GABA Receptor Regulation by Splicing Truncation

描述（由申请人提供）： 目的是确定GABAA受体α 4亚基的一种不寻常的选择性剪接形式的调节作用。GABA（γ-氨基丁酸）是大脑中主要的抑制性神经递质。它的A型受体，GABA门控氯离子通道，是用于治疗酒精戒断、癫痫、失眠、焦虑等的药物的作用部位，也可能是酒精本身的作用部位。在哺乳动物中已经克隆了许多亚基（6 α、3 β、3 γ、δ、π、π、3 ρ、θ）。alpha 4亚基尤其与酒精的作用有关。一些亚基的mRNA表现出选择性剪接，进一步增加亚基多样性。一种令人困惑的剪接形式描述为α 5，α 6和rho 1亚基，在那里它是罕见的，在编码N-末端胞外结构域的碱基中产生短缺失，使产生的亚基无功能。最近，我们发现了一种相对常见的α 4亚基mRNA的选择性剪接形式，值得注意的是，这种剪接产生的信息除了前两个编码外显子和最后一个编码外显子之外，什么都没有，它们之间有一个移码。这种剪接模式产生严重截短的mRNA，不受无义介导的mRNA衰变的影响，其编码2种可能的蛋白质。在信号肽之后的N末端的一小段似乎是唯一被制造的。剪接是发育和区域调节。电生理学数据表明，截短的mRNA，当与完整的α 4亚基共表达时，选择性地降低由于后者的电流。我们计划进一步探索截短的α 4蛋白是否在含有α 4亚基的GABAA受体的表达中起翻译后调节作用。这些研究可能建立一个新的和重要的机制，调节GABAA受体对酒精的反应。

DESCRIPTION (provided by applicant): The goal is to define the regulatory role of an unusual form of alternative splicing of GABAA receptor alpha4 subunits. GABA (gamma-aminobutyric acid) is the major inhibitory neurotransmitter in the brain. Its type A receptors, GABA-gated chloride channels, are the site of action of drugs used to treat alcohol withdrawal, epilepsy, insomnia, anxiety, etc., and are likely sites of action for alcohol itself. Many subunits (6 alpha, 3 beta, 3 gamma, delta, epsilon, pi, 3 rho, theta) have been cloned in mammals. The alpha4 subunit has been especially implicated in the actions of alcohol. The mRNAs for some subunits exhibit alternative splicing, further increasing subunit diversity. A puzzling form of splicing described for alpha5, alpha6, and rho1 subunits, where it is rare, creates short deletions in the bases coding for the N-terminal extracellular domain which make the resulting subunits nonfunctional. Recently we discovered a relatively common form of alternative splicing of the alpha4 subunit mRNA which, remarkably, creates a message missing everything except the first two coding exons and the last coding exon, with a frameshift between them. This pattern of splicing gives a severely truncated mRNA, not subject to nonsense-mediated mRNA decay, which codes for 2 possible proteins. A short piece of the N-terminus right after the signal peptide is the only one which seems to be made. The splicing is developmentally and regionally regulated. Electrophysiological data suggest that the truncated mRNA, when coexpresssed with the complete alpha4 subunit, selectively reduces currents due to the latter. We plan to explore further whether the truncated alpha4 protein plays a post-translational regulatory role in expression of GABAA receptors containing the alpha4 subunit. These studies may establish a novel and important mechanism of regulation of GABAA receptors responsive to alcohol.