Previous studies in our laboratory have shown that
mixed lineage kinase 3 (MLK3) can be activated following global
ischemia. In addition, other laboratories have reported that the activation of MLK3 may be linked to the accumulation of
free radicals. However, the mechanism of MLK3 activation remains incompletely understood. We report here that MLK3, overexpressed in HEK293 cells, is S-nitrosylated (forming SNO-MLK3) via a reaction with
S-nitrosoglutathione, an exogenous
nitric oxide (NO) donor, at one critical
cysteine residue (Cys-688). We further show that the S-nitrosylation of MLK3 contributes to its dimerization and activation. We also investigated whether the activation of MLK3 is associated with S-nitrosylation following rat
brain ischemia/reperfusion. Our results show that the administration of
7-nitroindazole, an inhibitor of neuronal
NO synthase (nNOS), or nNOS antisense
oligodeoxynucleotides diminished the S-nitrosylation of MLK3 and inhibited its activation induced by
cerebral ischemia/reperfusion. In contrast,
2-amino-5,6-dihydro-6-methyl-4H-1,3-thiazine (an inhibitor of inducible
NO synthase) or nNOS missense
oligodeoxynucleotides did not affect the S-nitrosylation of MLK3. In addition, treatment with
sodium nitroprusside (an exogenous NO donor) and
S-nitrosoglutathione or
MK801, an antagonist of the
N-methyl-D-aspartate receptor, also diminished the S-nitrosylation and activation of MLK3 induced by
cerebral ischemia/reperfusion. The activation of MLK3 facilitated its downstream
protein kinase kinase 4/7 (MKK4/7)-JNK signaling module and both nuclear and non-nuclear apoptosis pathways. These data suggest that the activation of MLK3 during the early stages of
ischemia/reperfusion is modulated by S-nitrosylation and provides a potential new approach for
stroke therapy whereby the post-translational modification machinery is targeted.