Uracil-DNA Glycosylase in Base Excision Repair and Adaptive Immunity SPECIES DIFFERENCES BETWEEN MAN AND MOUSE
Uracil-DNA Glycosylase in Base Excision Repair and Adaptive Immunity SPECIES DIFFERENCES BETWEEN MAN AND MOUSE
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DOI：
10.1074/jbc.m111.230052
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发表时间：
2011-05-13
影响因子：
4.8
通讯作者：
Kavli, Bodil
中科院分区：
文献类型：
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作者：
Doseth, Berit;Visnes, Torkild;Kavli, Bodil
基因组尿嘧啶是一种DNA损伤，也是适应性免疫中必不可少的关键中间体。在B细胞中，激活诱导胞苷脱氨酶将Ig基因中的胞嘧啶脱氨为尿嘧啶（U:G错配），从而启动抗体成熟。尿嘧啶-DNA糖基化酶（UDGs），如尿嘧啶n -糖基化酶（UNG）、单链选择性单功能尿嘧啶-DNA糖基化酶1 （SMUG1）和胸腺嘧啶-DNA糖基化酶，可从DNA中去除尿嘧啶。基因靶向小鼠模型被广泛用于研究这些酶在DNA修复和Ig多样化中的作用。然而，人类和小鼠在尿嘧啶处理过程中可能存在的物种差异尚未确定。为了解决这个问题，我们分析了人类和小鼠细胞系以及Ung（+/+）和Ung（-/-）回交小鼠脾B细胞中UDG的活性和数量。有趣的是，由于UNG水平较高，人类细胞显示出类似于15倍的总尿嘧啶切除能力。相比之下，SMUG1活性在小鼠细胞中高出8倍，占总U:G切除活性的50%，而在人类细胞中则不到1%。在活化的B细胞中，UNG和SMUG1的活性水平与小鼠细胞系的水平相当。此外，激活后每个细胞的SMUG1活性并未下调。因此，我们认为SMUG1可能在Ung（-/-）小鼠的类开关重组过程中作为UNG2的弱备份活动。我们的研究结果揭示了尿嘧啶基因组加工的显著物种差异。当将小鼠模型用于研究尿嘧啶DNA修复和适应性免疫时，应考虑到这些发现。
Genomic uracil is a DNA lesion but also an essential key intermediate in adaptive immunity. In B cells, activation-induced cytidine deaminase deaminates cytosine to uracil (U:G mispairs) in Ig genes to initiate antibody maturation. Uracil-DNA glycosylases (UDGs) such as uracil N-glycosylase (UNG), single strand-selective monofunctional uracil-DNA glycosylase 1 (SMUG1), and thymine-DNA glycosylase remove uracil from DNA. Gene-targeted mouse models are extensively used to investigate the role of these enzymes in DNA repair and Ig diversification. However, possible species differences in uracil processing in humans and mice are yet not established. To address this, we analyzed UDG activities and quantities in human and mouse cell lines and in splenic B cells from Ung(+/+) and Ung(-/-) backcrossed mice. Interestingly, human cells displayed similar to 15-fold higher total uracil excision capacity due to higher levels of UNG. In contrast, SMUG1 activity was similar to 8-fold higher in mouse cells, constituting similar to 50% of the total U:G excision activity compared with less than 1% in human cells. In activated B cells, both UNG and SMUG1 activities were at levels comparable with those measured for mouse cell lines. Moreover, SMUG1 activity per cell was not down-regulated after activation. We therefore suggest that SMUG1 may work as a weak backup activity for UNG2 during class switch recombination in Ung(-/-) mice. Our results reveal significant species differences in genomic uracil processing. These findings should be taken into account when mouse models are used in studies of uracil DNA repair and adaptive immunity.