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 Ca2+ leakage through destabilized ryanodine receptor type 2 (RyR2) Ca2+ release channels. We further found that downregulation of Rnd3 attenuated β2-adrenergic receptor (β2AR) lysosomal targeting and ubiquitination, which in turn resulted in the elevation of β2AR protein levels leading to the hyperactivation of protein kinase A (PKA) signaling. The PKA activation destabilized RyR2 channels. This irregular spontaneous Ca2+ release can be curtailed by PKA inhibitor treatment. Increases in the PKA activity along with elevated cyclic adenosine monophosphate (cAMP) levels were detected in Rnd3-null embryos, in neonatal rat cardiomyocytes, and non-cardiac cell lines with Rnd3 knockdown, suggesting a general mechanism for Rnd3-mediated PKA signaling activation. β2AR blocker treatment reduced arrhythmia and improved cardiac function.
Conclusions: Rnd3 is a novel factor involved in intracellular Ca2+ homeostasis regulation in the heart. Deficiency of the protein induces RyR2 dysfunction by a mechanism that attenuates Rnd3-mediated β2AR ubiquitination, which leads to the activation of PKA signaling. Increased PKA signaling in turn promotes RyR2 hyperphosphorylation, which contributes to arrhythmogenesis and heart failure.
- calcium leakage
- protein kinase A signaling
- β2-adrenergic receptor
- ryanodine receptor
- Received July 29, 2014.
- Revision received October 21, 2014.
- Accepted October 27, 2014.