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Surface expression and rapid internalization of macrosialin (mouse CD68) on elicited mouse peritoneal macrophages
H Kurushima1, M Ramprasad, N Kondratenko
1Department of Medicine, University of California, San Diego, La Jolla 92093-0682, USA.
Abstract:
Macrosialin, the mouse homolog of human CD68, is a heavily glycosylated transmembrane protein found almost exclusively in macrophages. Its function remains uncertain. It has a high affinity for oxidized low-density lipoprotein (LDL) in ligand blots and antibodies against the human homolog, CD68, inhibit the binding of oxidized LDL to a human monocyte-derived cell line (THP-1). However, there is still controversy as to whether macrosialin, found predominantly in late endosomes, is expressed at all on the plasma membrane. The present studies, done in thioglycollate-elicited peritoneal macrophages, confirm that macrosialin is predominantly intracellular but show clearly that 10-15% of it is expressed on the cell surface. Exchange with intracellular pools occurs at an extremely high rate. The results are compatible with a surface function, including internalization of bound ligands or adhesion to surfaces.
Insights
Macrosialin, a macrophage protein, is found on the cell surface, suggesting a role in binding and internalizing oxidized LDL or in cell adhesion.
Area of Science:
- Immunology
- Macrophage Biology
Background:
- Macrosialin, the mouse CD68 homolog, is a heavily glycosylated transmembrane protein in macrophages.
- Its precise function and cell surface expression remain debated, despite binding oxidized LDL.
Purpose of the Study:
- To investigate the cell surface expression of macrosialin in macrophages.
- To explore the functional implications of macrosialin's localization.
Main Methods:
- Utilized thioglycollate-elicited peritoneal macrophages.
- Quantified cell surface expression of macrosialin.
Main Results:
- Macrosialin is predominantly intracellular but 10-15% is expressed on the plasma membrane.
- Rapid exchange occurs between intracellular and cell surface pools.
Conclusions:
- Cell surface macrosialin supports potential roles in ligand internalization or cell adhesion.
- Findings reconcile previous controversies regarding macrosialin localization.