title: Uracil-DNA glycosylase in base excision repair and adaptive immunity: species differences between man and mouse.
abstract: 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 ∼15-fold higher total uracil excision capacity due to higher levels of UNG. In contrast, SMUG1 activity was ∼8-fold higher in mouse cells, constituting ∼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.
authors: Department of Cancer Research and Molecular Medicine, Faculty of Medicine, Norwegian University of Science and Technology, N-7491 Trondheim, Norway.
authors: Berit
authors: B
authors: Doseth
authors: Torkild
authors: T
authors: Visnes
authors: Anders
authors: A
authors: Wallenius
authors: Ida
authors: I
authors: Ericsson
authors: Antonio
authors: A
authors: Sarno
authors: Henrik Sahlin
authors: HS
authors: Pettersen
authors: Arnar
authors: A
authors: Flatberg
authors: Tara
authors: T
authors: Catterall
authors: Geir
authors: G
authors: Slupphaug
authors: Hans E
authors: HE
authors: Krokan
authors: Bodil
authors: B
authors: Kavli
mesh_terms: D000818:Animals; D004260:DNA Repair; D006801:Humans; D017578:Immunoglobulin Class Switching; D007136:Immunoglobulins / Q000737:chemistry; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D010641:Phenotype; D011995:Recombination, Genetic; D013045:Species Specificity; D044502:Thymine DNA Glycosylase / Q000737:chemistry; D051981:Uracil-DNA Glycosidase / Q000737:chemistry*
chemical_list: D007136:Immunoglobulins; D044502:Thymine DNA Glycosylase; D051981:Uracil-DNA Glycosidase