beta-Adrenergic Signaling Inhibits G(q)-Dependent Protein Kinase D Activation by Preventing Protein Kinase D Translocation

Rationale: Both -adrenergic receptor (-AR) and G(q)-coupled receptor (G(q)R) agonist-driven signaling play key roles in the events, leading up to and during cardiac dysfunction. How these stimuli interact at the level of protein kinase D (PKD), a nodal point in cardiac hypertrophic signaling, remains unclear.

Objective: To assess the spatiotemporal dynamics of PKD activation in response to -AR signaling alone and on coactivation with G(q)R-agonists. This will test our hypothesis that compartmentalized PKD signaling reconciles disparate findings of PKA facilitation and inhibition of PKD activation.

Methods and Results: We report on the spatial and temporal profiles of PKD activation using green fluorescent protein-tagged PKD (wildtype or mutant S427E) and targeted fluorescence resonance energy transfer-based biosensors (D-kinase activity reporters) in adult cardiomyocytes. We find that -AR/PKA signaling drives local nuclear activation of PKD, without preceding sarcolemmal translocation. We also discover pronounced interference of -AR/cAMP/PKA signaling on G(q)R-induced translocation and activation of PKD throughout the cardiomyocyte. We attribute these effects to direct, PKA-dependent phosphorylation of PKD-S427. We also show that phosphomimetic substitution of S427 likewise impedes G(q)R-induced PKD translocation and activation. In neonatal myocytes, S427E inhibits G(q)R-evoked cell growth and expression of hypertrophic markers. Finally, we show altered S427 phosphorylation in transverse aortic constriction-induced hypertrophy.

Conclusions: -AR signaling triggers local nuclear signaling and inhibits G(q)R-mediated PKD activation by preventing its intracellular translocation. PKA-dependent phosphorylation of PKD-S427 fine-tunes the PKD responsiveness to G(q)R-agonists, serving as a key integration point for -adrenergic and G(q)-coupled stimuli.