A thermophilic 8-oxoguanine DNA glycosylase from Thermococcus barophilus Ch5 is a new member of AGOG DNA glycosylase family

8-Oxoguanine DNA glycosylase protects cells from senescence via the p53-p21 pathway

Cellular senescence is an important factor leading to pulmonary fibrosis. Deficiency of 8-oxoguanine DNA glycosylase (OGG1) in mice leads to alleviation of bleomycin (BLM)-induced mouse pulmonary fibrosis, and inhibition of the OGG1 enzyme reduces the epithelial mesenchymal transition (EMT) in lung cells. In the present study, we find decreased expression of OGG1 in aged mice and BLM-induced cell senescence. In addition, a decrease in OGG1 expression results in cell senescence, such as increases in the percentage of SA-β-gal-positive cells, and in the p21 and p-H2AX protein levels in response to BLM in lung cells. Furthermore, OGG1 promotes cell transformation in A549 cells in the presence of BLM. We also find that OGG1 siRNA impedes cell cycle progression and inhibits the levels of telomerase reverse transcriptase (TERT) and LaminB1 in BLM-treated lung cells. The increase in OGG1 expression results in the opposite phenomenon. The mRNA levels of senescence-associated secretory phenotype (SASP) components, including IL-1α, IL-1β, IL-6, IL-8, CXCL1/CXCL2, and MMP-3, in the absence of OGG1 are obviously increased in A549 cells treated with BLM. Interestingly, we demonstrate that OGG1 binds to p53 to inhibit the activation of p53 and that silencing of p53 reverses the inhibition of OGG1 on senescence in lung cells. Additionally, the augmented cell senescence is shown in vivo in OGG1-deficient mice. Overall, we provide direct evidence in vivo and in vitro that OGG1 plays an important role in protecting tissue cells against aging associated with the p53 pathway.

Archaeal DNA alkylation repair conducted by DNA glycosylase and methyltransferase

Alkylated bases in DNA created in the presence of endogenous and exogenous alkylating agents are either cytotoxic or mutagenic, or both to a cell. Currently, cells have evolved several strategies for repairing alkylated base. One strategy is a base excision repair process triggered by a specific DNA glycosylase that is used for the repair of the cytotoxic 3-methyladenine. Additionally, the cytotoxic and mutagenic O⁶-methylguanine (O⁶-meG) is corrected by O⁶-methylguanine methyltransferase (MGMT) via directly transferring the methyl group in the lesion to a specific cysteine in this protein. Furthermore, oxidative DNA demethylation catalyzed by DNA dioxygenase is utilized for repairing the cytotoxic 3-methylcytosine (3-meC) and 1-methyladenine (1-meA) in a direct reversal manner. As the third domain of life, Archaea possess 3-methyladenine DNA glycosylase II (AlkA) and MGMT, but no DNA dioxygenase homologue responsible for oxidative demethylation. Herein, we summarize recent progress in structural and biochemical properties of archaeal AlkA and MGMT to gain a better understanding of archaeal DNA alkylation repair, focusing on similarities and differences between the proteins from different archaeal species and between these archaeal proteins and their bacterial and eukaryotic relatives. To our knowledge, it is the first review on archaeal DNA alkylation repair conducted by DNA glycosylase and methyltransferase. KEY POINTS: • Archaeal MGMT plays an essential role in the repair of O ⁶ -meG • Archaeal AlkA can repair 3-meC and 1-meA.