Coxsackie and adenovirus receptor (CAR): a multifunctional cell adhesion molecule

柯萨奇和腺病毒受体(CAR)是免疫球蛋白超家族黏附分子中的一员。顾名思义，它首先被鉴定为对腺病毒5型的高亲和力受体，5型腺病毒是最常用的基因转移的腺病毒载体。我的实验室之所以对CAR感兴趣，是因为我们经常使用腺病毒(Ad)载体将基因转移到肌肉、神经系统和肿瘤细胞。因此，我们一直对确定CAR的表达模式和调节其表达的方法感兴趣。在这个过程中，我们已经开始研究CAR在这些组织中的多种功能。*CAR的表达是以组织特异性的方式在发育中调节的。体外异位过表达研究表明，CAR的胞外区可以介导同型细胞间的黏附。因此，CAR定位于极化上皮中的紧密连接和粘连连接。CAR在产前和新生儿组织中的表达水平最高。这种表达模式表明，CAR可能在胚胎或新生儿组织的生长、迁移或分化中发挥作用。CAR在几种类型的癌症中的表达缺失的观察进一步支持了CAR的这种作用。我们首次证明了CAR的高度保守的细胞质结构域对于调节细胞迁移是必不可少的。通过下拉实验和蛋白质组学分析，我们已经确定了几个与CAR直接结合的结合伙伴，其中包括细胞骨架蛋白TuBulin和Actin。我们还证明了CAR被金属蛋白酶，特别是ADAM10处理，导致其胞外结构域脱落。随后，通过伽马分泌酶复合体的裂解产生细胞内的胞质片段，从而产生潜在的重要信号分子。*我们的长期目标是了解黏附分子(如CAR)如何将细胞外信号传递为细胞内信号。在过去的几年里，我们专注于两个生物系统，肿瘤细胞和神经元。在这两种类型的细胞中，CAR在细胞迁移中起着至关重要的作用。在肿瘤细胞中，CAR的表达导致迁移和侵袭的抑制，而在神经元中，CAR的表达促进突起的延伸(轴突生长)。*我们的具体目标是：*1)确定CAR的处理的功能相关性*2)确定CAR的胞浆结构域是否发挥信号作用*3)研究CAR在神经系统发育中的功能**

***The Coxsackie and adenovirus receptor (CAR) is a member of the immunoglobulin superfamily of adhesion molecules. As its name implies, it was first identified as the high affinity receptor for adenovirus type 5, the most commonly used adenoviral vector for gene transfer. My laboratory's interest in CAR stems from the fact that we routinely use adenovirus (Ad) vectors for gene transfer to muscle, nervous system and tumour cells. As such we have been interested in determining the expression pattern of CAR and means of modulating its expression. In the process, we have started studying the multiple functions of CAR in these tissues.***CAR expression is regulated developmentally and in a tissue-specific manner. Ectopic over expression studies in vitro indicate that the extracellular domain of CAR can mediate homotypic cell-cell adhesion. Accordingly CAR is localized to tight and adherens junctions in polarized epithelia. Highest levels of CAR expression are observed in prenatal and neonatal tissues. This pattern of expression suggests CAR could play a role in the growth, migration or differentiation of embryonic or neonatal tissues. Such a role for CAR is further supported by the observation of loss of CAR expression in several types of cancer. We were the first to show that the highly conserved cytoplasmic domain of CAR was essential for regulating cell migration. Through pulldown assays and proteomic analysis we have identified several binding partners, among which were the cytoskeletal proteins tubulin and actin, binding directly to CAR. We have also shown that CAR is processed by metalloproteases, specifically ADAM10, leading to shedding of its extracellular domain. This is followed by cleavage through the gamma-secretase complex to produce an intracellular cytoplasmic fragment, thus generating potentially important signalling molecules.***Our long term objective is to understand how an adhesion molecule such as CAR transmits extracellular cues into intracellular signals. In the past few years we have concentrated on two biological systems, tumour cells and neurons. In both cell types, CAR plays crucial roles in cell migration. In tumour cells, CAR expression leads to inhibition of migration and invasion while in neurons, CAR expression promotes process extension (neurite outgrowth).***Our specific aims are to:***1) determine the functional relevance of the processing of CAR***2) determine whether CAR's intracellular cytoplasmic domain plays a signaling role***3) study the function of CAR in the developing nervous system**