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In vertebrates, TANK Binding Kinase 1 (TBK1) plays an important role in innate immunity, mainly because it can mediate production of interferon to resist the invasion of pathogens. In mammals, cell division cycle-25a (Cdc25a) is a member of the Cdc25 family of cell division cycle proteins. It is a phosphatase that plays an important role in cell cycle regulation by dephosphorylating its substrate proteins. Currently, many phosphatases are reported to play a role in innate immunity. This is because the phosphatases can shut down or reduce immune signaling pathways by down-regulating phosphorylation signals. However, there are no reports on fish Cdc25a in innate immunity. In this paper, we conducted a preliminary study on the involvement of grass carp Cdc25a in innate immunity. First, we cloned the full-length cDNA of grass carp Cdc25a (CiCdc25a), and found that it shares the highest genetic relationship with that of Anabarilius grahami through phylogenetic tree comparison. In grass carp tissues and CIK cells, the expression of CiCdc25a mRNA was up-regulated under poly (I:C) stimulation. Therefore, CiCdc25a can respond to poly (I:C). The subcellular localization results showed that CiCdc25a is distributed both in the cytoplasm and nucleus. We also found that CiCdc25a can down-regulate the expression of IFN 1 with or without poly (I:C) stimulation. In other words, the down-regulation of IFN1 by CiCdc25a is independent of poly (I:C) stimulation. Further functional studies have shown that the inhibition of IFN1 expression by CiCdc25a may be related to decrease of TBK1 activity. We also confirmed that the phosphorylation of TBK1 at Ser172 is essential for production of IFN 1. In short, CiCdc25a can interact with TBK1 and subsequently inhibits the phosphorylation of TBK1, thereby weakens TBK1 activity. These results indicated that grass carp Cdc25a down-regulates IFN 1 expression by reducing TBK1 phosphorylation. • CiCdc25a can respond to poly (I:C) stimulation. • The phosphorylation at Ser172of CiTBK1 is particularly important for the production of CiIFN 1. • CiCdc25a can physically interact with CiTBK1. • CiCdc25a down-regulates CiIFN1 via CiTBK1. • CiCdc25a can attenuate the phosphorylation of CiTBK1 to inhibit its activity. [ABSTRACT FROM AUTHOR]

Mre11A is considered as a cytosolic DNA receptor in mammals. However, it is rarely known about Mre11A in other vertebrates. Recently, a mammalian ortholog of Mre11A has been identified in grass carp (Ctenopharyngodon idellus) in our lab. Phylogenetic-tree analysis provided evidence for a close genetic relationship between C.idellus Mre11A and Carassius auratus Mre11A. The tissue expression profile of CiMre11A was detected, with a relatively higher level of expression in kidney, intestines, liver and spleen than that in other tissues after grass carp reovirus (GCRV) infection. Similarly, CiMre11A was also up-regulated in CIK cells after treatment with GCRV. Q-PCR and dual-luciferase assays indicated that the transcription levels of IFN1 and ISG15 were inhibited by Ci Mre11A knockdown, but were gradually augmented after CIK cells were transfected with increasing amounts of Ci Mre11A. Subcellular localization assays showed that a part of Ci Mre11A was translocated from the nucleus to the cytoplasm. Co-immunoprecipitation and co-localization assays demonstrated that Ci Mre11A interacts with Ci STING in response to GCRV infection. In CIK cells, the expressions of both IFN1 and ISG15 were acutely up-regulated by Ci Mre11A overexpression, as well as by co-overexpression of Ci Mre11A and Ci STING. Ci Mre11A and Ci STING induced the phosphorylation and cytoplasmic-to-nuclear translocation of IRF7 in CIK cells. The multiplication of GCRV in CIK cells was inhibited by the overexpression of Ci Mre11A and Ci STING. • A Mre11A orthologous gene from grass carp (Ctenopharyngodon idella) is cloned and characterized. • GCRV induces the nuclear-to-cytoplasm translocation of Mre11A. • Mre11A interacts with STING and then initiates IFN 1 and ISG15 expression. • Mre11A and STING promote the phosphorylation and nuclear translocation of IRF7. • Mre11A and STING protect CIK cells against GCRV infection. [ABSTRACT FROM AUTHOR]