title: Serotonin activates S6 kinase in a rapamycin-sensitive manner in Aplysia synaptosomes.
abstract: The identification of tags that can specifically mark activated synapses is important for understanding how long-term synaptic changes can be restricted to specific synapses. The maintenance of synapse-specific facilitation in Aplysia sensory to motor neuron cultures can be blocked by inhibitors of translation and by the drug rapamycin, which specifically blocks a signaling pathway that regulates phosphorylation of translational regulators. One important target of rapamycin is the phosphorylation and subsequent activation of S6 kinase. To test whether S6 kinase is the target for the ability of rapamycin to block synapse-specific facilitation in Aplysia, we cloned Aplysia S6 kinase, its substrate S6, and the S6 kinase kinase phosphoinositide-dependent kinase 1 (PDK-1). Serotonin, which induces synapse-specific facilitation, increased phosphorylation of Aplysia S6 kinase at threonine 399 in a rapamycin-sensitive manner in Aplysia synaptosomes. The phosphorylation of threonine 399 by 5-HT was independent of phosphoinositide-3 kinase, dependent on PKA and PKC, and occluded by the phosphatase inhibitor calyculin-A. 5-HT also increased S6 kinase activity and led to increased phosphorylation of S6 in synaptosomes. 5-HT increased levels of S6 in synaptosomes because of a rapamycin-sensitive increase in translation-stabilization of S6. Aplysia PDK-1 bound to and phosphorylated Aplysia S6 kinase but only modulated phosphorylation of threonine 399 indirectly. These results suggest a mechanism by which the levels of translation factors can be increased specifically at activated synapses generating a long-lasting synaptic tag.
authors.affiliation: Department of Neurology and Neurosurgery, Montreal Neurological Institute, McGill University, Montreal, Quebec H3A 2B4, Canada.
authors.forename: A
authors.initials: A
authors.lastname: Khan
authors.forename: A M
authors.initials: AM
authors.lastname: Pepio
authors.forename: W S
authors.initials: WS
authors.lastname: Sossin
mesh_terms: D064413:3-Phosphoinositide-Dependent Protein Kinases; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001048:Aplysia; D001665:Binding Sites / Q000187:drug effects; D002460:Cell Line; D004791:Enzyme Inhibitors / Q000494:pharmacology; D017774:Long-Term Potentiation / Q000187:drug effects; D008387:Marine Toxins; D008969:Molecular Sequence Data; D009473:Neuronal Plasticity / Q000187:drug effects; D010080:Oxazoles / Q000494:pharmacology; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D038601:Ribosomal Protein S6; D019893:Ribosomal Protein S6 Kinases / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D012269:Ribosomal Proteins / Q000235:genetics / Q000378:metabolism; D012701:Serotonin / Q000378:metabolism* / Q000494:pharmacology; D020123:Sirolimus / Q000494:pharmacology*; D018411:Spodoptera; D013569:Synapses / Q000378:metabolism; D013574:Synaptosomes / Q000187:drug effects / Q000201:enzymology*; D013912:Threonine / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D004791:Enzyme Inhibitors; D008387:Marine Toxins; D010080:Oxazoles; D000081082:Phosphoinositide-3 Kinase Inhibitors; D038601:Ribosomal Protein S6; D012269:Ribosomal Proteins; D013912:Threonine; D012701:Serotonin; C059041:calyculin A; D064413:3-Phosphoinositide-Dependent Protein Kinases; D017346:Protein Serine-Threonine Kinases; D019893:Ribosomal Protein S6 Kinases; D020123:Sirolimus