Activity-dependent expression of RNA binding protein HuD and its association with mRNAs in neurons

The dendritic trafficking of RNA binding proteins (RBPs) is an important posttranscriptional process involved in the regulation of synaptic plasticity. For example, HuD RBP binds to AU-rich elements (AREs) in the 3' untranslated regions (3'UTR) of immediate-early gene (IEG) transcripts, whose protein products directly affect synaptic plasticity. However, the subcellular localization of HuD RBPs and associated mRNAs has not been investigated following neuronal stimulation. Immunofluorescence analysis revealed activity-dependent dendritic localization of HuD RBPs following KCl stimulation in hippocampal neurons, while immunoprecipitation demonstrated the association of HuD RBP with neuronal mRNAs encoding neuritin, Homerla, GAP-43, Neuroligins, Verge and CAMKII alpha. Activity-dependent expression of HuD involves activation of NMDAR as NMDA receptor I knockout mice (Nr1(neo-/-)) exhibited decreased expression of HuD. Moreover, translational regulation of HuD-associated transcripts was suggested by its co-localization with poly-A-binding protein (PABP) as well as the cap-binding protein (eIF4E). We propose that post-transcriptional regulation of neuronal mRNAs by HuD RBPs mediates protein synthesis-dependent changes in synaptic plasticity.