cGAS is a cytosolic DNA sensor that activates innate immune responses through production of the second messenger 2’3’-cGAMP, which activates the adaptor STING. cGAS senses dsDNA in a length-dependent but sequence-independent manner, and it cannot discriminate self-DNA from foreign DNA. In normal physiological conditions, cellular DNA is sequestered in the nucleus by nuclear envelope and in mitochondria by mitochondrial membrane. When self-DNA leaks into the cytosol during cellular stress, or during mitosis, the cGAS can be exposed to self-DNA and be activated. Recently, many studies have investigated how cGAS keeps inactive and avoids to be aberrantly activated by self-DNA. Thus, the aim of this narrative review is to summarize the mechanisms by which cGAS avoids to sense self-DNA under normal physiological conditions.

Trueperella pyogenes (T. pyogenes) can cause a variety of infections in animals and lead to economic loss in animal husbandry. TatD DNases are considered to be potential virulence factors in Plasmodium falciparum and Streptococcus pneumoniae. However, the function of TatD DNases in T. pyogenes is still unclear. Therefore, the aim of this study was to illustrate the function of TatD DNases of T. pyogenes (TpTatDs) and investigate whether luteolin is able to inhibit DNase function. The findings of our study are anticipated to be crucial to treating infections caused by T. pyogenes. Bioinformatic analysis has been used for the prediction of crucial functional residues of TpTatDs. The function of TpTatDs was investigated in the presence of divalent cations by hydrolyzing DNA with recombinant TatD proteins. Luteolin is a candidate nuclease inhibitor evaluated in our study. The interactions between luteolin and TpTatDs were tested using molecular docking analysis and surface plasmon resonance (SPR) assays. The inhibitory effect of luteolin on TpTatDs was analyzed by agarose gel electrophoresis. Two genes in the genome of T. pyogenes are suspected to encode TatD DNases. According to the length of their nucleotide sequences, they were named tatD960 and tatD825. Both of the TpTatDs, which are magnesium-dependent, were able to hydrolyze linear DNA and plasmids. In this study, we found through molecular docking analysis and SPR assays that luteolin can stably bind with TpTatDs. The gel assay revealed that luteolin can inhibit the DNase activity of TpTatDs. Our results indicated that TatD DNases from T. pyogenes are Mg2+-dependent DNases and exhibit DNA endonuclease activity. Moreover, luteolin reduced their DNA hydrolysis ability by decreasing the binding between TpTatDs and DNA.