Genetic deletion of Rnd3/RhoE results in mouse heart calcium leakage through upregulation of protein kinase A signaling.

RATIONALE:Rnd3, a small Rho GTPase, is involved in the regulation of cell actin cytoskeleton dynamics, cell migration, and proliferation. The biological function of Rnd3 in the heart remains unexplored. OBJECTIVE:To define the functional role of the Rnd3 gene in the animal heart and investigate the associated molecular mechanism. METHODS AND RESULTS:By loss-of-function approaches, we discovered that Rnd3 is involved in calcium regulation in cardiomyocytes. Rnd3-null mice died at the embryonic stage with fetal arrhythmias. The deletion of Rnd3 resulted in severe Ca(2+) leakage through destabilized ryanodine receptor type 2 Ca(2+) release channels. We further found that downregulation of Rnd3 attenuated β2-adrenergic receptor lysosomal targeting and ubiquitination, which in turn resulted in the elevation of β2-adrenergic receptor protein levels leading to the hyperactivation of protein kinase A signaling. The activation destabilized ryanodine receptor type 2 channels. This irregular spontaneous Ca(2+) release can be curtailed by duanyu1529 inhibitor treatment. Increases in the duanyu1529 activity along with elevated cAMP levels were detected in Rnd3-null embryos, in neonatal rat cardiomyocytes, and noncardiac cell lines with Rnd3 knockdown, suggesting a general mechanism for Rnd3-mediated duanyu1529 signaling activation. β2-Adrenergic receptor blocker treatment reduced arrhythmia and improved cardiac function. CONCLUSIONS:Rnd3 is a novel factor involved in intracellular Ca(2+) homeostasis regulation in the heart. Deficiency of the protein induces ryanodine receptor type 2 dysfunction by a mechanism that attenuates Rnd3-mediated β2-adrenergic receptor ubiquitination, which leads to the activation of duanyu1529 signaling. Increased duanyu1529 signaling in turn promotes ryanodine receptor type 2 hyperphosphorylation, which contributes to arrhythmogenesis and heart failure.

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