From the Institute of Pharmacology and Toxicology, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland and.
J Biol Chem. 2014 Mar 14;289(11):7738-46. doi: 10.1074/jbc.M113.541987. Epub 2014 Jan 30.
Regulation of cell surface expression of neurotransmitter receptors is crucial for determining synaptic strength and plasticity, but the underlying mechanisms are not well understood. We previously showed that proteasomal degradation of GABAB receptors via the endoplasmic reticulum (ER)-associated protein degradation (ERAD) machinery determines the number of cell surface GABAB receptors and thereby GABAB receptor-mediated neuronal inhibition. Here, we show that proteasomal degradation of GABAB receptors requires the interaction of the GABAB2 C terminus with the proteasomal AAA-ATPase Rpt6. A mutant of Rpt6 lacking ATPase activity prevented degradation of GABAB receptors but not the removal of Lys(48)-linked ubiquitin from GABAB2. Blocking ERAD activity diminished the interaction of Rtp6 with GABAB receptors resulting in increased total as well as cell surface expression of GABAB receptors. Modulating neuronal activity affected proteasomal activity and correspondingly the interaction level of Rpt6 with GABAB2. This resulted in altered cell surface expression of the receptors. Thus, neuronal activity-dependent proteasomal degradation of GABAB receptors by the ERAD machinery is a potent mechanism regulating the number of GABAB receptors available for signaling and is expected to contribute to homeostatic neuronal plasticity.
细胞表面神经递质受体的表达调控对于确定突触强度和可塑性至关重要，但其中的机制尚不清楚。我们之前的研究表明，通过内质网（ER）相关蛋白降解（ERAD）机制对 GABAB 受体进行蛋白酶体降解决定了细胞表面 GABAB 受体的数量，从而决定了 GABAB 受体介导的神经元抑制作用。在这里，我们表明 GABAB 受体的蛋白酶体降解需要 GABAB2 C 末端与蛋白酶体 AAA-ATPase Rpt6 的相互作用。缺乏 ATP 酶活性的 Rpt6 突变体阻止了 GABAB 受体的降解，但不阻止 GABAB2 上 Lys（48）连接的泛素的去除。阻断 ERAD 活性会减少 Rtp6 与 GABAB 受体的相互作用，导致 GABAB 受体的总表达和细胞表面表达增加。调节神经元活性会影响蛋白酶体活性，从而相应地影响 Rpt6 与 GABAB2 的相互作用水平。这导致受体的细胞表面表达发生改变。因此，神经元活性依赖性 ERAD 机制对 GABAB 受体的蛋白酶体降解是一种调节可用 GABAB 受体数量以进行信号转导的有效机制，并有望有助于神经元的自身稳定可塑性。
