Abstract

15-Deoxy-Δ^12,14-prostaglandin J₂(15-deoxy-PGJ₂), a naturally occurring ligand, activates the peroxisome proliferator-activated receptor-γ (PPAR-γ). Activation of PPAR-γ has been found to induce cell differentiation in such cells as adipose cells and macrophages. Herein, we investigated whether 15-deoxy-PGJ₂ has neuronal cell differentiation and possible underlying molecular mechanisms. Dopaminergic differentiating PC-12 cells treated with 15-deoxy-PGJ₂ (0.2 to 1.6 μM) alone showed measurable neurite extension and expression of neurofilament, a marker of cell differentiation. However, a much greater extent of neurite extension and expression of neurofilament was observed in the presence of NGF (50 ng/ml). In parallel with its increasing effect on the neurite extension and expression of neurofilament, 15-deoxy-PGJ₂ enhanced NGF-induced p38 MAP kinase expression and its phosphorylation in addition to the activation of transcription factor AP-1 in a dose-dependent manner. Moreover, pretreatment of 4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(pyridyl)1H-imidazole (SB203580), a specific inhibitor of p38 MAP kinase, inhibited the promoting effect of 15-deoxy-PGJ₂ (0.8 μM) on NGF-induced neurite extension. This inhibition correlated well with the ability of SB203580 to inhibit the enhancing effect of 15-deoxy-PGJ₂on the expression of p38 MAP kinase and activation of AP-1. The promoting ability of 15-deoxy-PGJ₂ did not occur through PPAR-γ because synthetic PPAR-γ agonist and antagonist did not change the neurite-promoting effect of 15-deoxy-PGJ₂. In addition, contrast to other cells (embryonic midbrain and neuroblastoma SK-N-MC cells), PPAR-γ was not expressed in PC-12 cells. Other structure-related prostaglandins (PGD₂ and PGE₂) acting via a cell surface G-protein-coupled receptor (GPCR) did not increase basal or NGF-induced neurite extension. Moreover, GPCR (PGE₂ and PGD₂ receptors) antagonists did not alter the promoting effect of 15-deoxy-PGJ₂ on neurite extension and activation of p38 MAP kinase, suggesting that the promoting effect of 15-deoxy-PGJ₂ may not be mediated by GPCR either. These data demonstrate that activation of p38 MAP kinase in conjunction with AP-1 signal pathway may be important in the promoting activity of 15-deoxy-PGJ₂ on the differentiation of PC-12 cells.