Phosphatidylinositol hydrolysis and an increase in Ca2+ concentration in the signal-transduction process triggered by murine Fc gamma RIII are not required for protein kinase C translocation

Autoantibody-induced internalization of CNS AQP4 water channel and EAAT2 glutamate transporter requires astrocytic Fc receptor

Aquaporin-4 (AQP4) water channel-specific IgG distinguishes neuromyelitis optica (NMO) from multiple sclerosis and causes characteristic immunopathology in which central nervous system (CNS) demyelination is secondary. Early events initiating the pathophysiological outcomes of IgG binding to astrocytic AQP4 are poorly understood. CNS lesions reflect events documented in vitro following IgG interaction with AQP4: AQP4 internalization, attenuated glutamate uptake, intramyelinic edema, interleukin-6 release, complement activation, inflammatory cell recruitment, and demyelination. Here, we demonstrate that AQP4 internalization requires AQP4-bound IgG to engage an astrocytic Fcγ receptor (FcγR). IgG-lacking Fc redistributes AQP4 within the plasma membrane and induces interleukin-6 release. However, AQP4 endocytosis requires an activating FcγR's gamma subunit and involves astrocytic membrane loss of an inhibitory FcγR, CD32B. Interaction of the IgG-AQP4 complex with FcγRs triggers coendocytosis of the excitatory amino acid transporter 2 (EAAT2). Requirement of FcγR engagement for internalization of two astrocytic membrane proteins critical to CNS homeostasis identifies a complement-independent, upstream target for potential early therapeutic intervention in NMO.

Induction of phagocytosis and intracellular signaling by an inhibitory channel catfish leukocyte immune-type receptor: evidence for immunoregulatory receptor functional plasticity in teleosts

Immunoregulatory receptors are categorized as stimulatory or inhibitory based on their engagement of unique intracellular signaling networks. These proteins also display functional plasticity, which adds versatility to the control of innate immunity. Here we demonstrate that an inhibitory catfish leukocyte immune-type receptor (IpLITR) also displays stimulatory capabilities in a representative myeloid cell model. Previously, the receptor IpLITR 1.1b was shown to inhibit natural killer cell-mediated cytotoxicity. Here we expressed IpLITR 1.1b in rat basophilic leukemia-2H3 cells and monitored intracellular signaling and functional responses. Although IpLITR 1.1b did not stimulate cytokine secretion, activation of this receptor unexpectedly induced phagocytosis as well as extracellular signal-related kinase 1/2- and protein kinase B (Akt)-dependent signal transduction. This novel IpLITR 1.1b-mediated response was independent of an association with the FcRγ chain and was likely due to phosphotyrosine-dependent adaptors associating with prototypical signaling motifs within the distal region of its cytoplasmic tail. Furthermore, compared to a stimulatory IpLITR, IpLITR 1.1b displayed temporal differences in the induction of intracellular signaling, and IpLITR 1.1b-mediated phagocytosis had reduced sensitivity to EDTA and cytochalasin D. Overall, this is the first demonstration of functional plasticity for teleost LITRs, a process likely important for the fine-tuning of conserved innate defenses.

Eupatilin blocks mediator release via tyrosine kinase inhibition in activated guinea pig lung mast cells

Eupatilin, an extract from Artemisia asiatica Nakai, is known to exert anti-gastric ulcer, anticancer, and anti-inflammatory effects. The aim of this study was to elucidate whether eupatilin has antiallergic reactions in activated guinea pig lung mast cells compared to apigenin and genistein. Mast cells were purified from guinea pig lung tissues by using enzyme digestion and rough and discontinuous density Percoll gradient. The purified mast cells were sensitized with immunoglobulin (Ig) G(1) (anti-OVA antibody) and challenged with ovalbumin (OVA). Histamine was assayed using an automated fluorometric analyzer, leukotrienes by radioimmunoassay, and tyrosine phosphorylation by immunoblotting. Intracellular Ca(2+) was analyzed by confocal laser scanning microscopy, protein kinase C (PKC) activity using protein phosphorylated with [gamma-(32)P]ATP, and phopholipase D activity (PLD) and phosphatidic acid by using labeled phosphatidyl alcohol. Eupatilin, apigenin, or genistein reduced histamine release and leukotriene synthesis in a does-dependent manner. Eupatilin inhibited mediators to a greater extent than apigenin or genistein. Eupatilin, apigenin, and genistein initially blocked phosphorylation of Syk tyrosine and Ca(2+) influx, PLD activity, phosphatidic acid, and Ca(2+)-dependent PKC alpha/betaII activities during mast cell activation in a dose-dependent manner. Our data suggest that eupatilin initially inhibits Syk kinase, and then blocks downstream multisignal pathways and Ca(2+) influx during mast cell activation triggered by a specific antigen-antibody reaction. Thus, eupatilin may have use clinically as a treatment for inflammatory disorders associated with allergic diseases including asthma.