Molecular Mechanism Of Grass Carp Lysine Acetyltransferase 8(KAT8) Regulating Type Ⅰ Interferon Expression And Apoptosis

Type I interferon(IFN)plays an important role in the host’s resistance to infection by pathogenic microorganisms,when the pathogenic microorganism is recognized by the pattern recognition receptor on the host cell,it can quickly produce a large number of interferon,activate the innate immune response,and resist the infection of pathogenic microorganism.Excessive or insufficient expression of type I interferon will cause certain damage to the host,so the expression of type I interferon is strictly and precisely regulated at all levels.Such as the stage of receptor recognition of pathogenic microorganisms,the stage of signal transmission of key linker molecules in downstream signaling pathways,and the regulation of activities of related enzymes and transcription factors,etc.Post-translational modifications of transcription factors IRF3 and IRF7 in the innate immune signaling pathway(such as classic phosphorylation and ubiquitination)strictly control the production of type I interferon.The non-classical post-translational modification,acetylation,regulates IRF3/IRF7 activity and thus controls the expression of type I interferon has not been systematically described.The results of the first part in this paper clarify that the acetylation modification inhibits the transcriptional activities of IRF3 and IRF7.Lysine acetyltransferase8(KAT8)has been known to participate in various physiological activities by regulating the proteins acetylation.However,few reports have reported the role of KAT8 in innate immunity,and there are many mysteries remain to be solved.In this study,we found that grass carp KAT8 negatively regulated the antiviral immune response.The results showed that KAT8 could be up-regulated by stimulation of poly(I:C),B-DNA and Z-DNA,GCRV and SVCV.Overexpression of KAT8 significantly inhibited the expression of IFN 1 and ISG15,whereas knockdown KAT8 significantly up-regulated the expression of IFN 1 and ISG15.Overexpression of KAT8 enhanced the replication of GCRV virus.Further studies showed that KAT8 could significantly inhibited IRF3/ IRF7-induced IFN 1 expression.Mechanism studies showed that KAT8 was an important regulatory molecule in the IRF3 and IRF7-mediated signaling pathway.KAT8 located in the nucleus and interacted directly with IRF3/IRF7 through its MYST domain(acetyltransferase domain)and promoted the acetylation of the latter two,thereby inhibiting the interaction between IRF3/IRF7 with ISRE(interferon-stimulated response element),then inhibiting IFN 1expression.This study provided important clues that acetylation regulated immune response and controlled activities of IRF3 and IRF7.Apoptosis is an active programmed death,it participates in the regulation of immune development,immune response and other physiological activities.Apoptotic occurrence is accompanied by the expression changes of a variety of related gene.Cell apoptosis is critical for body development and cell homeostasis.Therefore,in recent years,the molecular mechanism of regulating apoptosis-related pathways has become a hot field in biological research.The results of the second part in this paper elaborated the apoptotic roles of sirtuin 1(SIRT1)and KAT8 in grass carp,and the regulation of apoptosis mediated by acetylation modification between SIRT1,KAT8 and p53.The specific results were as followed: SIRT1 significantly inhibited the m RNA levels of Bax/Bcl2,caspase3 and caspase9;Knockdown of SIRT1 showed the opposite results.Knockdown of SIRT1 increased the number of apoptotic cells.KAT8 significantly up-regulated the m RNA levels of Bax/Bcl2,caspase3 and caspase9,and promoted the apoptosis of CIK cells.The opposite results were obtained from knockdown assays.The results also showed that SIRT1 inhibited the expression of pro-apoptotic gene induced by KAT8 in grass carp.Mechanism studies showed that SIRT1 located in the nucleus,directly binds to the MYST domain of KAT8,inhibited the expression of KAT8,and mediated the deacetylation of KAT8.Another molecular mechanism of apoptosis induced by KAT8 was that KAT8 directly interacted with p53 through its MYST domain and promoted the acetylation of p53,thus synergistically inducing the expression of apoptosis-related genes.Further studies found that SIRT1 bound to p53,inhibited the expression of p53 and mediated the deacetylation of p53,then inhibited the expression of p53 induced pro-apoptotic genes.In conclusion,the first part of this paper found a new function of grass carp lysine acetyltransferase KAT8 in negatively regulating the innate immune response.It was verified that non-classical post-translational modification-acetylation inhibited the transcriptional activity of IRF3 and IRF7.The molecular mechanism of grass carp KAT8 inhibiting type I interferon was revealed.The second part of this paper clarified the molecular mechanism of SIRT1 inhibiting apoptosis by targeting the acetylation of KAT8 and p53 in grass carp.The function of KAT8 in promoting p53 acetylation and inducing apoptosis of grass carp was described.Our work elucidated some fine-tuned mechanisms of homeostasis at different levels and deepens our understanding of host homeostasis.