Selective suppression of IL-10 transcription by calcineurin in dendritic cells through inactivation of CREB

Myeloid cells play a pivotal role in immune responses against bacterial and fungal infection. Among innate immune receptors, C-type lectin receptors (CLRs) can induce a wide spectrum of cytokines through immunoreceptor tyrosine-based activation motifs (ITAMs)-mediated signaling pathways. Dendritic cells (DCs) produce IL-10 through CLR stimulation; however, the regulatory mechanism of IL-10 expression has not been elucidated. In the current study, we report that calcium (Ca2+) signaling-deficient DCs produced more IL-10 than wild-type DCs. Mechanistically, Ca2+-dependent phosphatase calcineurin directly inactivates cAMP response element-binding protein (CREB), a transcription factor of Il10 in DCs, through dephosphorylating CREB at serine 133. In calcineurin-deficient DCs, CREB was highly phosphorylated and increased its binding to the Il10 promoter. Elimination of mitogen-activated protein kinase (MAPK) signaling that phosphorylates CREB, deficiency of CREB, as well as deletion of a CREB-binding site in the Il10 promoter could diminish IL-10 production in DCs. Our findings identified a novel substrate of calcineurin as well as a mechanism through which Ca2+ signaling regulates IL-10 expression downstream of CLRs. As IL-10 is a crucial immunosuppressive cytokine, this mechanism may counteract the over-activated IL-10-producing signals induced by CARD9 and MAPK pathways, preventing the ineffectiveness of the immune system during bacterial and fungal infection.