Fundamental Mechanisms of GPR56 Activation and Regulation

描述（由申请人提供）：大脑皮层发育异常可导致一系列不同的神经发育障碍，包括自闭症和阿斯伯格综合症。对复杂的多基因疾病如自闭症相关的皮层发育失调的新见解可以从对同样植根于大脑皮层异常发育的简单单基因疾病的研究中获得。其中一种疾病是双侧额顶叶多小回症（BFPP），患者表现出皮层连通性紊乱，导致严重的认知异常。BFPP是一种常染色体隐性综合征，由孤儿受体GPR56突变引起，GPR56是尚不清楚的G蛋白偶联受体粘附家族的一员。GPR56具有一个非常大的细胞外氨基末端（NT），与粘附蛋白具有同源性，并且在受体加工过程中被切割，但仍与受体的七跨膜（7TM）区域相关。然而，激活和调控GPR56信号的基本机制目前尚不清楚。我们的初步研究表明，野生型GPR56在异源细胞中的表达导致Rho和b-catenin/Tcf信号的强烈激活，并且截断大GPR56- nt导致受体被有效地运输到质膜，但不再激活上述信号通路。我们假设GPR56-NT与粘附伙伴的相互作用促进受体信号传导，并将通过阐明控制受体活性的GPR56-NT的结构决定因素来探索这一观点。我们进一步假设GPR56信号受到细胞质激酶、阻滞蛋白和PDZ支架的高度调节，并将在转染细胞和培养皮层神经元中使用磷酸化测定、成像研究、共免疫沉淀实验和siRNA敲低方法来探索这些可能性。从这些研究中获得的知识将为GPR56在人类疾病中的作用以及调节大脑皮层发育的基本机制提供新的见解。公共卫生相关性：大脑皮层发育异常可导致一系列不同的神经发育障碍，包括自闭症和阿斯伯格综合征。为了阐明导致这些疾病的因素，我们建议研究孤儿受体GPR56的基本特性，GPR56被认为在皮层发育中起关键作用，因为GPR56的突变导致一种罕见的遗传疾病，大脑皮层的发育严重扭曲。从这些关注GPR56正常功能的研究中获得的知识将为GPR56在人类疾病中的作用以及调节大脑皮层发育的基本机制提供新的见解。

DESCRIPTION (provided by applicant): Abnormalities in the development of the cerebral cortex can lead to a range of distinct neurodevelopmental disorders, including autism and Asperger's syndrome. Fresh insights into the dysregulation of cortical development associated with complex polygenetic disorders such as autism can be gained from studies on simpler monogenetic disorders that also are rooted in abnormal development of the cerebral cortex. One such disorder is bilateral frontoparietal polymicrogyria (BFPP), a condition in which patients exhibit disordered cortical connectivity resulting in profound cognitive abnormalities. BFPP is an autosomal recessive syndrome that results from mutations in the orphan receptor GPR56, which is a member of the poorly-understood adhesion family of G protein-coupled receptors. GPR56 possesses an extremely large extracellular amino-terminus (NT) that has homology to adhesion proteins and has been shown to be cleaved during receptor processing but yet remain associated with the seven-transmembrane (7TM) region of the receptor. However, the fundamental mechanisms of the activation and regulation of GPR56 signaling are presently unknown. Our preliminary studies have shown that expression of wild-type GPR56 in heterologous cells results in strong activation of Rho and b-catenin/Tcf signaling, and that truncation of the large GPR56-NT results in a receptor that is trafficked efficiently to the plasma membrane but no longer activates the aforementioned signaling pathways. We hypothesize that interaction of the GPR56-NT with an adhesion partner promotes receptor signaling, and will explore this idea by elucidating the structural determinants of the GPR56-NT that control receptor activity. We furthermore hypothesize that GPR56 signaling is highly regulated by cytoplasmic kinases, arrestins and PDZ scaffolds, and will explore these possibilities using a combination of phosphorylation assays, imaging studies, co-immunoprecipitation experiments, and siRNA knockdown approaches in both transfected cells and cultured cortical neurons. Knowledge gained from these studies will provide fresh insights into the role of GPR56 in human disease and also into the fundamental mechanisms that regulate the development of the cerebral cortex. PUBLIC HEALTH RELEVANCE: Abnormalities in the development of the cerebral cortex can lead to a range of distinct neurodevelopmental disorders, including autism and Asperger's syndrome. To shed light on the factors that contribute to such diseases, we propose to study the fundamental properties of the orphan receptor GPR56, which is believed to play a key role in cortical development since mutations in GPR56 cause a rare genetic disorder in which the development of the cerebral cortex is grossly distorted. Knowledge gained from these studies focused on the normal function of GPR56 will provide fresh insights into the role of GPR56 in human disease and also into the fundamental mechanisms that regulate the development of the cerebral cortex.