Methylpyridinium (MPP+)- and nerve growth factor-induced changes in pro- and anti-apoptotic signaling pathways in SH-SY5Y neuroblastoma cells

The parkinsonian neurotoxin methylpyridinium (MPP+) mimics the neuropathology of Parkinson's disease (PD) and likely kills neurons by inhibiting complex 1 of the electron transport chain and increasing oxidative stress. We examined the time course of activation/inactivation of multiple pro- and anti-apoptotic signaling pathways in MPP+-induced apoptotic death of SH-SY5Y neuroblastoma cells. We found an early increase and later decrease of transcriptional activity of the generally anti-apoptotic nuclear factor kappa-beta (NF-kappaB) and early increases in activating phosphorylation of the anti-apoptotic upstream kinase protein kinase B (PKB, also known as AKT). Sequestration-inducing phosphorylation of pro-apoptotic BAD protein increased early then declined. A small biphasic increase in the generally pro-apoptotic p38 kinase activity paralleled the biphasic rise in NF-kappaB-mediated transcription. Inhibition of p38 kinase with 5 muM SB203540, inhibition of MEK-ERK with 50 muM U0126, or inhibition of phosphatidylinositol-3-kinase (PI3K) with 10 muM LY294002 reduced cell viability by 4, 18 or 37%, respectively, after 24 h. All three kinase inhibitors increased cell death in response to 24 It of MPP+, with the greatest effect shown by LY294002. Nerve growth factor (NGF) caused an early increase in activating phosphorylation of PKB/AKT and MEK-ERK and increased cell survival during MPP+ exposure. We found that acute MPP+ exposure activates multiple interacting death- and survival-promoting pathways. Survival-promoting MEK-ERK and PI3K pathways contribute to viability during MPP+ exposure, both are activated by NGF, and loss of PI3K-mediated signaling and NF-kappaB-mediated transcription may commit cells irreversibly to apoptosis in this model. It remains unknown to what extent these signaling pathways modulate dopamine neuronal death in PD. (C) 2002 Published by Elsevier Science B.V.