Mammalian MutY Homolog (MYH or MUTYH) is Critical for Telomere Integrity under Oxidative Stress.

Telomeres consist of special features and proteins to protect the ends of each chromosome from deterioration and fusion. The telomeric DNA repeats are highly susceptible to oxidative damage that can accelerate telomere shortening and affect telomere integrity. Several DNA repair factors including MYH/MUTYH DNA glycosylase, its interacting partners Rad9/Rad1/Hus1 checkpoint clamp, and SIRT6 aging regulator, are associated with the telomeres. MYH prevents C:G to A:T mutation by removing adenine mispaired with a frequent oxidative DNA lesion, 8-oxoguanine. Here, we show that knockout (KO) human HEK-293T cells are more sensitive to HO treatment, have higher levels of DNA strand breaks and shorter telomeres than the control cells. SIRT6 foci increase at both the global genome and at telomeric regions in HO-treated cells. However, in untreated KO HEK-293T cells, SIRT6 foci only increase at the global genome, but not at the telomeric regions. In addition, the KO HEK-293T cells have increased extra-chromosomal and intra-chromosomal telomeres compared to the control cells, even in the absence of HO treatment. After HO treatment, the frequency of extra-chromosomal telomeres increased in control HEK-293T cells. Remarkably, in HO-treated KO cells, the frequencies of extra-chromosomal telomeres, intra-chromosomal telomeres, and telomere fusions are further increased. We further found that the sensitivity to HO and shortened telomeres of KO cells, are restored by expressing wild-type hMYH, and partially rescued by expressing hMYH mutant (defective in Hus1 interaction only), but not by expressing hMYH mutant (defective in both SIRT6 and Hus1 interactions). Thus, MYH interactions with SIRT6 and Hus1 are critical for maintaining cell viability and telomeric stability. Therefore, the failure to coordinate 8-oxoG repair is detrimental to telomere integrity.