmacology; D000818:Animals; D001921:Brain / Q000196:embryology* / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005333:Fetus / Q000378:metabolism*; D019922:GAP-43 Protein; D010716:Phosphatidylinositols / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D051381:Rats / Q000196:embryology / Q000378:metabolism; D013570:Synaptic Membranes / Q000378:metabolism
D019922:GAP-43 Protein; D010716:Phosphatidylinositols; D010750:Phosphoproteins; D000324:Adrenocorticotropic Hormone