Formation of the IS then mediated by F-actin rich protrusions that move around the distal SMAC (dSMAC, actin rich region) in a radial wave. antibodies indicated that phosphorylated receptor complexes underwent maturation as they trafficked toward the center of the cell. Additionally, imaging of fluorescent BtkPH domains indicated that 3-phosphoinositides propagated laterally away from the FcR microclusters. Conclusion We demonstrate that surface-associated but mobile IgG induces the formation of FcR microclusters at the pseudopod leading edge. These clusters recruit Syk and drive the production of diffusing PI(3,4,5)P3 that is coordinated with lamellar actin polymerization. Upon reaching maximal extension, FcR microclusters depart from the leading edge and are transported to the center of the cellular contact region to form a synapse-like structure, analogous to the process observed for T-cell receptors. Electronic supplementary material The online version of this article (doi:10.1186/s12865-016-0143-2) contains supplementary material, which is available to authorized users. strong class=”kwd-title” Keywords: Fc receptor, IgG, TIRF, Gestodene frustrated phagocytosis, receptor synapses, macrophage Background Macrophages phagocytize bacteria and viruses that are opsonized by immunoglobulin G (IgG) following activation of Fc receptors (FcR). FcR clustering is required for the phosphorylation of Immunoreceptor Tyrosine-Based Activation Motifs (ITAMs) in the FcR cytoplasmic tail (FcRIIa) and associated transmembrane adaptors such as the common gamma-chain for FcR I and III leading to the recruitment and activation of Syk kinase (Fig.?1a) Mouse monoclonal to CRKL [1C5]. Syk-mediated phosphorylation in-turn, drives remodeling of the actin cytoskeleton activating numerous downstream pathways including Rho-family Gestodene GTPases and phosphatidylinositol 3-kinase (PI3K) to coordinate the phagocytosis process and transcriptional activation of inflammatory pathways [4, 6]. FcR-mediated phagocytosis typically occurs via zippering mechanism, in which newly ligated FcR guides cell membranes over the opsonized particle [4, 7C10]. In this model, FcR-IgG signaling complexes drive extension of the pseudopod over the particle as new receptors are activated, at the leading edge, and then deactivated as the membrane advances (Fig.?1b-c) [11, 12]. FcR-IgG signaling complexes must coordinate the formation of the phagosome through the action of second messengers such as PI3K-mediated phosphorylation of the 3 position of PI(4,5)P2 (phosphatidylinositol 4,5-bisphosphate) to produce PI(3,4,5)P3 (phosphatidylinositol (3,4,5)-trisphosphate) [4, 13C17]. Locally synthesized PI(3,4,5)P3 recruits numerous downstream signaling molecules that shape the plasma membrane into the phagocytic cup [4, 9, 18]. Elevated PI(3,4,5)P3 concentration persists until closure of the phagosome while also increasing the activity of GEFs (guanine nucleotide exchange factor) for small GTPases. Thus, existing models for FcR signaling predict three signaling stages for the receptor: FcR clustering for activation, initiation of actin-driven protrusion (early signals) and late signals associated with phagosome Gestodene closure and identity. Open in a separate window Fig. 1 Model of FcR signaling and microclustering relative to actin and pseudopod extension. a FcR ligation by IgG drives phosphorylation of ITAMs and subsequent recruitment of signaling proteins including Syk and PI3K. Fluorescent labeling of IgG (red star) allowed observation of IgG-FcR complexes relative to the recruitment of Syk or BtkPH (gold stars) which specifically binds the PI3K product, PI(3,4,5)P3. b-c Frustrated phagocytosis in response to IgG-presented on a supported lipid bilayer is shown schematically. The zipper model, which describes macrophage engulfment of IgG-coated particles, suggests FcR-IgG interaction occurs through sequential engagement of new receptors during the advancement of the phagosome. Activated FcRs (blue) cluster and are initially driven forward by polymerizing actin (purple, b). These complexes then disengage from the polymerizing actin and move toward the center from the cell by attaching to retrograde Gestodene actin (green, c). New FcR complexes type as brand-new FcR bind IgG on Gestodene the industry leading (greyish). The direction is indicated with the arrows of.