Novel Roles for Peroxynitrite in Angiotensin II and CaMKII Signaling

Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) oxidation controls excitability and viability. While hydrogen peroxide (H(2)O(2)) affects Ca(2+)-activated CaMKII in vitro, Angiotensin II (Ang II)-induced CaMKIIδ signaling in cardiomyocytes is Ca(2+) independent and requires NADPH oxidase-derived superoxide, but not its dismutation product H(2)O(2). 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 Ca(2+)/CaM. Remarkably, this apokinase stimulation persists after mutating known oxidation targets (M281, M282, C290), suggesting a novel mechanism for increasing baseline Ca(2+)-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 CaMKIIδ 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.