Abstract
Fibroblast growth factor‐10 (FGF‐10), a mitogen for the epithelial cells lining the lower urinary tract, has been identified inside urothelial cells, despite its acknowledged role as an extracellular signaling ligand. Recombinant (r)FGF‐10 was determined by fluorescence microscopy optical sectioning to localize strongly to nuclei inside cultured urothelial cells. To clarify the possible role of a nuclear localization signal (NLS) in this translocation, a variant of rFGF‐10 was constructed which lacked this sequence. rFGF‐10(no NLS) was found in cytoplasm to a far greater degree than rFGF‐10, identifying this motif as a possible NLS. Furthermore, this variant displayed poor or non‐existent bioactivity compared to the wild‐type protein in triggering mitogenesis in quiescent urothelial cells. The presence of rFGF‐10(no NLS) in the nucleus suggested that additional interactions were also responsible for the nuclear accumulation of rFGF‐10. The FGF‐10 receptor was observed in cell nuclei regardless of the presence or concentration of exogenous rFGF‐10 ligand. Co‐localization studies between rFGF‐10 and the FGF‐10 receptor revealed a strong intracellular relationship between the two. This co‐localization was seen in nuclei for both rFGF‐10 and for rFGF‐10(no NLS), although the correlation was weaker for rFGF‐10(no NLS). These data show that an NLS‐like motif of rFGF‐10 is a partial determinant of its intracellular distribution and is necessary for its mitogenic activity. These advancements in the understanding of the activity of FGF‐10 present an opportunity to engineer the growth factor as a therapeutic agent for the healing of damaged urothelial tissue. J. Cell. Biochem. 102: 769–785, 2007. © 2007 Wiley‐Liss, Inc.