Fritz G, Tano K, Mitra S, Kaina B
Kernforschungszentrum Karlsruhe, Institut für Genetik und Toxikologie, Karlsruhe, Germany.
Mol Cell Biol. 1991 Sep;11(9):4660-8. doi: 10.1128/mcb.11.9.4660-4668.1991.
The inducibility of the mammalian O6-methylguanine-DNA methyltransferase (MGMT) gene encoding the MGMT protein (EC 2.1.1.63) responsible for removal of the procarcinogenic and promutagenic lesion O6-alkylguanine from DNA was examined by an analysis of transcription of the MGMT gene following exposure of repair-competent (Mex+) and repair-deficient (Mex-) cells to N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). While human and rodent Mex- cells (CHO-9, V79, HeLa MR) showed no detectable MGMT mRNA despite the presence of the gene in their genome, the amount of it in several Mex+ lines (NIH 3T3, HeLa S3, HepG2) paralleled their MGMT activity. However, none of these cell lines showed an increase in the MGMT mRNA level after treatment with various concentrations of MNNG. In contrast, MNNG-treated rat hepatoma cells, H4IIE and FTO-2B, both Mex+, had three- to fivefold more MGMT mRNA than the corresponding untreated controls as measured 12 to 72 h after alkylation. N-Methyl-N-nitrosourea, methyl methanesulfonate, N-hydroxyethyl-N-chloroethylnitrosourea, UV light, and X rays caused a similar accumulation of MGMT mRNA in rat hepatoma cells. Studies with inhibitors of RNA and protein synthesis indicate that the induced increase in the amount of MGMT mRNA was due to enhanced transcription of the gene. Furthermore, they revealed the turnover of the MGMT mRNA to be relatively low (half-life, greater than 7 h). Mutagen-induced increase of transcription of MGMT mRNA in H4IIE cells was accompanied by elevation of MGMT repair activity and resulted in reduction of mutation frequency after a challenge dose of MNNG. Although induction of MGMT mRNA transcription has been observed in two rodent hepatoma cell lines so far, this appears to be the first demonstration of inducibility of a mammalian gene encoding a clearly define DNA repair function. The transcription activation of the MGMT gene protects cells from the mutagenic effects of methylating agents.
通过分析具有修复能力（Mex+）和缺乏修复能力（Mex-）的细胞在暴露于N-甲基-N'-硝基-N-亚硝基胍（MNNG）后MGMT基因的转录情况，研究了编码负责从DNA中去除致癌和致突变性损伤O6-烷基鸟嘌呤的MGMT蛋白（EC 2.1.1.63）的哺乳动物O6-甲基鸟嘌呤-DNA甲基转移酶（MGMT）基因的可诱导性。尽管人类和啮齿动物的Mex-细胞（CHO-9、V79、HeLa MR）基因组中存在该基因，但未检测到可检测到的MGMT mRNA，而几种Mex+细胞系（NIH 3T3、HeLa S3、HepG2）中的MGMT mRNA量与它们的MGMT活性平行。然而，在用各种浓度的MNNG处理后，这些细胞系中没有一个显示MGMT mRNA水平增加。相比之下，经MNNG处理的大鼠肝癌细胞H4IIE和FTO-2B（均为Mex+），在烷基化后12至72小时测量，其MGMT mRNA比相应的未处理对照多三至五倍。N-甲基-N-亚硝基脲、甲磺酸甲酯、N-羟乙基-N-氯乙基亚硝基脲、紫外线和X射线在大鼠肝癌细胞中引起类似的MGMT mRNA积累。对RNA和蛋白质合成抑制剂的研究表明，MGMT mRNA量的诱导增加是由于该基因转录增强。此外，研究还表明MGMT mRNA的周转相对较低（半衰期大于7小时）。诱变剂诱导H4IIE细胞中MGMT mRNA转录增加，同时MGMT修复活性升高，并导致在MNNG激发剂量后突变频率降低。尽管到目前为止在两种啮齿动物肝癌细胞系中观察到了MGMT mRNA转录的诱导，但这似乎是首次证明编码明确的DNA修复功能的哺乳动物基因具有可诱导性。MGMT基因的转录激活保护细胞免受甲基化剂的诱变作用。
