title: Nerve growth factor in combination with second messenger analogues causes neuronal differentiation of PC12 cells expressing a dominant inhibitory Ras protein without inducing activation of extracellular signal-regulated kinases.
abstract: In the present work, nerve growth factor (NGF) was used in combination with the calcium ionophore, ionomycin or dibutyryl cyclic AMP (dbcAMP), to study the connection between neuronal differentiation and extracellular signal-regulated kinase (ERK) activation of PC12 rat pheochromocytoma cells expressing a dominant negative, Ha-Ras Asn17 protein. Due to the block of endogenous Ras activity, neurite outgrowth in response to NGF is completely inhibited in these cells. However, this blockade can be bypassed by combined treatment with NGF plus ionomycin or NGF plus dbcAMP. The mitogen-activated protein kinase (MAPK) /ERK kinase inhibitor, PD98059, proved to be insufficient in inhibiting the neurite outgrowth under these conditions. Moreover, although both long-term ERK activation and nuclear translocation of ERKs are believed to be key events in neuronal differentiation, neither detectable ERK phosphorylation, nor nuclear translocation of these enzymes, occurred upon combination treatments in our experimental system. However, the neuritogenesis induced by either the combination of NGF/ionomycin or NGF/dbcAMP was inhibited by the Trk inhibitor, K252a. Ras-independent pathways, originating from the NGF receptor, can thus synergize with second messenger analogues bypassing the ERK cascade but leading to the same biological result--neurite formation.
authors.affiliation: Department of Medical Biology, Medical School, University of Pécs, Pécs, Hungary, H-7624 Pécs, Szigeti 12., Hungary.
authors.forename: G
authors.initials: G
authors.lastname: Boglári
authors.forename: J
authors.initials: J
authors.lastname: Szeberényi
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000187:drug effects / Q000502:physiology; D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007150:Immunohistochemistry; D015759:Ionomycin / Q000494:pharmacology; D020928:Mitogen-Activated Protein Kinases / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D020932:Nerve Growth Factor / Q000378:metabolism* / Q000494:pharmacology; D009420:Nervous System / Q000196:embryology* / Q000201:enzymology / Q000254:growth & development; D016501:Neurites / Q000187:drug effects / Q000201:enzymology* / Q000648:ultrastructure; D016716:PC12 Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D021381:Protein Transport / Q000187:drug effects / Q000502:physiology; D051381:Rats; D015290:Second Messenger Systems / Q000187:drug effects / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D018631:ras Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*
chemical_list: D004791:Enzyme Inhibitors; D015759:Ionomycin; D003994:Bucladesine; D020932:Nerve Growth Factor; D020928:Mitogen-Activated Protein Kinases; D018631:ras Proteins