Dataset Information

Proximity to AGCT sequences dictates MMR-independent versus MMR-dependent mechanisms for AID-induced mutation via UNG2.

ABSTRACT: AID deaminates C to U in either strand of Ig genes, exclusively producing C:G/G:C to T:A/A:T transition mutations if U is left unrepaired. Error-prone processing by UNG2 or mismatch repair diversifies mutation, predominantly at C:G or A:T base pairs, respectively. Here, we show that transversions at C:G base pairs occur by two distinct processing pathways that are dictated by sequence context. Within and near AGCT mutation hotspots, transversion mutation at C:G was driven by UNG2 without requirement for mismatch repair. Deaminations in AGCT were refractive both to processing by UNG2 and to high-fidelity base excision repair (BER) downstream of UNG2, regardless of mismatch repair activity. We propose that AGCT sequences resist faithful BER because they bind BER-inhibitory protein(s) and/or because hemi-deaminated AGCT motifs innately form a BER-resistant DNA structure. Distal to AGCT sequences, transversions at G were largely co-dependent on UNG2 and mismatch repair. We propose that AGCT-distal transversions are produced when apyrimidinic sites are exposed in mismatch excision patches, because completion of mismatch repair would require bypass of these sites.

SUBMITTER: Thientosapol ES

PROVIDER: S-EPMC5389528 | biostudies-literature | 2017 Apr

REPOSITORIES: biostudies-literature

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Proximity to AGCT sequences dictates MMR-independent versus MMR-dependent mechanisms for AID-induced mutation via UNG2.

Thientosapol Eddy Sanchai ES Sharbeen George G Lau K K Edwin KKE Bosnjak Daniel D Durack Timothy T Stevanovski Igor I Weninger Wolfgang W Jolly Christopher J CJ

Nucleic acids research 20170401 6

AID deaminates C to U in either strand of Ig genes, exclusively producing C:G/G:C to T:A/A:T transition mutations if U is left unrepaired. Error-prone processing by UNG2 or mismatch repair diversifies mutation, predominantly at C:G or A:T base pairs, respectively. Here, we show that transversions at C:G base pairs occur by two distinct processing pathways that are dictated by sequence context. Within and near AGCT mutation hotspots, transversion mutation at C:G was driven by UNG2 without require ...[more]

PMID: 28039326

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Project description:Somatically acquired mutations in the E1 ubiquitin-activating enzyme UBA1 within hematopoietic stem and progenitor cells (HSPCs) were recently identified as the cause of the adult-onset autoinflammatory syndrome VEXAS (vacuoles, E1 enzyme, X linked, autoinflammatory, somatic)1. Most VEXAS-associated mutations occur at Met41 in UBA1 and lead to clonal expansion within the HSPC and myeloid, but not lymphoid, compartments. Despite its severity and prevalence, the mechanisms whereby UBA1 mutations cause multiorgan autoinflammation and hematologic disease are unknown. Here, we employ mRNA-based electroporation of adenine base editing enzymes to mutate endogenous Uba1, generating canonical VEXAS-associated Met41 mutations in murine or human HSPCs and macrophages. Expression of Met41-mutant UBA1 in macrophages aberrantly triggered apoptotic and necroptotic inflammatory cell death programs upon exposure to TNF or LPS, which could be fully reversed by combined deletion of Mlkl or Ripk3 plus Casp8, or partially by genetic or pharmacologic targeting of RIPK1 kinase activity. In mice challenged with TNF or LPS, the UBA1 inhibitor TAK-243 exacerbated inflammation, which was mediated by RIPK1 kinase activity and RIPK3-Caspase-8, respectively. In contrast, Uba1-mutant HSPCs displayed an unfolded protein response signature and spontaneous myeloid skewing that were independent of RIPK3-Caspase-8, thereby propagating an inflammatory cycle driven by their mature myeloid progeny. Mechanistically, we traced the dysregulated cell death response of Uba1-mutant macrophages to a cascading, kinetic defect in Lys63/Met1 (i.e., linear) polyubiquitylation of inflammatory signaling complexes. Collectively, our results link the pathogenesis of VEXAS with that of rarer germline monogenic causes of autoinflammation; highlight specific ubiquitin-associated defects stemming from an apical mutation in the ubiquitylation cascade; and nominate the RIPK1-RIPK3-caspase-8 death axis as a therapeutic target in VEXAS.

Dataset Information

Proximity to AGCT sequences dictates MMR-independent versus MMR-dependent mechanisms for AID-induced mutation via UNG2.

Publications

Proximity to AGCT sequences dictates MMR-independent versus MMR-dependent mechanisms for AID-induced mutation via UNG2.

Similar Datasets

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