Transient dimerization and interaction with ERGIC-53 occur in the fibroblast growth factor receptor 3 early secretory pathway

• Published in: The international journal of biochemistry & cell biology Vol. 40; no. 11; pp. 2649 - 2659
• Main Authors: Lievens, Patricia M-J., De Servi, Barbara, Garofalo, Silvio, Lunstrum, Gregory P., Horton, William A., Liboi, Elio
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier Ltd 2008
• Subjects: Animals; Brefeldin A - metabolism; Cell Line; Dimerization; ERGIC-53; FGFR3; Humans; Mannose-Binding Lectins - chemistry; Mannose-Binding Lectins - genetics; Mannose-Binding Lectins - metabolism; Membrane Proteins - chemistry; Membrane Proteins - genetics; Membrane Proteins - metabolism; Mice; Mutation; Protein Synthesis Inhibitors - metabolism; Quality control; Receptor, Fibroblast Growth Factor, Type 3 - chemistry; Receptor, Fibroblast Growth Factor, Type 3 - genetics; Receptor, Fibroblast Growth Factor, Type 3 - metabolism; Recombinant Fusion Proteins - genetics; Recombinant Fusion Proteins - metabolism; Secretory pathway; Thanatophoric Dysplasia - genetics; ERGIC; RTK; EndoH; ERGIC-53; ER; Secretory pathway; TDII; Quality control; PDGFR; HA; BFA; FGFR3; wt; PNGaseF; YFP-PCA
• ISSN: 1357-2725; 1878-5875
• DOI: 10.1016/j.biocel.2008.05.017

The fibroblast growth factor receptor 3 (FGFR3) secretory pathway includes N-linked glycosylation in the endoplasmic reticulum where a stringent quality control system ensures that only correctly folded receptor reaches the cell surface from where mature-functional FGFR3 signals upon ligand-mediated dimerization. We have previously shown that the increased kinase activity associated with FGFR3 bearing the thanatophoric dysplasia type II (TDII) mutation hampers its maturation, enabling the receptor to signal from the endoplasmic reticulum. Here we investigate if this biosynthetic disturbance could be explained by premature dimerization of the receptor. Our observations show that a limited fraction of the immature high-mannose, mutant receptor dimerizes in the early secretory pathway, as does the immature wild type FGFR3. In contrast, the mature fully glycosylated wild type receptor reaches the cell surface as monomer suggesting that dimerization is a transient event. The kinase activity of mutant FGFR3 is not required for dimerization to occur, although it increases dimerization efficiency. Furthermore, mutant FGFR3 trans-phosphorylates the immature wild type receptor indicating that dimerization occurs in the endoplasmic reticulum. Visualization of protein interaction inside the secretory pathway confirms receptor dimerization. In addition, it shows that both wild type and TDII FGFR3 interact with the mannose-specific lectin ERGIC-53. We conclude that transient dimerization is an obligatory step in FGFR3 biosynthesis acting as a pre-assembly quality control mechanism. Furthermore, the TDII/ERGIC-53 complex formation may function as a checkpoint for FGFR3 sorting downstream the endoplasmic reticulum. These findings have implications for understanding the pathogenesis of FGFR3-related disorders.