A nuclear export sequence located on a beta-strand in fibroblast growth factor-1

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Fibroblast growth factor-1 (FGF-1) has intracellular functions beyond activating cell surface receptors.
• Internalized FGF-1 translocates to the cytosol and nucleus, suggesting nuclear roles.
• Nuclear protein kinase C delta phosphorylates FGF-1, initiating nuclear export.

Purpose of the Study:

• Identify the nuclear export sequence (NES) of FGF-1.
• Characterize the mechanism of FGF-1 nuclear export.
• Investigate the role of phosphorylation and exportin-1 in FGF-1 nuclear export.

Main Methods:

• Site-directed mutagenesis to create FGF-1 mutants.
• Reporter protein assays to assess NES activity in vivo.
• Co-immunoprecipitation to detect protein complex formation.
• Peroxisomal targeting assays to confirm in vivo complex formation.

Main Results:

• A leucine-rich NES was identified at the C terminus of FGF-1.
• Mutating hydrophobic residues in the NES abolished or reduced nuclear export.
• FGF-1 forms a complex with exportin-1 and Ran-GTP, dependent on phosphorylation and sensitive to leptomycin B.
• The FGF-1 NES is located in a beta-strand, a novel finding for NESs.

Conclusions:

• FGF-1 possesses a unique beta-strand NES crucial for its nuclear export.
• Phosphorylation of FGF-1 is essential for its nuclear export via the exportin-1/Ran-GTP pathway.
• This study reveals a novel mechanism for nuclear export of intracellular signaling proteins.