Bromophenacyl bromide binding to the actin-bundling protein l-plastin inhibits inositol trisphosphate-independent increase in Ca2+ in human neutrophils.

Abstract

Ligation of IgG Fc receptors on polymorphonuclear leukocytes causes an increase in the concentration of fre intracytoplasmic Ca2+ ([Ca2+1J which arises from release of intracellular stores but is Independent of inositol 1,4,5-trisphosphate. We found that bromophenacyl bromide (BPB), an alkylating agent which Inhibits leukocyte degranulation, adherence, and phagocytosis, inhibited IgG-stimulated These data suggest that the actin cytoskeleton is essential for signal tru ction from plasma membrane Fc receptors and that l-plastin has a critical role in activation of this pathway.The rise in intracytosolic Ca2+ concentration ([Ca2~+f) induced by Fc receptor (FcR) ligation is necessary for fusion of secretory granules with the plasma membrane, increased expression of other receptors, phagosome-lysosome fusion, and perhaps chemotaxis (1-6). Increases in [Ca2+]i can occur after ligation ofeither FcRII or FcRIII (7-9) and are produced entirely through release from intracellular stores, without a contribution from extracellular Ca2+ (7,9,10). This [Ca2+] rise, in contrast to fMet-Leu-Phe receptor stimulation, proceeds via a pertussis toxin-insensitive pathway which is independent of inositol 1,4,5-trisphosphate (IP3) generation (10). rise. These data demonstrate that rearrangements in the actin cytoskeleton triggered by FcR ligation are critical in release ofCa2+ from intracellular stores and suggest that I-plastin has a role in this process.MATERIALS AND METHODS General Methods. PMNs were purified and loaded with fura-2, fluorescence was measured, and [Ca2+]i was calculated exactly as described (7, 10, 18). All buffers contained 1.5 mM Ca2+. Agonists including aggregated IgG, immune complexes, and stock solutions of platelet-activating factor, fMet-Leu-Phe, and phorbol 12,13-dibutyrate were prepared, and phagocytosis of IgG-opsonized sheep erythrocytes was measured as described (7,10,18

Antileukoproteinase: Modulation of neutrophil function and therapeutic effects on anti–type II collagen antibody–induced arthritis

“…Since there is ample evidence for the involvement of Lpl in cytoskeletal reorganization in activated leukocytes (19,24), we decided to study the effect of recombinant human ALP on the assembly of G-actin into its filamentous polymer (F-actin), by flow cytometry. Whereas untreated neutrophils exhibited a significant rise in F-actin content upon stimulation with sheep erythrocyte-coated IgG, the F-actin assembly ( Figure 4A) in the ALP-treated cells remained unchanged and in the range of unstimulated controls ( Figure 4C).…”

“…However, the underlying immune complex-dependent pathology in antibody transferinduced arthritis has provoked a different focus on the antiinflammatory effects of ALP and has finally led to the detection of new facets of action in the present investigations. Thus, in an initial attempt to identify cytosolic ALP ligands that might be involved in immune complex-induced inflammatory pathways, we detected the binding of ALP to Lpl, a leukocyte-specific actinbundling protein that has been implicated in regulating PMN signal transduction (24).…”

A polydnavirus-encoded protein of an endoparasitoid wasp is an immune suppressor.

“…This suggests that polydnavirus infection of the host insect interferes with the cellular activation of haemocytes. The observation that cytochalasin D causes similar effects suggests that haemocyte activation, including exposure of HPL-binding sites on the haemocyte surface and microparticle formation, requires a functional cytoskeleton, as shown in vertebrate blood cells (Rosales et al, 1994 ;Yano et al, 1994). Cytochalasin D-treated haemocytes (Fig.…”

“…The presence of PS is known to enhance coagulation processes in vertebrate systems. Since both degranulation and microparticle formation involve a rearrangement of the cytoskeleton (Rosales et al, 1994 ;Yano et al, 1994), the absence of functional actin filaments in CrV1-treated haemocytes is probably the primary cause of haemocyte inactivation. More specifically, the inactivation of actin filaments by CrV1 probably precludes cellular activation reactions of haemocytes similar to cytochalasin D inactivation in vertebrate blood cells (Bengtsson et al, 1993 ;Mooney et al, 1995).…”

Immune Complex-induced Integrin Activation and L-plastin Phosphorylation Require Protein Kinase A

“…Alternatively, phosphorylated LPL in nonradioactive cells was detected by Western blotting immunoprecipitates with the anti-phospho-LPL antibody. In some experiments, membranes were blotted with LPL 4A.1 (26) to detect total phosphorylated and unphosphorylated LPL protein.…”