title: Novel mechanism of regulation of Rac activity and lamellipodia formation by RET tyrosine kinase.
abstract: Rac activation in neuronal cells plays an important role in lamellipodia formation that is a critical event for neuritogenesis. It is well known that the Rac activity is regulated via activation of phosphatidylinositol 3-kinase (PI3K) by a variety of receptor tyrosine kinases. Here we show that increased serine phosphorylation on RET receptor tyrosine kinase following cAMP elevation promotes lamellipodia formation of neuronal cells induced by glial cell line-derived neurotrophic factor (GDNF). We identified serine 696 in RET as a putative phosphorylation site by protein kinase A and found that mutation of this serine almost completely inhibited lamellipodia formation by GDNF without affecting activation of the PI3K/AKT signaling pathway. Mutation of tyrosine 1062 in RET, whose phosphorylation is crucial for activation of PI3K, also inhibited lamellipodia formation by GDNF. Inhibition of lamellipodia formation by mutation of either serine 696 or tyrosine 1062 was associated with decrease of the Rac1-guanine nucleotide exchange factor (GEF) activity, suggesting that this activity is regulated by two different signaling pathways via serine 696 and tyrosine 1062 in RET. Moreover, in the presence of serine 696 mutation, lamellipodia formation was rescued by replacing tyrosine 687 with phenylalanine. These findings propose a novel mechanism that receptor tyrosine kinase modulates actin dynamics in neuronal cells via its cAMP-dependent phosphorylation.
authors.affiliation: Department of Pathology, Nagoya University Graduate School of Medicine, 65 Tsurumai-cho, Showa-ku, Nagoya, Japan.
authors.forename: Toshifumi
authors.initials: T
authors.lastname: Fukuda
authors.forename: Kazutoshi
authors.initials: K
authors.lastname: Kiuchi
authors.forename: Masahide
authors.initials: M
authors.lastname: Takahashi
mesh_terms: D000242:Cyclic AMP / Q000378:metabolism; D029721:Drosophila Proteins; D005455:Fluorescent Antibody Technique; D051100:Glial Cell Line-Derived Neurotrophic Factor; D051097:Glial Cell Line-Derived Neurotrophic Factor Receptors; D006801:Humans; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D009414:Nerve Growth Factors; D009419:Nerve Tissue Proteins / Q000502:physiology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D051096:Proto-Oncogene Proteins c-ret; D020794:Receptor Protein-Tyrosine Kinases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012694:Serine / Q000737:chemistry / Q000378:metabolism; D014443:Tyrosine / Q000737:chemistry / Q000378:metabolism; D020744:rac GTP-Binding Proteins / Q000378:metabolism*
chemical_list: D000242:Cyclic AMP; D029721:Drosophila Proteins; D051100:Glial Cell Line-Derived Neurotrophic Factor; D051097:Glial Cell Line-Derived Neurotrophic Factor Receptors; D009414:Nerve Growth Factors; D009419:Nerve Tissue Proteins; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D051096:Proto-Oncogene Proteins c-ret; D020794:Receptor Protein-Tyrosine Kinases; D012694:Serine; D014443:Tyrosine; D020744:rac GTP-Binding Proteins; C495039:GDNF protein, human; C416649:Ret protein, Drosophila; C494918:AKT1 protein, human