GABA_A receptor associated proteins: a key factor regulating GABA_A receptor function

Abstract

c-Aminobutyric acid (GABA), an important inhibitory neurotransmitter in both vertebrates and invertebrates, acts on GABA receptors that are ubiquitously expressed in the CNS. GABA A receptors also represent a major site of action of clinically relevant drugs, such as benzodiazepines, barbiturates, ethanol, and general anesthetics. It has been shown that the intracellular M3-M4 loop of GABA A receptors plays an important role in regulating GABA A receptor function. Therefore, studies of the function of receptor intracellular loop associated proteins become important for understanding mechanisms of regulating receptor activity. Recently, several labs have used the yeast two-hybrid assay to identify proteins interacting with GABA A receptors, for example, the interaction of GABA A receptor associated protein (GABARAP) and Golgispecific DHHC zinc finger protein (GODZ) with c subunits, PRIP, phospholipase C-related, catalytically inactive proteins (PRIP-1) and (PRIP-2) with GABARAP and receptor c2 and b subunits, Plic-1 with some a and b subunits, radixin with the a5 subunit, HAP1 with the b1 subunit, GABA A receptor interacting factor-1 (GRIF-1) with the b2 subunit, and brefeldin A-inhibited GDP/GTP exchange factor 2 (BIG2) with the b3 subunit. These proteins have been shown to play important roles in modulating the activities of GABA A receptors ranging from enhancing trafficking, to stabilizing surface and internalized receptors, to regulating modification of GABA A receptors. This article reviews the current studies of GABA A receptor intracellular loop-associated proteins. Keywords: GABA A receptor, GABA A receptor associated proteins, yeast two-hybrid assay, trafficking, clustering, internalization. J. Neurochem. (2007) 100, 279-294. c-Aminobutyric acid (GABA), an important inhibitory neurotransmitter in both vertebrates and invertebrates, acts on ionotropic GABA A receptors as well as metabotropic GABA B receptors that are ubiquitously expressed in the CNS. In vertebrates, 19 related GABA A receptor subunit genes have been detected, a1-6, b1-3, c1-3, d, e, h, p, and q1-3. The subunits are combined into approximately 20 different native heteropentameric isoforms (Macdonald and Olsen 1994;Sieghart and Sperk 2002). GABA A receptors are members of the ligand-gated ion channel superfamily, which includes nicotinic acetylcholine (nACh), glycine, and 5-HT 3 receptors. They are composed of five subunits, which assemble to form an ion channel. Each subunit possesses a long exracellular N-terminus that in some cases carries the neurotransmitter binding site, four membrane-spanning domains, including the ion channel wall primarily in M2, and a large variable sequence intracellular loop between M3 and M4. GABA A receptors also represent a major site of Received March 27, 2006; revised manuscript received June 19, 2006; accepted June 25, 2006. Address correspondence and reprint requests to Dr Richard W. Olsen, Department of Molecular and Medical Pharmacology, 650 Charles Young Drive South, David Geffen Sch...

Decreased anticonvulsant efficacy of allopregnanolone during ethanol withdrawal in female Withdrawal Seizure-Prone vs. Withdrawal Seizure-Resistant mice

“…Certainly, chronic ethanol exposure and withdrawal significantly alters the expression and peptide levels of several GABA A receptor subunits in the hippocampus of male rats (↓ α1, ↑ α4, ↑ γ2, ↓ δ; Cagetti et al, 2003;Grobin et al, 2000;Matthews et al, 1998), but the relevance of these changes in expression to GABA A receptor subunit assembly or trafficking, composition of synaptic versus extra-synaptic receptors, or phosphorylation state of GABA A receptors (see Kumar et al, 2004;Liang et al, 2004) to the present findings is not known. Additional factors influencing GABA A receptor function are the rapid diffusion of hippocampal receptors from extra-synaptic to synaptic domains (Thomas et al, 2005) and GABA A receptor associated proteins (Chen and Olsen, 2007). Taken in conjunction with the finding that the effects of ALLO on GABAergic transmission in the amydgala may depend on neural network activity (Wang et al, 2007), it is possible that multiple mechanisms affect GABA A receptor sensitivity to ALLO within a coordinated limbic convulsion circuit and thereby contribute to the tolerance to the anticonvulsant effect of ALLO in WSP mice during ethanol withdrawal.…”

Effect of the α subunit subtype on the macroscopic kinetic properties of recombinant GABAA receptors

“…As a result, there is the potential for differences in channel characteristics compared to native receptors because of neuron-specific processes that regulate receptor function. Neuronal receptors are likely to be subject to modulation by post-translational modifications such as phosphorylation (Brandon et al, 2002), interactions with cytoskeletal proteins (Chen and Olsen, 2007), and differences in assembly and membrane targeting (Fritschy et al, 1998;Brünig et al, 2002;Klausberger et al, 2002). However, virtually all neurons and neuronal cell lines that express GABARs produce multiple subunit subtypes (Wisden et al, 1992;Laurie et al, 1992a;Tyndale et al, 1994;Neelands et al, 1998) and neuronal populations which express only one or two of the α subtypes are extremely rare.…”

“…It is also possible that the relatively slow application rate associated with the whole-cell recording configuration could influence our ability to accurately capture the peak current, and therefore alter the measured EC 50 . In addition, the disruption of interactions of the receptor with cytoskeletal proteins through the process of patch excision could also alter channel properties and could result in differences between whole-cell and outside-out patch recordings (Chen and Olsen, 2007;Lagrange et al, 2007).…”

Increased GABAA channel subunits expression in CD8+ but not in CD4+ T cells in BB rats developing diabetes compared to their congenic littermates

“…We examined if proteins known to cluster the channels at synaptic and extrasynaptic sites like gephyrin (Kneussel et al, 1999) and radixin (Loebrich et al, 2006), respectively, were expressed in the lymphocytes. We further examined if the GABA A receptor associated protein (GABARAP, (Chen and Olsen, 2007)) that is involved in intracellular transport of the channels and affects their pharmacology is present and whether HAP-1 (Huntington associated protein -1, (Sheng et al, 2006)) that may stabilize the channels in intracellular vesicles and aid their recycling to the plasma membrane is expressed in the T cells. The results are shown in Fig.…”