Abstract
The regulation of cell function by fibroblast growth factors (FGFs) classically occurs through a dual receptor system of a tyrosine kinase receptor (FGFR) and a heparan sulfate proteoglycan co-receptor. Mutations in some consensus N-glycosylation sites in human FGFR result in skeletal disorders and craniosynostosis syndromes, and biophysical studies in vitro suggest that N-glycosylation of FGFR alters ligand and heparan sulfate binding properties. The evolutionarily conserved FGFR signaling system of Caenorhabditis elegans has been used to assess the role of N-glycosylation in the regulation of FGFR signaling in vivo. The C. elegans FGF receptor, EGL-15, is N-glycosylated in vivo, and genetic substitution of specific consensus N-glycosylation sites leads to defects in the maintenance of fluid homeostasis and differentiation of sex muscles, both of which are phenotypes previously associated with hyperactive EGL-15 signaling. These phenotypes are suppressed by hypoactive mutations in EGL-15 downstream signaling components or activating mutations in the phosphatidylinositol 3-kinase pathway, respectively. The results show that N-glycans negatively regulate FGFR activity in vivo supporting the notion that mutation of N-glycosylation sites in human FGFR may lead to inappropriate activation of the receptor.
Highlights
4), a homologue of a mammalian leucine-rich repeat protein and a component of FGFR downstream signaling [44]. These results strongly suggest that asparagine substitutions of consensus N-glycosylation sites lead to overactivation of EGL-15 signaling in C. elegans
We have shown that the C. elegans FGF receptor, EGL-15, is N-glycosylated in vivo and that genetic removal of consensus sites for N-glycosylation in the domain 3 (D3) of EGL-15 leads to phenotypic consequences associated with receptor overactivation
Some of the mutations introduced are orthologous to FGFR mutations found in human patients of Crouzon syndrome [17] and in hypochondroplasia [15], which have been suggested to result in receptor activation
Summary
Strains—C. elegans strains were maintained at 20 °C essentially as described [34] unless otherwise stated. Molecular modeling of the EGL-15 D2 and D3 shows that the three asparagines that are conserved across species, Asn-401, Asn-433, and Asn-474, are at the surface of the protein (supplemental Fig. S1) and occupy a similar spatial position to the orthologous sites in human FGFRs [18, 39, 40]. Asparagine 449 of EGL-15 occupies a similar spatial position to asparagine 317 of human FGFR1, suggesting conserved functions for these residues, they do not align in the two-dimensional sequence comparison. Images human FGFR3 associated with hypochondroplasia [41], were captured using Axiovision and further cropped and scaled which is orthologous to Asn-401 in the C. elegans EGL-15 using Adobe Photoshop CS3
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
