Two distinct regulatory mechanisms of neurotransmitter release by phosphatidylinositol 3-kinase.
Recent studies have indicated that various growth factors are involved in synaptic functions; however, the precise mechanisms remain unclear. In order to elucidate the molecular mechanisms of the growth factor-mediated regulation of presynaptic functions, the effects of epidermal growth factor (EGF) and insulin-like growth factor-1 (IGF-1) on neurotransmitter release were studied in rat PC12 cells. Brief treatment with EGF and IGF-1 enhanced Ca2+-dependent dopamine release in a concentration-dependent manner. EGF activated both mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3-kinase) pathways, and the EGF-dependent enhancement of DA release was suppressed by a MAPK kinase inhibitor as well as by PI3-kinase inhibitors. In striking contrast, IGF-1 activated the PI3-kinase pathway but not the MAPK pathway, and IGF-1-dependent enhancement was suppressed by a PI3-kinase inhibitor but not by a MAPK kinase inhibitor. The enhanced green fluorescent protein-tagged pleckstrin homology (PH) domain of protein kinase B, which selectively binds to phosphatidylinositol 3,4-bisphosphate and phosphatidylinositol 3,4,5-triphosphate, was translocated to the plasma membrane after treatment with either EGF or NGF. By contrast, no significant redistribution was induced by IGF-1. These results indicate that PI3-kinase participates in the enhancement of neurotransmitter release by two distinct mechanisms: EGF and NGF activate PI3-kinase in the plasma membrane, whereas IGF-1 activates PI3-kinase possibly in the intracellular membrane, leading to enhancement of neurotransmitter release in a MAPK-dependent and -independent manner respectively.
Kitasato University School of Medicine, Kanagawa Japan.
Makoto
M
Itakura
Saori
S
Yamamori
Reiko
R
Kuwahara
Mariko
M
Sekiguchi
Masami
M
Takahashi
D000818:Animals; D015153:Blotting, Western / Q000379:methods; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D004298:Dopamine / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004815:Epidermal Growth Factor / Q000494:pharmacology; D005110:Extracellular Space / Q000187:drug effects / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000378:metabolism / Q000493:pharmacokinetics; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D015759:Ionomycin / Q000494:pharmacology; D007476:Ionophores / Q000494:pharmacology; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D016716:PC12 Cells / Q000187:drug effects / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000493:pharmacokinetics; D021381:Protein Transport / Q000187:drug effects; D011518:Proto-Oncogene Proteins / Q000493:pharmacokinetics; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D013997:Time Factors
D002118:Calcium; D004298:Dopamine; D004791:Enzyme Inhibitors; D004815:Epidermal Growth Factor; D049452:Green Fluorescent Proteins; D007334:Insulin-Like Growth Factor I; D015759:Ionomycin; D007476:Ionophores; D020928:Mitogen-Activated Protein Kinases; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt