title: The novel GTPase Rit differentially regulates axonal and dendritic growth.
abstract: The Rit GTPase is widely expressed in developing and adult nervous systems, and our previous data with pheochromocytoma cells implicate Rit signaling in NGF-induced neurite outgrowth. In this study, we investigated a role for Rit in neuronal morphogenesis. Expression of a dominant-negative (dn) Rit mutant in hippocampal neurons inhibited axonal growth but potentiated dendritic growth. Conversely, a constitutively active (ca) Rit mutant promoted axonal growth but inhibited dendritic growth. Dendritogenesis is regulated differently in sympathetic neurons versus hippocampal neurons in that sympathetic neurons require NGF and bone morphogenetic proteins (BMPs) to trigger dendritic growth. Despite these differences, dnRit potentiated and caRit blocked BMP7-induced dendritic growth in sympathetic neurons. Biochemical studies indicated that BMP7 treatments that caused dendritic growth also decreased Rit GTP loading. Additional studies demonstrate that caRit increased extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation and pharmacological inhibition of MEK1 (mitogen-activated protein kinase/ERK 1) blocked the axon-promoting and dendrite-inhibiting effects of caRit. These observations suggest that Rit is a convergence point for multiple signaling pathways and it functions to promote axonal growth but inhibit dendritic growth via activation of ERK1/2. Modulation of the activational status of Rit may therefore represent a generalized mechanism across divergent neuronal cell types for regulating axonal versus dendritic growth modes.
authors: Center for Research on Occupational and Environmental Toxicology, Oregon Health & Science University, Portland, Oregon 97239, USA. leinp@ohsu.edu
authors: Pamela J
authors: PJ
authors: Lein
authors: Xin
authors: X
authors: Guo
authors: Geng-Xian
authors: GX
authors: Shi
authors: Melissa
authors: M
authors: Moholt-Siebert
authors: Donald
authors: D
authors: Bruun
authors: Douglas A
authors: DA
authors: Andres
mesh_terms: D000818:Animals; D001369:Axons / Q000201:enzymology*; D055419:Bone Morphogenetic Protein 7; D019485:Bone Morphogenetic Proteins / Q000494:pharmacology; D002470:Cell Survival / Q000502:physiology; D002478:Cells, Cultured; D003712:Dendrites / Q000187:drug effects / Q000201:enzymology*; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D049452:Green Fluorescent Proteins / Q000235:genetics; D006624:Hippocampus / Q000166:cytology; D020935:MAP Kinase Signaling System / Q000502:physiology; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D009154:Mutation; D009474:Neurons / Q000201:enzymology* / Q000648:ultrastructure; D016716:PC12 Cells; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D017783:Superior Cervical Ganglion / Q000166:cytology; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000494:pharmacology; D018631:ras Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: C525821:Bmp7 protein, rat; D055419:Bone Morphogenetic Protein 7; D019485:Bone Morphogenetic Proteins; D012333:RNA, Messenger; D016212:Transforming Growth Factor beta; D049452:Green Fluorescent Proteins; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; C486777:Rit protein, rat; D018631:ras Proteins