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Mechanisms of lysosomal enzyme release from human polymorphonuclear leukocytes. Effects of phorbol myristate acetate
Abstract:
PMA enhanced release of the azurophil granule enzyme, beta-glucuronidase, as well as lysozyme, from cytochalasin B-treated PMN's exposed to either zymosan particles or C5a. PMA was active at nanomolar concentrations, was not toxic to the cells, and was most effective when present for brief durations (0-1 min) before exposure of the cells to the stimuli. Beta-glucuronidase was not released in significant amounts from PMN's exposed to PMA alone, in the absence of stimuli such as zymosan or C5a. In contrast, only the specific granule enzyme, lysozyme, was released from unstimulated cells. Electron micrographs of cells exposed to PMA revealed an increase in the number of visible cytoplasmic microtubules as compared to control cells. Enhancement of lysosomal enzyme (beta-glucuronidase) release by PMA appears to be independent of effects on release of specific granule enzymes (lysozyme), but rather is likely due to PMA-induced elevations of cellular cGMP.
Insights
Phorbol 12-myristate 13-acetate (PMA) boosts the release of specific enzymes from neutrophils (PMNs) when stimulated. This effect, linked to increased cGMP, enhances the release of lysosomal enzymes more than specific granule enzymes.
Area of Science:
- Immunology
- Cell Biology
Background:
- Neutrophils (PMNs) are crucial immune cells involved in pathogen clearance.
- Granule release is a key mechanism for PMN effector functions.
Purpose of the Study:
- To investigate the effect of Phorbol 12-myristate 13-acetate (PMA) on neutrophil degranulation.
- To elucidate the mechanisms by which PMA modulates enzyme release from different neutrophil granule populations.
Main Methods:
- Utilized cytochalasin B-treated human neutrophils (PMNs).
- Stimulated PMNs with zymosan particles or C5a in the presence or absence of PMA.
- Quantified the release of beta-glucuronidase (azurophil granule enzyme) and lysozyme (specific granule enzyme).
- Examined cellular changes using electron microscopy.
Main Results:
- PMA significantly enhanced the release of beta-glucuronidase and lysozyme from stimulated PMNs.
- PMA was effective at nanomolar concentrations and required brief exposure times.
- PMA alone did not induce significant beta-glucuronidase release without stimuli.
- Lysozyme release occurred from unstimulated cells, but was also enhanced by PMA.
- PMA treatment led to an increase in visible cytoplasmic microtubules.
- Enhanced beta-glucuronidase release by PMA was independent of lysozyme release and likely mediated by elevated cellular cGMP.
Conclusions:
- PMA potentiates the release of both azurophil and specific granule enzymes from neutrophils.
- The mechanism involves increased cellular cGMP and is distinct for different granule types.
- PMA's effects on degranulation are stimulus-dependent and involve cytoskeletal changes.