Expression and purification of intracrine human FGF 11 and study of its FGFR-dependent biological activity

Fibroblast growth factor 11 (FGF11) is one of intracrine FGFs (iFGFs), which function within cells. Unlike canonical FGFs, FGF11 remains intracellularly and plays biological roles in FGF receptor (FGFR)-independent manner. Here, we established an expression system of recombinant FGF11 proteins in E. coli and investigated whether the extracellular administration of FGF11 can activate cellular signaling. Human FGF11 has two isoforms, FGF11a and FGF11b, depending on the presence of nuclear localization sequences (NLSs) in the N-terminus. Because these two isoforms are unstable, we prepared an FGF11a-Mut by substituting three cysteine residues in the NLS with serine and FGF11b-ΔC with C-terminal truncation. The introduction of mutation in the NLS improved the solubility of FGF11 prepared from E. coli. Exogenous addition of FGF11b and FGF11b-ΔC to BALB3T3 increased cell proliferation, while FGF11a-Mut exerted no effect. FGF11b-ΔC showed higher cell proliferation activity and FGFR signaling than FGF11b. The cell-proliferating activities of FGF11b and FGF11b-ΔC were blocked by an FGFR1 inhibitor or a recombinant FGFR1, confirming the FGFR1-dependent extracellular activity of FGF11b. The analysis of circular dichroism suggested that the C-terminus of FGF11 has an α-helical structure, which may affect its interaction with FGFR1. These results suggest that the N-and C-terminus of recombinant FGF11 are involved in the activation of FGFR1. The above results provide novel insights into the function and mechanism of FGF11 that may aid the development of useful ligands for FGFR regulation.