IF=32.4|Ubigene’s STING1 KO cell line helps reveal polyamine metabolism orchestrating cGAS activity
Viral diseases, such as new coronavirus pneumonia, influenza and viral hepatitis, seriously endanger human health. If the virus is not cleared in time after infection and persists in cells, it will not only turn the host an important source of infection, but also induce the occurrence of chronic progressive diseases and even tumors.
Upon virus infection, the genetic material (such as DNA or RNA) produced by the virus will activate the immune system while it replicates rapidly in the host cell. Cyclic GMP-AMP (cGAMP) synthase(cGAS) is an important cytoplasmic DNA recognition receptor, which plays an important role in anti infection and tumor immunity [1,2].cGAS binds to the backbone of dsDNA and generates the second messenger, cGAMP, which activates the stimulator of interferon genes (STING).The STING, in turn, recruits TANK-binding kinase 1 (TBK1) to initiate type I interferon (IFN) expression and inflammatory responses. However, if the expression of type I IFN was low, and the virus could not be effectively cleared; If the inflammatory reaction is too strong, it will cause damage to its own tissues and organs. Therefore, it is very important to study the regulation mechanism of CGAs activity in order to prevent and treat viral diseases, and avoid excessive activation.
Last month, a research article titled “Polyamine metabolism controls B-to-Z DNA transition to orchestrate DNA sensor cGAS activity”written by researchers in Shandong University was published on Immunity (IF=32.4). In this study, the HeLa cell line with STING1 gene knockout constructed by Ubigene was used to discover a new mechanism of polyamine metabolism regulating cGAS activity by controlling the conformational transition of B-to-Z DNA, which provided a theoretical basis for further understanding the regulation of cGAS activity and the prevention and treatment of viral diseases.
Method and results
To test the effect of intracellular environment on cGAS activity, the researches first incubated interferon-stimulating DNA (ISD) with different metabolic small molecules, filtered the free small molecules and reacted with the lysate of mouse peritoneal macrophages. It was found that spermine and spermidine could significantly inhibit ISD induced cGAMP production. Spermine and spermidine could inhibit the expression of type I interferon induced by HSV-1 infection in HeLa cells, but not in STING1-/- (the gene encoding STING).
Figure 1. Spermine and spermidine selectively inhibited cGAS-STING signaling
Spermine and spermidine can inhibit the expression of interferon-stimulated genes (ISGs) mRNA induced by HSV-1 infection, including interferon-induced protein with tetratricopeptide repeats 1 (Ifit1), Ifit2 and Isg15, and promote the replication of HSV-1.
Figure 2. Spermine and spermidine attenuated the expression of interferon-stimulated genes (ISGs) induced by HSV-1 infection
Results of immunoprecipitation and electro phoretic mobility shift assay (EMSA) showed that spermine and spermidine can inhibit the binding of cGAS and ISD.With further Chromatin immunoprecipitation (ChIP) and Immuno blot analysis, they discovered that spermine and spermidine can induce the generation of Z-DNA. In addition, the immunoprecipitation and a competition assay showed that the binding affinity of B-DNA to cGAS was higher than that of Z-DNA, suggesting that spermine and spermidine induce DNA into Z-DNA with lower affinity in vivo, so as to avoid excessive activation of CGAs.
The researchers further explored the physiological correlation between spermine and spermidine in regulating cGAS activity, and found that the concentration of spermine and spermidine decreased significantly after viral infection, and this process was regulated by spermine/spermidine N1-acetyltransferase 1 (SAT1). SAT1 is a rate-limiting enzyme in polyamine catabolism, and its expression increases rapidly after virus infection. SAT1 can reduce the levels of spermine and spermidine in cells, enhance the activation level of cGAS by inhibiting the accumulation of Z-DNA in cytoplasm, and effectively eliminate virus. In addition, spermine or spermidine supplementation and SAT1 gene knockout will lead to the decline of anti-HSV-1 virus ability in mice.
Figure 3. Polyamine metabolism regulates cGAS activity pattern by controlling Z-DNA formation
To sum up, this study found that the two conformations of DNA (B-DNA and Z-DNA) had different affinity with cGAS; The endogenous metabolism of small molecules spermine, spermidine and polyamine catabolism key enzyme SAT1 regulates cGAS activity by inducing DNA conformational transition; It reveals a additional mechanism for preventing abnormal cytoDNA recognition and providing promising therapeutic targets for the treatment of diseases involving improper cGAS activation.
 Ablasser, A., and Chen, Z.J. (2019). cGAS in action: Expanding roles in immunity and inflammation. Science 363, eaat8657.10.1126/science.aat8657.
 Motwani, M., Pesiridis, S., and Fitzgerald, K.A. (2019). DNA sensing by the cGAS-STING pathway in health and disease. Nat Rev Genet 20, 657-674. 10.1038/s41576-019-0151-1.
 Zhao, C., Ma, Y., Zhang, M., Gao, X., Liang, W., Qin, Y., ... & Zhao, W. (2023). Polyamine metabolism controls B-to-Z DNA transition to orchestrate DNA sensor cGAS activity. Immunity.