title: Molecular dissection of the semaphorin 4D receptor plexin-B1-stimulated R-Ras GTPase-activating protein activity and neurite remodeling in hippocampal neurons.
abstract: Plexins serve as receptors for repulsive axonal guidance molecules semaphorins. The cytoplasmic domain of the semaphorin 4D (Sema4D) receptor, Plexin-B1 has two separated Ras GTPase-activating protein (GAP)-homologous domains, C1 and C2. Recently, we reported that the Rho family small GTPase Rnd1 associates with Plexin-B1, and the Plexin-B1-Rnd1 complex stimulates GTPase activity of R-Ras, inducing growth cone collapse in hippocampal neurons in response to Sema4D. However, the molecular mechanisms by which Plexin-B1 exhibits the GAP activity remain unclear. In this report, critical roles of Rnd1 and Sema4D in Plexin-B1-stimulated R-Ras GAP activity and neurite remodeling were examined. The N-terminal region of the cytoplasmic domain of Plexin-B1 containing the C1 domain interacts with the C-terminal region containing the C2 domain, and Rnd1 disrupts this interaction. On the other hand, Sema4D induces clustering of Rnd1-bound Plexin-B1, in parallel with inactivation of R-Ras in cells. Antibody clustering of the recombinant cytoplasmic domain of Plexin-B1 in the presence of Rnd1 triggers the R-Ras GAP activity. Deletion of the extracellular domain of Plexin-B1 causes ligand-independent clustering of the receptor, rendering the receptor constitutively active in the presence of Rnd1, and induces contraction of COS-7 cells and inhibition of neurite outgrowth in hippocampal neurons. These results indicate that Rnd1 opens the two R-Ras GAP domains of Plexin-B1, and Sema4D-induced receptor clustering stimulates R-Ras GAP activity and neurite remodeling in hippocampal neurons.
authors.affiliation: Laboratory of Molecular Neurobiology, Graduate School of Biostudies, Kyoto University, Kyoto 606-8502, Japan.
authors.forename: Izumi
authors.initials: I
authors.lastname: Oinuma
authors.forename: Hironori
authors.initials: H
authors.lastname: Katoh
authors.forename: Manabu
authors.initials: M
authors.lastname: Negishi
mesh_terms: D020816:Amino Acid Motifs; D000818:Animals; D015703:Antigens, CD / Q000378:metabolism; D001665:Binding Sites; D019556:COS Cells; D002478:Cells, Cultured; D002522:Chlorocebus aethiops; D020558:GTP Phosphohydrolases / Q000378:metabolism; D020690:GTPase-Activating Proteins / Q000378:metabolism; D006624:Hippocampus / Q000166:cytology* / Q000378:metabolism*; D009416:Nerve Regeneration; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D016501:Neurites / Q000502:physiology; D009474:Neurons / Q000378:metabolism* / Q000648:ultrastructure*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D051381:Rats; D011956:Receptors, Cell Surface / Q000737:chemistry / Q000378:metabolism / Q000502:physiology; D039961:Semaphorins / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D018631:ras Proteins / Q000378:metabolism; D020741:rho GTP-Binding Proteins / Q000378:metabolism
chemical_list: D015703:Antigens, CD; C093224:CD100 antigen; D020690:GTPase-Activating Proteins; D009419:Nerve Tissue Proteins; D011956:Receptors, Cell Surface; D039961:Semaphorins; D020558:GTP Phosphohydrolases; D018631:ras Proteins; D020741:rho GTP-Binding Proteins