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Receptors for maleylated proteins regulate secretion of neutral proteases by murine macrophages
Abstract:
Receptors for maleylated or acetylated proteins as well as for alpha-2-macroglobulin-protease complexes on macrophages serve as scavengers by mediating the uptake of macromolecules from the extracellular compartment. Described in this report is a novel function of these receptors on macrophages: regulation of neutral protease secretion. The binding of maleylated bovine serum albumin to macrophages triggered secretion of three neutral proteases: neutral caseinases, plasminogen activator, and cytolytic proteinase. Release of acid phosphatase, however, was not induced. An important biological consequence of protease secretion by macrophages, tumor-cytolysis, was also triggered by engagement of the receptor for maleylated bovine serum albumin. By contrast, the binding of alpha-2-macroglobulin-protease complexes to the macrophages suppressed secretion of all three proteases. Thus two receptors heretofore believed to serve principally as scavengers also regulate secretory functions of macrophages.
Insights
Macrophage scavenger receptors, typically involved in clearing cellular debris, also regulate the secretion of neutral proteases. Engagement with maleylated proteins stimulates protease release and tumor-cytolysis, while alpha-2-macroglobulin complexes suppress it.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Macrophages possess scavenger receptors that internalize macromolecules like maleylated proteins and alpha-2-macroglobulin-protease complexes.
- These receptors are primarily known for their role in cellular debris clearance and nutrient uptake.
Purpose of the Study:
- To investigate a novel function of macrophage scavenger receptors beyond their known scavenging roles.
- To determine if these receptors regulate the secretion of neutral proteases.
Main Methods:
- Macrophages were treated with maleylated bovine serum albumin and alpha-2-macroglobulin-protease complexes.
- Secretion of neutral proteases (caseinases, plasminogen activator, cytolytic proteinase) and acid phosphatase was measured.
- Macrophage-mediated tumor-cytolysis was assessed.
Main Results:
- Binding of maleylated bovine serum albumin to macrophages induced the secretion of three neutral proteases.
- Macrophage engagement with maleylated albumin also triggered tumor-cytolysis.
- Conversely, alpha-2-macroglobulin-protease complexes suppressed the secretion of these neutral proteases.
Conclusions:
- Macrophage scavenger receptors have a dual function, acting as both uptake mediators and regulators of protease secretion.
- These receptors play a significant role in modulating macrophage secretory functions, impacting processes like tumor-cytolysis.