Histone deacetylase SIRT1 modulates and deacetylates DNA base excision repair enzyme thymine DNA glycosylase

Abstract

Thymine DNA glycosylase (TDG) is an essential multifunctional enzyme involved in DNA base excision repair, DNA demethylation, and transcription regulation. TDG is the predominant enzyme to remove thymine from T/G mispair, which arises due to deamination of 5-methylcytosine at the CpG dinucleotide, thereby preventing C to T mutations. SIRT1 is a member of class III NAD+-dependent histone/protein deacetylases. In this study, we demonstrate that SIRT1 interacts with the residues 67–110 of human TDG (hTDG). In addition, SIRT1 enhances TDG glycosylase activity and deacetylates acetylated TDG. TDG acetylation weakens its interaction with SIRT1. Although acetylated TDG has reduced glycosylase activity toward T/G, 5-formylcytosine/G, and 5-carboxylcytosine/G, it has a stronger activity toward 5-fluorouracil/G substrate as compared to unmodified TDG. SIRT1 weakly stimulates acetylated hTDG activity toward T/G, 5-formylcytosine/G, and 5-carboxylcytosine/G as compared to control hTDG. Sirt1 knockout mouse embryonic fibroblast cells have higher levels of TDG expression and acetylation. The physical and functional interactions between SIRT1 and TDG may mediate DNA repair, gene expression, and FU-mediated cytotoxicity.

Structural basis of damage recognition by thymine DNA glycosylase: Key roles for N-terminal residues

“…Previous studies also indicate that some portion of the N-terminal region comprising residues 55–110, which is enriched in Arg and Lys, is required for efficient binding and catalytic processing of G·T mispairs, and for efficient binding to non-specific DNA (16,22,31). In addition, N-terminal residues of TDG mediate interactions with other proteins, including CBP/p300, Dnmt3A/B, the 9-1-1 complex and SIRT1 (14,16,17,32). Importantly, all residues of the new TDG 82-308 construct are native to human TDG, because the entire poly-His purification tag is removed via protease cleavage, as described below.…”

The multifaceted influence of histone deacetylases on DNA damage signalling and DNA repair

“…DNA glycosylases differ in their substrate and enzymatic activity: the monofunctional uracil-DNA glycosylase or the N -methylpurine-DNA glycosylase only contain glycosylase activity, while bifunctional glycosylases such as 8-oxo-guanine glycosylase also contain lyase activity, allowing for the cleavage of the sugar–phosphate backbone 3′ to the AP site (62). The substrate specificity of the monofunctional thymine DNA glycosylase (TDG) is regulated via the deacetylase SIRT1 (63). Human SIRT1 is a nuclear SIRT (64–66).…”

“…Human SIRT1 is a nuclear SIRT (64–66). The deacetylation of TDG by SIRT1 stimulates active DNA demethylation as un-acetylated TDG excises 5-formylcytosine and 5-carboxylcytosine (61), while acetylated TDG has a higher substrate specificity toward 5-fluorouracil (63), induced by the chemotherapeutic 5-FU (Figure 1A). The low expression of SIRT1 in colorectal cancers (34) (Table 1), should, therefore, very likely contribute to this cancer's resistance to 5-FU.…”

Multifaceted roles for thymine DNA glycosylase in embryonic development and human carcinogenesis

“…In fact, TDG possesses the capability to excise a range of mismatched pyrimidine bases, which include oxidized pyrimidines such as thymine glycol Tg [20,21], 5-formyl-U, 5-hydroxy-U, 5-hydroxymethyl-U [22], N 4 -ethenocytosine [21,23,24], and 5-hydroxycytosine ( Fig. 1A) [21,25].…”

“…TDG also interacts with histone/protein deacetylases, such as SIRT1. SIRT1 interacts with aa 67-110 of human TDG, deacetylates TDG, and enhances its glycosylase activity in vitro and in vivo [22].…”