Jeong Hyun Sik, Kim Seong Won, Baek Kwang Jin, Lee Hee Sung, Kwon Nyoun Soo, Kim Young-Myeong, Yun Hye-Young
Department of Biochemistry, College of Medicine, Chung-Ang University, Seoul, Korea.
J Neurooncol. 2002 Nov;60(2):97-107. doi: 10.1023/a:1020627106602.
Nitric oxide (NO) plays a key role in attenuation of tumor growth by activated macrophages that generate large amount of cytotoxic/cytostatic free radicals. However, some tumor cells may survive from NO cytotoxicity and continue to proliferate to malignant tumors. Since a protooncogene product Ras was shown to be activated by NO, this study investigated the involvement of Ras in the cell survival in response to NO cytotoxicity in pheochromocytoma (PC12) cells. Treatment with Ras inhibitor or constitutive expression of dominant negative Ras markedly increased NO-induced cell death. NO-resistant PC12 cells (PC12-NO-R) exhibited higher steady state Ras activity than the parental PC12 cells. Inducible expression using tetracycline-on (Tet-on) system of Ras mutants (dominant negative Ras or dominant active Ras) demonstrated that blockade of Ras activity increased NO-induced cell death whereas enhancement of Ras activity attenuated NO-induced cell death. Furthermore, inducible expression of NO-insensitive mutant Ras selectively increased cellular vulnerability to NO but not to ROS. NO, Ras inhibitor and extracellular signal-regulated kinase (Erk) blocker synergistically increased cell death. These observations suggest that Ras activity may be a critical factor for survival response of tumor cells to NO toxicity and pharmacological agents affecting Ras activity may enhance efficacy of NO-mediated tumor therapies.
一氧化氮（NO）在活化巨噬细胞介导的肿瘤生长抑制过程中发挥关键作用，活化的巨噬细胞可产生大量具有细胞毒性/细胞增殖抑制作用的自由基。然而，一些肿瘤细胞可能会在NO的细胞毒性作用下存活下来，并继续增殖形成恶性肿瘤。由于原癌基因产物Ras已被证明可被NO激活，因此本研究探讨了Ras在嗜铬细胞瘤（PC12）细胞中对NO细胞毒性的细胞存活反应中的作用。用Ras抑制剂处理或组成型表达显性负性Ras可显著增加NO诱导的细胞死亡。对NO具有抗性的PC12细胞（PC12-NO-R）的稳态Ras活性高于亲代PC12细胞。使用四环素诱导（Tet-on）系统对Ras突变体（显性负性Ras或显性活性Ras）进行诱导表达表明，阻断Ras活性会增加NO诱导的细胞死亡，而增强Ras活性则会减弱NO诱导的细胞死亡。此外，对NO不敏感的突变体Ras的诱导表达选择性地增加了细胞对NO的敏感性，但对活性氧（ROS）不敏感。NO、Ras抑制剂和细胞外信号调节激酶（Erk）阻滞剂协同增加细胞死亡。这些观察结果表明，Ras活性可能是肿瘤细胞对NO毒性存活反应的关键因素，影响Ras活性的药物可能会增强NO介导的肿瘤治疗效果。
