RESUMEN
Semaphorin3A (Sema3A), a secreted factor that navigates axons and dendrites of developing neurons, facilitates axonal transport. However, little is known about the mechanism underlying Sema3A-induced facilitation and its functional implications. Here we show that Sema3A induces facilitation of axonal transport via local calcium signaling in growth cone. The facilitation of axonal transport was blocked by inhibitors of voltage-gated sodium channels (tetrodotoxin, TTX), L-type voltage-gated calcium channel, and ryanodine receptor (RyR). Sema3A evoked intracellular Ca(2+) elevation in growth cone by local application of Sema3A to growth cone. Sema3A also activated RyR in growth cone as well as cell body. Notably, TTX suppressed Sema3A-induced RyR activation in cell body but not in growth cone. Our results identify a novel mechanism of Sema3A-induced axonal transport, and further suggest that Sema3A-induced local calcium signaling in growth cone is propagated to cell body in a TTX-sensitive manner.
Asunto(s)
Axones/metabolismo , Señalización del Calcio , Activación del Canal Iónico/fisiología , Semaforina-3A/metabolismo , Canales de Sodio/metabolismo , Animales , Axones/efectos de los fármacos , Bloqueadores de los Canales de Calcio/farmacología , Canales de Calcio Tipo L/metabolismo , Línea Celular , Embrión de Pollo , Ganglios Espinales/efectos de los fármacos , Ganglios Espinales/metabolismo , Conos de Crecimiento/efectos de los fármacos , Conos de Crecimiento/metabolismo , Activación del Canal Iónico/efectos de los fármacos , Canal Liberador de Calcio Receptor de Rianodina/metabolismo , Bloqueadores de los Canales de Sodio/farmacología , Tetrodotoxina/farmacologíaRESUMEN
An impressive body of evidence has been accumulated indicating that local protein synthesis is implicated in navigation of neurite extension induced by guidance cues, such as semaphorin3A (Sema3A). We found previously that a Src type tyrosine kinase Fyn and cyclin-dependent kinase 5 (Cdk5) mediate Sema3A-signaling. We also showed that Sema3A elicits axonal transport through neuropilin-1, a receptor for Sema3A, located at the growth cones. Here, we investigate the relationship between Sema3A-induced local signaling, protein synthesis, and axonal transport. Lavendustin A, a tyrosine kinase inhibitor, and olomoucine, a cyclin-dependent kinase inhibitor, suppressed Sema3A-induced facilitation of anterograde and retrograde axonal transport in dorsal root ganglion (DRG) neuron with and without the cell body. Sema3A-induced facilitation of axonal transport was attenuated in DRG neurons of fyn- (fyn-/-) and a Cdk5 activator, p35 (p35-/-)-deficient mice when compared with those of wild-type or heterozygous mice. Inhibition of protein synthesis suppressed Sema3A-induced facilitation of axonal transport in the DRG neuron with and without the cell body. Sema3A enhanced the level of immunoreactivity of phosphorylated eukaryotic translation initiation factor 4E (eIF-4E) within 5 min in growth cones in a time course similar to that of the facilitated axonal transport. This enhanced signal for phospho-eIF4E was blocked by lavendustin A or olomoucine and was not detected in the fyn-/- and p35-/- neurons. These results provide evidence for a mutual regulatory mechanism between local protein synthesis and axonal transport.