Zhou H, Fuks A, Alcaraz G, Bolling T J, Stanners C P
McGill Cancer Centre, McGill University, Montreal, Quebec, Canada.
J Cell Biol. 1993 Aug;122(4):951-60. doi: 10.1083/jcb.122.4.951.
Both carcinoembryonic antigen (CEA) and neural cell adhesion molecule (NCAM) belong to the immunoglobulin supergene family and have been demonstrated to function as homotypic Ca(++)-independent intercellular adhesion molecules. CEA and NCAM cannot associate heterotypically indicating that they have different binding specificities. To define the domains of CEA involved in homotypic interaction, hybrid cDNAs consisting of various domains from CEA and NCAM were constructed and were transfected into a CHO-derived cell line; stable transfectant clones showing cell surface expression of CEA/NCAM chimeric-proteins were assessed for their adhesive properties by homotypic and heterotypic aggregation assays. The results indicate that all five of the Ig(C)-like domains of NCAM are required for intercellular adhesion while the COOH-terminal domain containing the fibronectin-like repeats is dispensable. The results also show that adhesion mediated by CEA involves binding between the Ig(V)-like amino-terminal domain and one of the Ig(C)-like internal repeat domains: thus while transfectants expressing constructs containing either the N domain or the internal domains alone were incapable of homotypic adhesion, they formed heterotypic aggregates when mixed. Furthermore, peptides consisting of both the N domain and the third internal repeat domain of CEA blocked CEA-mediated cell aggregation, thus providing direct evidence for the involvement of the two domains in adhesion. We therefore propose a novel model for interactions between immunoglobulin supergene family members in which especially strong binding is effected by double reciprocal interactions between the V-like domains and C-like domains of antiparallel CEA molecules on apposing cell surfaces.
癌胚抗原（CEA）和神经细胞黏附分子（NCAM）都属于免疫球蛋白超基因家族，并且已被证明可作为同型非钙离子依赖性细胞间黏附分子发挥作用。CEA和NCAM不能异型结合，这表明它们具有不同的结合特异性。为了确定CEA中参与同型相互作用的结构域，构建了由CEA和NCAM的各个结构域组成的杂交cDNA，并将其转染到CHO衍生的细胞系中；通过同型和异型聚集试验评估显示CEA/NCAM嵌合蛋白细胞表面表达的稳定转染克隆的黏附特性。结果表明，NCAM的所有五个Ig(C)样结构域都是细胞间黏附所必需的，而包含纤连蛋白样重复序列的COOH末端结构域则是可有可无的。结果还表明，CEA介导的黏附涉及Ig(V)样氨基末端结构域与一个Ig(C)样内部重复结构域之间的结合：因此，单独表达包含N结构域或内部结构域构建体的转染子不能进行同型黏附，但当混合时它们会形成异型聚集体。此外，由CEA的N结构域和第三个内部重复结构域组成的肽阻断了CEA介导的细胞聚集，从而为这两个结构域参与黏附提供了直接证据。因此，我们提出了一种免疫球蛋白超基因家族成员之间相互作用的新模型，其中在相对细胞表面上反平行CEA分子的V样结构域和C样结构域之间的双相互补相互作用产生了特别强的结合。
