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 mu M 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 mu M LY294002. Akt activity decreased following the addition of 10 mu M LY294002. In addition, we found that LY294002 increased the JNK activity, which is known to mediate some types of cell death in cultured PNS neurons. We also observed elevated expression of c-Jun by LY294002 in HK+ or LK+ + 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 cultured 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. (C) 1999 Elsevier Science B.V. All rights reserved.