Analysis of the role of calmodulin binding and sequestration in neuromodulin (GAP-43) function.
We demonstrated previously that forced expression of the neuronal phosphoprotein neuromodulin (also known as GAP-43, F1, B-50, and p57) in mouse anterior pituitary AtT-20 cells enhances depolarization-mediated secretion and alters cellular morphology. Here we analyze the role of calmodulin binding by neuromodulin in these responses. In cells expressing wild-type neuromodulin, a complex with calmodulin that is sensitive to intracellular calcium and phosphorylation is localized to the plasma membrane. Transfection of several mutant forms of neuromodulin shows that the effects of this protein on secretion are dependent on both calmodulin binding and association with the plasma membrane. In contrast, the morphological changes depend only on membrane association. Thus, the multitude of effects of neuromodulin noted in previous studies may result from divergent properties of this protein.
R. S. Dow Neurological Sciences Institute, Good Samaritan Hospital and Medical Center, Portland, Oregon 97209, USA.
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Gamby
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Waage
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Allen
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Baizer
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002147:Calmodulin / Q000378:metabolism*; D002148:Calmodulin-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D003432:Cross-Linking Reagents; D019922:GAP-43 Protein; D006624:Hippocampus / Q000166:cytology / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D009474:Neurons / Q000166:cytology / Q000378:metabolism; D010766:Phosphorylation; D011188:Potassium / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism
D002147:Calmodulin; D002148:Calmodulin-Binding Proteins; D003432:Cross-Linking Reagents; D019922:GAP-43 Protein; D008562:Membrane Glycoproteins; D009419:Nerve Tissue Proteins; D011493:Protein Kinase C; D011188:Potassium; D002118:Calcium