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  • Title: Selective control of type I IFN induction by the Rac activator DOCK2 during TLR-mediated plasmacytoid dendritic cell activation.
    Author: Gotoh K, Tanaka Y, Nishikimi A, Nakamura R, Yamada H, Maeda N, Ishikawa T, Hoshino K, Uruno T, Cao Q, Higashi S, Kawaguchi Y, Enjoji M, Takayanagi R, Kaisho T, Yoshikai Y, Fukui Y.
    Journal: J Exp Med; 2010 Apr 12; 207(4):721-30. PubMed ID: 20231379.
    Abstract:
    Plasmacytoid dendritic cells (pDCs) play a key role in antiviral immunity, but also contribute to the pathogenesis of certain autoimmune diseases, by producing large amounts of type I IFNs. Although activation of pDCs is triggered by engagement of nucleotide-sensing toll-like receptors (TLR) 7 and 9, type I IFN induction additionally requires IkappaB kinase (IKK) alpha-dependent activation of IFN regulatory factor (IRF) 7. However, the signaling pathway mediating IKK-alpha activation is poorly defined. We show that DOCK2, an atypical Rac activator, is essential for TLR7- and TLR9-mediated IFN-alpha induction in pDCs. We found that the exposure of pDCs to nucleic acid ligands induces Rac activation through a TLR-independent and DOCK2-dependent mechanism. Although this Rac activation was dispensable for induction of inflammatory cytokines, phosphorylation of IKK-alpha and nuclear translocation of IRF-7 were impaired in Dock2-deficient pDCs, resulting in selective loss of IFN-alpha induction. Similar results were obtained when a dominant-negative Rac mutant was expressed in wild-type pDCs. Thus, the DOCK2-Rac signaling pathway acts in parallel with TLR engagement to control IKK-alpha activation for type I IFN induction. Owing to its hematopoietic cell-specific expression, DOCK2 may serve as a therapeutic target for type I IFN-related autoimmune diseases.
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