An S116R Phosphorylation Site Mutation in Human Fibroblast Growth Factor-1 Differentially Affects Mitogenic and...

Area of Science:

• Biochemistry
• Molecular Biology
• Endocrinology

Background:

• Fibroblast growth factor-1 (FGF-1) exhibits both receptor-mediated and nuclear signaling pathways.
• Phosphorylation at serine 116 (S116) is hypothesized to regulate FGF-1's intracrine (nuclear) signaling.
• The C-terminal loop containing S116 is critical for multiple FGF-1 functions.

Purpose of the Study:

• To investigate the functional role of FGF-1 phosphorylation at S116.
• To characterize the biophysical and functional consequences of a non-phosphorylatable S116R mutation in human FGF-1.

Main Methods:

• Site-directed mutagenesis to create the S116R variant of human FGF-1.
• Biophysical and structural characterization of the S116R mutant.
• Assessment of NIH 3T3 fibroblast mitogenic activity.
• Evaluation of fibroblast growth factor receptor-1c activation.
• In vivo studies using ob/ob hyperglycemic mice to measure glucose lowering effects.

Main Results:

• The S116R mutation did not alter the biophysical or structural properties of FGF-1.
• S116R FGF-1 showed reduced mitogenic stimulation of NIH 3T3 fibroblasts.
• Activation of fibroblast growth factor receptor-1c was increased by S116R FGF-1.
• S116R FGF-1 demonstrated a prolonged duration of glucose lowering in hyperglycemic mice.

Conclusions:

• FGF-1 phosphorylation at S116 plays a significant role in regulating its signaling pathways.
• The S116R mutation provides a tool to study the effects of abrogated intracrine signaling.
• A novel FGF-1/fibroblast growth factor receptor-1c dimerization interaction may contribute to the observed functional effects of non-phosphorylatable FGF-1.