A Sprouty4 Mutation Identified in Kallmann Syndrome Increases the Inhibitory Potency of the Protein towards FGF and Connected Processes

Abstract

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.

Sprouty3, but Not Sprouty1, Expression Is Beneficial for the Malignant Potential of Osteosarcoma Cells

“…For determining the induction of MAPK pathway, 10 5 cells were treated as described [ 56 ] by using 20% FCS.…”

Role of SPRY4 in health and disease

“…This can contribute to the occurrence and development of tumors.①Gene mutations: Missense mutations in the coding sequence of the SPRY4 gene generate SPRY4 protein variants (amino acid residue 241 changes from tyrosine to serine). Mutations in the SPRY4 protein inhibit cell migration in osteosarcoma-derived cell lines ( 57 ). Another SPRY4 protein variant is generated when the cytosine at the 701st nucleotide position in the SPRY4 coding sequence mutates to thymine, resulting in threonine-to-methionine substitution at amino acid residue 234.…”

Sprouty4 is epigenetically upregulated in human colorectal cancer

“…In terms of SPRY4 mutants, only two disease-associated variants of SPRY4 have been characterized. In hormonal disorders like Kallmann syndrome, an amino acid change occurs at position 241, where serine is converted into tyrosine, resulting in SPRY4's inability to negatively regulate epithelial growth factor signalling while simultaneously increasing its negative regulator function on fibroblast growth factor (FGF) signalling [ 17 ]. In addition, SPRY4 variant c.701C>T,p.Thr234Met results in increased expression, leading to increased cell viability and colony formation in familial nonmedullary thyroid cancer cells [ 18 ].…”