[Show abstract][Hide abstract] ABSTRACT: Tissue infiltration of activated lymphocytes is a hallmark of transplant rejection and organ-specific autoimmune diseases. Migration and activation of lymphocytes depend on DOCK2, an atypical Rac activator predominantly expressed in hematopoietic cells. Although DOCK2 does not contain Dbl homology domain typically found in guanine nucleotide exchange factors, DOCK2 mediates the GTP-GDP exchange reaction for Rac through its DHR-2 domain. Here, we have identified 4-[3'-(2″-chlorophenyl)-2'-propen-1'-ylidene]-1-phenyl-3,5-pyrazolidinedione (CPYPP) as a small-molecule inhibitor of DOCK2. CPYPP bound to DOCK2 DHR-2 domain in a reversible manner and inhibited its catalytic activity in vitro. When lymphocytes were treated with CPYPP, both chemokine receptor- and antigen receptor-mediated Rac activation were blocked, resulting in marked reduction of chemotactic response and T cell activation. These results provide a rational of and a chemical scaffold for development of the DOCK2-targeting immunosuppressant.
[Show abstract][Hide abstract] 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.
Full-text · Article · Mar 2010 · Journal of Experimental Medicine
[Show abstract][Hide abstract] ABSTRACT: During chemotaxis, activation of the small guanosine triphosphatase Rac is spatially regulated to organize the extension of
membrane protrusions in the direction of migration. In neutrophils, Rac activation is primarily mediated by DOCK2, an atypical
guanine nucleotide exchange factor. Upon stimulation, we found that DOCK2 rapidly translocated to the plasma membrane in a
phosphatidylinositol 3,4,5-trisphosphate–dependent manner. However, subsequent accumulation of DOCK2 at the leading edge required
phospholipase D–mediated synthesis of phosphatidic acid, which stabilized DOCK2 there by means of interaction with a polybasic
amino acid cluster, resulting in increased local actin polymerization. When this interaction was blocked, neutrophils failed
to form leading edges properly and exhibited defects in chemotaxis. Thus, intracellular DOCK2 dynamics are sequentially regulated
by distinct phospholipids to localize Rac activation during neutrophil chemotaxis.