Internalization of glial cell-derived neurotrophic factor receptor GFR alpha 1 in the absence of the ret tyrosine kinase coreceptor.
1. Glial cell-derived neurothrophic factor (GDNF) interacts with a cell surface receptor, GFRalpha1, that is linked via a glycosyl-phosphatidylinositol (GPI) lipid to the cell membrane. The neurotrophic activities of GDNF are mediated by binding to GFRalpha1 and further interaction of the GDNF-GFRalpha1 complex with a coreceptor tyrosine kinase encoded by the c-Ret protooncogene. There is also evidence for the existence of cell signaling by GDNF and GFRalpha1 in the absence of Ret. 2. To further delineate the Ret-dependent and -independent functions of GDNF, cellular internalization of GDNF and GFRalpha1 was examined in cells lines and primary neurons. 3. Relative to other GPI-anchored receptors, efficient endocytosis (approximately 30-40% of total surface-bound ligand internalized after 2 min) of GNDF and GFRalpha1 was observed in neuroblastoma and transfected-fibroblast cell lines that lack Ret. Primary hippocampal neurons from transgenic mice that express a wild-type GFRalpha1 together with a mutant, tyrosine kinase-inactive Ret also internalized GDNF efficiently (approximately 20% of total surface-bound ligand internalized after 2 min). We also observed a ligand dependence for GFRalpha1 internalization in the cell lines that lack Ret. Furthermore, a comparison in the presence and absence of Ret indicates that this coreceptor tyrosine kinase slows internalization at early time points. 4. The data suggest different mechanisms of internalization for GDNF-GFRalpha1 in the absence and presence of the Ret coreceptor.
Vieira
P
P
Laboratory for Metabolic and Endocrine Research, Simon Fraser University, Burnaby, British Columbia, Canada.
Thomas-Crusells
J
J
Vieira
A
A
D016475:3T3 Cells; D000818:Animals; D029721:Drosophila Proteins; D004705:Endocytosis / Q000235:genetics; D051100:Glial Cell Line-Derived Neurotrophic Factor; D051097:Glial Cell Line-Derived Neurotrophic Factor Receptors; D006801:Humans; D051379:Mice; D008822:Mice, Transgenic; D009414:Nerve Growth Factors / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis* / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism*; D051096:Proto-Oncogene Proteins c-ret; D020794:Receptor Protein-Tyrosine Kinases / Q000096:biosynthesis* / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D029721:Drosophila Proteins; C495039:GDNF protein, human; C494987:GFRA1 protein, human; C495040:Gdnf protein, mouse; C494988:Gfra1 protein, mouse; D051100:Glial Cell Line-Derived Neurotrophic Factor; D051097:Glial Cell Line-Derived Neurotrophic Factor Receptors; D009414:Nerve Growth Factors; D011518:Proto-Oncogene Proteins; D051096:Proto-Oncogene Proteins c-ret; D020794:Receptor Protein-Tyrosine Kinases; C416649:Ret protein, Drosophila; C494999:Ret protein, mouse