Mono‐ubiquitinated annexin A1 and heavy metal induced mutagenesis

Annexin A1 is mono‐ubiquitinated by Rad 6 following exposure to DNA damaging agents, and exhibits helicase‐like activity. DNA annealing is regulated by Ca 2+ , and the heavy metals, As 3+ and Cr 6+ , can replace Ca 2+ . Although alone these heavy metals are not directly mutagenic, they promote the mutagenic effects of DNA damaging agent. This led us to postulate that mono‐ubiquitinated annexin A1 is involved in heavy metal‐induced mutagenesis. To test this hypothesis, we investigated if purified mono‐ubiquitinated annexin A1 shows increased affinity for damaged DNA and if it promotes translesion DNA synthesis by Polβ. Single Gs were replaced with 8‐oxo‐Gs in a synthesized 80‐mer polynucleotide to model DNA damaged by oxidative stress. Mono‐ubiquitinated annexin A1 exerts 2–4 fold higher affinity for polynucleotides containing a single 8‐oxo‐G, and stimulated translesion DNA synthesis as an ssDNA binding protein by around 3 folds. Heavy metals further increased translesion DNA synthesis in nuclear extracts of L5178 lymphoma cells, which was blocked by anti‐annexin A1 antibody. These findings support the hypothesis that mono‐ubiquitinated annexin A1 is involved in heavy metal‐induced mutagenesis.