Enhancement Of Degranulation Research Articles

Rictor negatively regulates high-affinity receptors for IgE-induced mast cell degranulation.

Rictor is a regulatory component of the mammalian target of rapamycin (mTOR) complex 2 (mTORC2). We have previously demonstrated that rictor expression is substantially downregulated in terminally differentiated mast cells as compared with their immature or transformed counterparts. However, it is not known whether rictor and mTORC2 regulate mast cell activation. In this article, we show that mast cell degranulation induced by aggregation of high-affinity receptors for IgE (FcεRI) is negatively regulated by rictor independently of mTOR. We found that inhibition of mTORC2 by the dual mTORC1/mTORC2 inhibitor Torin1 or by downregulation of mTOR by short hairpin RNA had no impact on FcεRI-induced degranulation, whereas downregulation of rictor itself resulted in an increased sensitivity (∼50-fold) of cells to FcεRI aggregation with enhancement of degranulation. This was linked to a similar enhancement in calcium mobilization and cytoskeletal rearrangement attributable to increased phosphorylation of LAT and PLCγ1. In contrast, degranulation and calcium responses elicited by the G protein-coupled receptor ligand, C3a, or by thapsigargin, which induces a receptor-independent calcium signal, was unaffected by rictor knockdown. Overexpression of rictor, in contrast with knockdown, suppressed FcεRI-mediated degranulation. Taken together, these data provide evidence that rictor is a multifunctional signaling regulator that can regulate FcεRI-mediated degranulation independently of mTORC2.

Hypertonic saline enhances neutrophil elastase release through activation of P2 and A3 receptors

Hypertonic saline (HS) holds promise as a novel resuscitation fluid for the treatment of trauma patients because HS inhibits polymorphonuclear neutrophil (PMN) activation and thereby prevents host tissue damage and associated posttraumatic complications. However, depending on conditions of cell activation, HS can increase PMN degranulation, which could exacerbate tissue damage in trauma victims. The cellular mechanism by which HS increases degranulation is unknown. In the present study, we tested whether HS-induced ATP release from PMN and feedback via P1 and/or P2 receptors may be involved in the enhancement of degranulation by HS. We found that HS enhances elastase release and ERK and p38 MAPK activation when HS is added after activation of PMN with formyl peptide (fMLP) or phorbol ester (PMA). Agonists of P2 nucleotide and A3 adenosine receptors mimicked these enhancing effects of HS, whereas antagonists of A3 receptors or removal of extracellular ATP with apyrase diminished the response to HS. A1 adenosine receptor antagonists increased the enhancing effect of HS, whereas A1 receptor agonists inhibited elastase release. These data suggest that HS upregulates degranulation via ATP release and positive feedback through P2 and A3 receptors. We propose that these feedback mechanisms can serve as potential pharmacological targets to fine-tune the clinical effectiveness of HS resuscitation.

Nicotine-induced release of elastase and eicosanoids by human neutrophils

We examined the direct effects of nicotine on a variety of neutrophil functions at concentrations achievable in lung and oral tissues from cigarette smoking. The results show dose-dependent suppression of chemotaxis and phagocytosis, and enhancement of degranulation and eicosanoid generation, but not superoxide production. Cell viability was not affected by the concentrations of nicotine used in these experiments, as shown by trypan blue dye exclusion and MTT assays. These results implicate nicotine as the ingredient in cigarette smoke responsible for inflammatory damage to lungs and oral tissues observed in cigarette smokers.

Recombinant Human Interleukin-1 Beta Primes Human Polymorphonuclear Leukocytes for Stimulus-Induced Myeloperoxidase Release

Recombinant human Interleukin-1 (rhIL-1) beta was found to enhance stimulus-induced granule exocytosis from human polymorphonuclear leukocytes (PMNs). PMNs were incubated with rhIL-1 beta and then stimulated with either heat-aggregated IgG (Hagg) or N-formyl-methionyl leucylphenylalanine (FMLP). The release of the azurophil enzyme myeloperoxidase (MPO) was measured. Low concentrations of stimuli (10 micrograms/ml Hagg, 2.5 X 10(-9) M FMLP) did not stimulate degranulation in the absence of rhIL-1 beta. However, such concentrations elicited marked degranulation from PMNs preincubated with rhIL-1 beta (0.2-100 ng/ml). The enhancement of degranulation was dependent on the concentration of rhIL-1 beta employed and on the period of incubation. In other experiments, the effect of rhIL-1 beta on the PMN oxidative response was determined. rhIL-1 beta did not directly stimulate the production of superoxide anions or enhance the oxidative response to Hagg or FMLP. It is suggested that in rheumatoid joints, IL-1 beta may potentiate PMN degranulation, but not their oxidative response.

Influence of Diesel Soot Particles and Sulfite on Functions of Polymorphonuclear Leukocytes

Aqueous suspensions of diesel soot particles in combination with sulfite influence certain functions of human polymorphonuclear neutrophils in vitro. Chemiluminescence, generated after activation by opsonized zymosan as well as oxygen uptake were decreased, whereas phagocytosis was increased. An enhancement of degranulation could not be observed. The single substances show little or no effects on the above properties. The results indicate that combinations of air pollutants such as diesel soot and sulfite may modulate vital functions of activated leukocytes in vivo.