title: Activation of Rac1 by phosphatidylinositol 3-kinase in vivo: role in activation of mitogen-activated protein kinase (MAPK) pathways and retinoic acid-induced neuronal differentiation of SH-SY5Y cells.
abstract: Rho GTPases such as RhoA, Rac1 and Cdc42 are crucial players in the regulation of signal transduction pathways required for neuronal differentiation. Using an in vitro cell culture model of neuroblastoma SH-SY5Y cells, we demonstrated previously that RhoA is an in vivo substrate of tissue transglutaminase (TGase) and retinoic acid (RA) promoted activation of RhoA by transamidation. Although activation of RhoA promoted cytoskeletal rearrangement in SH-SY5Y cells, it was not involved in induction of neurite outgrowth. Here, we demonstrate that RA promotes activation of Rac1 in SH-SY5Y cells in a transamidation-independent manner. RA-induced activation of Rac1 is mediated by phosphatidylinositol 3-kinase (PI3K), probably because of phosphorylation of the p85 regulatory subunit by Src kinases. Over-expression of constitutively active PI3K or Rac1-V12 induces neurite outgrowth, activation of mitogen activated protein kinases (MAPKs), and expression of neuronal markers. The PI3K inhibitor LY294002, or over-expression of dominant negative Rac1-N17, blocks RA-induced neurite outgrowth, activation of MAPKs, and expression of neuronal markers, suggesting that activation of PI3K/Rac1 signaling represents a potential mechanism for regulation of neuronal differentiation in SH-SY5Y cells.
authors.affiliation: Cardiovascular Research Institute, Department of Internal Medicine, The Texas A&M University System Health Science Center, College of Medicine, Temple, Texas 76504, USA.
authors.forename: Jing
authors.initials: J
authors.lastname: Pan
authors.forename: Yu-Lin
authors.initials: YL
authors.lastname: Kao
authors.forename: Suchitra
authors.initials: S
authors.lastname: Joshi
authors.forename: Seena
authors.initials: S
authors.lastname: Jeetendran
authors.forename: Donald
authors.initials: D
authors.lastname: Dipette
authors.forename: Ugra S
authors.initials: US
authors.lastname: Singh
mesh_terms: D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology*; D045744:Cell Line, Tumor; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D006801:Humans; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism*; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D009479:Neuropeptides / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D014212:Tretinoin / Q000494:pharmacology*; D020744:rac GTP-Binding Proteins / Q000378:metabolism*; D020830:rac1 GTP-Binding Protein
chemical_list: D009479:Neuropeptides; C107953:RAC1 protein, human; D014212:Tretinoin; D019869:Phosphatidylinositol 3-Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; D020744:rac GTP-Binding Proteins; D020830:rac1 GTP-Binding Protein