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Cell surface and serum protein phosphorylation by U-937 cell ectoprotein kinases
1Department of Medical Biochemistry and Biophysics, Karolinska Institutet, Stockholm, Sweden.
Biochemistry and Molecular Biology International
|February 1, 1997
Summary
Monocytic cell ectokinases phosphorylate cell surface and serum proteins, including complement factor 1s (C1s). This extracellular kinase activity may regulate immune responses and cell interactions.
Area of Science:
- Cell biology
- Biochemistry
- Immunology
Background:
- Monocytic cells play crucial roles in immune responses.
- Extracellular protein phosphorylation is a key regulatory mechanism.
Purpose of the Study:
- To investigate the extracellular kinase activity of monocytic cells.
- To identify cell surface and serum proteins phosphorylated by these ectokinases.
Main Methods:
- Incubation of U-937 cells with [gamma-32P]ATP.
- Analysis of protein radiolabelling in intact cells and in the presence of serum.
- Testing purified human serum proteins for specific phosphorylation.
Main Results:
- U-937 cells exhibited Mg(2+)-independent radiolabelling of ~40 cell surface proteins.
- Serum proteins (170, 85, 61 kDa) and complement factor 1s (C1s) 28 kDa subunit were specifically phosphorylated.
- Phosphorylation intensity varied with cell differentiation.
Conclusions:
- Monocytic cell ectokinases phosphorylate cell surface and extracellular proteins.
- This activity may regulate cell-environment interactions and immune responses via complement system modulation.