Functional analyses of novel tumor suppressor genes by gene targeting

DRS基因最初是作为一种抑制v-src转化的基因被分离出来的。DRS蛋白有一个跨膜结构域和三个共识重复序列，称为Sushi基序。在多种人类肿瘤细胞系和组织中，DRS基因的表达明显下调，提示DRS基因是一种肿瘤抑制基因。本研究对DRS的功能及其抑制肿瘤的机制进行了研究，获得了以下结果：(1)DRS通过ASY/Nogo-B/RTN-Xs、caspase-12、caspase-9和caspase-3介导的新途径诱导人癌细胞凋亡。(2)通过建立基因敲除小鼠，研究DRS的体内抑瘤作用及其在细胞凋亡中的生理作用。在46只DRS基因敲除(KO)小鼠中，约25%发生了包括淋巴瘤、肺腺癌、肝癌和肉瘤在内的恶性肿瘤。(3)通过逆转录病毒载体将DRS重新导入DRS KO小鼠肺腺癌来源的肺癌细胞系，可抑制裸鼠的成瘤性，并通过激活caspase-3促进细胞凋亡。(4)DRS KO MEF细胞对某些凋亡诱导剂如雷帕霉素和地塞米松表现出耐药性。(5)葡萄糖耗竭的DRS KO MEF细胞可诱导凋亡。提示DRS诱导的细胞凋亡通路与mTOR信号通路密切相关。这些结果表明，DRS基因在恶性肿瘤的发生中发挥了肿瘤抑制作用，并在某些生理条件下的细胞凋亡通路中发挥作用。

The drs gene was originally isolated as a suppressor against v-src transformation.Drs protein has one transmembrane domain and three consensus repeat called Sushi motif. Expression of drs mRNA was markedly downregulated in a variety of human cancer cell lines and tissues, suggesting that the drs gene acts as a tumor suppressor. In this study, we investigated the function of Drs and the mechanism of tumor suppression by this gene and obtained the following results.(1)Drs induces apoptosis by a novel pathway mediated by ASY/Nogo-B/RTN-xS, caspase-12, caspase-9 and caspase-3 in human cancer cells.(2)We investigated the tumor suppressor function in vivo of drs and its physiological roles in apoptosis by generating a gene-knockout mouse. Malignant tumors including lymphomas, lung adenocarcinomas, hepatomas, and sarcoma were generated in about 25% of 46 drs-knockout(KO)mice. No tumors were detected in all (23) wild-type mice examined at the same age.(3)Re-introduction of drs by retrovirus vector into a lung cancer cell line derived from a lung adenocarcinoma of a drs KO mouse caused suppression of tumorigenicity in nude mouse and elevation of apoptosis mediated by activation of caspase-3.(4)Drs KO MEF cells showed resistance to certain apoptosis-inducing reagent such as rapamycine and dexamethazone.(5)Apoptosis was induced in glucose-depleted Drs KO MEF cells, suggesting the closstalk between Drs-induced apoptosis pathway and mTOR signal pathway.These results idicate that the drs gene acts as a tumor suppressor in genesis of malignant tumors and that drs play a role in certain apoptotic pathways in physiological conditions.