Research ArticleCell Biology

The Golgi apparatus is a functionally distinct Ca2+ store regulated by the PKA and Epac branches of the β1-adrenergic signaling pathway

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Sci. Signal.  13 Oct 2015:
Vol. 8, Issue 398, pp. ra101
DOI: 10.1126/scisignal.aaa7677

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A distinct calcium store in cardiomyocytes

In cardiomyocytes, contraction can be triggered by large influxes of calcium (Ca2+) into the cytoplasm from the sarcoplasmic reticulum. Yang et al. found that Ca2+ released from the Golgi apparatus had a distinct function from the Ca2+ stored in the sarcoplasmic reticulum. Instead of triggering contraction, Golgi-released Ca2+ promoted the trafficking of a receptor to the surface of cardiomyocytes. The adrenaline receptor β1-AR enhanced the release of Ca2+ from the Golgi through a process involving two pathways downstream of the second messenger cAMP. Cardiomyocytes from rats with experimentally induced heart failure showed increased release of Ca2+ from the Golgi, which was associated with decreased abundance of phosphodiesterases in the PDE3 and PDE4 families, which degrade cAMP. Thus, the Golgi apparatus releases Ca2+ in response to changes in cAMP concentrations, such as those that occur during adrenergic stimulation or heart failure.

Abstract

Ca2+ release from the Golgi apparatus regulates key functions of the organelle, including vesicle trafficking. We found that the Golgi apparatus was the source of prolonged Ca2+ release events that originated near the nuclei of primary cardiomyocytes. Golgi Ca2+ release was unaffected by depletion of sarcoplasmic reticulum Ca2+, and disruption of the Golgi apparatus abolished Golgi Ca2+ release without affecting sarcoplasmic reticulum function, suggesting functional and spatial independence of Golgi and sarcoplasmic reticulum Ca2+ stores. β1-Adrenoceptor stimulation triggers the production of the second messenger cAMP, which activates the Epac family of Rap guanine nucleotide exchange factors and the kinase PKA (protein kinase A). Phosphodiesterases (PDEs), including those in the PDE3 and PDE4 families, degrade cAMP. Activation of β1-adrenoceptors stimulated Golgi Ca2+ release, an effect that required activation of Epac, PKA, and the kinase CaMKII. Inhibition of PDE3s or PDE4s potentiated β1-adrenergic–induced Golgi Ca2+ release, which is consistent with compartmentalization of cAMP signaling near the Golgi apparatus. Interventions that stimulated Golgi Ca2+ release appeared to increase the trafficking of vascular endothelial growth factor receptor–1 (VEGFR-1) from the Golgi apparatus to the surface membrane of cardiomyocytes. In cardiomyocytes from rats with heart failure, decreases in the abundance of PDE3s and PDE4s were associated with increased Golgi Ca2+ release events. These data suggest that the Golgi apparatus is a focal point for β1-adrenergic–stimulated Ca2+ signaling and that the Golgi Ca2+ store functions independently from the sarcoplasmic reticulum and the global Ca2+ transients that trigger contraction in cardiomyocytes.

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