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.