Differential effects of ischemia and reperfusion on c-Jun N-terminal kinase isoform protein and activity

Activation of the c-Jun N-terminal (JNK) or stress-activated protein kinase s (SAPK) is associated with a wide range of disparate cellular responses to extracellular stimuli, including either induction of or protection from ap optosis. This study investigates the effect of ischemia and reperfusion on JNK isoform activities using a reversible rabbit spinal cord ischemia model . High basal JNK activity, attributed to the p46 JNK1 isoform, was expresse d in the CNS of untreated rabbits. JNK activity decreased in the lumbar spi nal cord of rabbits occluded for 15-60 min. During reperfusion animals occl uded for 15 min recovered neurological function and JNK activity returned t o normal levels. In contrast animals occluded for 60 min remained permanent ly paraplegic and JNK activity was half the control activity after 18 h of repel-fusion. In these animals proteolytic fragments of JNK1 and JNK3 were observed and protein levels, but not activity, of JNK isoforms increased in a detergent-in soluble fraction. Two novel c-Jun (and ATF-2) kinase activi ties increased during reperfusion of animals occluded for 60 min. An activi ty designated p46(slow) was similar in M-r to a JNK2 isoform induced in the se animals. A second 30-kDa activity associated with the detergent-insolubl e fraction co-migrated with a JNK3 N-terminal fragment. The results show th at JNK1 is active in the normal CNS and increased activity is not associate d with durations of ischemia and reperfusion that induce cell death. Howeve r, specific JNK isoform activation may participate in the cell death pathwa ys as increased activity of novel c-Jun (ATF-2) kinase activities was obser ved in paraplegic animals. (C) 2001 Elsevier Science BY All rights reserved .