c-Jun N-terminal protein kinase (JNK) activation and subsequent c-Jun phosphorylation which stimulates its transcriptional
activity have been well studied in cerebral ischemia. To
determine whether mitogen-activated protein kinase kinase 7 (MKK7) play a
role in JNK activation in response to the stress of global cerebral ischemia,
we tested the activation of such a kinase by using phospho-Ser and phospho-Thr
antibodies. Immunoprecipitation and Western
blot analysis revealed that MKK7 was expressed at similar levels in all
conditions, whereas phospho-MKK7 was highly augmented from 1 to 5 days and reached its
peak at 3 days after 15 min of ischemia. Consistent with the active phase, the
interaction of MLK3, ASK1 and phospho-JNK with MKK7
was increased compared with sham control, as shown by coimmunoprecipitation
experiments. Moreover, MKK7 activation was markedly reduced by pretreatment of
the free radical scavenging thiol antioxidant N-acetylcysteine (NAC). Together with previous studies, the
late activation of MKK7 in hippocampal CA1 region may
contribute to delayed cell death, and the protective effects of antioxidant
against ischemia-induced injury may be partially mediated by the
down-regulation of JNK signal pathway.
