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Translocation of the FGR protein-tyrosine kinase as a consequence of neutrophil activation
1Laboratory of Cellular Development and Oncology, National Institute of Dental Research, Bethesda, MD 20892.
Abstract:
Recent studies of the FGR protooncogene have shown that expression of its mRNA is limited to mature peripheral blood granulocytes, monocytes, and tissue macrophages. In the present study, we have investigated p55c-fgr expression in normal human neutrophils [polymorphonuclear leukocytes (PMN)] and have found enzymatically active p55c-fgr to be abundant in lysates of PMN and murine fibroblasts transfected with a FGR expression plasmid but not control cells. Fractionation studies revealed that neutrophil p55c-fgr was present in plasma membrane-enriched fractions as well as fractions containing secondary and tertiary granules. Little change in the distribution of p55c-fgr or FGR kinase activity was observed under conditions favoring tertiary granule release. In contrast, when secondary granule secretion was induced with the chemoattractant peptide, formyl-Met-Leu-Phe, a marked decrease in p55c-fgr and FGR kinase was observed in fractions depleted of secondary granules. Concomitantly, the relative concentration of p55c-fgr and its enzymatic activity were increased in fractions containing plasma membrane. From these findings we conclude that p55c-fgr is associated with functional secretory granules and is redistributed within normal neutrophils in response to their activation.
Insights
The FGR kinase, p55c-fgr, is found in human neutrophils and moves to the plasma membrane when secondary granules are released during cell activation.
Area of Science:
- Cell Biology
- Molecular Biology
- Immunology
Background:
- The FGR protooncogene is expressed in myeloid cells like granulocytes and macrophages.
- p55c-fgr is the active form of the FGR kinase.
Purpose of the Study:
- Investigate p55c-fgr expression and localization in normal human neutrophils.
- Determine how p55c-fgr distribution changes upon neutrophil activation.
Main Methods:
- Studied p55c-fgr in human neutrophil lysates and transfected murine fibroblasts.
- Used cell fractionation to isolate different cellular components.
- Assessed FGR kinase activity.
- Induced secondary and tertiary granule release.
Main Results:
- Enzymatically active p55c-fgr is abundant in neutrophil lysates.
- p55c-fgr localizes to plasma membrane and granules (secondary and tertiary).
- Activation-induced secondary granule release causes p55c-fgr to move to the plasma membrane.
Conclusions:
- p55c-fgr associates with secretory granules in neutrophils.
- Neutrophil activation leads to p55c-fgr redistribution, particularly to the plasma membrane.