Post-translational modifications regulate β2-Adrenoceptor signaling in cardiac myocytes
β2AR (β2 adrenoceptor) is a prototypical G-protein coupled receptor (GPCR) that plays an important role in cardiovascular and pulmonary physiology through activation of the classic Gs-adenylate cyclase-cyclic adenosine monophosphate (cAMP)-protein kinase A (PKA) signaling pathway. In the mammalian heart, increasing cAMP-PKA activity leads to phosphorylation of an array of proteins involved in increasing heart contractility and rate. β2AR also has a cardiac protective role through utilizing multiple mechanisms to reduce receptor signaling. This includes β2AR desensitization, β2AR coupling to Gαi, and β2AR degradation, all of which are tightly regulated by post-translational modifications of the C-terminal region of β2AR. Over past decades, these modifications have been extensively characterized biochemically in fibroblasts, such as phosphorylation by PKA (serines 261, 262, 345 and 346) and G protein coupled receptor kinases (GRKs) (serines 355, 356 and 364), ubiquitination (lysines 348, 372 and 375) and palmitoylation (cysteine 341). However, the physiological role of these modifications on β2AR signaling regulation in the heart remains unclear. This study provides new insight into the role of three post-translational modifications on β2AR signaling regulation in cardiac myocytes. We find that palmitoylation, the fatty acid modification of β2AR at cysteine 341 is not required for receptor targeting to the plasma membrane caveolae. Instead, both palmitoylation and GRK phosphorylation are required to mediate the association of β2AR with β-arrestin 2/ phosphodiesterase 4D complexes to regulate cAMP signaling. In addition, we provide a new mechanism explaining β2AR coupling from Gas to Gai, which is agonist dose dependent and controlled by both PKA and GRK phosphorylation of the receptor. Moreover, we demonstrate that mutation of either PKA or GRK phosphorylation sites on β2AR leads to rapid receptor degradation than that of wild type β2AR. Interestingly, our data also suggest that degradation of β2AR is coordinated by both lysosomes and proteasomes: the extracellular domains are degraded by lysosomes and the intracellular domains are degraded by proteasomes. Together, all three post-translational modifications coordinate to regulate β2AR signaling in cardiac tissue under physiological conditions.
post-translational modification, adrenergic, cardiomyoyctes, degradation, G proteins (guanine nucleotide-binding proteins), phosphodiesterase
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign