beta-Bungarotoxin blocks phorbol ester-stimulated phosphorylation of MARCKS, GAP-43 and synapsin I in rat brain synaptosomes.
The phospholipase A2 neurotoxin, beta-bungarotoxin, presynaptically blocks acetylcholine release. Its mechanism of action is unknown; however, our previous studies suggest that it inhibits phosphorylation of synaptosomal proteins, which might be expected to decrease neurotransmitter release. In our present study, we found that 1 nM beta-BuTX blocked phorbol ester-stimulated phosphorylation of GAP-43, MARCKS and synapsin I without affecting their basal phosphorylation. In contrast, a 1 nM concentration of the non-neurotoxic enzyme. Naja naja atra phospholipase A2 did not affect the phorbol ester-stimulated phosphorylation of these proteins but increased the basal phosphorylation of GAP-43 and MARCKS. Although it has been suggested that cytosolic calmodulin is increased by phosphorylation of the protein kinase C substrates, GAP-43 and MARCKS, we found no change in calmodulin levels by phorbol ester or beta-bungarotoxin. The stimulation of phosphorylation by Naja naja atra phospholipase A2 may be due to products liberated as a result of its phospholipase A2 activity. In contrast, the inhibition of phosphorylation by beta-bungarotoxin appears to be due to an action which may be unrelated its relatively weak phospholipase A2 activity. Inhibition of phosphorylation by beta-bungarotoxin is a possible mechanism by which it could block acetylcholine release. Furthermore, beta-bungarotoxin may be a useful tool to study the physiological role of phosphorylation of synaptosomal proteins in neurotransmitter release.
Ueno
E
E
Section of Pharmacology and Toxicology, School of Pharmacy, University of Connecticut, Storrs 06269, USA.
Rosenberg
P
P
D000818:Animals; D001345:Autoradiography; D002038:Bungarotoxins / Q000494:pharmacology*; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D019922:GAP-43 Protein; D015151:Immunoblotting; D066298:In Vitro Techniques; D047908:Intracellular Signaling Peptides and Proteins; D008297:Male; D008562:Membrane Glycoproteins / Q000378:metabolism*; D008565:Membrane Proteins; D000076250:Myristoylated Alanine-Rich C Kinase Substrate; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D010703:Phorbol Esters / Q000494:pharmacology*; D010741:Phospholipases A / Q000378:metabolism; D054467:Phospholipases A2; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D016704:Synapsins / Q000378:metabolism*; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism*
D002038:Bungarotoxins; D019922:GAP-43 Protein; D047908:Intracellular Signaling Peptides and Proteins; C000619712:Marcks protein, rat; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D010703:Phorbol Esters; D010750:Phosphoproteins; D011506:Proteins; D016704:Synapsins; D000076250:Myristoylated Alanine-Rich C Kinase Substrate; D011493:Protein Kinase C; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D010741:Phospholipases A; D054467:Phospholipases A2