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Glucocorticoid receptors and glucocorticoid-sensitive secretion of neutral proteinases in a macrophage line
Abstract:
A continuous line of mouse macrophages (P388D1) has been shown to secrete elastase, collagenase, and plasminogen activator at activities comparable to those of macrophages elicited by an inflammatory stimulus in vivo. At physiologic concentrations anti-inflammatory glucocorticoids selectively and reversibly inhibited secretion of the three proteinases but did not inhibit secretion of lysozyme, a constitutive enzyme produced by the P388D1 cells. The secretion of the neutral proteinases was inhibited 50% by 2 to 10 nM dexamethasone. Proliferation of the macrophages was also glucocorticoid sensitive. The P388D1 macrophages contained about 4000 saturable glucocorticoid-binding sites per cell. Concentrations of hormone saturating the high affinity receptor site (for dexamethasone the dissociation constant for steroid-receptor binding, Kd, was 4 nM) correlated well with concentrations inhibiting secretion of the proteinases. Only glucocorticoids and progesterone competed for binding to the specific receptors. Temperature-sensitive translocation of hormone-receptor complexes from "cytoplasm" to nucleus similar to that found with rat thymocytes was demonstrated. Thus, the interaction between glucocorticoids and the P388D1 cell line provides a model for the regulation of macrophage secretion of neutral proteinases under normal and stress conditions.
Insights
Glucocorticoids reversibly inhibit proteinase secretion in mouse macrophages (P388D1) by binding to specific receptors. This provides a model for regulating macrophage proteinase release during inflammation and stress.
Area of Science:
- Cell Biology
- Immunology
- Endocrinology
Background:
- Mouse macrophages (P388D1) secrete neutral proteinases like elastase, collagenase, and plasminogen activator.
- These proteinases are released at levels comparable to in vivo inflammatory stimuli.
- Lysozyme, a constitutive enzyme, is also secreted by P388D1 cells.
Purpose of the Study:
- To investigate the effect of anti-inflammatory glucocorticoids on macrophage proteinase secretion.
- To characterize glucocorticoid-binding sites and their role in regulating P388D1 cell function.
- To establish a cellular model for studying glucocorticoid-mediated regulation of macrophage activity.
Main Methods:
- Utilized a continuous mouse macrophage cell line (P388D1).
- Assessed the impact of dexamethasone on proteinase and lysozyme secretion.
- Quantified glucocorticoid-binding sites and determined receptor binding affinity (Kd).
- Investigated hormone-receptor complex translocation.
Main Results:
- Glucocorticoids selectively and reversibly inhibited secretion of elastase, collagenase, and plasminogen activator.
- Lysozyme secretion remained unaffected by glucocorticoid treatment.
- Dexamethasone (2-10 nM) inhibited neutral proteinase secretion by 50%.
- P388D1 cells possess approximately 4000 high-affinity glucocorticoid-binding sites per cell (Kd = 4 nM for dexamethasone).
- Glucocorticoid concentrations correlated with proteinase inhibition and receptor saturation.
- Temperature-sensitive translocation of hormone-receptor complexes to the nucleus was observed.
Conclusions:
- P388D1 macrophages provide a valuable model for studying glucocorticoid regulation of neutral proteinase secretion.
- Glucocorticoid action involves specific receptor binding and subsequent translocation, impacting inflammatory mediator release.
- This system elucidates mechanisms controlling macrophage function under normal and stress conditions.