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Role of cytoskeletal elements in expression of monocyte urokinase plasminogen activator receptor,
1Department of Neurology, Wayne State University School of Medicine, Detroit, Michigan 48201, USA.
Abstract:
Peripheral blood monocytes exposed to bacterial products, phorbol esters, cyclic AMP, and cyclic AMP analogs express cell surface activation protein Mo3, which is the human urokinase plasminogen activator receptor (uPA-R). uPA-R is expressed by circulating monocytes from patients with multiple sclerosis (MS). We examined the role of cytoskeletal elements in the surface expression and subcellular distribution of uPA-R in nonactivated and lipopolysaccharide-activated monocytes and in monocytes from patients with MS. By using immunofluorescence techniques and confocal laser microscopy, we found that in unactivated monocytes, cytoplasmic uPA-R is found to one side of the nucleus, colocalizing with the Golgi. Upon activation with lipopolysaccharide, cytoplasmic Mo3-uPA-R becomes dispersed throughout the cytoplasm and projections concomitant with an increase in the monocyte perimeter (spreading). Cytoplasmic dispersion, as well as cell surface deposition, is dependent on microtubule integrity. Cell surface deposition of uPA-R upon activation is reduced by colchicine, which disrupts microtubules; however, once associated at the cell surface, uPA-R becomes associated with microfilaments via vinculin. Disruption of microfilaments with cytochalasin also alters surface expression of immunologically reactive uPA-R, as well as the distribution pattern. Monocytes from patients with MS display the uPA-R distribution pattern characteristic of an activated monocyte.
Insights
Monocyte activation involves the cell surface protein Mo3 (urokinase plasminogen activator receptor, uPA-R). Its distribution is regulated by cytoskeletal elements, and MS monocytes show an activated uPA-R pattern.
Area of Science:
- Cell Biology
- Immunology
- Neuroscience
Background:
- Peripheral blood monocytes express cell surface activation protein Mo3, identified as the human urokinase plasminogen activator receptor (uPA-R).
- uPA-R is found on circulating monocytes in patients with multiple sclerosis (MS).
Purpose of the Study:
- To investigate the role of cytoskeletal elements in the surface expression and subcellular distribution of uPA-R.
- To compare uPA-R distribution in nonactivated, activated, and MS patient monocytes.
Main Methods:
- Immunofluorescence techniques.
- Confocal laser microscopy.
- Use of pharmacological agents to disrupt microtubule and microfilament integrity (colchicine, cytochalasin).
Main Results:
- In unactivated monocytes, uPA-R colocalizes with the Golgi apparatus.
- LPS activation disperses uPA-R throughout the cytoplasm and projections, dependent on microtubule integrity.
- Cell surface uPA-R deposition is reduced by microtubule disruption but associates with microfilaments via vinculin upon activation.
- Microfilament disruption alters uPA-R surface expression and distribution.
- Monocytes from MS patients exhibit an activated uPA-R distribution pattern.
Conclusions:
- Cytoskeletal elements, specifically microtubules and microfilaments, are crucial for regulating uPA-R surface expression and subcellular localization during monocyte activation.
- The altered uPA-R distribution in MS monocytes suggests a role for cytoskeletal regulation in the disease pathophysiology.