Crawford D R, Amstad P A, Foo D D, Cerutti P A
Department of Carcinogenesis, Swiss Institute for Experimental Cancer Research, Lausanne.
Mol Carcinog. 1989;2(3):136-43. doi: 10.1002/mc.2940020306.
Because oxidative processes can participate in tumor promotion, it is likely that the cellular antioxidant defense also plays a role. We have compared the levels of the three major antioxidant enzymes, Cu,Zn-superoxide dismutase (SOD), catalase and glutathione peroxidase (GPx), in promotable mouse epidermal JB6 cells clone 41 and nonpromotable cells, clone 30. We found that the constitutive activities of SOD and catalase were approximately twice as high in clone 41 as in clone 30 while the GPx activities were comparable. Correspondingly, catalase protein concentrations were higher in clone 41, according to immunoblots. Northern blot analysis indicated that the steady-state mRNA concentrations for SOD and catalase, but not for GPx, were considerably higher in clone 41 than in clone 30. Southern blot analysis showed no difference between the two clones in their complements of the SOD and catalase genes. Clone 41 also contained slightly higher constitutive levels of glutathione. The higher antioxidant capacity of promotable clone 41 may protect it from excessive toxicity of oxidant promoters and allow growth stimulation. Certain tumor promoters that lack oxidizing properties may generate a cellular prooxidant state by a variety of mechanisms (e.g., it had been reported that the phorbol ester PMA decreases the activities of catalase and SOD in mouse skin). We found for JB6 cells that this loss of enzyme activity was due to a decrease in the steady-state concentrations of catalase and SOD mRNA. No significant changes in the rates of transcription were detected in nuclear run-off experiments. The observed decreases in catalase and SOD can be considered as part of the complex reprogramming of gene expression that is set in motion by phorbol-12-myristate-13-acetate.
由于氧化过程可能参与肿瘤促进作用，细胞抗氧化防御系统很可能也发挥了作用。我们比较了可促进肿瘤发生的小鼠表皮JB6细胞克隆41和不可促进肿瘤发生的细胞克隆30中三种主要抗氧化酶，即铜锌超氧化物歧化酶（SOD）、过氧化氢酶和谷胱甘肽过氧化物酶（GPx）的水平。我们发现，克隆41中SOD和过氧化氢酶的组成性活性大约是克隆30中的两倍，而GPx活性相当。相应地，根据免疫印迹分析，克隆41中的过氧化氢酶蛋白浓度更高。Northern印迹分析表明，克隆41中SOD和过氧化氢酶的稳态mRNA浓度比克隆30中高得多，而GPx的则不然。Southern印迹分析显示，两个克隆在SOD和过氧化氢酶基因的互补性方面没有差异。克隆41中谷胱甘肽的组成性水平也略高。可促进肿瘤发生的克隆41具有较高的抗氧化能力，这可能保护它免受氧化型启动子的过度毒性，并允许生长刺激。某些缺乏氧化特性的肿瘤启动子可能通过多种机制产生细胞促氧化状态（例如，据报道佛波酯PMA会降低小鼠皮肤中过氧化氢酶和SOD的活性）。我们发现，对于JB6细胞来说，这种酶活性的丧失是由于过氧化氢酶和SOD mRNA的稳态浓度降低所致。在核转录实验中未检测到转录速率的显著变化。观察到的过氧化氢酶和SOD的降低可被视为由佛波醇-12-肉豆蔻酸酯-13-乙酸酯引发的基因表达复杂重编程的一部分。
