Excision of mutagenic replication-blocking lesions suppresses cancer but promotes cytotoxicity and lethality in nitrosamine-exposed mice

Abstract

SummaryN-nitrosodimethylamine (NDMA) is a DNA methylating agent that has been discovered to contaminate water, food and drugs. The alkyladenine glycosylase (AAG) removes methylated bases to initiate the base excision repair (BER) pathway. To understand how gene-environment interactions impact disease susceptibility, we studied Aag−/− and Aag-overexpressing mice that harbor increased levels of either replication-blocking lesions (3-methyladenine, or 3MeA) or strand breaks (BER intermediates), respectively. Remarkably, the disease outcome switched from cancer to lethality simply by changing AAG levels. To understand the underlying basis for this observation, we integrated a suite of molecular, cellular and physiological analyses. We found that unrepaired 3MeA is somewhat toxic but highly mutagenic (promoting cancer), whereas excess strand breaks are poorly mutagenic and highly toxic (suppressing cancer and promoting lethality). We demonstrate that the levels of a single DNA repair protein tips the balance between blocks and breaks, and thus dictates the disease consequences of DNA damage.

“Loss of alkyladenine DNA glycosylase alters gene expression in the developing mouse brain and leads to reduced anxiety and improved memory”

“…1B). Similarly, the number of endogenous γH2AX foci was previously shown to be reduced in Aag -/mouse liver and fibroblasts [35,36]. To determine whether the observed effect was global, or specific to defined hippocampal regions, number of γH2AX foci was analyzed next in the dentate gyrus (DG), cornum ammonis (CA) 1 and CA3 regions.…”

Multipartite super-enhancers function in an orientation-dependent manner

“…To do this we inverted a region of the mouse α-globin locus containing all five enhancers within the confines of the highly conserved syntenic regulatory domain (5’- Rhbdf1 - Mpg - Nprl3 - Hba-x - Hba-a1/2 - Hba-q1/2 -3’). Since disruption of the Mpg or Nprl3 genes would heighten susceptibility to genotoxicity and lead to developmental abnormalities, respectively 51, 52 , we inverted a 50kb region containing Mpg , Nprl3 , and the α-globin regulatory elements in their entirety. To achieve this, convergent LoxP sites were integrated at flanking insertion sites devoid of chromatin features associated with regulatory elements (Figure S2, shaded orange bars).…”

AOP report: Development of an adverse outcome pathway for oxidative DNA damage leading to mutations and chromosomal aberrations

“…Models of DNA repair deficiency such as knock‐out cell lines and rodent models (e.g., Agg −/− mice [Kay et al, 2021]) can be used to determine which pathway is critical for repairing the genotoxic lesion (Olivieri et al, 2020).…”