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

* 科萨基和腺病毒受体（CAR）是粘附分子免疫球蛋白超家族的成员。顾名思义，它首先被鉴定为5型腺病毒的高亲和力受体，5型腺病毒是最常用的基因转移腺病毒载体。我的实验室对CAR的兴趣源于这样一个事实，即我们通常使用腺病毒（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表达在发育过程中以组织特异性方式调节。体外异位过表达研究表明，CAR的胞外结构域可以介导同型细胞-细胞粘附。因此，CAR定位于极化上皮中的紧密连接和粘附连接。在产前和新生儿组织中观察到最高水平的CAR表达。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的这种作用进一步得到了几种类型癌症中CAR表达丧失的观察结果的支持。我们是第一个表明CAR的高度保守的胞质结构域对于调节细胞迁移是必不可少的。通过下拉分析和蛋白质组学分析，我们已经确定了几个结合伙伴，其中包括细胞骨架蛋白微管蛋白和肌动蛋白，直接结合到CAR。我们还表明，CAR被金属蛋白酶，特别是ADAM 10加工，导致其胞外结构域脱落。随后通过γ-分泌酶复合物裂解产生细胞内胞质片段，从而产生潜在的重要信号分子。我们的长期目标是了解粘附分子如CAR如何将细胞外信号传递到细胞内信号。在过去的几年里，我们集中在两个生物系统，肿瘤细胞和神经元。在这两种细胞类型中，CAR在细胞迁移中起着至关重要的作用。在肿瘤细胞中，CAR表达导致对迁移和侵袭的抑制，而在神经元中，CAR表达促进过程延伸（神经突生长）。我们的具体目标是：*1）确定CAR加工的功能相关性 *2）确定CAR的细胞内胞质结构域是否起信号传导作用 *3）研究CAR在发育中的神经系统中的功能 **

***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**