Tyrosyl-DNA phosphodiesterases are involved in mutagenic events at a ribonucleotide embedded into DNA in human cells

Untargeted Mutation Triggered by Ribonucleoside Embedded in DNA

DNA polymerases frequently misincorporate ribonucleoside 5'-triphosphates into nascent DNA strands. This study examined the effects of an incorporated ribonucleoside on untargeted mutations in human cells. Riboguanosine (rG) was introduced into the downstream region of the supF gene to preferentially detect the untargeted mutations. The plasmid containing rG was transfected into U2OS cells and the replicated DNA was recovered after 48 h. The mutation analysis using the indicator Escherichia coli RF01 strain showed the frequent induction of untargeted base substitutions at the G bases of 5'-GpA-3' dinucleotides, similar to action-at-a-distance mutations induced by an oxidatively damaged base, 8-oxo-7,8-dihydroguanine, and an apolipoprotein B mRNA-editing enzyme, catalytic polypeptide-like 3 (APOBEC3) cytosine deaminase. APOBEC3B was then knocked down by RNA interference and the plasmid bearing rG was introduced into the knockdown cells. The untargeted mutations at 5'-GpA-3' sites were reduced by ~80%. These results suggested that ribonucleosides embedded in DNA induce base substitution mutations at G bases in the same strand by an APOBEC3B-dependent mechanism, implying that ribonucleosides contribute to APOBEC3-dependent cancer initiation events.

The Role of RNA in DNA Breaks, Repair and Chromosomal Rearrangements

Incorrect reparation of DNA double-strand breaks (DSB) leading to chromosomal rearrangements is one of oncogenesis's primary causes. Recently published data elucidate the key role of various types of RNA in DSB formation, recognition and repair. With growing interest in RNA biology, increasing RNAs are classified as crucial at the different stages of the main pathways of DSB repair in eukaryotic cells: nonhomologous end joining (NHEJ) and homology-directed repair (HDR). Gene mutations or variation in expression levels of such RNAs can lead to local DNA repair defects, increasing the chromosome aberration frequency. Moreover, it was demonstrated that some RNAs could stimulate long-range chromosomal rearrangements. In this review, we discuss recent evidence demonstrating the role of various RNAs in DSB formation and repair. We also consider how RNA may mediate certain chromosomal rearrangements in a sequence-specific manner.