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Uncoupling of cell proliferation and differentiation activities of basic fibroblast growth factor
1Institut de Pharmacologie et de Biologie Structurale du CNRS, 205 Route de Narbonne, 31077 Toulouse Cedex 4, France.
Abstract:
FGF-2 exerts its pleiotropic effects on cell growth and differentiation by interacting with specific cell surface receptors. In addition, exogenously added FGF-2 is translocated from outside the cell to the nucleus during G1-S transition. In this study, we show that a single point mutation in FGF-2 (substitution of residue serine 117 by alanine) is sufficient to drastically reduce its mitogenic activity without affecting its differentiation properties. The FGF-2(S117A) mutant binds to and activates tyrosine kinase receptors and induces MAPK and p70S6K activation as strongly as the wild-type FGF-2. We demonstrate that this mutant enters NIH3T3 cells, is translocated to the nucleus, and is phosphorylated similar to the wild-type growth factor. This suggests that FGF-2 mitogenic activity may require, in addition to signaling through cell surface receptors and nuclear translocation, activation of nuclear targets. We have previously shown that, in vitro, FGF-2 directly stimulates the activity of the casein kinase 2 (CK2), a ubiquitous serine/threonine kinase involved in the control of cell proliferation. We report that, in vivo, FGF-2(WT) transiently interacts with CK2 and stimulates its activity in the nucleus during G1-S transition in NIH3T3 cells. In contrast, the FGF-2(S117A) mutant fails to interact with CK2. Thus, our results show that FGF-2 mitogenic and differentiation activities can be dissociated by a single point mutation and that CK2 may be a new nuclear effector involved in FGF-2 mitogenic activity.-Bailly, K., Soulet, F., Leroy, D., Amalric, F., Bouche, G. Uncoupling of cell proliferation and differentiation activities of basic fibroblast growth factor (FGF-2).
Insights
A single mutation in fibroblast growth factor-2 (FGF-2) reduces its cell proliferation effects but not differentiation. This FGF-2 mutant fails to interact with casein kinase 2 (CK2), suggesting CK2 is crucial for FGF-2
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Fibroblast growth factor-2 (FGF-2) mediates cell growth and differentiation via cell surface receptors.
- Exogenous FGF-2 translocates to the nucleus during G1-S phase transition.
- The precise mechanisms underlying FGF-2's pleiotropic effects are not fully elucidated.
Purpose of the Study:
- To investigate the role of specific FGF-2 residues in its mitogenic and differentiation activities.
- To identify nuclear targets and pathways involved in FGF-2's proliferative signaling.
- To determine if FGF-2's mitogenic activity is linked to its interaction with casein kinase 2 (CK2).
Main Methods:
- Site-directed mutagenesis to create FGF-2(S117A) mutant.
- Cell culture (NIH3T3) and stimulation experiments.
- Western blotting to assess MAPK and p70S6K activation.
- Immunofluorescence and cell fractionation for nuclear translocation.
- Co-immunoprecipitation and kinase assays to study FGF-2/CK2 interaction and activity.
Main Results:
- The FGF-2(S117A) mutant retained receptor binding and activation of MAPK/p70S6K, similar to wild-type (WT) FGF-2.
- FGF-2(S117A) exhibited significantly reduced mitogenic activity but preserved differentiation properties.
- Both WT FGF-2 and the mutant translocated to the nucleus and were phosphorylated.
- WT FGF-2 interacted with and activated nuclear casein kinase 2 (CK2) during G1-S transition.
- The FGF-2(S117A) mutant failed to interact with CK2, indicating a dissociation of activities.
Conclusions:
- A single point mutation (S117A) in FGF-2 can uncouple its mitogenic and differentiation functions.
- FGF-2's mitogenic activity, beyond receptor signaling and nuclear translocation, may depend on the activation of nuclear targets like CK2.
- Casein kinase 2 (CK2) emerges as a potential nuclear effector mediating FGF-2's proliferative effects.