CONSTITUTIVE RECEPTOR ACTIVATION BY CROUZON SYNDROME MUTATIONS IN FIBROBLAST GROWTH-FACTOR RECEPTOR (FGFR)-2 AND FGFR2 NEU CHIMERAS/

Crouzon syndrome is an autosomal dominant condition primarily characte rized by craniosynostosis. This syndrome has been associated with a va riety of amino acid point mutations in the extracellular domain of fib roblast growth factor receptor 2 (FGFR2). FGFR2/Neu chimeras were gene rated by substituting the extracellular domain of Neu with that of FGF R2 containing the following Crouzon mutations: Tyr-340-->His; Cys-342- ->Tyr; Cys-342-->Arg; Cys-342-->Ser; Ser-354-->Cys; and Delta 17 (dele tion of amino acids 345-361). Each of the mutant chimeric FGFR2/Neu co nstructs stimulated focus formation in NIH 3T3 cells, indicating that Crouzon mutations can stimulate signal transduction through a heterolo gous receptor tyrosine kinase. In vitro kinase assay results indicate that FGFR2 receptors containing Crouzon mutations have increased tyros ine kinase activity and, when analyzed under nonreducing conditions, e xhibited disulfide-bonded dimers. Thus the human developmental abnorma lity Crouzon syndrome arises from constitutive activation of FGFR2 due to aberrant intermolecular disulfide-bonding. These results together with our earlier observation that achondroplasia results from constitu tive activation of the related receptor FGFR3, leads to the prediction that other malformation syndromes attributed to FGFRs, such as Pfeiff er syndrome and Thanatophoric dysplasia, also arise from constitutive receptor activation.