Surface Expression of GABAA Receptors Is Transcriptionally Controlled by the Interplay of cAMP-response Element-binding Protein and Its Binding Partner Inducible cAMP Early Repressor

Abstract

The regulated expression of type A ␥-aminobutyric acid (GABA) receptor (GABA A R) subunit genes plays a critical role in neuronal maturation and synaptogenesis. It is also associated with a variety of neurological diseases. Changes in GABA A receptor ␣1 subunit gene (GABRA1) expression have been reported in animal models of epilepsy, alcohol abuse, withdrawal, and stress. Understanding the genetic mechanism behind such changes in ␣ subunit expression will lead to a better understanding of the role that signal transduction plays in control over GABA A R function and brings with it the promise of providing new therapeutic tools for the prevention or cure of a variety of neurological disorders. Here we show that activation of protein kinase C increases ␣1 subunit levels via phosphorylation of CREB (pCREB) that is bound to the GABRA1 promoter (GABRA1p). In contrast, activation of protein kinase A decreases levels of ␣1 even in the presence of pCREB. Decrease of ␣1 is dependent upon the inducible cAMP early repressor (ICER) as directly demonstrated by ICER-induced down-regulation of endogenous ␣1-containing GABA A Rs at the cell surface of cortical neurons. Taken together with the fact that there are less ␣1␥2-containing GABA A Rs in neurons after protein kinase A stimulation and that activation of endogenous dopamine receptors down-regulates ␣1 subunit mRNA levels subsequent to induction of ICER, our studies identify a transcriptional mechanism for regulating the cell surface expression of ␣1-containing GABA A Rs that is dependent upon the formation of CREB heterodimers. ␥-Aminobutyric acid (GABA)4 type A receptors (GABA A Rs) are ligand-gated chloride ion channels that mediate the majority of fast synaptic inhibition in the mammalian brain (1). They are pentameric in structure and are composed of multiple subunit isoforms coming from eight distinct classes: ␣, ␤, ␥, ␦, , ⑀, , and . Diversity in receptor subtypes is controlled by the regulated expression of 19 different subunit genes and the alternative splicing of individual subunit transcripts (2-4). Most importantly, differential receptor subunit composition produces functionally and pharmacologically distinct GABA A Rs at certain times during development and in certain regions of the brain (5-8).The transcription of different GABA A R subunit genes (GABRs) is likely to involve a complex system of regulatory controls that remain to be identified. Several lines of evidence suggest that ␣1 subunit expression is activity-dependent (9 -11). Treatment with N-methyl-D-aspartate, a selective activator of an important class of excitatory ligand-gated ion channels, stimulates ␣1 subunit expression in cultured cerebellar granule cells (12, 13). In contrast, chronic treatment of cortical neurons with GABA decreases levels of GABA A R ␣1 subunit mRNAs (14 -16), which is dependent on voltage-gated calcium channel activity and most likely an alteration in transcription (15). In addition, prolonged benzodiazepine (BZ) treatment decreases ␣1 mRNA levels in the rat hippocampal CA...

Brief Dark Exposure Reduces Tonic Inhibition in Visual Cortex

“…1A). Moreover, we confirmed in a subset of 9 cells that, at this age (Ͻ5 weeks), ambient GABA is insufficient to significantly activate tonic current (Jang et al, 2010): the difference in holding current between before adding GABA and after BMI, as shown in Figure 1A, was minimal (3.1 Ϯ 1.6 pA) compared with the current determined in 5 M GABA (51.2 Ϯ 5.2 pA). To compare results from cells of different sizes, we normalized the tonic current values by the cell capacitance, a direct measure of the cell surface (see Materials and Methods).…”

“…Tonic inhibition was quantified as the postsynaptic current induced by bath application of 5 M GABA, a concentration at which GABA maximally activates the extrasynaptic receptors responsible for tonic inhibition, but without affecting synaptic receptors involved in fast GABAergic transmission (Jang et al, 2010). Therefore, the difference in the holding current recorded first in the presence of GABA and then after adding the GABA A blocker BMI (20 M) provided a direct estimate of the total tonic conductance available in a given cell (Fig.…”

“…These results suggest that the early phases of homeostatic adaptations to sensory deprivation might result from modulation of GABAergic function at multiple levels. (Jang et al, 2010) that is strongly modulated by a variety of G-protein receptors and is severely altered in several pathological conditions, including epilepsy (Roberts et al, 2005;Ferando and Mody, 2012;Grabenstatter et al, 2012) stroke (Hines et al, 2012, and injury (Imbrosci et al, 2013). Notably, however, the possible role of sensory experience in tonic inhibition remains largely unknown.…”

“…Western blot was performed using traditional methods in the Russek laboratory (Hu et al, 2008). Protein (30 g) extracted from frontal and visual cortices was loaded onto 10% Tris-glycine gels and run for 1.5-2 h at 115 V. Blots were transferred to a nitrocellulose membrane and blocked in 5% milk/TBS with Tween 20 (TBS-T).…”

ICER expression inhibits leukemia phenotype and controls tumor progression

“…Moreover, ICER-lowered expression prevents CREB/ICER heterodimerization, which would lead CREB protein to degrade. 48,49 Future studies will implement this mechanism to influence CREB/ICER expression in tumor. 50 The newly discovered function of ICER in mediating leukemia gives new insight into future treatment strategies for clinical implementation.…”