title: Multiple GPI-anchored receptors control GDNF-dependent and independent activation of the c-Ret receptor tyrosine kinase.
abstract: Glial cell line-derived neurotrophic factor (GDNF) mediates neuronal survival through a receptor complex composed of the c-Retproto-oncogene and GFR alpha-1, a member of a family of GPI-anchored receptors. The extent of cross-talk between GDNF and GFR alpha receptors and its possible significance for c-Ret activation is presently unclear. Using chemical crosslinking we demonstrate here a specific interaction between GDNF and GFR alpha-2 expressed in COS cells, albeit of a lower affinity than the one between GDNF and GFR alpha-1. In addition, GFR alpha-2 mediated crosslinking of GDNF of c-Ret as well as ligand-dependent stimulation of c-Ret tyrosine phosphorylation. We also describe the isolation of a novel, more divergent member of the GFR alpha family, GFR alpha-3, which did not bind GDNF directly, but was able to mediate crosslinking of GDNF to c-Ret when both receptors were coexpressed in COS cells. Thus, all three GFR alpha receptors mediate GDNF binding to c-Ret with efficiencies GFR alpha-1 > GFR alpha-2 > GFR alpha-3. c-Ret showed high levels of constitutive tyrosine autophosphorylation upon overexpression in COS cells, which was inhibited in a dose-dependent manner by coexpression with any of the GFR alpha receptors, suggesting that GFR alpha s may also provide a gain control mechanism to increase the signal-to-noise ratio of the response to ligand. GFR alpha-2 showed a dynamic pattern of expression in rat brain, distinct from that of GFR alpha-1, characterized by high expression in cortex, basal forebrain, and specific layers of the olfactory bulb, and low or no expression in substantia nigra, cerebellum, and motor nuclei. GFR alpha-2, but not GFR alpha-3 mRNA expression was highly induced in several nuclei after stimulation with kainic acid. In contrast to GFR alpha-1 and GFR alpha-2, GFR alpha-3 expression in postnatal and adult brain was highly restricted. Developmentally regulated expression of GFR alpha-3 was, however, detected in several peripheral organs and ganglia. Together, these results indicate complementary roles for GFR alpha receptors in the regulation of c-Ret activity and the maintenance of distinct neuronal circuits in the central and peripheral nervous systems.
authors.affiliation: Department of Neuroscience, Karolinska Institute, Stockholm, Sweden.
authors.forename: M
authors.initials: M
authors.lastname: Trupp
authors.forename: C
authors.initials: C
authors.lastname: Raynoschek
authors.forename: N
authors.initials: N
authors.lastname: Belluardo
authors.forename: C F
authors.initials: CF
authors.lastname: Ibáñez
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000831:Animals, Newborn; D001921:Brain / Q000378:metabolism; D019556:COS Cells; D003001:Cloning, Molecular; D029721:Drosophila Proteins; D004789:Enzyme Activation; D005333:Fetus; D018507:Gene Expression Regulation, Developmental / Q000235:genetics; D051100:Glial Cell Line-Derived Neurotrophic Factor; D051097:Glial Cell Line-Derived Neurotrophic Factor Receptors; D017261:Glycosylphosphatidylinositols / Q000378:metabolism*; D006801:Humans; D008024:Ligands; D008297:Male; D008562:Membrane Glycoproteins; D008969:Molecular Sequence Data; D009414:Nerve Growth Factors; D009419:Nerve Tissue Proteins / Q000378:metabolism / Q000502:physiology*; D010766:Phosphorylation; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D051096:Proto-Oncogene Proteins c-ret; D051381:Rats; D017208:Rats, Wistar; D020794:Receptor Protein-Tyrosine Kinases / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D011956:Receptors, Cell Surface / Q000096:biosynthesis / Q000235:genetics; D017475:Receptors, Nerve Growth Factor; D014443:Tyrosine / Q000378:metabolism
chemical_list: D029721:Drosophila Proteins; C495039:GDNF protein, human; C494987:GFRA1 protein, human; C494990:GFRA2 protein, human; C494993:GFRA3 protein, human; C495041:Gdnf protein, rat; C494989:Gfra1 protein, rat; C494992:Gfra2 protein, rat; C494995:Gfra3 protein, rat; D051100:Glial Cell Line-Derived Neurotrophic Factor; D051097:Glial Cell Line-Derived Neurotrophic Factor Receptors; D017261:Glycosylphosphatidylinositols; D008024:Ligands; D008562:Membrane Glycoproteins; D009414:Nerve Growth Factors; D009419:Nerve Tissue Proteins; D011518:Proto-Oncogene Proteins; D011956:Receptors, Cell Surface; D017475:Receptors, Nerve Growth Factor; D014443:Tyrosine; D051096:Proto-Oncogene Proteins c-ret; D020794:Receptor Protein-Tyrosine Kinases; C416649:Ret protein, Drosophila; C495001:Ret protein, rat