科研之友
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摘要
Small-molecule, ligand-activated G protein-coupled receptors are generally thought to be rapidly desensitized within a period of minutes through receptor phosphorylation and internalization after repeated or prolonged stimulation. This transient G protein-coupled receptor activation remains at odds with many observed long-lasting cellular and physiological responses. Here, using live cell imaging of cAMP with a FRET-based biosensor and myocyte contraction assay, we show that the catecholamine-activated beta(1) adrenergic receptor (beta(1)AR) continuously stimulates second messenger cAMP synthesis in primary cardiac myocytes and neurons, which lasts for more than 8 h (a decay t(1/2) of 3.9 h) in cardiac myocytes. However, the beta(1)AR-induced cAMP signal is counterbalanced and masked by the receptor-bound phosphodiesterase (PDE) 4D8-dependent cAMP hydrolysis. Inhibition of PDE4 activity recovers the receptor-induced cAMP signal and promotes contractile response in mouse hearts during extended periods of agonist stimulation. beta(1)AR associates with PDE4D8 through the receptor C-terminal PDZ motif-dependent binding to synaptic-associated protein 97 (SAP97). Knockdown of SAP97 or mutation of the beta(1)AR PDZ motif disrupts the complex and promotes sustained agonist-induced cAMP activity, PKA phosphorylation, and cardiac myocyte contraction response. Together, these findings unveil a long lasting adrenergic signal in neurons and myocytes under prolonged stimulation and an underappreciated role of PDE that is essential in classic receptor signaling desensitization and in maintaining a long lasting cAMP equilibrium for ligand-induced physiological response.
- 出版日期2014-5-23
- 单位华中科技大学
