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Phagocytic and macropinocytic activity in MARCKS-deficient macrophages and fibroblasts
E Carballo1, D M Pitterle, D J Stumpo
1Office of Clinical Research and Laboratory of Signal Transduction, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709, USA.
Abstract:
Macrophages express high levels of the myristoylated, alanine-rich, C kinase substrate (MARCKS), an actin cross-linking protein. To investigate a possible role of MARCKS in macrophage function, fetal liver-derived macrophages were generated from wild-type and MARCKS knockout mouse embryos. No differences between the wild-type and MARCKS-deficient macrophages with respect to morphology (Wright's stain) or actin distribution (staining with rhodamine-phalloidin, under basal conditions or after treatment with phorbol esters, lipopolysaccharide, or both) were observed. We then evaluated phagocytosis mediated by different receptors: Fc receptors tested with IgG-coated sheep red blood cells, complement C3b receptors tested with C3b-coated yeast, mannose receptors tested with unopsonized zymosan, and nonspecific phagocytosis tested with latex beads. We also studied fluid phase endocytosis in macrophages and mouse embryo fibroblasts by using FITC-dextran to quantitate this process. In most cases, there were no differences between the cells derived from wild-type and MARCKS-deficient mice. However, a minor but significant and reproducible difference in rates of zymosan phagocytosis at 45-60 min was observed, with lower rates of phagocytosis in the MARCKS-deficient cells. Our data indicate that MARCKS deficiency may lead to slightly decreased rates of zymosan phagocytosis.
Insights
Myristoylated, alanine-rich, C kinase substrate (MARCKS) deficiency in macrophages slightly reduces zymosan phagocytosis. This actin cross-linking protein
Area of Science:
- Immunology
- Cell Biology
- Protein Function
Background:
- Macrophages are key immune cells involved in phagocytosis.
- Myristoylated, alanine-rich, C kinase substrate (MARCKS) is an actin cross-linking protein highly expressed in macrophages.
- The precise role of MARCKS in macrophage function remains largely uncharacterized.
Purpose of the Study:
- To investigate the role of MARCKS in macrophage phagocytosis and endocytosis.
- To determine if MARCKS deficiency impacts macrophage morphology and actin organization.
Main Methods:
- Generated fetal liver-derived macrophages from wild-type and MARCKS knockout mouse embryos.
- Assessed macrophage morphology using Wright's stain and actin distribution via rhodamine-phalloidin staining.
- Quantified phagocytosis mediated by Fc receptors, complement C3b receptors, and mannose receptors.
- Evaluated fluid phase endocytosis using FITC-dextran.
Main Results:
- No significant differences were observed in macrophage morphology or actin distribution between wild-type and MARCKS-deficient cells.
- Phagocytosis mediated by Fc receptors, C3b receptors, and nonspecific phagocytosis showed no significant differences.
- A minor but significant decrease in zymosan phagocytosis rates was observed in MARCKS-deficient macrophages at 45-60 minutes.
Conclusions:
- MARCKS deficiency leads to a slight reduction in mannose receptor-mediated zymosan phagocytosis in macrophages.
- MARCKS does not appear to be essential for general macrophage morphology, actin organization, or other phagocytic pathways.
- These findings suggest a specific, albeit minor, role for MARCKS in certain phagocytic processes.