Soans C, Holash J A, Pasquale E B
La Jolla Cancer Research Foundation, California 92037.
Oncogene. 1994 Nov;9(11):3353-61.
Cek8 is a receptor-type tyrosine kinase gene that was identified by screening a 10 day chicken embryo library with a DNA probe corresponding to the related kinase Cek4 (Sajjadi & Pasquale, 1993). Here we report the characterization of the Cek8 protein and its expression in embryonic tissues and tumor cell lines. The 120 kd Cek8 protein is detected early in embryogenesis, is developmentally regulated and preferentially, but not exclusively, expressed in neural tissues. In the stage 24 chick embryo, Cek8 immunoreactivity is prominent in the spinal cord and spinal nerves. At embryonic day 6, Cek8 expression becomes concentrated to the ventral portion of the spinal nerves, suggesting a role in axonogenesis of specific subsets of neurons. Cek8 is expressed in nearly all of the tumor cell lines examined, including cell lines derived from tumors of the central nervous system. Although the phosphorylation on tyrosine of Cek8 during development is moderate or undetectable, Cek8 is substantially phosphorylated on tyrosine (and thus presumably activated) in many of the transformed cell lines. Because of its high frequency of expression in tumor cell lines, Cek8 differs from previously investigated Eph-related kinases. However, as we show, Cek8 is not unique among the Eph-related kinases: another member of the Eph subclass, Cek5, has similar patterns of expression and phosphorylation in tumor cells. Based on its binding to a variety of lectin columns, Cek8 contains complex N-linked oligosaccharides. Cross-linking of Cek8 molecules on the cell surface with wheat germ agglutinin caused their rapid phosphorylation on tyrosine. Autophosphorylation on tyrosine is typically the first step in the activation of a receptor tyrosine kinase by a ligand.
Cek8是一种受体型酪氨酸激酶基因，它是通过用与相关激酶Cek4对应的DNA探针筛选10日龄鸡胚文库而鉴定出来的（萨贾迪和帕斯夸莱，1993年）。在此我们报告Cek8蛋白的特性及其在胚胎组织和肿瘤细胞系中的表达。120kd的Cek8蛋白在胚胎发生早期即可检测到，其表达受发育调控，且优先但并非唯一地在神经组织中表达。在24期鸡胚中，Cek8免疫反应性在脊髓和脊神经中很突出。在胚胎第6天，Cek8表达集中在脊神经的腹侧部分，提示其在特定神经元亚群的轴突发生中起作用。Cek8在几乎所有检测的肿瘤细胞系中都有表达，包括源自中枢神经系统肿瘤的细胞系。尽管Cek8在发育过程中的酪氨酸磷酸化程度中等或无法检测到，但在许多转化细胞系中，Cek8在酪氨酸上大量磷酸化（因此推测被激活）。由于其在肿瘤细胞系中的高表达频率，Cek8与先前研究的Eph相关激酶不同。然而，正如我们所展示的，Cek8在Eph相关激酶中并非独一无二：Eph亚类的另一个成员Cek5在肿瘤细胞中具有相似的表达和磷酸化模式。基于其与多种凝集素柱的结合，Cek8含有复杂的N连接寡糖。用小麦胚凝集素使细胞表面的Cek8分子交联导致其酪氨酸快速磷酸化。酪氨酸自磷酸化通常是配体激活受体酪氨酸激酶的第一步。
