Down-regulation of DNA polymerase β accompanies somatic hypermutation in human BL2 cell lines
Down-regulation of DNA polymerase β accompanies somatic hypermutation in human BL2 cell lines
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DOI：
10.1016/j.dnarep.2006.10.003
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发表时间：
2007-02-04
期刊：
影响因子：
3.8
通讯作者：
Wilson, Samuel H.
中科院分区：
文献类型：
--
作者：
Poltoratsky, Vladimir;Prasad, Rajendra;Wilson, Samuel H.
体细胞超突变（SHM）是免疫球蛋白基因成熟的一个基本过程，导致抗体对抗原的亲和力增加。在解释人类B细胞中SHM的一种假设中，该过程是通过免疫球蛋白基因V区中胞嘧啶酶促脱氨基为尿嘧啶而启动的，这反过来触发尿嘧啶-DNA碱基切除修复（BER）的突变倾向形式。然而，该模型的不确定性在于哺乳动物细胞中尿嘧啶-DNA的BER通常是无错误的，其中DNA聚合酶β（pol β）根据沃森-克里克规则通过插入碱基进行间隙填充合成。为了评估这种不一致性，我们检测了各种SHM熟练的人BL 2细胞系亚系中的pol β表达。我们报告说，在SHM熟练的细胞系中，pol β的表达被强烈下调。相反，在其它BL 2亚克隆中，我们发现SHM是缺陷，且pol β表达比SHM熟练亚克隆中高得多。我们还发现重组人pol β在SHM熟练亚克隆中的过表达消除了其SHM能力。这些结果表明，下调正常BER缺口填充DNA聚合酶，pol β，伴随诱导SHM在BL 2细胞。这与以下假设一致：正常的无错误BER必须被沉默，以便为体细胞超突变期间可能需要的易错BER过程让路。(c)2006 Elsevier B. V.保留所有权利。
Somatic hypermutation (SHM) is a fundamental process in immunoglobulin gene maturation that results in increased affinity of antibodies toward antigens. In one hypothesis explaining SHM in human B cells, the process is initiated by enzymatic deamination of cytosine to uracil in the immunoglobulin gene V-region and this in turn triggers mutation-prone forms of uracil-DNA base excision repair (BER). Yet, an uncertainty with this model is that BER of uracil-DNA in mammalian cells is generally error-free, wherein DNA polymerase beta (pol beta) conducts gap-filling synthesis by insertion of bases according to Watson-Crick rules. To evaluate this inconsistency, we examined pol beta expression in various SHM proficient human BL2 cell line subcIones. We report that expression of pol beta in SHM proficient cell lines was strongly down-regulated. in contrast, in other BL2 subclones, we found that SHM was deficient and that pol beta expression was much higher than in the SHM proficient subclones. We also found that overexpression of recombinant human pol beta in a SHM proficient subclone abrogated its capacity for SHM. These results suggest that down-regulation of the normal BER gap-filling DNA polymerase, pol beta, accompanies induced SHM in BL2 cells. This is consistent with the hypothesis that normal error-free BER must be silenced to make way for an error-prone BER process that may be required during somatic hypermutation. (c) 2006 Elsevier B.V. All rights reserved.