Ashery U, Koch H, Scheuss V, Brose N, Rettig J
Department of Membrane Biophysics, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, D-37077 Goettingen, Germany.
Proc Natl Acad Sci U S A. 1999 Feb 2;96(3):1094-9. doi: 10.1073/pnas.96.3.1094.
ADP ribosylation factors (ARFs) represent a family of small monomeric G proteins that switch from an inactive, GDP-bound state to an active, GTP-bound state. One member of this family, ARF6, translocates on activation from intracellular compartments to the plasma membrane and has been implicated in regulated exocytosis in neuroendocrine cells. Because GDP release in vivo is rather slow, ARF activation is facilitated by specific guanine nucleotide exchange factors like cytohesin-1 or ARNO. Here we show that msec7-1, a rat homologue of cytohesin-1, translocates ARF6 to the plasma membrane in living cells. Overexpression of msec7-1 leads to an increase in basal synaptic transmission at the Xenopus neuromuscular junction. msec7-1-containing synapses have a 5-fold higher frequency of spontaneous synaptic currents than control synapses. On stimulation, the amplitudes of the resulting evoked postsynaptic currents of msec7-1-overexpressing neurons are increased as well. However, further stimulation leads to a decline in amplitudes approaching the values of control synapses. This transient effect on amplitude is strongly reduced on overexpression of msec7-1E157K, a mutant incapable of translocating ARFs. Our results provide evidence that small G proteins of the ARF family and activating factors like msec7-1 play an important role in synaptic transmission, most likely by making more vesicles available for fusion at the plasma membrane.
ADP核糖基化因子（ARFs）是一类小的单体G蛋白家族，它们从无活性的GDP结合状态转变为有活性的GTP结合状态。该家族的一个成员ARF6在激活时从细胞内区室转位到质膜，并与神经内分泌细胞中受调控的胞吐作用有关。由于体内GDP的释放相当缓慢，ARF的激活由特定的鸟嘌呤核苷酸交换因子如细胞黏附分子-1（cytohesin-1）或ARNO促进。在这里，我们表明msec7-1是细胞黏附分子-1的大鼠同源物，它能使活细胞中的ARF6转位到质膜。msec7-1的过表达导致非洲爪蟾神经肌肉接头处基础突触传递增加。含有msec7-1的突触自发突触电流频率比对照突触高5倍。在刺激时，过表达msec7-1的神经元所产生的诱发突触后电流的幅度也会增加。然而，进一步刺激会导致幅度下降，接近对照突触的值。msec7-1E157K是一种不能使ARFs转位的突变体，其过表达会强烈降低这种对幅度的瞬时效应。我们的结果提供了证据，表明ARF家族的小G蛋白和像msec7-1这样的激活因子在突触传递中起重要作用，很可能是通过使更多的囊泡可用于在质膜处融合。
