Different intracellular trafficking of FGF1 endocytosed by the four homologous FGF receptors

Abstract

Many growth factors and cytokines bind to more than one receptor, but in many cases the different roles of the separate receptors in signal transduction are unclear. Intracellular sorting of ligand-receptor complexes may modulate the signalling, and we have here studied the intracellular trafficking of ligand bound to receptors for fibroblast growth factors (FGFs). For this purpose, we transfected HeLa cells with any one of the four tyrosine kinase FGF receptors (FGFR1-4). In cells expressing any one of these receptors, externally added FGF1 was localized to sorting/early endosomes after 15 minutes at 37°C. After longer incubation times, FGF1 internalized in cells expressing FGFR1 was localized mainly to late endosomes/lysosomes, similarly to EGF. By contrast, FGF1 internalized in cells expressing FGFR4 followed largely the same intracellular pathway as the recycling ligand, transferrin. In cells expressing FGFR2 or FGFR3, sorting of FGF1 to lysosomes was somewhat less efficient than that observed for FGFR1. Furthermore, FGF1 was more slowly degraded in cells expressing FGFR4 than in cells expressing FGFR1-3 and in addition, internalized FGFR4 as such was more slowly degraded than the other receptors. The data indicate that after endocytosis, FGFR4 and its bound ligand are sorted mainly to the recycling compartment, whereas FGFR1-3 with ligand are sorted mainly to degradation in the lysosomes. Alignment of the amino acid sequence of the intracellular part of the four FGFRs revealed several lysines conserved in FGFR1-3 but absent in FGFR4. Lysines are potential ubiquitylation sites and could thus target a receptor to lysosomes for degradation. Indeed, we found that FGFR4 is less ubiquitylated than FGFR1, which could be the reason for the different sorting of the receptors.

High-Affinity Internalizing Human scFv-Fc Antibody for Targeting FGFR1-Overexpressing Lung Cancer

“…Using U2OS-R1 cells, we showed that externally added scFvD2-Fc was localized to early endosomes after 15 minutes, similarly to FGF2, which is in line with earlier reports describing the trafficking of endocytosed FGFR1 (40,41,48). Furthermore, we have demonstrated that scFvD2-Fc is efficiently and specifically internalized and accumulated in squamous, small-cell and also large-cell lung cancer cells overexpressing FGFR1, which makes this antibody a promising targeting agent for drug delivery in a significant population of lung cancer patients.…”

Roles of Fibroblast Growth Factor Receptors in Carcinogenesis

“…Endocytosis followed by degradation of FGFRs in lysosomes leads to termination of signaling (21,145). Disruptions in any of the endocytic components required for this pathway may delay signal termination and lead to oncogenesis (146).…”

Directing traffic in neural cells: determinants of receptor tyrosine kinase localization and cellular responses

“…Cbl-induced ubiquitination is required for the exit of the EGFR from the early endosome and for fusion of these vesicles with the late endosome (Ravid et al 2004). In Chinese hamster ovary cells, the targeting of the homologous FGFR subtypes FGFR1 and 4 to lysosomal or recycling vesicles, respectively, has been attributed to several conserved lysine residues within the sequence of FGFR1 (Haugsten et al 2005).…”