GABA_AReceptor-Associated Protein Traffics GABA_AReceptors to the Plasma Membrane in Neurons

Abstract

The trafficking of GABA A receptors is an important component of the pathway that regulates plasticity of inhibitory synapses. The 17 kDa GABA A receptor-associated protein (GABARAP) has been implicated in the trafficking of GABA A receptors because of its ability to interact not only with the ␥2 subunit of the receptor but also with microtubules and the N-ethylmaleimide-sensitive factor (NSF). To elucidate the role of GABARAP in the trafficking of GABA A receptors, we have constructed a yellow fluorescent protein (YFP) fusion protein of GABARAP and expressed it in neurons using adenovirus, so that its function may be examined. YFP-GABARAP colocalized with ␥2 subunit-containing GABA A receptors and NSF to the perinuclear cytoplasm in cultured hippocampal neurons and to the proximal regions of dendrites that are making synaptic contact. Expression of YFP-GABARAP in Cos7 cells and cultured hippocampal neurons was able to increase the level of GABA A receptors detected at the plasma membrane, even at low levels of YFP-GABARAP expression. This effect is specific to the function of GABARAP on GABA A receptor trafficking, because point mutations in the ␥2-binding domain of YFP-GABARAP interfered with the ability of YFP-GABARAP to increase GABA A receptor surface levels. These mutations also disrupted the colocalization of YFP-GABARAP with the ␥2 subunit and with NSF in hippocampal neurons. The results of this study show for the first time that GABARAP has a functional effect on the trafficking of GABA A receptors and provide decisive evidence for the role of GABARAP in transporting GABA A receptors to the plasma membrane in neurons.

GABARAPs regulate PI4P-dependent autophagosome:lysosome fusion

“…GABARAPs may direct trafficking of palmitoylated PI4KIIα from the Golgi to autophagosomes, analogous to their previously identified role as facilitators of GABA A trafficking to the plasma membrane (2). Second, PI4KIIα has already been implicated in constitutive exocytic, endo/lysosomal trafficking (6,15,16), and its recruitment to autophagosomes is decreased by GABARAP depletion.…”

“…Mammals have at least six Atg8 orthologs that can be broadly classified into two large subfamilies: LC3s (light-chain 3) and GABARAPs (γ-aminobutyric acid receptor-associated proteins)/ GATE-16s (Golgi-associated ATPase enhancer of 16 kDa), hereafter referred to collectively as GABARAPs. GABARAPs were initially identified as trafficking modulators for transmembrane receptors from the Golgi to the plasma membrane (2), and subsequently as Atg8s (1). Functional studies in mammalian cells have placed GABARAPs downstream of LC3 during autophagy (3).…”

Sustained Structural Change of GABAA Receptor-Associated Protein Underlies Long-Term Potentiation at Inhibitory Synapses on a Cerebellar Purkinje Neuron

“…GABARAP plays a role in trafficking of GABA A R toward the postsynaptic membrane of dendritic inhibitory synapses and in regulation of the GABA A R number on the plasma membrane in hippocampal neurons (Leil et al, 2004). Thus, we examined whether inhibition of GABARAP and GABA A R␥2 association affects the subcellular localization of GABA A R in a PN.…”

“…3A) (Leil et al, 2004), we examined whether the suppressive effect of ⌬27 GABARAP on RP is mediated by direct binding of the mutant GABARAP to GABA A R␥2 subunit. As shown in Figure 3D, the suppressive effect of ⌬27 GABARAP on RP was abolished by the point mutation P37A (2 min, 193 Ϯ 15%, p Ͼ 0.25; 30 min, 156 Ϯ 8%, p Ͻ 0.001) compared with ⌬27, suggesting that impairment of RP was attributable to direct association of GABA A R␥2 and the mutant GABARAP lacking the tubulin binding region.…”

“…Among them, we attended to GABARAP, a linker protein between GABA A R and tubulin (Wang et al, 1999). The number and/or function of surface GABA A R can be regulated by GABARAP in both heterologous expression systems and neurons (Chen et al, 2000(Chen et al, , 2005Nymann-Andersen et al, 2002;Everitt et al, 2004;Leil et al, 2004;Luu et al, 2006). However, implication of GABARAP in synaptic plasticity has not been explored.…”