Ca2+/calmodulin-dependent protein kinase II (CaMKII) oxidation controls excitability and viability. While hydrogen peroxide (H2O2) affects Ca2+-activated CaMKII in vitro, Angiotensin II (Ang II)-induced CaMKIIIδ signaling in cardiomyocytes is Ca2+ independent and requires NADPH oxidase-derived superoxide, but not its dismutation product H2O2. To better define the biological regulation of CaMKII activation and signaling by Ang II, we evaluated the potential for peroxynitrite (ONOO-) to mediate CaMKII activation and downstream Kv4.3 channel mRNA destabilization by Ang II. In vitro experiments show that ONOO- oxidizes and modestly activates pure CaMKII in the absence of Ca2+/CaM. Remarkably, this apokinase stimulation persists after mutating known oxidation targets (M281, M282, C290), suggesting a novel mechanism for increasing baseline Ca2+-independent CaMKII activity. The role of ONOO- in cardiac and neuronal responses to Ang II was then tested by scavenging ONOO- and preventing its formation by inhibiting nitric oxide synthase. Both treatments blocked Ang II effects on Kv4.3, tyrosine nitration and CaMKIIIδ oxidation and activation. Together, these data show that ONOO- participates in Ang II-CaMKII signaling. The requirement for ONOO- in transducing Ang II signaling identifies ONOO-, which has been viewed as a reactive damaging byproduct of superoxide and nitric oxide, as a mediator of GPCR-CaMKII signaling.
