MOTONEURON APOPTOSIS IS BLOCKED BY CEP-1347 (KT-7515), A NOVEL INHIBITOR OF THE JNK SIGNALING PATHWAY

Neurons undergoing apoptosis can be rescued by trophic factors that si multaneously increase the activity of extracellular signal-regulated k inase (ERK) and decrease c-Jun N-terminal kinase (JNK) and p38. We ide ntified a molecule, CEP-1347 (KT7515), that rescues motoneurons underg oing apoptosis and investigated its effect on ERK1 and JNKI activity. Cultured rat embryonic motoneurons, in the absence of trophic factor, began to die 24-48 hr after plating. During the first 24 hr ERK1 activ ity was unchanged, whereas JNK1 activity increased four-fold. CEP-1347 completely rescued motoneurons for at least 72 hr with an EC50 of 20 +/- 2 nM. CEP-1347 did not alter ERK1 activity but rapidly inhibited J NKI activation. The IC50 of CEP-1347 for JNK1 activation was the same as the EC50 for motoneuron survival. Inhibition of JNKI activation by CEP-1347 was not selective to motoneurons. CEP-1347 also inhibited JNK 1 activity in Cos7 cells under conditions of ultraviolet irradiation, osmotic shock, and inhibition of glycosylation. Inhibition by CEP-1347 of the JNK1 signaling pathway appeared to be selective, because CEP-1 347 did not inhibit p38-regulated mitogen-activated protein kinase-act ivated protein kinase-2 (MAPKAP2) activity in Cos7 cells subjected to osmotic shock. The direct molecular target of CEP-1347 was not JNK1, b ecause CEP-1347 did not inhibit JNK1 activity in Cos7 cells cotransfec ted with MEKK1 and JNK1 cDNA constructs. This is the first demonstrati on of a small organic molecule that promotes motoneuron survival and t hat simultaneously inhibits the JNK1 signaling cascade.