Kallmann syndrome is the result of innate genetic defects in the
fibroblast growth factor (FGF) regulated signaling network causing diminished signal transduction. One of the rare mutations associated with the syndrome alters the Sprouty (Spry)4
protein by converting the
serine at position 241 into a
tyrosine. In this study, we characterize the
tyrosine Spry4
mutant protein in the primary human embryonic lung fibroblasts WI-38 and
osteosarcoma-derived cell line U2OS. As demonstrated in a cell signaling assay, Spry4 gains the capability of inhibiting FGF, but not epithelial
growth factor (
EGF)-induced signaling as a consequence of the
tyrosine substitution. Additionally, migration of normal embryonic lung fibroblasts and
osteosarcoma-derived cells is potently inhibited by the
tyrosine Spry4 variant, while an effect of the wildtype Spry4
protein is hardly measureable. Concerning cell proliferation, the unaltered Spry4
protein is ineffective to influence the WI-38 cells, while the mutated Spry4
protein decelerates the cell doubling. In summary, these data emphasize that like the other mutations associated with
Kallmann syndrome the described Spry4 mutation creates a hyperactive version of a selective inhibitory molecule and can thereby contribute to a weakened FGF signaling. Additionally, the study pinpoints a Spry4 variation expanding the applicability of Spry4 in a potential
cancer therapy.