Localized Exocytosis of Primary (Lysosomal) Granules During Phagocytosis: Role of Ca2+-Dependent Tyrosine Phosphorylation and Microtubules

Abstract

The uptake and killing of bacteria by human neutrophils are dependent on the fusion of secretory granules with forming phagosomes. The earliest component of exocytosis was found to precede phagosome closure, so that granular membrane constituents were detectable on the plasmalemma. We show that during phagocytosis of IgG-opsonized particles, this early secretory response is highly polarized in the case of primary granules, but less so for specific granules. The vectorial discharge of primary granules was dependent on calcium, but no evidence was found that calcium is involved in determining the polarity of exocytosis. In particular, a redistribution of endomembrane calcium stores toward forming phagosomes could not be detected. Polarized granule exocytosis was accompanied by focal tyrosine phosphorylation and actin polymerization, although the latter was not required for the response. Instead, microtubules seemed to contribute to the vectorial nature of the response. During particle ingestion, the microtubule-organizing center relocated toward forming phagosomes, and colchicine treatment altered the pattern of exocytosis, reducing its directionality. We hypothesize that the focal activation of tyrosine kinases generates localized signals that induce exocytosis in a calcium-dependent manner, and that reorientation of microtubules facilitates preferential delivery of granules toward the forming phagosome.

Synovial fluid exoglycosidases are predictors of rheumatoid arthritis and are effective in cartilage glycosaminoglycan depletion

“…The capacity for Ca 2ϩ -regulated exocytosis of lysosomal enzymes has been shown for platelets, neutrophils, mast cells, macrophages, cytotoxic T cells, and B cells (36)(37)(38). We found higher ␤-D-glucuronidase activity in blood cells 2170 ORTUTAY ET AL (particularly in granulocytes) of RA patients, which supports the concept of the inflammatory cell origin of the glycosidases.…”

Cytoplasmic Linker Protein-170 Enhances Spreading and Phagocytosis in Activated Macrophages by Stabilizing Microtubules

“…Kinesin has not only been implicated in the control of cell shape, but also in pseudopod formation (18). Characteristically, Fc␥R-mediated phagocytosis is accompanied by pseudopodial extension (58), as well as by focal exocytosis (59). The coordination of both pseudopodial extension and focal exocytic membrane insertion requires PI3K activity, because engulfment of large particles is completely blocked by the PI3K inhibitors wortmannin and LY294002 (58).…”

A Large T Cell Invagination with CD2 Enrichment Resets Receptor Engagement in the Immunological Synapse

“…Arf6 is required for the membrane insertion of recycling endosomes and critical in phagocytosis (31) and macropinocytosis (32). Elevations in the intracellular calcium concentration play a central role in exocytosis in nonsecretory cells (49), including the insertion of cell membrane mass by exocytosis before the formation of phagosomes (50). PI3K and Cdc42 activity were required for T cell invaginations, similar to phagocytosis (38,39) and macropinocytosis (40,44).…”