Compartment-specific, differential regulation of eukaryotic elongation factor 2 and its kinase within Aplysia sensory neurons.

Long-term facilitation (LTF) in Aplysia is a leading model for elucidating the biochemical mechanisms of synaptic plasticity underlying learning. LTF requires translational control downstream of target of rapamycin complex 1. Our lab has previously shown that treatment with the facilitating neurotransmitter, 5-hydroxytryptamine (5-HT), causes a target of rapamycin complex 1-mediated decrease in phosphorylation of eukaryotic elongation factor 2 (eEF2) within the neurites of sensory neurons involved in LTF. Here, we characterize the Aplysia orthologue of eEF2 kinase (eEF2K). We show that the Aplysia eEF2K orthologue contains an S6 kinase phosphorylation site and that a serine-to-alanine mutation at this site blocks the ability of 5-HT to decrease eEF2 phosphorylation in neurites. We also show that within the soma, 5-HT has the opposite effect, decreasing eEF2K phosphorylation at the S6 kinase site and, concomitantly, increasing eEF2 phosphorylation. Surprisingly, while eEF2K over-expression inhibits translation of a marker for internal ribosome entry site-dependent translation, it stimulates the translation of a marker for cap-dependent translation. This study demonstrates that eEF2 is differentially regulated in separate compartments and contributes to a growing body of evidence that inhibition of elongation can stimulate the translation of certain transcripts.