Retinoic acid (RA) induces the differentiation of many cell lines, including those derived from neuroblastoma. RA treatment of SH-SY5Y cells induces the appearance of functional Trk B and Trk C receptors. Acute stimulation of RA-predifferentiated SH-SY5Y cells with brain-derived neurotrophic factor (BDNF), neurotrophin 3 (NT-3), or neurotrophin 4/5 (NT-4/5), but not nerve growth factor (NGF), induces Trk autophosphorylation, followed by phosphorylation of Akt and the extracellular signalregulated kinases (ERKs) 1 and 2. In addition, BDNF, NT-3, or NT-4/5, but not NGF, promotes cell survival and neurite outgrowth in serum-free medium. The mitogenactivated protein kinase and ERK kinase (MEK) inhibitor PD98059 blocks BDNF-induced neurite outgrowth and growth-associated protein-43 expression but has no effects on cell survival. On the other hand, the phosphatidylinositol 3-kinase inhibitor LY249002 reverses the survival response elicited by BDNF, leading to a cell death with morphological features of apoptosis.

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J. Neurochem. (2008) 104, 1599–1612. Abstract Mitochondrial alterations have been associated with the cytotoxic effect of 6‐hydroxydopamine (6‐OHDA), a widely used toxin to study Parkinson’s disease. In previous work, we have demonstrated that 6‐OHDA increases mitochondrial membrane permeability leading to cytochrome c release, but the precise mechanisms involved in this process remain unknown. Herein we studied the mechanism of increased mitochondrial permeability of SH‐SY5Y neuroblastoma cells in response to 6‐OHDA. Cytochrome c release induced by 6‐OHDA occurred, in both SH‐SY5Y cells and primary cultures, in the absence of mitochondrial swelling or a decrease in mitochondrial calcein fluorescence, suggesting little involvement of the mitochondrial permeability transition pore in this process. In contrast, 6‐OHDA‐induced cell death was associated with a significant translocation of the pro‐apoptotic Bax protein from the cytosol to mitochondria and with a significant induction of the BH3‐only protein PUMA. Experiments in mouse embryonic fibroblasts deficient in Bax or PUMA demonstrated a role for both proteins in 6‐OHDA‐induced apoptosis. Although 6‐OHDA elevated both total and nuclear p53 protein levels, activation of p53 was not essential for subsequent cell death. In contrast, we found that p38 mitogen‐activated protein kinase (MAPK) was activated early during 6‐OHDA‐induced apoptosis, and that treatment with the p38 MAPK inhibitor SKF86002 potently inhibited PUMA induction, green fluorescent protein‐Bax redistribution and apoptosis in response to 6‐OHDA. These data demonstrate a critical involvement of p38 MAPK, PUMA, and Bax in 6‐OHDA‐induced apoptosis.

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