The kinase activity of fibroblast growth factor receptor 3 with activation loop mutations affects receptor trafficking and signaling.
Amino acid substitutions at the Lys-650 codon within the activation loop kinase domain of fibroblast growth factor receptor 3 (FGFR3) result in graded constitutive phosphorylation of the receptor. Accordingly, the Lys-650 mutants are associated with dwarfisms with graded clinical severity. To assess the importance of the phosphorylation level on FGFR3 maturation along the secretory pathway, hemagglutinin A-tagged derivatives were studied. The highly activated SADDAN (severe achondroplasia with developmental delay and acanthosis nigricans) mutant accumulates in its immature and phosphorylated form in the endoplasmic reticulum (ER), which fails to be degraded. Furthermore, the Janus kinase (Jak)/STAT pathway is activated from the ER by direct recruitment of Jak1. Abolishing the autocatalytic property of the mutated FGFR3 by replacing the critical Tyr-718 reestablishes the receptor full maturation and inhibits signaling. Differently, the low activated hypochondroplasia mutant is present as a mature phosphorylated form on the plasma membrane, although with a delayed transition in the ER, and is completely processed. Signaling does not occur in the presence of brefeldin A; instead, STAT1 is activated when protein secretion is blocked with monensin, suggesting that the hypochondroplasia receptor signals at the exit from the ER. Our results suggest that kinase activity affects FGFR3 trafficking and determines the spatial segregation of signaling pathways. Consequently, the defect in down-regulation of the highly activated receptors results in the increased signaling capacity from the intracellular compartments, and this may determine the severity of the diseases.
Division of Biochemistry, Department of Neurological Sciences, University of Verona Medical School, 37134 Verona, Italy.
Patricia M-J
PM
Lievens
Chiara
C
Mutinelli
Darcie
D
Baynes
Elio
E
Liboi
D000818:Animals; D015153:Blotting, Western; D020126:Brefeldin A / Q000494:pharmacology; D002384:Catalysis; D002460:Cell Line; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism; D003062:Codon; D018076:DNA, Complementary / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D015536:Down-Regulation; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006031:Glycosylation; D006388:Hemagglutinins / Q000737:chemistry; D006801:Humans; D007150:Immunohistochemistry; D047468:Immunoprecipitation; D053613:Janus Kinase 1; D008239:Lysine / Q000737:chemistry; D051379:Mice; D008856:Microscopy, Fluorescence; D009154:Mutation; D010766:Phosphorylation; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D051381:Rats; D051498:Receptor, Fibroblast Growth Factor, Type 3; D017468:Receptors, Fibroblast Growth Factor / Q000378:metabolism*; D050794:STAT1 Transcription Factor; D015398:Signal Transduction; D015534:Trans-Activators / Q000378:metabolism; D014162:Transfection; D014443:Tyrosine / Q000737:chemistry
D003062:Codon; D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D006388:Hemagglutinins; D017468:Receptors, Fibroblast Growth Factor; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; C494080:Stat1 protein, mouse; C494081:Stat1 protein, rat; D015534:Trans-Activators; D020126:Brefeldin A; D014443:Tyrosine; C496365:FGFR3 protein, human; C496366:Fgfr3 protein, mouse; D011505:Protein-Tyrosine Kinases; D051498:Receptor, Fibroblast Growth Factor, Type 3; C507904:JAK1 protein, human; C507905:Jak1 protein, mouse; C507906:Jak1 protein, rat; D053613:Janus Kinase 1; D008239:Lysine