ISOLATION OF NOVEL ONCOGENES BY AN EFFICIENT EXPRESSION CLONING SYSTEM

利用实验室开发的高效表达克隆系统。一 新癌基因命名为ost的是从大鼠骨肉瘤cDNA中分离的 图书馆克隆的ostcDNA具有较高的转化活性， NIH/3 T3细胞。ost产物通过截短其N-末端而被激活。 末端结构域，并且在裸鼠测定中具有高度致瘤性。 的 随后分离出全长ost cDNA，并编码预测的 100千道尔顿的蛋白质，含有OH（dbl同源物）和PH （普列克底物蛋白同源性）结构域。 OST主要在丝氨酸上磷酸化 并定位于细胞质中。 在检查的组织中。大脑显示 Ost的最高表达。尤其是在神经元和α-伸长细胞中。 杆状病毒表达的Ost可以催化鸟嘌呤核苷酸交换， Rho和Ras家族成员中的RhoA和Cdc 42。奥斯特没有 可检测地与RhoA或Cdc 42缔合。而是与 Rac 1的GTP结合形式。 这些结果暗示Ost是一个关键的 调节组分，其连接信号转导途径， 流经Rac 1、RhoA和Cdc 42。

Using an efficient expression cloning system developed in the lab. a novel oncogene. designated ost was isolated from a rat osteosarcoma cDNA library. The cloned ost cDNA possesses high transforming activity in NIH/3T3 cells. The ost product was activated by truncation of its N- terminal domain and was highly tumorigenic in nude mouse assays. The full-length ost cDNA was subsequently isolated and encodes a predicted protein of 100 kilodaltons containing the OH (dbl homology) and PH (pleckstrin homology) domains. Ost is mainly phosphorylated on serine and localized in the cytoplasm. Among the tissues examined. brain showed the highest expression of Ost. especially in neurons and alpha-tanycytes. Baculovirus-expressed Ost can catalyze guanine nucleotide exchange on RhoA and Cdc42 among Rho and Ras family members tested. Ost did not detectably associate with RhoA or Cdc42. but interacted specifically with the GTP-bound form of Rac1. These results implicate Ost as a critical regulatory component which links the signal transduction pathways that flow through Rac1, RhoA and Cdc42.