title: Rit promotes MEK-independent neurite branching in human neuroblastoma cells.
abstract: Rit, by sequence homology, is a member of the Ras subfamily of small guanine triphosphatases (GTPases). In PC6 cells, Rit signals through pathways both common to and different from those activated by Ras to promote cell survival and neurite outgrowth. However, the specific morphological changes induced by Rit in human cells are not known. Here, we show in a human neuronal model that Rit increases neurite outgrowth and branching through MEK-dependent and MEK-independent signaling mechanisms, respectively. Adenoviral expression of wild-type or constitutively active Rit increased neurite initiation, elongation and branching on endogenous matrix or a purified laminin-1 substratum of SH-SY5Y cells as assessed using image analysis. This outgrowth was morphologically distinct from that promoted by constitutively active Ras or Raf (evidenced by increased branching and elongation). Constitutively active Rit increased phosphorylation of ERK 1/2, but not Akt, and the MEK inhibitor PD 098059 blocked constitutively active Rit-induced neurite initiation but not elongation or branching. These results suggest that Rit plays a key role in human neuronal development and regeneration through activating both known and as yet undefined signaling pathways.
authors.affiliation: Department of Anatomy and Neurobiology, University of Kentucky Medical Center, Lexington, KY 40536-0298, USA. dlhynd0@uky.edu
authors.forename: DiAnna L
authors.initials: DL
authors.lastname: Hynds
authors.forename: Mike L
authors.initials: ML
authors.lastname: Spencer
authors.forename: Douglas A
authors.initials: DA
authors.lastname: Andres
authors.forename: Diane M
authors.initials: DM
authors.lastname: Snow
mesh_terms: D000256:Adenoviridae / Q000235:genetics; D015153:Blotting, Western; D002454:Cell Differentiation; D002460:Cell Line; D045744:Cell Line, Tumor; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005109:Extracellular Matrix / Q000378:metabolism; D005419:Flavonoids / Q000494:pharmacology; D049452:Green Fluorescent Proteins; D006801:Humans; D007797:Laminin / Q000378:metabolism; D008164:Luminescent Proteins / Q000378:metabolism; D020935:MAP Kinase Signaling System; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009447:Neuroblastoma / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism*; D010766:Phosphorylation; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism; D015398:Signal Transduction; D019076:Transgenes; D018631:ras Proteins / Q000378:metabolism / Q000502:physiology*
chemical_list: D004791:Enzyme Inhibitors; D005419:Flavonoids; D007797:Laminin; D008164:Luminescent Proteins; C121346:laminin 1; D049452:Green Fluorescent Proteins; D019908:Proto-Oncogene Proteins c-raf; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; C486776:RIT1 protein, human; D018631:ras Proteins; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one