C012 FAN1 cuts CAG-containing hairpin extrusions to potentially combat repeat expansion

<h3>Background</h3> FAN1 is a DNA repair protein that has been shown to contract CAG repeats in the Huntingtin (HTT) gene and delay the onset and progression of Huntington’s disease (HD). When going through DNA replication and transcription, the CAG triplet expansions in HTT can form slipped-CAG intermediates, creating extrahelical hairpins that may cause further CAG expansions, and worsen disease progression. FAN1 has both endonuclease and exonuclease activity, enabling it to carry out functions in DNA repair which may be a mechanism to prevent CAG expansion. <h3>Aims</h3> Here, using nuclear extracts, we aim to assess FAN1’s nuclease activity on CAG hairpin DNA. <h3>Methods/Techniques</h3> CAG hairpin DNA substrates were exposed to WT or mutant FAN1 protein IP and then run on polyacrylamide gels to determine the length of the DNA substrates. <h3>Results/Outcome</h3> We found that WT FAN1 produces endonuclease and exonuclease cuts on CAG hairpin substrates, which are not present in the nuclease-dead FAN1 variant, D960A. <h3>Conclusions</h3> These results show that FAN1 may be involved in repairing slipped-CAG repeats and an important target for HD therapeutics.