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UNG shapes the specificity of AID-induced somatic hypermutation.

Pérez-Durán P, Belver L, de Yébenes VG, Delgado P, Pisano DG, Ramiro AR - J. Exp. Med. (2012)

Bottom Line: Activation-induced deaminase (AID) initiates both processes by deaminating cytosine residues in immunoglobulin genes.The resulting U:G mismatch can be processed by alternative pathways to give rise to a mutation (SHM) or a DNA double-strand break (CSR).We used next generation sequencing to analyze the contribution of UNG to the resolution of AID-induced lesions.

View Article: PubMed Central - HTML - PubMed

Affiliation: B Cell Biology Laboratory, Centro Nacional de Investigaciones Cardiovasculares (CNIC), 28029 Madrid, Spain.

ABSTRACT
Secondary diversification of antibodies through somatic hypermutation (SHM) and class switch recombination (CSR) is a critical component of the immune response. Activation-induced deaminase (AID) initiates both processes by deaminating cytosine residues in immunoglobulin genes. The resulting U:G mismatch can be processed by alternative pathways to give rise to a mutation (SHM) or a DNA double-strand break (CSR). Central to this processing is the activity of uracil-N-glycosylase (UNG), an enzyme normally involved in error-free base excision repair. We used next generation sequencing to analyze the contribution of UNG to the resolution of AID-induced lesions. Loss- and gain-of-function experiments showed that UNG activity can promote both error-prone and high fidelity repair of U:G lesions. Unexpectedly, the balance between these alternative outcomes was influenced by the sequence context of the deaminated cytosine, with individual hotspots exhibiting higher susceptibility to UNG-triggered error-free or error-prone resolution. These results reveal UNG as a new molecular layer that shapes the specificity of AID-induced mutations and may provide new insights into the role of AID in cancer development.

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UNG shapes the specificity of AID-induced mutations. The diagram summarizes the main findings of this work (see text for details). Alternative processing pathways leading to the generation of double-strand breaks or A/T mutations are purposely excluded from the model for the sake of clarity (polβ, DNA polymerase β; TLS, translesion synthesis).
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fig6: UNG shapes the specificity of AID-induced mutations. The diagram summarizes the main findings of this work (see text for details). Alternative processing pathways leading to the generation of double-strand breaks or A/T mutations are purposely excluded from the model for the sake of clarity (polβ, DNA polymerase β; TLS, translesion synthesis).

Mentions: Our data raise the question of how specific sequence motifs can influence the molecular pathways acting downstream of the glycosylation reaction. It is tempting to speculate that the sequence surrounding the uracil could influence the dynamics of UNG-mediated uracil removal, allowing the specific recruitment of translesion synthesis polymerases and leading to transversion mutations in some sequence contexts, while favoring the recruitment of polβ and error-free repair in others. Although our study has only addressed this issue in the context of AID-mediated deaminations, this sequence dependency could be inherent to UNG activity itself (Nilsen et al., 1995). Alternatively, it remains possible that specific sequence contexts could increase the residence time of AID itself, thus preventing repair at those sites, as proposed previously (Delbos et al., 2007). Regardless of the molecular mechanism responsible for this effect, this is to our knowledge the first evidence that sequence environment influences the outcome of UNG activity and contributes to the mutagenic resolution of AID-induced U:G mismatches (Fig. 6).


UNG shapes the specificity of AID-induced somatic hypermutation.

Pérez-Durán P, Belver L, de Yébenes VG, Delgado P, Pisano DG, Ramiro AR - J. Exp. Med. (2012)

UNG shapes the specificity of AID-induced mutations. The diagram summarizes the main findings of this work (see text for details). Alternative processing pathways leading to the generation of double-strand breaks or A/T mutations are purposely excluded from the model for the sake of clarity (polβ, DNA polymerase β; TLS, translesion synthesis).
© Copyright Policy - openaccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC3405504&req=5

fig6: UNG shapes the specificity of AID-induced mutations. The diagram summarizes the main findings of this work (see text for details). Alternative processing pathways leading to the generation of double-strand breaks or A/T mutations are purposely excluded from the model for the sake of clarity (polβ, DNA polymerase β; TLS, translesion synthesis).
Mentions: Our data raise the question of how specific sequence motifs can influence the molecular pathways acting downstream of the glycosylation reaction. It is tempting to speculate that the sequence surrounding the uracil could influence the dynamics of UNG-mediated uracil removal, allowing the specific recruitment of translesion synthesis polymerases and leading to transversion mutations in some sequence contexts, while favoring the recruitment of polβ and error-free repair in others. Although our study has only addressed this issue in the context of AID-mediated deaminations, this sequence dependency could be inherent to UNG activity itself (Nilsen et al., 1995). Alternatively, it remains possible that specific sequence contexts could increase the residence time of AID itself, thus preventing repair at those sites, as proposed previously (Delbos et al., 2007). Regardless of the molecular mechanism responsible for this effect, this is to our knowledge the first evidence that sequence environment influences the outcome of UNG activity and contributes to the mutagenic resolution of AID-induced U:G mismatches (Fig. 6).

Bottom Line: Activation-induced deaminase (AID) initiates both processes by deaminating cytosine residues in immunoglobulin genes.The resulting U:G mismatch can be processed by alternative pathways to give rise to a mutation (SHM) or a DNA double-strand break (CSR).We used next generation sequencing to analyze the contribution of UNG to the resolution of AID-induced lesions.

View Article: PubMed Central - HTML - PubMed

Affiliation: B Cell Biology Laboratory, Centro Nacional de Investigaciones Cardiovasculares (CNIC), 28029 Madrid, Spain.

ABSTRACT
Secondary diversification of antibodies through somatic hypermutation (SHM) and class switch recombination (CSR) is a critical component of the immune response. Activation-induced deaminase (AID) initiates both processes by deaminating cytosine residues in immunoglobulin genes. The resulting U:G mismatch can be processed by alternative pathways to give rise to a mutation (SHM) or a DNA double-strand break (CSR). Central to this processing is the activity of uracil-N-glycosylase (UNG), an enzyme normally involved in error-free base excision repair. We used next generation sequencing to analyze the contribution of UNG to the resolution of AID-induced lesions. Loss- and gain-of-function experiments showed that UNG activity can promote both error-prone and high fidelity repair of U:G lesions. Unexpectedly, the balance between these alternative outcomes was influenced by the sequence context of the deaminated cytosine, with individual hotspots exhibiting higher susceptibility to UNG-triggered error-free or error-prone resolution. These results reveal UNG as a new molecular layer that shapes the specificity of AID-induced mutations and may provide new insights into the role of AID in cancer development.

Show MeSH
Related in: MedlinePlus