Sorting of the FGF receptor 1 in a human glioma cell line
- 740 Downloads
Fibroblast growth factor receptor 1 (FGFR1) is a receptor tyrosine kinase promoting tumor growth in a variety of cancers, including glioblastoma. Binding of FGFs triggers the intracellular Ras/Raf/ERK signaling pathway leading to cell proliferation. Down-regulation of FGFR1 and, consequently, inactivation of its signaling pathways represent novel treatment strategies for glioblastoma. In this study, we investigated the internalization and endocytic trafficking of FGFR1 in the human glioma cell line U373. Stimulation with FGF-2 induced cell rounding accompanied by increased BrdU and pERK labeling. The overexpression of FGFR1 (without FGF treatment) resulted in enhanced phosphorylated FGFR1 suggesting receptor autoactivation. Labeled ligand (FGF-2-Cy5.5) was endocytosed in a clathrin- and caveolin-dependent manner. About 25 % of vesicles carrying fluorescently tagged FGFR1 represented early endosomes, 15 % transferrin-positive recycling endosomes and 40 % Lamp1-positive late endosomal/lysosomal vesicles. Stimulation with FGF-2 increased the colocalization rate in each of these vesicle populations. The treatment with the lysosomal inhibitor leupeptin resulted in FGFR1 accumulation in lysosomes, but did not enhance receptor recycling as observed in neurons. Analysis of vesicle distributions revealed an accumulation of recycling endosomes in the perinuclear region. In conclusion, the shuttling of receptor tyrosine kinases can be directly visualized by overexpression of fluorescently tagged receptors which respond to ligand stimulation and follow the recycling and degradation pathways similarly to their endogenous counterparts.
KeywordsTrafficking Recycling Degradation Endosomes Lysosomes Leupeptin U373 cells
This study was supported by the Austrian Cancer Society (Tyrol) and by the Medical Research Fund (MFF). Special thanks go to Markus Hutterer for providing U373 cells, to Markus Offterdinger for valuable help with microscopy and image analysis, to Roland Irschick for performing data analysis in Fig. S1 and to Ellen M. Haugsten for corrections on the manuscript.
- Hausott B, Schlick B, Vallant N, Dorn R, Klimaschewski L (2008) Promotion of neurite outgrowth by fibroblast growth factor receptor 1 overexpression and lysosomal inhibition of receptor degradation in pheochromocytoma cells and adult sensory neurons. Neuroscience 153:461–473PubMedCrossRefGoogle Scholar
- Rand V, Huang J, Stockwell T, Ferriera S, Buzko O, Levy S, Busam D, Li K, Edwards JB, Eberhart C, Murphy KM, Tsiamouri A, Beeson K, Simpson AJ, Venter JC, Riggins GJ, Strausberg RL (2005) Sequence survey of receptor tyrosine kinases reveals mutations in glioblastomas. Proc Natl Acad Sci USA 102:14344–14349PubMedCrossRefGoogle Scholar