Functional analyses of novel tumor suppressor genes by gene targeting

dr基因最初是作为抑制v-src转化的基因分离出来的。dr蛋白具有1个跨膜结构域和3个一致重复序列，称为Sushi motif。在多种人类癌细胞系和组织中，drs mRNA的表达明显下调，表明drs基因具有肿瘤抑制作用。在本研究中，我们研究了dr基因的功能和该基因抑制肿瘤的机制，得到了以下结果。(1) dr通过ASY/Nogo-B/ rn - xs、caspase-12、caspase-9、caspase-3介导的新途径诱导人癌细胞凋亡。(2)通过基因敲除小鼠，研究了drs在体内的抑瘤功能及其在细胞凋亡中的生理作用。在46只dr -knockout（KO）小鼠中，约25%产生了恶性肿瘤，包括淋巴瘤、肺腺癌、肝癌和肉瘤。23只同龄野生型小鼠均未发现肿瘤。(3)逆转录病毒载体将dr重新导入由dr - KO小鼠肺腺癌衍生的肺癌细胞系，可抑制裸鼠的致瘤性，并通过激活caspase-3介导细胞凋亡。(4) dr . KO MEF细胞对雷帕胺、地塞米松等凋亡诱导试剂有耐药性。(5)葡萄糖耗竭的dr KO MEF细胞可诱导凋亡，提示dr诱导凋亡途径与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起抑瘤作用，并且在生理条件下drs在某些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.