Nitric Oxide Induces Ca2+-independent Activity of the Ca2+/Calmodulin-dependent Protein Kinase II (CaMKII)

Both signaling by nitric oxide (NO) and by the Ca2+/calmodulin (CaM)-dependent protein kinase II alpha isoform (CaMKII alpha) are implicated in two opposing forms of synaptic plasticity underlying learning and memory, as well as in excitotoxic/ischemic neuronal cell death. For CaMKII alpha, these functions specifically involve also Ca2+-independent autonomous activity, traditionally generated by Thr-286 autophosphorylation. Here, we demonstrate that NO-induced S-nitrosylation of CaMKII alpha also directly generated autonomous activity, and that CaMKII inhibition protected from NO-induced neuronal cell death. NO induced S-nitrosylation at Cys-280/289, and mutation of either site abolished autonomy, indicating that simultaneous nitrosylation at both sites was required. Additionally, autonomy was generated only when Ca2+/CaM was present during NO exposure. Thus, generation of this form of CaMKII alpha autonomy requires simultaneous signaling by NO and Ca2+. Nitrosylation also significantly reduced subsequent CaMKII alpha autophosphorylation specifically at Thr-286, but not at Thr-305. A previously described reduction of CaMKII activity by S-nitrosylation at Cys-6 was also observed here, but only after prolonged (>5 min) exposure to NO donors. These results demonstrate a novel regulation of CaMKII by another second messenger system and indicate its involvement in excitotoxic neuronal cell death.