title: Phosphorylation of STEF/Tiam2 by protein kinase A is critical for Rac1 activation and neurite outgrowth in dibutyryl cAMP-treated PC12D cells.
abstract: The second messenger cAMP plays a pivotal role in neurite/axon growth and guidance, but its downstream pathways leading to the regulation of Rho GTPases, centrally implicated in neuronal morphogenesis, remain elusive. We examined spatiotemporal changes in Rac1 and Cdc42 activity and phosphatidylinositol 3,4,5-triphosphate (PIP(3)) concentration in dibutyryl cAMP (dbcAMP)-treated PC12D cells using Förster resonance energy transfer-based biosensors. During a 30-min incubation with dbcAMP, Rac1 activity gradually increased throughout the cells and remained at its maximal level. There was no change in PIP(3) concentration. After a 5-h incubation with dbcAMP, Rac1 and Cdc42 were activated at the protruding tips of neurites without PIP(3) accumulation. dbcAMP-induced Rac1 activation was principally mediated by protein kinase A (PKA) and Sif- and Tiam1-like exchange factor (STEF)/Tiam2. STEF depletion drastically reduced dbcAMP-induced neurite outgrowth. PKA phosphorylates STEF at three residues (Thr-749, Ser-782, Ser-1562); Thr-749 phosphorylation was critical for dbcAMP-induced Rac1 activation and neurite extension. During dbcAMP-induced neurite outgrowth, PKA activation at the plasma membrane became localized to neurite tips; this localization may contribute to local Rac1 activation at the same neurite tips. Considering the critical role of Rac1 in neuronal morphogenesis, the PKA-STEF-Rac1 pathway may play a crucial role in cytoskeletal regulation during neurite/axon outgrowth and guidance, which depend on cAMP signals.
authors: Laboratory of Bioimaging and Cell Signaling, Graduate School of Biostudies, Kyoto University, Sakyo-ku, Kyoto, Japan.
authors: Akihiro
authors: A
authors: Goto
authors: Mikio
authors: M
authors: Hoshino
authors: Michiyuki
authors: M
authors: Matsuda
authors: Takeshi
authors: T
authors: Nakamura
mesh_terms: D000818:Animals; D003994:Bucladesine / Q000494:pharmacology*; D002462:Cell Membrane / Q000378:metabolism; D048430:Cell Shape / Q000187:drug effects; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects*; D031541:Fluorescence Resonance Energy Transfer; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000378:metabolism*; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism; D020932:Nerve Growth Factor / Q000494:pharmacology; D016501:Neurites / Q000187:drug effects / Q000378:metabolism*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D016716:PC12 Cells; D010716:Phosphatidylinositols / Q000378:metabolism; D010766:Phosphorylation; D021381:Protein Transport; D051567:Proto-Oncogene Proteins c-vav / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D000075684:T-Lymphoma Invasion and Metastasis-inducing Protein 1; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism; D020830:rac1 GTP-Binding Protein / Q000378:metabolism*
chemical_list: D020662:Guanine Nucleotide Exchange Factors; D009363:Neoplasm Proteins; D010716:Phosphatidylinositols; D051567:Proto-Oncogene Proteins c-vav; D011993:Recombinant Fusion Proteins; D000075684:T-Lymphoma Invasion and Metastasis-inducing Protein 1; C513259:Tiam1 protein, rat; C483312:phosphoinositide 3-phosphate; D003994:Bucladesine; D020932:Nerve Growth Factor; D017868:Cyclic AMP-Dependent Protein Kinases; C499134:Rac1 protein, rat; D020764:cdc42 GTP-Binding Protein; D020830:rac1 GTP-Binding Protein