Inhibition of phosphatidylinositol 3-kinase activity elevates c-Jun N-terminal kinase activity in apoptosis of cultured cerebellar granule neurons.

Cerebellar granule neurons maintained in medium containing 26 mM potassium or in medium (5 mM potassium) with 50 ng/ml brain-derived neurotrophic factor (BDNF) undergo an apoptotic cell death when exposed to 10 microM LY294002, an inhibitor of phosphatidylinositol 3-kinase (PI3-K). To investigate the intracellular signaling mechanism of LY294002-induced apoptosis, the activities of Akt and c-Jun N-terminal kinase (JNK) were measured in cells in HK (26 mM potassium) medium or LK+ (5 mM potassium) medium containing BDNF, with or without 10 microM LY294002. Akt activity decreased following the addition of 10 microM LY294002. In addition, we found that LY294002 increased the JNK activity, which is known to mediate some types of cell death in PNS neurons. We also observed elevated expression of c-Jun by LY294002 in HK+ BDNF. These findings demonstrated that apoptosis induced by inhibition of PI3-K activity involves suppression of the Akt activity and elevation of the JNK activity in cerebellar granule neurons. Our results suggested that the PI3-K-Akt pathway suppresses the activation of JNK and c-Jun expression, and as a result prevents the neuronal cell death in cerebellar granule neurons.