Modulation of B-50 phosphorylation and polyphosphoinositide metabolism in synaptic plasma membranes by protein kinase C, phorbol diesters and ACTH.
One of the major phosphoproteins in synaptic plasma membranes (SPM) is the neuron-specific protein B-50 (Mr 48 kDa, IEP 4.5). Addition of purified protein kinase C (PKC) to native SPM increases B-50 phosphorylation. Exogenous PKC also phosphorylates B-50 in heat-inactivated SPM. Endogenous phosphorylation of B-50 in SPM is enhanced in a concentration-dependent manner by the tumor-promoting phorbol diesters 4 beta-phorbol 12-myristate, 13-acetate, 4 beta-phorbol 12,13-dibutyrate (PDB) and 4 beta-phorbol 12,13-diacetate, with an EC50 of 7 x 10(-8) M, 3 x 10(-7) M and 10(-6) M, respectively. This increase in the B-50 phosphorylation can be inhibited by ACTH1-24. PDB (10(-6) M) also stimulates B-50 phosphorylation by exogenous PKC in native and heat-inactivated SPM (204 and 712%, respectively). The increase in B-50 phosphorylation induced by the addition of PKC to SPM is accompanied by a decrease in the [32P]-incorporation into phosphatidylinositol 4,5-bisphosphate (PIP2). These data support the hypothesis that in neuronal membranes the degree of B-50 phosphorylation exerts a negative control on receptor-mediated hydrolysis of PIP2 in receptor systems coupled to phospholipase C.
De Graan
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Rudolf Magnus Institute for Pharmacology, University of Utrecht, The Netherlands.
Dekker
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De Wit
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Schrama
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Gispen
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D000818:Animals; D003366:Cosyntropin / Q000494:pharmacology*; D019922:GAP-43 Protein; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism*; D008958:Models, Molecular; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D010703:Phorbol Esters / Q000494:pharmacology*; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols / Q000378:metabolism*; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D051381:Rats; D011919:Rats, Inbred Strains; D013570:Synaptic Membranes / Q000378:metabolism*
D019922:GAP-43 Protein; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D010703:Phorbol Esters; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols; D003366:Cosyntropin; D011493:Protein Kinase C