Skorpen F, Skjelbred C, Alm B, Aas P A, Schønberg S A, Krokan H E
UNIGEN Center for Molecular Biology, Norwegian University of Science and Technology, Trondheim, Norway.
Mutat Res. 1998 Jun;407(3):227-41. doi: 10.1016/s0921-8777(97)00067-0.
We studied the repair of cyclobutane pyrimidine dimers (CPDs) in the 5' terminal part of the transcriptionally inactive O6-methylguanine-DNA methyltransferase (MGMT) gene of MGMT-deficient human cell lines (A172, A-253 and WI-38 VA13) and in a proficient cell line (HaCaT), in which the MGMT gene was transcribed. Repair rates in the MGMT gene were compared with those in the active uracil-DNA glycosylase (UNG) and c-myc genes, and those in the repressed X-linked 754 locus and the RNA polymerase I-transcribed ribosomal gene cluster. In the active MGMT gene, there was a distinct strand specificity with more repair in the template (transcribed) strand (TS) than in the non-template strand (NTS). In contrast, no apparent strand bias in the repair of CPDs was observed in the inactive MGMT gene in the MGMT deficient cell lines, although the rates of repair varied between different cell lines. Repair in the inactive MGMT gene was consistently lower than repair in the NTSs of the expressed genes, and approached the generally poor repair of the repressed 754 locus. Whereas repair in the UNG gene was strand-specific in HaCaT, A-172 and WI-38 VA13 cells, no clear strand bias in repair of this gene was evident in A253 cells and repair was relatively inefficient. Although the repair kinetics was essentially similar in the two strands of the c-myc gene in all cell lines examined, the rate and extent of repair were in general significant, probably due to an observed transcription of both strands in the c-myc region. In conclusion, our results indicate that the relative rates of repair in inactive MGMT genes are comparable to those of repressed loci and are lower than repair rates in the NTSs of active genes, but the absolute rate of repair varies between different transformed cells.
我们研究了MGMT缺陷型人细胞系（A172、A - 253和WI - 38 VA13）以及MGMT基因可转录的正常细胞系（HaCaT）中，转录失活的O6 - 甲基鸟嘌呤 - DNA甲基转移酶（MGMT）基因5'末端部分环丁烷嘧啶二聚体（CPD）的修复情况。将MGMT基因中的修复率与活性尿嘧啶 - DNA糖基化酶（UNG）基因、c - myc基因以及沉默的X连锁754位点和RNA聚合酶I转录的核糖体基因簇中的修复率进行了比较。在活性MGMT基因中，存在明显的链特异性，模板（转录）链（TS）中的修复比非模板链（NTS）更多。相比之下，在MGMT缺陷细胞系的非活性MGMT基因中，未观察到CPD修复的明显链偏向，尽管不同细胞系之间的修复率有所不同。非活性MGMT基因中的修复始终低于表达基因NTS中的修复，并接近沉默的754位点普遍较差的修复水平。在HaCaT、A - 172和WI - 38 VA13细胞中，UNG基因的修复具有链特异性，但在A253细胞中该基因的修复没有明显的链偏向且修复效率相对较低。尽管在所检测的所有细胞系中，c - myc基因两条链的修复动力学基本相似，但修复的速率和程度总体上较为显著，这可能是由于在c - myc区域观察到两条链都有转录。总之，我们的结果表明，非活性MGMT基因中的相对修复率与沉默位点的相当，低于活性基因NTS中的修复率，但不同转化细胞之间的绝对修复率有所不同。
