ABSTRACT
Plasticity is a remarkable feature of the brain, allowing neuronal structure and function to accommodate to patterns of electrical activity. One component of these long-term changes is the activity-driven induction of new gene expression, which is required for both the long-lasting long-term potentiation of synaptic transmission associated with learning and memory, and the activity dependent survival events that help to shape and wire the brain during development. We have characterized molecular mechanisms by which neuronal membrane depolarization and subsequent calcium influx into the cytoplasm lead to the induction of new gene transcription. We have identified three points within this cascade of events where the specificity of genes induced by different types of stimuli can be regulated. By using the induction of the gene that encodes brain-derived neurotrophic factor (BDNF) as a model, we have found that the ability of a calcium influx to induce transcription of this gene is regulated by the route of calcium entry into the cell, by the pattern of phosphorylation induced on the transcription factor cAMP-response element (CRE) binding protein (CREB), and by the complement of active transcription factors recruited to the BDNF promoter. These results refine and expand the working model of activity-induced gene induction in the brain, and help to explain how different types of neuronal stimuli can activate distinct transcriptional responses.
Subject(s)
Brain-Derived Neurotrophic Factor/genetics , Calcium/physiology , Gene Expression Regulation , Neurons/physiology , Animals , Humans , Models, Neurological , Signal Transduction , Synapses/physiology , Synaptic Transmission , Transcriptional ActivationABSTRACT
EphB receptor tyrosine kinases are enriched at synapses, suggesting that these receptors play a role in synapse formation or function. We find that EphrinB binding to EphB induces a direct interaction of EphB with NMDA-type glutamate receptors. This interaction occurs at the cell surface and is mediated by the extracellular regions of the two receptors, but does not require the kinase activity of EphB. The kinase activity of EphB may be important for subsequent steps in synapse formation, as perturbation of EphB tyrosine kinase activity affects the number of synaptic specializations that form in cultured neurons. These findings indicate that EphrinB activation of EphB promotes an association of EphB with NMDA receptors that may be critical for synapse development or function.
Subject(s)
Membrane Proteins/metabolism , Neurons/cytology , Receptor Protein-Tyrosine Kinases/metabolism , Receptors, N-Methyl-D-Aspartate/metabolism , Synapses/physiology , Animals , Blotting, Western , Cells, Cultured , Cerebral Cortex/metabolism , Ephrin-B1 , Humans , Immunohistochemistry , Microscopy, Confocal , Neurons/metabolism , Point Mutation , Precipitin Tests , Rats , Receptor Protein-Tyrosine Kinases/chemistry , Receptor Protein-Tyrosine Kinases/genetics , Receptor, EphB4 , Receptors, Eph Family , Receptors, N-Methyl-D-Aspartate/chemistry , Recombinant Fusion Proteins/genetics , Recombinant Fusion Proteins/metabolism , Time Factors , TransfectionABSTRACT
A mechanism by which the Ras-mitogen-activated protein kinase (MAPK) signaling pathway mediates growth factor-dependent cell survival was characterized. The MAPK-activated kinases, the Rsks, catalyzed the phosphorylation of the pro-apoptotic protein BAD at serine 112 both in vitro and in vivo. The Rsk-induced phosphorylation of BAD at serine 112 suppressed BAD-mediated apoptosis in neurons. Rsks also are known to phosphorylate the transcription factor CREB (cAMP response element-binding protein) at serine 133. Activated CREB promoted cell survival, and inhibition of CREB phosphorylation at serine 133 triggered apoptosis. These findings suggest that the MAPK signaling pathway promotes cell survival by a dual mechanism comprising the posttranslational modification and inactivation of a component of the cell death machinery and the increased transcription of pro-survival genes.
