GABA Receptor Regulation by Splicing Truncation

描述(由申请人提供)： 目标是确定GABAA受体α4亚单位的一种不寻常形式的选择性剪接的调节作用。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，即GABA门控氯离子通道，是用于治疗酒精戒断、癫痫、失眠、焦虑等药物的作用部位，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(6α、3β、3伽马、Delta、epsilon、pi、3 Rho、theta)。Alpha4亚基尤其与酒精的作用有关。一些亚基的mRNAs表现出选择性剪接，进一步增加了亚基的多样性。对于alpha5、alpha6和ro1亚基描述的一种令人费解的剪接形式，在这种情况下是罕见的，它在编码N-端胞外域的碱基中产生短的缺失，从而使得到的亚基不起作用。最近，我们发现了一种相对常见的Alpha4亚单位mRNA选择性剪接形式，值得注意的是，这种剪接产生了一种信息，除了前两个编码外显子和最后一个编码外显子之外，所有信息都丢失了，它们之间存在移码。这种剪接模式给出了一个严重截断的mRNA，不受无意义介导的mRNA衰变的影响，它编码两种可能的蛋白质。信号肽后面的一小段N-末端似乎是唯一可以合成的。这种剪接受到发育和地区的调节。电生理学数据表明，当截短的mRNA与完整的α4亚基共表达时，选择性地减少了由于后者而产生的电流。我们计划进一步探索截短的Alpha4蛋白是否在包含Alpha4亚基的GABAA受体的表达中发挥翻译后调节作用。这些研究可能建立一种新的重要的GABAA受体对酒精反应的调节机制。

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.