Stephen J. Moss Laboratory

GABA_Α

Molecular and biochemical studies have revealed that GABA_Α receptors are pentameric hetero-oligomers that can be assembled from 7 subunit classes: α(1-6), β(1-3), γ(1-3), δ, ε, θ and π. However, in vivo the majority of synaptic benzodiazepine-sensitive GABA_Α receptor subtypes are composed of α, β and γ2 subunits. Receptors composed of αβ or αβδ subunits are believed to form extrasynaptic receptors that mediate tonic inhibition but are insensitive to functional modulation by classic benzodiazepines.

We are principally interested in understanding how neurons regulate the accumulation of GABA_Α receptors at the appropriate subcellular specialization. We also study the endogenous mechanisms neurons use to control GABA_Α receptor functional expression with particular emphasis on the roles played by post-translational modifications of receptor structure such as phosphorylation and ubiquitination. To address these issue we combine molecular, imaging, biochemical, genetic, electrophysiological and pharmacological approaches.

Our studies have revealed that GABA_Α receptors are dynamic entities on the cell surface of neurons that undergo rapid rates of constitutive clathrin-mediated endocytosis and recycling, processes that determine the cell surface number of GABA_Α receptors, together with the efficacy of synaptic inhibition. Moreover the “membrane trafficking” of GABA_Α receptors is subject to dynamic modulation by receptor phosphorylation and via their interaction with specific receptor associated proteins (Kittler and Moss, 2003).

With regard to phosphorylation it is evident that GABA_Α receptors are phosphorylated in neurons and that this process is subject to dynamic modulation by metabotropic neurotransmitters and growth factor receptors that modify the activity of protein kinases and phosphatases (Brandon et al., 2002; Jovanovic et al., 2004; Kittler et al., 2005; Chen et al., 2006). Modified phosphorylation in turn regulates the binding of GABA_Α receptors to the AP2 adaptin, a critical regulator of GABA_Α receptor endocytosis.

Recently we have demonstrated that GABA_Α receptor endocytic sorting, is regulated by direct binding to Huntingtin-associated protein (HAP1; Kittler et al., 2004). In addition it is also evident that receptor insertion at the plasma membrane is regulated via interaction with 2 other distinct receptor associated proteins GABARAP and Plic-1 respectively (Kittler and Moss, 2003). In addition using RNAi and live imaging we have established that the inhibitory postsynaptic scaffold protein gephyrin regulates GABA_Α receptor lateral mobility, promoting the accumulation of these receptors at inhibitory synapses (Jacob et al., 2005).

Currently we are utilizing homologous recombination to make mouse lines in which the phosphorylation of individual subunits or their ability to bind specific receptor associated proteins has been abolished. These animals will allow us to ascertain the role that these putative regulatory mechanisms play in the control of synaptic inhibition and animal behavior in addition to pathological conditions such as epilepsy.

Last Updated: 07-Apr-2006