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FMIP, a novel Fms-interacting protein, affects granulocyte/macrophage differentiation
Abstract:
Hematopoietic cell growth, differentiation, and commitment to a restricted lineage are guided by a set of cytokines acting exclusively on cells expressing the corresponding cytokine receptor. The macrophage colony stimulating factor (M-CSF, also termed CSF-1) and its cognate receptor, the tyrosine kinase c-Fms, are essential for monocyte and macrophage development. The underlying molecular mechanism, however, is poorly understood. Here we identified a novel Fms-interacting protein (FMIP, MW 78 kDa) which binds transiently via its N-terminal 144 residues to the cytoplasmic domain of activated Fms-molecules. Binding of FMIP was paralleled by rapid tyrosine phosphorylation within the binding domain which drastically reduced its ability to associate with Fms. Binding was specific as evidenced by co-immunoprecipitation and association with recombinant GST-Fms fusion proteins. No binding was observed with the tyrosine phosphorylated cytoplasmic domains of c-Kit, TrkA, c-Met, and the insulin receptor. The role of FMIP in hematopoietic differentiation was studied in the bipotential myeloid progenitor cell line, FDC-P1Mac11. Overexpression of FMIP prevented M-CSF induced macrophage differentiation. Instead, cells differentiated into granulocytes. Our data suggest that the level of FMIP expression could form a threshold that decides about differentiation either into macrophages or into granulocytes.
Insights
A novel protein, Fms-interacting protein (FMIP), influences hematopoietic cell differentiation. Its expression level determines whether myeloid progenitor cells differentiate into macrophages or granulocytes.
Area of Science:
- Hematology
- Molecular Biology
- Cell Signaling
Background:
- Cytokines regulate hematopoietic cell differentiation via specific receptors.
- Macrophage colony-stimulating factor (M-CSF) and its receptor c-Fms are crucial for monocyte/macrophage development.
- The molecular mechanisms governing M-CSF-driven differentiation are not fully understood.
Purpose of the Study:
- To identify and characterize novel proteins interacting with the Fms receptor.
- To elucidate the role of Fms-interacting protein (FMIP) in M-CSF-mediated hematopoietic differentiation.
Main Methods:
- Co-immunoprecipitation assays to confirm Fms-FMIP interaction.
- Use of recombinant GST-Fms fusion proteins to assess binding specificity.
- Overexpression studies in the FDC-P1Mac11 myeloid progenitor cell line.
Main Results:
- A novel 78 kDa protein, Fms-interacting protein (FMIP), was identified.
- FMIP binds transiently to the activated Fms cytoplasmic domain, with binding reduced upon tyrosine phosphorylation.
- FMIP specifically binds Fms, not other tyrosine kinase receptors like c-Kit or c-Met.
- Overexpression of FMIP in FDC-P1Mac11 cells blocked M-CSF-induced macrophage differentiation, promoting granulocyte differentiation instead.
Conclusions:
- FMIP is a novel Fms-interacting protein involved in hematopoietic cell differentiation.
- FMIP levels may act as a critical threshold regulating the lineage commitment of myeloid progenitor cells towards macrophages or granulocytes.