Guo Jianxia, Pan Su-Shu, Singh Shivendra V
Department of Pharmacology and University of Pittsburgh Cancer Institute, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15213, USA.
Mol Carcinog. 2003 Feb;36(2):67-73. doi: 10.1002/mc.10097.
We have shown previously that the alpha class murine glutathione transferase (GST) isoenzyme mGSTA1-1, unlike other mammalian class alpha GSTs, is highly efficient in catalyzing the glutathione (GSH) conjugation of (7R,8S)-dihydroxy-(9S,10R)-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene [(+)-anti-BPDE], which is the ultimate carcinogenic metabolite of benzo[a]pyrene. The present studies were undertaken to determine the efficacy of mGSTA1-1 in cellular protection against (+)-anti-BPDE-induced DNA damage in HepG2 cells stably transfected with mGSTA1 cDNA. Untransfected HepG2 cells, vector-transfected HepG2 cells (HepG2-vector), and cells transfected with mGSTA4 cDNA (HepG2-mGSTA4), an alpha class murine GST isoenzyme with low (+)-anti-BPDE-GSH conjugating activity, were used as controls for comparison. Intracellular GSH conjugation of (+)-anti-BPDE was significantly higher in mGSTA1-1-overexpressing HepG2 cells (HepG2-mGSTA1) than in HepG2-vector or HepG2-mGSTA4 cells. The formation of DNA-adducts of (+)-anti-BPDE, following a 10-, 20-, or 30-min exposure to 0.1, 0.5, or 1.0 microM 3H-anti-BPDE, was reduced significantly in cells transfected with mGSTA1-1 compared with HepG2-vector or untransfected HepG2 cells. Consistent with the results with purified protein, overexpression of mGSTA4-4 had no effect on (+)-anti-BPDE-induced DNA damage. The results of the present study indicated that mGSTA1-1 was exceptionally effective in affording protection against (+)-anti-BPDE-induced DNA damage in a cellular system.
我们之前已经表明，α类小鼠谷胱甘肽转移酶（GST）同工酶mGSTA1-1与其他哺乳动物α类GST不同，在催化（7R,8S）-二羟基-（9S,10R）-环氧-7,8,9,10-四氢苯并[a]芘[（+）-反式BPDE]的谷胱甘肽（GSH）结合反应方面效率很高，而（+）-反式BPDE是苯并[a]芘的最终致癌代谢产物。进行本研究以确定mGSTA1-1在稳定转染了mGSTA1 cDNA的HepG2细胞中对（+）-反式BPDE诱导的DNA损伤的细胞保护作用。未转染的HepG2细胞、载体转染的HepG2细胞（HepG2-载体）以及转染了mGSTA4 cDNA的细胞（HepG2-mGSTA4）（一种对（+）-反式BPDE-GSH结合活性较低的α类小鼠GST同工酶）用作对照进行比较。在过表达mGSTA1-1的HepG2细胞（HepG2-mGSTA1）中，（+）-反式BPDE的细胞内GSH结合反应显著高于HepG2-载体或HepG2-mGSTA4细胞。在用0.1、0.5或1.0微摩尔[3H]（+）-反式BPDE处理10、20或30分钟后，与HepG2-载体或未转染的HepG2细胞相比，转染了mGSTA1-1的细胞中（+）-反式BPDE的DNA加合物形成显著减少。与纯化蛋白的结果一致，mGSTA4-4的过表达对（+）-反式BPDE诱导的DNA损伤没有影响。本研究结果表明，mGSTA1-1在细胞系统中对（+）-反式BPDE诱导的DNA损伤具有异常有效的保护作用。
