Aldehyde exposure unmasks genome instability in cells heterozygous for clinically relevant BRCA2 mutations

Abnormalities provoked in human cells heterozygous for clinically relevant truncating mutations in BRCA2 by their exposure to naturally occurring aldehydes define a mechanism promoting carcinogenesis in mutation carriers. The ubiquitous metabolite and environmental toxin, formaldehyde, triggers replication fork instability and structural chromosomal aberrations in BRCA2 heterozygous cells. These abnormalities arise from a previously unrecognized effect of formaldehyde to selectively induce the proteasomal degradation of BRCA2, inducing functional haploinsufficiency only in cells where BRCA2 expression is already compromised by a heterozygous mutation. Similar effects are observed with acetaldehyde, a toxic product of alcohol catabolism. Replication fork instability and chromosomal aberrations in aldehyde-exposed cells arise from the unscheduled accumulation of RNA-DNA hybrids, revealing a mechanism driving genomic instability in BRCA2 heterozygous cells. We propose a model for cancer pathogenesis in which aldehyde exposure unmasks the carcinogenic potential of heterozygous BRCA2 mutations, with public health implications in mutation carriers.