Gong Q, Hart B A
Department of Biochemistry, University of Vermont College of Medicine, Burlington 05405-0068, USA.
Toxicology. 1997 May 16;119(3):179-91. doi: 10.1016/s0300-483x(96)03608-6.
This study examined cadmium-induced alterations in metallothionein-1 (MT), glutathione-S-transferase Ya (GST), and heme oxygenase-1 (HO) gene expression in an adult rat lung epithelial cell line. Elevations in MT mRNA and HO mRNA occurred as early as 1 h after exposure to a sub-toxic concentration of CdCl(2) (10 microM) whereas GST expression did not increase significantly until 4 h after Cd addition. At t = 8 h, levels of GST, MT, and HO mRNA were elevated 9-fold, 27-fold, and 44-fold, respectively, over basal expression. By 24 h, MT expression was almost back to baseline levels. GST mRNA and HO mRNA were also reduced, compared to 8 h, but to a lesser extent than MT expression. The MT gene was more responsive to low Cd concentrations (5 microM) than the genes for HO or GST whereas HO was induced more than the others at higher Cd doses (10-20 microM). Pro-oxidant conditions play a role in Cd-induced gene expression, as suggested by the rapid decline (15-30 min) in glutathione (GSH), amounting to 25-30% of baseline, that occurred after exposure to 10 microM CdCl(2). This was followed by resynthesis of GSH to a concentration higher than the initial. Depleting GSH by treatment of cells with buthionine sulfoximine (BSO) enhanced Cd-induced expression of MT, GST, and HO whereas thiol supplementation, by treatment with N-acetyl cysteine (NAC), had an attenuating effect. BSO and NAC pretreatment had no effect on basal gene expression or Cd uptake. In summary, this study has shown that: (1) Cd increases MT, GST, and HO gene expression in a time- and dose-dependent fashion: (2) MT gene expression appears to be most sensitive to Cd whereas the HO gene is most inducible at higher Cd concentrations; (3) Cd-induced expression is enhanced by GSH depletion and suppressed by thiol supplementation.
本研究检测了镉对成年大鼠肺上皮细胞系中金属硫蛋白-1（MT）、谷胱甘肽-S-转移酶Ya（GST）和血红素加氧酶-1（HO）基因表达的影响。暴露于亚毒性浓度的CdCl₂（10微摩尔）后1小时，MT mRNA和HO mRNA水平就开始升高，而直到添加镉后4小时，GST表达才显著增加。在t = 8小时时，GST、MT和HO mRNA水平分别比基础表达升高了9倍、27倍和44倍。到24小时时，MT表达几乎恢复到基线水平。与8小时相比，GST mRNA和HO mRNA也有所降低，但降低程度小于MT表达。MT基因对低镉浓度（5微摩尔）的反应比HO或GST基因更敏感，而在较高镉剂量（10 - 20微摩尔）下，HO的诱导程度比其他基因更高。如暴露于10微摩尔CdCl₂后谷胱甘肽（GSH）迅速下降（15 - 30分钟），降至基线的25 - 30%，这表明促氧化条件在镉诱导的基因表达中起作用。随后GSH重新合成至高于初始浓度。用丁硫氨酸亚砜胺（BSO）处理细胞耗尽GSH可增强镉诱导的MT、GST和HO表达，而用N-乙酰半胱氨酸（NAC）进行硫醇补充则具有减弱作用。BSO和NAC预处理对基础基因表达或镉摄取没有影响。总之，本研究表明：（1）镉以时间和剂量依赖的方式增加MT、GST和HO基因表达；（2）MT基因表达似乎对镉最敏感，而HO基因在较高镉浓度下最易被诱导；（3）GSH耗竭增强镉诱导的表达，硫醇补充则抑制该表达。
