Kato Akihiko, Fukazawa Yugo, Ozawa Fumiko, Inokuchi Kaoru, Sugiyama Hiroyuki
Department of Biology, Faculty of Science, Graduate School of Science, Kyushu University, Higashi, Fukuoka 812-8581, Japan.
Brain Res Mol Brain Res. 2003 Oct 21;118(1-2):33-44. doi: 10.1016/j.molbrainres.2003.07.005.
The Vesl-1S/Homer-1a protein is induced during long-term potentiation (LTP), and contains a motif that binds postsynaptic proteins. We have previously reported that synaptic accumulation of Vesl-1S/Homer-1a immunoreactivity (IR) at synapses on the contour of neuronal somata is promoted by stimulation of cells with phorbol esters, 90 mM KCl or proteasome inhibitors. In the present study, we investigated the intracellular mechanism that results in the synaptic accumulation of this protein at synapses. MEK inhibitors completely blocked the effects of phorbol esters and KCl on the accumulation of Vesl-1S/Homer-1a and partially blocked the effect of proteasome inhibitors. Conversely, brain-derived neurotrophic factor (BDNF) and NT3 promoted the accumulation of Vesl-1S/Homer-1a IR at synapses. The extent of this accumulation is correlated with the level of activation of extracellular signal-regulated kinases, ERK following treatment with BDNF. BDNF also caused an increase in the amount of Vesl-1S/Homer-1a protein, but this occurred after Vesl-1S/Homer-1a had accumulated at the synapses. In addition, inhibition of de novo protein synthesis did not affect the phorbol ester-mediated accumulation of Vesl-1S/Homer-1a IR at synapses. These results indicate that activation of the ERK cascade plays a crucial role in the synaptic accumulation of Vesl-1S/Homer-1a IR, and suggest that this accumulation occurs mainly by re-localization of Vesl-1S/Homer-1a protein, and not through an increase in the level of Vesl-1S/Homer-1a. Activity-dependent release of neurotrophins or depolarization may cause local activation of the ERK cascade to produce the synapse-specific localization of Vesl-1S/Homer-1a.
Vesl-1S/Homer-1a蛋白在长时程增强（LTP）过程中被诱导产生，且包含一个能结合突触后蛋白的基序。我们之前曾报道，佛波酯、90 mM KCl或蛋白酶体抑制剂刺激细胞可促进Vesl-1S/Homer-1a免疫反应性（IR）在神经元胞体轮廓上的突触处进行突触积累。在本研究中，我们探究了导致该蛋白在突触处进行突触积累的细胞内机制。MEK抑制剂完全阻断了佛波酯和KCl对Vesl-1S/Homer-1a积累的影响，并部分阻断了蛋白酶体抑制剂的作用。相反，脑源性神经营养因子（BDNF）和NT3促进了Vesl-1S/Homer-1a IR在突触处的积累。这种积累的程度与用BDNF处理后细胞外信号调节激酶ERK的激活水平相关。BDNF还导致Vesl-1S/Homer-1a蛋白量增加，但这发生在Vesl-1S/Homer-1a在突触处积累之后。此外，抑制从头合成蛋白质并不影响佛波酯介导的Vesl-1S/Homer-1a IR在突触处的积累。这些结果表明，ERK级联的激活在Vesl-1S/Homer-1a IR的突触积累中起关键作用，并表明这种积累主要通过Vesl-1S/Homer-1a蛋白的重新定位发生，而非通过Vesl-1S/Homer-1a水平的增加。神经营养因子的活性依赖性释放或去极化可能导致ERK级联的局部激活，从而产生Vesl-1S/Homer-1a的突触特异性定位。
